A "Modern Radiator" Crossroads for my Super-Dooper Trooper

[BonzaiDuck]

After my experience this summer with the "Little Repair-Shop of Horrors and the Mechanic from Hell"*[footnote] -- I resolved to begin doing more maintenance work on my 95 Trooper myself.

At this juncture, I checked my spreadsheet repair history with odometer readings and expenses. The Trooper was overdue for a cooling system flush. I contemplated other spreadsheet indicators. In 2009, the water-pump froze up, caused the engine to overheat, damaged the radiator and broke the timing belt. That was about 30,000 miles ago. We replaced the radiator, timing belt, water-pump at that time. Timing belt still has 30,000 miles left before recommended replacement. The water pump and the radiator should seem likely to last a lot longer than 30,000 miles.

But these new radiators, and even the original OEM unit, are a composite construction of aluminum and plastic.

I proceeded with the cooling system flush with the Prestone flush product, 9 gallons of distilled water, and new anti-freeze. Then, I noticed some minor leaks. Most readily, I discovered the radiator cap wasn't holding the pressure, at least it wasn't doing so after the car was parked and ignition turned off. So a few drops would leak from the cap and drool on the garage floor. I know this, because I could see the indications of fresh coolant just below the radiator cap. But once I'd taken care of the radiator cap, I still began to notice small amounts of anti-freeze on the drop pan after running the car and letting it sit in the garage overnight.

I went through an OCD panic, worrying about the water-pump and its seals. Checked that out: no noise coming from the pump, and the underside of the engine below the water pump was dry as a bone. Finally, I located this new leak.

It was coming from the oil-cooling pipes that circulate coolant to the transmission oil-cooler. The leak was coming from the flange-nut where a pipe connects to the bottom of the radiator. I examined it more closely. The flange nut and other metal fittings were secure, but the fitting includes a spongy rubber part -- component of the radiator. If I pushed this fitting with my fingers, the rubber seal would spooge out drops of anti-freeze. This was not causing a gusher of coolant loss. It would be a matter of a few drops -- a small puddle about 3 inches diameter -- after the car had been run, allowed to cool off sitting in the garage.

I researched some "stop-leak" formulations. Most of them did not address the problem, and are designed for head-gasket leaks or leaks in metal components. But some of the web-sites also recommended a product called ATP AT-205 Re-Seal . Looking at this more closely, none of the product promotions mentions using the product in the cooling system's anti-freeze. It seems to be a product specified exclusively for engine oil, transmission oil, gear-boxes etc.Yet the review sites suggest it as a "radiator stop leak". It DOES specifically swell and rejuvenate rubber seals.

Anyway, I ran by my newly-preferred repair-shop today, and asked them how that rubber fitting can be repaired. It can't be repaired, because there is no apparent way of digging it out of the radiator and re-installing it. I was advised that I would have to replace the radiator to address the leak. The price was reasonable, given my own research of a radiator replacement at about $150. They would get the best radiator available for about $190 -- showing their mark-up -- something that must be expected from repair shops. The total bill would be $400, which was less than my former long-time repair-shop charged me for the radiator replacement of 2009.

They can't fit me into their queue until next week -- about 10 days from today. I'm planning to call them on Monday next week to proceed.

But meanwhile, I'm wondering if I should try this ATP AT-205 Re-Seal. I can siphon off an appropriate amount of anti-freeze from the radiator cap (avoiding the trouble of fiddling with the petcock under the car). Supposedly this stuff will seal or fix rubber components within 5 hours.

But should I worry about other side-effects? I can't imagine that it would damage my radiator hoses. If it was meant to be added to engine oil to address head-gasket leaks, adding it to the coolant side of that equation shouldn't have any adverse effect.

As I said, I'm perfectly fine with replacing the radiator, but I expect my radiator to last more than 30,000 miles. And if I'm going to add this stuff to my coolant -- something that one Q&A indication on a web-site said was not an appropriate application -- I have to do it in the next couple days. As I said, reviews of "radiator stop-leak" products included AT-205 in their list of options. It is not a petroleum-based product. I could perhaps see replacing all the antifreeze to purge it from the system after it works any magic. I'm just reticent about any unknown risks or simply a misapplication.

