a part "fell" off of my car

[jjzelinski]

I'm not sure how it happened, but the cap on my coolant reservoir is gone. Driving only about a mile or so around a small area, my engine compartment started steaming. I opened up the food to find coolant bubbling to of my reservoir with no cap to be found.

Anyhow, this brings me to two questions i wasn't hoping someone could help me answer:

1.) Is it normal (and I assume it is) for coolant to bubble up that when the engine is running without the cap on?

2.) Caps aren't standardized are they? I will need a new one, but I'm not sure what my chances are in finding one from a 1993 BMW 735i

Thanks for any insights.

UPDATE: 16 March

Thanks for all the replies. now some new info.

I replaced the cap and put some more coolant in. Now I'm finding the car is overheating. The coolant system is gurgling and now continuously wants to spit up coolant. Of the symptoms of a gasket issue that may be an issue, it does seem like I'm putting out a considerable amount of vapor from my exhaust however I don't see any contamination in the reservoir or oil. My wallet doesn't need this right now

 

[CrackRabbit]

Some coolant going from the radiator to the reservoir is normal and vice versa. However if it appears to be boiling or large amounts of bubbles are coming in you might want to start looking for the orther signs of a bad head gasket or a cracked head.

 

[jjzelinski]

Originally posted by: CrackRabbit
Some coolant going from the radiator to the reservoir is normal and vice versa. However if it appears to be boiling or large amounts of bubbles are coming in you might want to start looking for the orther signs of a bad head gasket or a cracked head.

wow, ok Any tips on how I can determine this?

 

[Bignate603]

What type of car is it?

 

[CrackRabbit]

Originally posted by: jjzelinski

Originally posted by: CrackRabbit
Some coolant going from the radiator to the reservoir is normal and vice versa. However if it appears to be boiling or large amounts of bubbles are coming in you might want to start looking for the orther signs of a bad head gasket or a cracked head.

wow, ok Any tips on how I can determine this?

Check your oil, if it looks like a milkshake or a shaken bottle of Italian dressing then you have coolant getting into the oil. Same for the coolant, when cold open the radiator cap and look for whitish sludge.

Look for excessive amounts of water vapor (white smoke) coming out of the tail pipe once the car is warmed up. Check and see if it has a slightly sweet smell to it.

Take it to a mechanic a cooling system leakdown test done.

 

[Vette73]

Yes it will boil if you lose the cap. Your car is probable fine.

Basic science, water boils at 100degrees in regular athomsphereic pressure. If you increase that pressure then it raises the temperature needed to boil. That is how the coolant/water in your car can be over 200 degrees and not boil.

So OP go to Advance/AZ and get a new cap ASAP. Driving without one though can cause engine damage.

 

[boomerang]

Originally posted by: Marlin1975
Yes it will boil if you lose the cap. Your car is probable fine.

Basic science, water boils at 100degrees in regular athomsphereic pressure. If you increase that pressure then it raises the temperature needed to boil. That is how the coolant/water in your car can be over 200 degrees and not boil.

So OP go to Advance/AZ and get a new cap ASAP. Driving without one though can cause engine damage.

You're switching between Celsius and Fahrenheit or something here.

 

[Bignate603]

Originally posted by: boomerang

Originally posted by: Marlin1975
Yes it will boil if you lose the cap. Your car is probable fine.

Basic science, water boils at 100degrees in regular athomsphereic pressure. If you increase that pressure then it raises the temperature needed to boil. That is how the coolant/water in your car can be over 200 degrees and not boil.

So OP go to Advance/AZ and get a new cap ASAP. Driving without one though can cause engine damage.

You're switching between Celsius and Fahrenheit or something here.

I think he's talking about how a radiator cap pressurizes the system which raises the boiling point of the water. However, none I've heard of raise the boiling point anywhere near 100 degrees. It's usually more like 20-40 degrees from what I remember. Some vehicles could be more, but 100 degrees above boiling is quite a bit.

Also, from what I've gathered he's talking about the cap on his reservoir not his radiator. I've only run into a few modern vehicles (the older XJ cherokees are the only one I can think of) that don't run an open system where the reservoir is atmospheric pressure. The cap on those reservoir tanks are pretty much just to keep junk from falling into the tank.

 

[LTC8K6]

I have seen lots of cars with a pressurised reservoir.

If it's a pressurized reservoir system then a head gasket leak can overpressure the system and blow the cap off, I believe.

Or maybe the cap just got old and worn and couldn't hold the pressure anymore and blew off?

The first thing to do is fill up the cooling system and get a new cap on there and see what happens.

I can't find a listing for a 1993 735i though...

 

[LTC8K6]

Quick research seems to indicate that other BMWs of that era had a closed system, so I'm guessing his reservoir has a pressure cap.

 

[Bignate603]

Originally posted by: LTC8K6
I have seen lots of cars with a pressurised reservoir.

If it's a pressurized reservoir system then a head gasket leak can overpressure the system and blow the cap off, I believe.

Or maybe the cap just got old and worn and couldn't hold the pressure anymore and blew off?

The first thing to do is fill up the cooling system and get a new cap on there and see what happens.

I can't find a listing for a 1993 735i though...

That makes sense, I just hadn't realized the pressurized tank was that common. What other vehicles use that design?

