LS1 overheating...

[96Firebird]

Just started happening today on my way home from work. Saw the temperature creeping up towards 260, but never getting there. Normally it runs at 210 or below. Sitting in traffic, I watched it go from 210 up pretty quickly to the third tick mark, which is when I cranked the heat and it stayed at the third tick, then went back down to 210.

My options are a bad thermostat, air in the system (hasn't been opened in a while), low coolant, fans not turning on.

Just went out to check the coolant, looks fine. Started it up to see if it would happen again. Let it idle for a couple minutes, got up to just below 210 and stayed there. Gave it some gas for a minute, didn't budge on temperature but the fan turned on. Let it idle a couple minutes longer and it stayed below 210.

Not sure what it could be. I'm leaning towards thermostat, and am thinking about just flushing the whole cooling system and replacing the thermostat. Anything else stick out?

 

[Wingznut]

Thermostats *usually* aren't intermittent. But fans sure can be. Did it only get hot when you were sitting still? Did the temp go down when you started driving (and air was moving across the radiator)?

I presume this is on a 1996 Firebird (although, I thought they still used the LT1 in '96...)? I don't recall exactly, so be sure to research, but I think the fans have their own thermo-switch to turn them on and off. If you determine it could be the fan(s) not coming on, the switch is definitely something to check.

 

[96Firebird]

The car is a 2002 Trans Am.

I'm not really sure if it went down as I started moving, don't really remember. I had the heat blasting to try to keep it cool.

I'll have to see how the fan works with my car, I think I read somewhere the PCM controls when they come on. I know they definitely came on in my driveway while I was testing things.

 

[Jimzz]

Yea if it runs cool when moving but hot when not then that's usually the fans.

Thermostats usually locks up in one position (closed or open) So it just over heats or runs to cool.

 

[boomerang]

Check the air dam down low under the fascia too. If that is damaged, the air will not be funneled into the radiator.

Edit: Just read your whole post. The air dam doesn't come into play until the car is moving. Sorry for not reading the whole thing the first time. Editing like a mad man, I've got too much going on right now to reply coherently.

 

[local]

2002 Camaro here.

Yes the fans are controlled by the PCM. I believe the first one comes on around 200 and the second at 230 or something like that, the second fan will also come on when the AC is turned on. But since you said the fans came on while testing then I doubt that is the problem unless your fan relay got stuck off or something but that is very unlikely to fix itself.

I would lean towards the t-stat going out. When mine got stuck closed I could force it open with higher revs and it would stay open until the temps dropped below 160 then it would stick closed again.

 

[96Firebird]

I think it may have been a fan issue, as I usually remember hearing the fans kick off when I shut the car off but don't recall that happening when I got to the gym that day. Weird that they would work when I tested it in my driveway though. Not sure how I would even diagnose a fan issue if it is intermittent. I guess that might be why so many people have a manual fan switch...

The air damn is fine, I checked that during my testing.

I think I'm going to just do a coolant flush and change the thermostat using this guide. Last year I swapped out the stock power steering cooler because it was leaking coolant into the PS fluid and PS fluid into the coolant. I want to clear all that out with a full flush and make sure it is as clean as I can get it. If the culprit ends up being the fans after doing everything, I'll look into wiring up a manual fan switch.

 

[rommelrommel]

I think it may have been a fan issue, as I usually remember hearing the fans kick off when I shut the car off but don't recall that happening when I got to the gym that day. Weird that they would work when I tested it in my driveway though. Not sure how I would even diagnose a fan issue if it is intermittent. I guess that might be why so many people have a manual fan switch...

The air damn is fine, I checked that during my testing.

I think I'm going to just do a coolant flush and change the thermostat using this guide. Last year I swapped out the stock power steering cooler because it was leaking coolant into the PS fluid and PS fluid into the coolant. I want to clear all that out with a full flush and make sure it is as clean as I can get it. If the culprit ends up being the fans after doing everything, I'll look into wiring up a manual fan switch.

Sounds like a good plan as you should probably change that coolant anyways.

 

[iamwiz82]

How do your radiator fins look? Beaten up and clogged fins will lead to overheating when slow/stopped.

 

[LTC8K6]

One other possibility is that the fan is working on high speed, but not on low speed. So it is not coming on until the higher temp is reached.

 

[boomerang]

Here's a trick I was taught to get the coolant topped off on the first try. I would still recommend you check the level the next day though when the coolant is cold. You may want to have two people to do this as it makes it easier. Follow that guide you linked to if you wish and fill the radiator as was said. Start the car and keep an eye on the coolant in the radiator. When the thermostat starts to open, you will start to see some circulation. When you see that, rev the engine up to about 3000 rpm (you don't have to be exact on this by any means) and hold it there. You will see the coolant level drop as the water pump starts pulling coolant from the radiator. Immediately top off the radiator and put the cap on. Do not lower the rpm until the cap is on and seated or you will get a bath. It's far easier with one guy holding the throttle open while the other tops off the radiator and gets the cap on.

This is the method we used on the race cars and we never had to top off the coolant afterwards. A full fill every time.

 

[Gillbot]

Get someone with efi live or hp tuners to take control of the PCM and turn the fans on. Drive the car around and see if it overheats. You can also get someone to turn the fan points down in the PCM. I did that on my camaro, set them to 180 and 185 just to be sure.

It's also not uncommon for the system to get a bubble trapped, especially if any work has been done recently that may have affected the cooling system. If you look on ls1 tech, there's a few other people that had cooling system issues where it turned out to be a bubble in the system.