----------------
* Repair-shop of Horrors and the Mechanic From Hell. I have posted this story in part or in whole in other threads, but it was the biggest serial cluster-f*** I had ever experienced from an independent repair shop. I got the car back with everything set right. But I probably spent $600 on a valve-cover gasket replacement that might have been deferred a year or two, and there was a severe inconvenience to the various additional visits to fix things the Mechanic from Hell had broken. In the end, I discovered a blown fuse indicative of negligence for removing the dashboard without disconnecting the battery first, and I fixed my horn -- a connection that had been pulled loose. Told them to check everything the first time around, but they didn't. And that's why I decided to do routine maintenance myself from now on.

 

[NutBucket]

Never use stop leak on a vehicle you care about. Given it's not a massive leak and temps are cool/cold I'd just nurse it along until you can get it fixed properly.

 

[BonzaiDuck]

Never use stop leak on a vehicle you care about. Given it's not a massive leak and temps are cool/cold I'd just nurse it along until you can get it fixed properly.

Some more forum posts elsewhere about AT-205 Re-Seal suggests it has properties like paint thinner, but it's not a petroleum distillate. If it were promoted for use as poured into the radiator fill-port, I'd be more inclined to try it. Essentially I'd just want it to swell that rubber bushing.

But I agree with you. I could probably nurse the leak indefinitely, but I'm going to schedule the radiator replacement for next week.

Since I didn't notice this particular leak until after I'd flushed the radiator, I could only wonder what a bottle of Prestone Flush (9 oz), 9 gallons of distilled water and new antifreeze would do to that rubber seal.

I think, in the future, I'll defer "comprehensive" cooling system flushes by simply draining and replacing anti-freeze by a gallon every six months. And, of course -- always use the same brand and formulation of anti-freeze.

I would do the radiator replacement myself. But since I have other things to do -- taking care of my elderly Moms and disabled brother -- I cannot afford to have the Trooper in a state of dis-assembly for more than a day. I tend to take my time with these things, and the DIY mechanic doesn't have the experience of repetition to assure "quick work".

So it's worth it to me to take it to the repair shop, where they'll have it done in less than a day's time. The labor will be barely more than the part, and the part is only marked up by about $40.

 

[BonzaiDuck]

Never use stop leak on a vehicle you care about. Given it's not a massive leak and temps are cool/cold I'd just nurse it along until you can get it fixed properly.

I've been categorizing the advice I'm getting. Where I thought I remember that you said "get it repaired", you belong in the same category as that wherein I put myself: " . . . start by nursing it . . . "

We're going to try an experiment. Next week, I'll notify the repair shop of a postponement in the $400 radiator replacement. The repairshop owner is in his own category: he wants the business; he might not recommend viable solutions that have uncertain affects on his own warranty arrangements; he'll incline -- even honestly -- toward solutions indifferent to his parts markup but with greater potential for his labor charges.

K-Seal's customer support responded to my query: "no go for K-seal with rubber-to-metal surfaces -- only works with plastic-to-metal or metal-metal surfaces". Similarly, customer-support for AT-205 Re-Sealer was emphatic for it being a "no go" as well.

HOWEVER. There is what I call the "glass-boat-swimming-pool repair strategy".

FLEX SEAL TAPE, plus FLEX SEAL GLUE. TAPE plus SPOOGE equals promising KLOODGE.

Tell me if I'm wrong, but the pressure in PSI builds up in the radiator just after a warm/hot running engine has been turned off. Then, the pressure changes, and drops with cooling and/or overflow to the overflow reservoir. Loss from a leak will be restrained if it's a tiny leak and all other leaks are sealed.

So I'm going to try using the FLEX SEAL products, and watch it for as little time or long time as it takes.

People might want to watch this thread, just to see if there are decent automotive applications for flex seal . . .

 

[NutBucket]

You're a bit off on how a pressurized cooling system works. Temperature rises which causes the thermostat to open. Then as more heat is introduced the pressure rises. The radiator cap maintains about 15psi of "static" pressure in the system. Increasing the pressure above atmospheric increases the boiling point of the fluid. If there's too much pressure the excess liquid escapes to the overflow. Then when it cools down it gets sucked back in to the system.