 

[LTC8K6]

My 97 Z24 did as did many GM cars I have seen, and my 08 Grand Cherokee does as well. My brother's 2005, 2006 and 2008 Jeeps all did also.

I've read many discussions here and at other forums about closed systems and their reservoir caps, so they must be pretty common.

If it's the same as the 1993 535i reservoir cap it's rated for 30 pounds and is about $14 at Auto Zone.

 

[Bignate603]

Originally posted by: LTC8K6
My 97 Z24 did as did many GM cars I have seen, and my 08 Grand Cherokee does as well. My brother's 2005, 2006 and 2008 Jeeps all did also.

I've read many discussions here and at other forums about closed systems and their reservoir caps, so they must be pretty common.

If it's the same as the 1993 535i reservoir cap it's rated for 30 pounds and is about $14 at Auto Zone.

Strange, I've got a Toyota, Jeep, and GM vehicle and they're all open systems. You learn something new every day.

 

[Black88GTA]

My 1994 BMW 840 uses a closed system with a pressurized reserve tank. It wouldn't surprise me if the OP's car had the same exact tank in it.

Just an FYI - the original tanks (yellowish somewhat transparent plastic) had a design flaw which made them prone to cracking without warning. If this occurs, you lose your coolant (obviously) and the engine overheats very quickly, often leading to warped heads and other damage. There was another model tank released by BMW with the problem fixed that they used in later cars...might not be a bad idea to just pick up a whole new tank and replace the whole deal as preventative maintenance.

All of this is assuming, of course, that your car uses a similar tank to mine. I only brought it up because your car is only one model year off from mine, so it stands to reason that yours may have similar flaws with the expansion tank.

 

[jjzelinski]

Thanks for all the replies. now some new info.

I replaced the cap and put some more coolant in. Now I'm finding the car is overheating. The coolant system is gurgling and now continuously wants to spit up coolant. Of the symptoms of a gasket issue that may be an issue, it does seem like I'm putting out a considerable amount of vapor from my exhaust however I don't see any contamination in the reservoir or oil. My wallet doesn't need this right now

 

[boomerang]

Originally posted by: Bignate603

Originally posted by: LTC8K6
My 97 Z24 did as did many GM cars I have seen, and my 08 Grand Cherokee does as well. My brother's 2005, 2006 and 2008 Jeeps all did also.

I've read many discussions here and at other forums about closed systems and their reservoir caps, so they must be pretty common.

If it's the same as the 1993 535i reservoir cap it's rated for 30 pounds and is about $14 at Auto Zone.

Strange, I've got a Toyota, Jeep, and GM vehicle and they're all open systems. You learn something new every day.

A closed system is the result of the design of the vehicle itself. The radiator cap needs to be the highest point in the system for obvious reasons. If the design of the vehicle precludes this, an expansion or surge tank must be added and the "radiator" cap will reside there.

The tanks act as both a vessel to contain the coolant as it naturally expands when heated and a reservoir for the coolant besides being the high point of the cooling system. You'll see a warning label or sticker on the tank telling you that it's pressurized. So many cars come with just an unpressurized reservoir that the warning truly needs to be there.

I've heard them referred to as surge tanks or expansion tanks. I'm sure there are other terms used.

 

[radioouman]

You probably need to purge the cooling system. THere should be a port or a plug somewhere so you can purge the air that is trapped in the engine.

 

[jjzelinski]

I think you're right about the cooling system. I've noticed that one side of my radiator is hot while the other is cool indicating that coolant is not being circulated. Also, when the engine has been running, the coolant expands, into the overflow tank (with gurgling), once I turn the engine off, after about a minute or the coolant gets sucked back out of the overflow tank and I hear this rapid clicking noise coming from the area of the the thermostat (not sure if it's the water pump, not that mechanically savvy.)

I've been pouring over Google trying to see what this all means, and one of the the possibilities is an issue with the head that is allowing combustion gasses to seep into the cooling system. I hope to hell it's not that Alternatively, there's the chance that it's simply air trapped in the cooling system which I would be thrilled about if that were the case but i suspect otherwise.

 

[Bignate603]

Originally posted by: boomerang

Originally posted by: Bignate603

Originally posted by: LTC8K6
My 97 Z24 did as did many GM cars I have seen, and my 08 Grand Cherokee does as well. My brother's 2005, 2006 and 2008 Jeeps all did also.

I've read many discussions here and at other forums about closed systems and their reservoir caps, so they must be pretty common.

If it's the same as the 1993 535i reservoir cap it's rated for 30 pounds and is about $14 at Auto Zone.

Strange, I've got a Toyota, Jeep, and GM vehicle and they're all open systems. You learn something new every day.

A closed system is the result of the design of the vehicle itself. The radiator cap needs to be the highest point in the system for obvious reasons. If the design of the vehicle precludes this, an expansion or surge tank must be added and the "radiator" cap will reside there.

The tanks act as both a vessel to contain the coolant as it naturally expands when heated and a reservoir for the coolant besides being the high point of the cooling system. You'll see a warning label or sticker on the tank telling you that it's pressurized. So many cars come with just an unpressurized reservoir that the warning truly needs to be there.

I've heard them referred to as surge tanks or expansion tanks. I'm sure there are other terms used.

Thanks for the explanation, that makes sense.