Coolant goes missing, what the heck?

[Oldmactech]

Sons e36 uses coolant like crazy. For example, he filled the reservoir 3/4 full, did the bleed, drove it 60 miles home and the level had dropped 3 inches. He went to drive it today (sat overnight) and the level was all the way to bottom of tank.

No drips or obvious leaks. Gonna do a pressure test when he gets home from school. Had him put a cardboard flat under to check for drips, nothing. No coolant smell either.

Possible hard pipe under intake? He did have a bout with rodents chewing wires once?




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[Eric93se]

Has it ever overheated?

Any reason for air to be in the system, was any work done to it recently?

[Oldmactech]

No recent work. Has been consistently been dropping coolant for nearly a year with no sign of coolant on the ground. No evidence of overheating - oil is normal, no oil in coolant, no coolant in oil. No power loss or extra pressure in cooling system.

My son regularly tops off with bmw coolant and distilled water. I went through a bleed with him the other day and got all the air out, cabin heat was good. He drove it 60 miles and the tank level warm was down 3 inches, another 60 miles and it was down a few more inches.

Lots of coolant going somewhere. Will try to do a coolant system pressure test if he comes home over the weekend.






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[spyderg0d]

If the carpets not wet in the footwells, its not the heater core leaking. If theres no coolant drips under the car, its not leaking. If the engine isnt wet with drip spots, its not leaking. Its not internally leaking so bad to make smoke, but enough to be serious. If indeed it hasent been overheated, the gasket is old and lost seal and is eating coolant. Coolant doeant just turn to humidity and disapear when the tank is opened. Bad luck,.

[Oldmactech]

Hmm. Guess I should have added that there is no tailpipe smoke. So if what you say is true, if the coolant is getting past the gasket, wouldn’t there be some symptom? Smoke, burning coolant smell? Drips? Weeping Waterpump? Thermostat? Etc.

I guess I could do a cylinder leakdown along with the coolant pressure test.

Thanks.


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[zellamay]

A mirror is a good way to see water coming out the exhaust that you might not see as smoke. Read only after engine and exhaust are fully warmed up. .... Also, you can read this thread, just below yours: https://www.bimmerforums.com/forum/s...rk-plugs-toast

[spyderg0d]

not neccesarily smoke. if a car is running and driving, lets say 2000rpm, for the 60 miles you said, wich is probably atleast an hour even on highway.. and you lost 2 inches in the expansion tank. thats probably about a teaspoon a mile.. thats not going to make noticable smoke. wont make smoke sitting still and revving. but you will notice in another hudred miles that your coolant is completely gone and your car overheating again. thats a small leak, but any leak will be, and cause, more damage. chances are a compression test wont show much, nor a leak down test on a leak that smally. it is what it is. if you have continued coolant loss and no leaks anywhere.... the engine is eating it. it is what it is.

[Eric93se]

Next step is coolant UV dye.

[R Shaffner]

Sorry for your frustration. It could be a slow leak that is just hard to spot.

Have you had the bottom engine cover off as you're checking for leaks? You should. With some cars it's easy for coolant (or oil) to drip onto the cover, puddle there, and then come out on the road while you drive. Take the cover off and leave it off for a few days while you figure this out.

It's also possible for a leak to go from a hose or a component straight to the ground, and only while the engine is running. So it doesn't leave symptoms on the car or the ground that are easy to see.

I like your idea of putting cardboard under the car (with the bottom cover off). Do that with the car idling for a while with a warm engine (at least 15 minutes for the cooling system to pressurize). And park above the cardboard for a while after the car has been for a good drive, while the engine is hot.

If it's not leaking externally anywhere, then it could be a slow leak that turns into steam in the exhaust, so slowly that you can't see it. Depends on the car and I don't know that engine, but the head or head gasket is the usual suspect for coolant making it into the cylinders. If that's the case, then it will probably get worse and you'll ultimately find out.

Another thing to check is whether your cooling system holds pressure, and whether that affects your leak. If you use a rag and slowly, carefully unscrew the coolant cap just a bit with the engine warm, what happens? Does air start to escape? If not, what happens if you unscrew it more, or off? A bad cap can affect the system in different ways. If the cap won't hold pressure or releases it too soon, it's possible that it would let the coolant boil and steam would come out of the cap as you drove. On the other hand, if the cap doesn't open when it should, it can let the system build too much pressure and cause leaking elsewhere.