 

[BonzaiDuck]

You're a bit off on how a pressurized cooling system works. Temperature rises which causes the thermostat to open. Then as more heat is introduced the pressure rises. The radiator cap maintains about 15psi of "static" pressure in the system. Increasing the pressure above atmospheric increases the boiling point of the fluid. If there's too much pressure the excess liquid escapes to the overflow. Then when it cools down it gets sucked back in to the system.

I don't disagree, but a running engine's circulating coolant is not as hot as it would be after the engine has stopped running so the coolant is no longer circulating and air is no longer drawn through the radiator fins. That's when I find the tiny leaks occurring.

Either way, it is counterintuitive that an external patch would cure a tiny leak at a point where a rubber gasket meets metal. I want to see how effective this Flex Seal stuff really is. Couldn't do any harm.

The other transmission ATF line and rubber plug at the radiator is dry as a bone. Someone else suggested my use of Prestone Flush & Cleaner may have removed corrosion on the ATF pipe at the rubber plug, causing the coolant to weep slightly between the pipe and rubber plug when I park the car and turn it off. But I can't see how I should worry about a little corrosion on the tranny ATF pipe after only 30,000 miles on the current radiator and a history of reasonable attention to the cooling system over 9 years. There's no strawberry milkshake, no vanilla milkshake, and no lemon-lime milkshake in any of the three fluid reservoirs where I might respectively find them.

I just don't want to see that happen, because the repairs will be expensive.

 

[mrblotto]

Is replacing the radiator yourself an option? Looks like they're about $100 on rock auto

Of course I have no idea how long it would take:
-drain old rad
-remove rad
-clean up/trim ends of hoses if needed
-replace rad/fill
-pray for no leaks lol

Of course, I've never replaced a rad myself before, but I'd be more inclined to, esp if the vehicle wasn't my DD and could afford a few days of non-use

 

[Sgt. York]

I would just swap out the radiator and be done with it. I don't have time to be stressed over something that can be easily repaired.

 

[BonzaiDuck]

Is replacing the radiator yourself an option? Looks like they're about $100 on rock auto
Of course I have no idea how long it would take:
-drain old rad
-remove rad
-clean up/trim ends of hoses if needed
-replace rad/fill
-pray for no leaks lol
Of course, I've never replaced a rad myself before, but I'd be more inclined to, esp if the vehicle wasn't my DD and could afford a few days of non-use

Abso-tively, Posi-lutely -- yes. I've replaced a radiator before, but not in this SUV. I've been over the factory shop manual per the radiator shroud and other incidentals. Given my daily obligations, the Trooper would be "out of service" for more than just a day. I incline to take my time.

On the other hand, the repair-shop markup and the labor charges are reasonable. Of course I could save myself maybe $50 on the radiator and another $200 on the labor, but I have two disabled people to take care of and this car especially needs to be available for use for emergencies and so on. But your point is well-taken. Perhaps my biggest reservation is my inclination to finish the work in the least amount of time.

I would just swap out the radiator and be done with it. I don't have time to be stressed over something that can be easily repaired.

That's also important. Look how much time I put into making these posts? The reason I do these things derives from being retired, with no need to earn more money but only to save what I have. I spend hours just contemplating certain tasks -- time I wouldn't have in my previous life, even as I did more DIY vehicle repairs during that double-candle-burning multi-task-juggling time.

I ran the Trooper out on an errand earlier this morning. I'd cleaned up a thimbleful of antifreeze from the drop pan before I left -- what had dripped out over a three-day period after the last excursion. Checking under the radiator in the various parking lots where I left the SUV during three or four stops, there wasn't a drop coming out while the engine sat there hot. I know it will drool out another thimbleful between now and tomorrow or the following day.

But I'm convinced there's no significant loss of coolant when the Trooper is running at full temperature! None! The reservoir remains at approximately the "MAX" line, even when the engine is cold. When the radiator has cooled and I remove the cap, it is full to the brim -- no air or vapor pocket.

So I'm going to try this FLEX SEAL strategy before I run it down to the mechanic, or order my own radiator for a DIY episode.