 

[BUTCH1]

Here's a trick I was taught to get the coolant topped off on the first try. I would still recommend you check the level the next day though when the coolant is cold. You may want to have two people to do this as it makes it easier. Follow that guide you linked to if you wish and fill the radiator as was said. Start the car and keep an eye on the coolant in the radiator. When the thermostat starts to open, you will start to see some circulation. When you see that, rev the engine up to about 3000 rpm (you don't have to be exact on this by any means) and hold it there. You will see the coolant level drop as the water pump starts pulling coolant from the radiator. Immediately top off the radiator and put the cap on. Do not lower the rpm until the cap is on and seated or you will get a bath. It's far easier with one guy holding the throttle open while the other tops off the radiator and gets the cap on.

This is the method we used on the race cars and we never had to top off the coolant afterwards. A full fill every time.

My car has no radiator cap, just a coolant tank near the firewall.

 

[boomerang]

My car has no radiator cap, just a coolant tank near the firewall.

Same difference. Just think of it as a radiator cap. The only thing to keep in mind is that there is a big hole in the top of that tank, but a small hose running to the radiator. It will be easy to pour it faster than the cooling system can suck it in. You probably won't see any circulation (some newer tanks do have coolant circulating through them, early ones functioned more like a reservoir) so you'll want to feel the upper radiator hose or watch the temp gage before revving and starting the pour.

The team I crewed on raced Corvettes and when I first got involved the cars had conventional radiators with caps. In later models, the top of the radiator was no longer the high point of the system and we had to run surge tanks (what you have) the same as the factory builds. We filled them using the same procedure.

http://www.djrace.com/

When I first starting crewing, we were racing SCCA locally and a few regional events. When I finally got burned out on it, we were building the cars and racing in the Speedvision World Challenge GT series. After that, I was totally burned out on mechanics and moved to computers. My wrenching skills are rusty and I always try to mention that if I get in too deep in a topic here or I just don't get involved in the topic at all. I've found out more than once here just how much I am behind the curve on some topics.

 

[phucheneh]

That car probably has the kinda-wonky two fan/three relay system. It's possible to have one bad relay that will knock out part of your fan operation, but not all of it.

Overheating at idle/in traffic is usually related to the fan(s). But it needs to be qualified by posing one question: does the overheating go away once you're moving at speed?

With a mild overheating condition, the return of proper airflow across the radiator will usually bring the temps back down. There are other issues that can cause overheating at idle- but it's usually not limited to JUST at idle. A general lack of coolant flow or cooling ability (gunked up radiator, restrictions inside cooling passages, corroded water pump impeller, ect) will commonly only manifest themselves with the car at speed, but then the overheat condition starts to run away while sitting in traffic. Reason being, it's the higher RPM's and engine load that cause the overheat, but it's ALSO the increased coolant flow at higher RPM's that keep things from really getting out of hand.

Does the LS1 still have the electric water pump? I can't remember if that was just the LT1 or not.

 

[schmuckley]

Umm..I have Areca Arc 1261...and I put a bigger sink off of some old ..something on it and keep a fan on it..it helps.

 

[Gillbot]

That car probably has the kinda-wonky two fan/three relay system. It's possible to have one bad relay that will knock out part of your fan operation, but not all of it.

Overheating at idle/in traffic is usually related to the fan(s). But it needs to be qualified by posing one question: does the overheating go away once you're moving at speed?

With a mild overheating condition, the return of proper airflow across the radiator will usually bring the temps back down. There are other issues that can cause overheating at idle- but it's usually not limited to JUST at idle. A general lack of coolant flow or cooling ability (gunked up radiator, restrictions inside cooling passages, corroded water pump impeller, ect) will commonly only manifest themselves with the car at speed, but then the overheat condition starts to run away while sitting in traffic. Reason being, it's the higher RPM's and engine load that cause the overheat, but it's ALSO the increased coolant flow at higher RPM's that keep things from really getting out of hand.

Does the LS1 still have the electric water pump? I can't remember if that was just the LT1 or not.

Neither have an electric water pump.

 

[SpatiallyAware]

I'm pretty sure most LS setups have 2 fans where the primary fan is controlled by the ECM and the secondary fan is controlled by a fan switch. Could be a bad fan switch or fan relay.

If so, my bet is either the secondary fan switch or relay.

If both fans are controlled by the ECM then my bet is on a sticky tstat.

 

[96Firebird]

I haven't been driving it because of rain, but tomorrow I'll be taking it to work. We'll see how it behaves. I ordered a thermostat, should be here Friday. I am busy all weekend, so hopefully sometime next week I'll do the flush.

I don't think my tuner changed my fan settings when I got my dynotune, but either way it has been running fine for 2 years since I got the tune. We'll see how it behaves tomorrow, I'll keep a closer eye on it.

It has a mechanical water pump, BTW.

 

[phucheneh]

I'm pretty sure most LS setups have 2 fans where the primary fan is controlled by the ECM and the secondary fan is controlled by a fan switch. Could be a bad fan switch or fan relay.

If so, my bet is either the secondary fan switch or relay.

If both fans are controlled by the ECM then my bet is on a sticky tstat.

I googled it to be sure...it's like I said- two fans, three relays. All three relays are PCM controlled. What you're describing is generally more common on Japanese cars, especially in the 90's and early 2000's. GM has used ECT's and PCM control in most everything for probably a solid 20 years.

Here's a pretty simple diagram I pulled up. Easier to follow that the factory wiring diagram.

When the coil for relay 1 is energized, the fans are in series and running on 'low' because they're only getting 6v a piece. When 2/3 come on, both fans get 12v.

If relay 1 is bad, you will have no low speed operation at all, and fan 1 will not work on high.

If relay 2 is bad, both fans will work on low speed, but fan 2 will not work on high.

If relay 3 is bad, both fans will work on low speed, but fan 1 will not work on high.

And I dunno where I pulled the electric water pump thing from. I could've sworn GM tried electric pumps on one of the 5.7L iterations. But google says I'm smoking crack on that one.