And finally, these systems are somewhat self-bleeding. In some of these cars it's hard to get all the air to the radiator and out the bleed screw while it's parked. As you drive it any remaining air in the system will promptly make it to the top radiator, and as the coolant expands and contracts it will get pushed into the expansion tank. That will make the coolant level in the tank go down, as it takes the place of the air elsewhere in the system. (I usually have to add a few inches of coolant when the engine cools down, after I've filled and bled it.) You can tell how much that self-bleeding lowered the level after the car is cold, by watching the level as you loosen the bleed screw. (That will let air back into the top of the system, which will let coolant flow back into the expansion tank.)

But I agree that you shouldn't have to keep adding coolant more than once or twice after a good fill-up and bleed.

Good luck!

[XnWarden]

Good general info from Mr Shaffner. But in regards to the E36, there is no lower engine cover. And these cars are not self-bleeding. Get a cooling system pressure tester and some UV dye from your local auto parts store.

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[pbonsalb]

Does the upper radiator hose stay hard for hours or even overnight after driving? If so, the cooling system is pressurizing from a combustion chamber leak (blown gasket or warped head or cracked head).

Hope that is not it. Study the heater valve hoses in the driver’s rear corner of the engine compartment, including the hose to that corner of the cylinder head. Use mirror and light riser if undersides are wet. Feel if possible but space is tight with the intake manifold in place.

[Oldmactech]

Thanks to all.

Having had an X5 with a blown headgasket and warped head I understand the concepT. The X5 would blow the top off the coolant tank from pressure in the cooling system.

After driving it a few miles the other day (up to operating temp) I cracked the bleed screw and there was no excess pressure. Both heater hoses were hot but not tight with pressure. That tells me that no exhaust gas is entering the coolant.

I did notice a small bit of coolant at the lower coolant tank fitting (plastic nut) and it was a tiny bit loose but the excessive coolant loss continued after that.


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[R Shaffner]

Good general info from Mr Shaffner. But in regards to the E36, there is no lower engine cover. And these cars are not self-bleeding. Get a cooling system pressure tester and some UV dye from your local auto parts store.

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Thx. I'm pretty sure all the BMW's of that generation are somewhat self bleeding. That is, if you get it mostly bled, the hot and cold cycles of driving will get it all the way. Here's a link I started to share what I think I know, and to learn from others.

https://www.bimmerforums.com/forum/s...ding-Explained

Try this in your e36. When the engine is cold, check the coolant level, remove the coolant cap and then open the bleed screw. Does the coolant level rise in the expansion tank? I bet so. Then close it all up and drive it normally. The next morning, or whenever the engine is cold again, check the coolant level. I bet it will be back down to where it started the day before. That's what I mean by somewhat self-bleeding. And that's why a variety of different bleeding approaches will work, so long as one gets it close and keeps rechecking/topping off the coolant when it is low.

[R Shaffner]

Thanks to all.

Having had an X5 with a blown headgasket and warped head I understand the concepT. The X5 would blow the top off the coolant tank from pressure in the cooling system.

After driving it a few miles the other day (up to operating temp) I cracked the bleed screw and there was no excess pressure. Both heater hoses were hot but not tight with pressure. That tells me that no exhaust gas is entering the coolant.

I did notice a small bit of coolant at the lower coolant tank fitting (plastic nut) and it was a tiny bit loose but the excessive coolant loss continued after that.


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Wait. You cracked the bleed screw while the engine was warm and what? You said no excess pressure. Not sure what that means? Did air or coolant come out? Was the cap on or off when you loosened the bleed screw? Was the engine running then or not?

I suggest trying to loosen the expansion tank cap, just a bit, when the engine is off and plenty warm. You should hear a rush of air start escaping, and you might hear some boiling as you release pressure. If you don't then your system isn't building and holding pressure. If you had a fast leak, I'd suspect that was why it didn't have pressure. But if your leak is slow and you have low/no pressure, that's different. Then I'd look for a reason why the pressure is escaping. First suspect would be the cap.

[Oldmactech]

I opened the bleed screw with a warm engine, operating temp anyway. No steam of coolant. No rushing sound.
Cracked the coolant tank top and no wooshing sound or evidence of pressure. Radiator hoses are kinda squishy but hot. When I had a blown head gasket my lower rad hose was very tight under a lot of pressure.


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[R Shaffner]

Another likely cause for low system pressure, without a rapid loss of coolant, would be the bleed screw. Does it have a good O-ring on it to seal it?