Also, I've discovered that (of course) there's a radiator for the manual drive version of the 95 Trooper -- without these infernal rubber plugs and the transmission cooler built-in. There is also a "transmission cooler" -- pipes with fins-- supposedly for the 95 Trooper that can be applied with something like zip ties through the main radiator (and AC condenser) fins. That's a possible option to this, although I'm not sure how there might be room for this external transmission cooler.

The FLEX SEAL likely arrives before middle of the upcoming week. No harm in postponing any other work until I see if it works.

[AN HOUR LATER] I have a Ryobi "air cannon" 18" circular fan, which can sit on my grille-guard and radiator-core-support. I sometimes use it to cool down the engine and radiator quickly. So now, the radiator feels to be room temperature, and I see that a small drop half the diameter of a dime is on the drop pan where there was none when the engine was hot.

The coolant mix is weaker than recommended -- I'm guessing that it is about 45 parts ethylene glycol to 55 parts water. And I'm wondering if there isn't a graph somewhere that shows how coolant expands and contracts at different concentrations. Any pointers to such data on the web will be vastly appreciated. In another hour or so, I'm going to siphon off a quart of anti-freeze (easier than fiddling with the petcock underneath), and replace it with 100% ethylene glycol. The cooling system capacity is 2.4 gallons or just under 10 quarts.

ALSO -- I note that with the radiator still filled to the cap and now at room temperature, the reservoir is still filled to the "MAX" line. This little leak is not losing much in the way of coolant, as I observed before, and it doesn't seem to leak on parking lot pavements when the engine has sat there cooling off for as much as an hour grocery-shopping-time.

[AND AN HOUR AFTER THAT . . . . ] There are white papers available on the web [ "Volumetric Properties . . . Aqueous Solutions . . . Ethylene Glycol . . ." ] which would seem to indicate that the coefficient of expansion increases with greater concentrations of ethylene glycol. I'm still going to add a quart of 100% EG to the radiator, but what I'm really waiting for is the impact of sealing the rubber plug in the radiator with FLEX SEAL. This is really a minor, "weeping" leak in the Trooper's cooling system . . .

 

[NutBucket]

Given the mild climate, being off by a few percentage points isn't a big deal. Antifreeze lowers the freezing point more than it raises the boiling point anyway.

 

[BonzaiDuck]

Given the mild climate, being off by a few percentage points isn't a big deal. Antifreeze lowers the freezing point more than it raises the boiling point anyway.

Mindful of boiling-point elevation, I was more interested in the volumetric expansion of the coolant.

The radiator cap was replaced a month ago -- the previous cap would leak -- vent a few drops of fluid. The new cap is rated at 17 PSI. As soon as I replaced that cap, I noticed the weeping of fluid from the ATF-pipe's rubber plug in the radiator. This seems to be an iterative exercise in playing whack-a-mole with weepy-leaks.

Otherwise, as I said earlier, I ran the Trooper out on errands today and filled up the gas tank. It's a stand-up ride. I'm eager for my January registration renewal's required smog-test, so I can see a new set of numbers . . .

 

[NutBucket]

17 sounds high? Is that the OEM spec?

 

[BonzaiDuck]

17 sounds high? Is that the OEM spec?

Just checked the factory workshop manual to be sure. It's a "spec range" of 12.8 to 17.1 PSI (or kPa "Kilo-pascal" 88 to 117).

When I suspected the old radiator cap of being faulty, I ordered one from RockAuto and picked up a second from O'Reilly's. One of these last two continued to weep anti-freeze, so I swapped in the second one which had 17 PSI stamped on the cap. Both caps were specified for the 95 Trooper, and I didn't buy them with any definite choice of PSI -- I just bought them because they were offered for the Trooper. Now, after the radiator cap no longer leaks, as I said before, the cooling system weeps anti-freeze from the rubber-plug surrounding the ATF cooling line into (or out of) the radiator.

 

[BonzaiDuck]

AN UPDATE -- REPLACE OR REPAIR?

Here's the factory shop manual diagram of my radiator -- with my annotation about a rubber seal::



After replacing the radiator cap, antifreeze began to weep from around the oil cooler pipe connection on the radiator side -- between the plug and the pipe for the internal transmission cooler pipe and fins. This would occur as the car was cooling off toward room temperature. At most, I'd lose a thimbleful; at least, maybe a drop half the diameter of a dime or nickel. The puddle in the drop pan -- if you can call it that -- doesn't seem to grow after the car sits in the garage for a couple days.

