For years I've been fighting cooling system problems with my E36. In 2016 I replaced the radiator, water pump and thermostat housing because I was losing coolant and found a crack in the radiator. Since then I've stopped driving it as my primary car and now put 500-1500 miles on it per year. It will leak/burn/evaporate 1/2 gallon of coolant every 500 miles of around town driving. It will leak/burn/evaporate 1 gallon every 250 miles of sustained highway driving.
No visible leaks or drips even idling for 30 minutes
No smoke out the tailpipe
No water in the oil(visible or according to Blackstone)
Pressure test cold showed a drop from 20-13psi in 20 minutes
Pressure test warm showed a drop from 20-18 in 45 minutes
What is my next step in determining the leak? Compression test? UV dye? Burn it to the ground and start over?
UV Dye would at least give you a location it's leaking from.
I'm only partially coherent on E36 cooling system's since mine only uses a factory style rad. The overflow can is in good shape? Not seeping out of the sensor fitting in the side of the rad?
02Pilot
UltraDork
9/29/21 3:34 p.m.
I don't know much about the E36 system specifically, but I've dealt with a lot of BMW cooling systems, and I'd be looking real hard at the expansion tank and cap if it were mine. The differential in usage between city and highway is interesting - I need to think more about what that might suggest.
IMO, the best thing you can do is replace the entire system at once as preventative maintenance, but you may not want that sort of time commitment and expense.
Going to go out on a limb and say when you were previously losing coolant due to a radiator crack you probably overheated her and blew the head gasket. Losing 1 gallon would leave plenty of residue if an external leak was present so guessing you are burning it off. Pull plugs and check for steam cleaning and or check valves by pulling the intake manifold. If one or two are abnormally clean I am guessing a trip to the head mill and a new OEM gasket are in your future.
Been there bought the tee shirt. Really a pretty straightforward job if I am right.
When the head gasket leak in my Volvo got bad enough to smoke/misfire on cold starts, it still had not cleaned the carbon from the piston. Absence of evidence here is not evidence of absence.
I guess I'm a little surprised that it burns that quickly and doesn't leave any evidence anywhere, but everything else about it screams head gasket (or maybe slightly warped head?) to me. Considering cold pressure loss is almost nothing it's not too surprising that it doesn't smoke on startup and nothing's getting into the oil.
Blown headgasket.
Go to autozone or advance and rent the fluid tester that detects combustion gases in the overflow. Simple test.
Slippery said:
Blown headgasket.
Go to autozone or advance and rent the fluid tester that detects combustion gasses in the overflow. Simple test.
Mine passed. Still had headgasket blown. Just a heads up as the snake oil liquid is not 100%.
OP,
Does your car hold pressure once the system is cold? Another symptom is pressure release when you pull the coolant cap after the engine has cooled.
Pete. (l33t FS) said:
When the head gasket leak in my Volvo got bad enough to smoke/misfire on cold starts, it still had not cleaned the carbon from the piston. Absence of evidence here is not evidence of absence.
I must be an idiot as I read this 3 times and still dont know what you mean. My e36 m3 (same car as the OP) had a beautifully cleaned piston on a single cylinder after having been driving for under 1k miles. Maybe my memory is shot.
Lack of evidence is inconclusive. Evidence on the other hand. Well, that would be conclusive as E36 M3.
My e36 m3 looked like this when the head came off after a bhg:
On the other hand, I've inadvertantly driven over 3 hours in the winter with very little coolant in the system (95 M3). Wondered why I was freezing and ice was building on the inside of the windshield. Got to destination, let it cool for a few hours while I worked, added coolant, heater worked, and zero consequences for thousands of miles afterward.
I wonder if it isn't the expansion tank. The pressure numbers seem fine. If the expansion tank is leaking, the engine won't take the fluid back when it cools. BMW plastics in the cooling system aren't awesome.
This is to say, I wouldn't be in a big hurry to pull the head yet.
Olemiss540 said:
Pete. (l33t FS) said:
When the head gasket leak in my Volvo got bad enough to smoke/misfire on cold starts, it still had not cleaned the carbon from the piston. Absence of evidence here is not evidence of absence.
I must be an idiot as I read this 3 times and still dont know what you mean. My e36 m3 (same car as the OP) had a beautifully cleaned piston on a single cylinder after having been driving for under 1k miles. Maybe my memory is shot.
Lack of evidence is inconclusive. Evidence on the other hand. Well, that would be conclusive as E36 M3.
It means, just because the pistons aren't cleaned off doesn't mean it can't have a head gasket leak.
I pulled the sparkplugs. All 6 look the same, standard straw colored electrodes. Shining a light down the bores, all 6 pistons have carbon deposits.
Olemiss540 said:
Does your car hold pressure once the system is cold? Another symptom is pressure release when you pull the coolant cap after the engine has cooled.
Yes. It does. I didn't know that was bad.
buzzboy said:
I pulled the sparkplugs. All 6 look the same, standard straw colored electrodes. Shining a light down the bores, all 6 pistons have carbon deposits.
Olemiss540 said:
Does your car hold pressure once the system is cold? Another symptom is pressure release when you pull the coolant cap after the engine has cooled.
Yes. It does. I didn't know that was bad.
Pull the head. Replace the gasket.
That's bad news. When the coolant is cold, it should be at atm pressure. If it still has residual pressure that means pressure was introduced into the system from something OTHER than temp increase of the fluid.
Pressure comes from combustion chamber into the coolant due to HG failure.
Pete. (l33t FS) said:
Olemiss540 said:
Pete. (l33t FS) said:
When the head gasket leak in my Volvo got bad enough to smoke/misfire on cold starts, it still had not cleaned the carbon from the piston. Absence of evidence here is not evidence of absence.
I must be an idiot as I read this 3 times and still dont know what you mean. My e36 m3 (same car as the OP) had a beautifully cleaned piston on a single cylinder after having been driving for under 1k miles. Maybe my memory is shot.
Lack of evidence is inconclusive. Evidence on the other hand. Well, that would be conclusive as E36 M3.
It means, just because the pistons aren't cleaned off doesn't mean it can't have a head gasket leak.
Agreed. But if a piston IS cleaned off, whamo.