The repair-shop-owner/mechanic says "replace the radiator". But no metal or plastic part of the radiator is defective: this is a seal between a rubber plug and a transmission cooling pipe! As I said earlier, the replacement radiator will cost about $190 with the mechanic's markup, and maybe $130 to $150 if I buy it myself. And -- I could do that, and I could even perform the labor myself. This could be a matter of convenience versus a total bill of $400.

But it seems to me that I should be able to repair the seal between the rubber plug, the ATF pipe and the metal of the radiator.

All I need to do is drain the radiator of 0.9 gallon 50-50 antifreeze, allowing me to wash the pipe, rubber, and surrounding metal with isopropanol. Then, using a tool similar to a dentist's pick, pull apart the rubber from the metal surfaces, and apply a sealant or adhesive.

What sort of sealant or adhesive, to be applied externally?

I actually thought of the TV-advertised FLEX-SEAL glue and FLEX-SEAL tape. So I spent about $25 on both. I also sent an e-mail to FLEX-SEAL asking for their comment about the prospects. Their stuff is good up to about 200F. The coolant in the UPPER radiator may be 230F, but we're talking about external surfaces or interfaces between rubber and metal in the LOWER radiator. Of course, if the pipe is the "input" from the transmission, then the ATF will be pretty hot.

The Chuckleheads wrote back -- "Don't use our product under the hood of your vehicle" for "safety" reasons. They're telling me something similar to saying that I shouldn't use clear postal packing tape to secure a wire in my engine compartment! I was merely asking them if I needed to clean off the ethylene glycol, since they say their product bonds under water! Chuckleheads! I'm sure my car is going to blow up for a few drops of sealant applied to the bottom of the radiator! My wheels may come off! Te-wibble things will happen! So much for soliciting opinions.

Looking at the application suggestions for FLEX-SEAL (in addition to using it on RV's and other "mobile devices"), they note that it bonds to "vulcanized silicone rubber", all metal and plastic surfaces, PVC pipe, etc. etc. etc.

But automotive RTV (room temperature vulcanized) silicone adhesive/sealant does the same thing. And it's good to 400F, as opposed to 200F.

I cannot see getting this stuff inside the radiator; it's not going to be "sucked in", but I want to seal the surfaces from about half-way through the plug to the outer surface.

It's either going to work, or it isn't. But if it does -- then I defied all advice toward a $400 repair bill, as opposed to spending $30 total on "tubes of stuff".

So I'm going to drain the radiator, spray with isopropanol, spooge on some RTV sealant getting it between the metal and rubber, and then I'm going to apply FLEX-SEAL and FLEX SEAL tape on top of that!

If it don't work, THEN I'll replace the radiator which only has 30,000 miles of usage. And that . . . is that . . .

 

[mrblotto]

It would be nice to know what the 'seal' actually looks like before you go rooting around in there, or even if just the seal is replaceable. Trip to the salvage yard maybe? I dunno, just throwing stuff out there

 

[BonzaiDuck]

It would be nice to know what the 'seal' actually looks like before you go rooting around in there, or even if just the seal is replaceable. Trip to the salvage yard maybe? I dunno, just throwing stuff out there

"Throwing stuff out there" is fine and what we'd hope for on a forum like this, short of some socket-set-veteran familiar with greater particulars.

Here's where I'm beginning to think my 72-year-old mind is starting to "lose it". I was sure, when I was examining the lower radiator where those ATF lines are connected, that there were soft RUBBER plugs there. I THOUGHT I had felt them, THOUGHT that they exhibited "rubber" elasticity. I went out there this morning again with my LED headlight and flashlight, got under the car with my "biker" bandanna on to keep my hair clean, and looked again closely.

Those pipe fittings go into a PLASTIC plug -- solid -- like bakelite. Therefore, according to the K-Seal manufacturer, their product WOULD actually work with this leak. On the other hand, sealing it from the outside with RTV adhesive sealant and strips of rubber adhesive hose bandage might also work. The RTV and hose bandage strips might be "messy", but pulling them off later won't damage anything -- not the ATF pipes and hex-nuts, not the plastic, not the metal around those plastic plugs.

I must have been HALLUCINATING when I first looked at the bottom of that radiator. No "rubber" -- no "soft" parts. I think I should see a neurologist or something!

In any case, the leak is no "gusher". The car has to cool off and sit in the garage over the drop pan before the coolant loss amounts to half a thimbleful. I just don't see this as sufficient to replace the entire radiator. Or if I entertain that prospect, I need to weigh the pros and cons and "in-place" repair possibilities some more. If the radiator NEEDED to be replaced -- sure -- either $150 with DIY effort or $400 employing the repair-shop is reasonable.

ADDENDA
Look at all the time I've spent exploring this little anti-freeze leak problem! All that I've written here! But if a person is totally "retired", the car runs very well, there are "little things" to fix, I can devote hours to save pennies. Time? I have plenty of time. Money? I have "enough' money. Money and Time: the two universals of economic thinking. But for me, Time is only Money for the matter of Saving Money.

So now I have a clear idea of what is happening with this. The radiator is "defective" (as my mechanic tells me) only insofar and the radiator coolant leaks between the plastic fitting in the bottom of the radiator and the metal ATF cooling lines. There are no "cracks" in the plastic. If the plastic is like "Bakelite", it may shrink slightly over a long time.

Now I have re-examined the prospect of using an "additive". Like anything else, I have to look at online web-advice, the promotional information of different products, the customer reviews -- and sort out which are True, which are Accurate, and which aren't.

There are additives which provide "permanent" leak-stoppage, and those which are considered "temporary". There are additives for which some customers report problems, for instance -- blockage in heater-core channels (more trouble or even disaster than makes the product worthy). There are additives which only enhance those in anti-freeze for reducing corrosion, leveling pH and even "lubricating" water-pump seals.

Now I'm looking closely at Bar's Leaks HDC Radiator Stop Leak Tablet . The manufacturer promotion, which one should take with a grain of salt, seems informative, and their own "selective" customer reviews cite examples of building managers with central heating using boilers who've used these tablets to stop pinhole leaks, and save thousands of dollars -- something I know from being a condominium association treasurer. Customer reviews at Amazon are numerous -- suggesting a popular product -- in excess of 130. Ratings and remarks only show 9% total dissatisfaction. Usually customers with legitimate gripes are more inclined to post reviews than people who are satisfied, and among those 9%, some of the users might instead have dissolved the tablets first, since some of the complaints spoke to "clogging" due to insertion of whole tablets.

My strategy will be to use the Bar's Leaks tablets first, run the car, see if it seals the leak I've described. Whether it does or it doesn't, I will then attempt an "external seal" with RTV silicone rubber adhesive sealant and rubber self-adhesive hose bandage.

Not holding off any more. I'm going to do this -- going to do it TOOOO-DAYYYY!

 

[BonzaiDuck]

FORGET THE BAR'S LEAKS additive for now.

Ingredients:
1 nitrile surgical glove lifted from my medical clinic waiting for the doctor
1 tube of Permatex RTV Silicone Adhesive Sealant
1 LED headlight with fresh battery
1 hot radiator . . .

It doesn't leak when hot; it leaks when it cools. There is a rubber O-ring inside the plastic fitting for the ATF pipe. The O-ring seals under pressure. When the anti-freeze cools, it seeps out and puddles a half-cc on the drop pan.

So I "spooged" the ATF pipe joint at the radiator with RTV sealant. We'll let it cool. If it doesn't drip then, I'll spooge on some more of it.

Then we'll find out how long it will last until we finally replace the radiator. Meanwhile, I told the shop-owner-mechanic he can replace my rear brakes and turn the drums for $250 instead of hoping for the radiator replacement anytime soon.

Work I was going to have done anyway on the rear brakes, and $400 saved on the radiator replacement.

But ---- we . . . . . shall see . . . . . won't we? It either leaks, or it doesn't. Gonna find out now.

And like Arnie said in "The Terminator" -- "Ah'll be back" -- to report on the result . . .

 

[BonzaiDuck]

UPDATE

So I'm just posting this stuff, because my beloved Trooper means so much to me. I've probably invested $4,000 in it during the last three years -- 60% of which was simply to restore the entire suspension system. Now we're talking about "sunk cost", but as I've said too many times, the 188,000-mile-engine is running, smog-testing and failing to consume oil as if it only had 18,800 miles on it.

Like I said already, I got some clear RTV silicone adhesive/sealant and spooged it around the fitting for the ATF fluid cooling line where I'd located the leak. And I blindly had speculated that the radiator would "seal" itself under pressure, and then begin drooling a little anti-freeze after cooling off. The RTV sealant seems to have done the trick.

So . . . . no Bar's Leaks tablets or liquid. I'm not going to do that. I'll just keep an eye on this. I think I've stopped just about every Dexron, engine-oil and anti-freeze leak in the vehicle -- as I watch the drop pans. I may replace the ATF cooling-line hoses -- a cheap item, because they seem a bit too stiff and old.

FURTHER UPDATE
This strange, unpressurized leak that occurs when the radiator cools is indeed stopped by applying RTV silicone as I said. However, that wasn't the "whole leak". It still leaks from the front of the radiator opposite the leak that I sealed.

So -- new radiator next week. Suppose I chose to repair the remaining leak the same way? I'd have to pull the radiator from the car to get to it. I might as well replace it -- either myself, or through a repair shop. And since I can't leave the car disassembled for more than a day, the work broken and interrupted by other responsibilities, I'll simply pay to have it done.

As I said, then --- "That . . . is . . . that."

 

[skyking]

I'll drop this in here for future reference.
It is perfectly acceptable to run a lower pressure radiator cap , even to the point of a zero pressure cap, if it does not result in excess coolant usage or temperature excursions. The example I am thinking of is the cracked -53 block on 1998.5 ~ 2002 Cummins ISB engine in the Dodge truck. People have limped along with this cracked block for many thousands of miles by loosening the cap.
I'd put a new radiator in your Trooper too
It's not nearly as nice to seek out a new engine block for those Dodges

 

[BonzaiDuck]

I'll drop this in here for future reference.
It is perfectly acceptable to run a lower pressure radiator cap , even to the point of a zero pressure cap, if it does not result in excess coolant usage or temperature excursions. The example I am thinking of is the cracked -53 block on 1998.5 ~ 2002 Cummins ISB engine in the Dodge truck. People have limped along with this cracked block for many thousands of miles by loosening the cap.
I'd put a new radiator in your Trooper too
It's not nearly as nice to seek out a new engine block for those Dodges

Thank you for the reply.

Here is the final analysis of what apparently happened with my 30,000-mile-old radiator. In post #14, I included the factory-manual diagram of the OEM radiator. Notice that there is a small clasp bolted/attached to the bottom of the radiator just to the left of the petcock/drain-plug. It holds in place the transmission cooling pipe which extends to the driver-side radiator -- where I'd discovered the original leak. This clasp had apparently loosened or fallen off, so that fiddling with the drain-plug or the hoses on the transmission cooling lines would disturb the seal where that particular cooling line enters the radiator.

I was able to repair this leak with RTV silicone sealant, but there continued to be a leak coming from some inaccessible point at the bottom of the radiator -- perhaps some spot under the cooling line intersection that I couldn't reach.

This is just the way those damn radiators are designed for model versions with automatic transmission. One option might be to use the radiator specified for the manual transmission version, and attach an oil cooler for the transmission separately:

Typical oil-cooler kit at E-Bay

Instead, I just told the repair-shop owner to pick the best radiator possible as designed like the original OEM for auto transmissions.

Perhaps I might have limped along for years with the existing leaky radiator. Perhaps I might have used Bar's Stop-Leak radiator tablets to seal the leak -- provided that the leak was not occurring at a point with a rubber o-ring or gasket. A lot of "ifs". "If the leak doesn't get bigger and suddenly hemorrhage", for instance.

But the $400 to pay someone else for selection and labor is acceptable as part of my "2020 Isuzu Trooper maintenance budget". I might have done it myself and saved $250, but this way -- it goes into the shop in the morning, comes out in the afternoon, finished, tested and warrantied.