Overheating. Head gasket or other
Moderator: martauto
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Captain_Birdseye
- E30 Zone Regular
- Posts: 874
- Joined: Sun Mar 25, 2012 11:00 pm
- Location: Bristol (and Cheltenham)
Well, technical expertise will no doubt be along soon in the form of Brian. To diagnose properly there will be a correct procedure to follow. If you wanted a quick thing to try you could flush the coolant, instructions here on the zone. Test the thermostat too...
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drakesmith
- E30 Zone Newbie
- Posts: 180
- Joined: Sat Nov 05, 2016 11:00 pm
- Location: London
Try this trick.
Take the top off the expansion tank and turn over. If you see a fountain out of it, head gasket.
Take the top off the expansion tank and turn over. If you see a fountain out of it, head gasket.
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Can't really see how unburnt petrol could get into the coolant, whatever is wrong with the car.
What makes you think that the head gasket has failed, rather than something like a simple coolant leak? I've never come across a M20 head gasket that has spontaneously failed and caused overheating, rather than overheating for some other reason that has caused a gasket to fail.
A simple compression test would be one of the first things to do, or better still, a leak down test, which would pressurise each cylinder in turn, allowing you to see the effect on the coolant level in the tank.
What makes you think that the head gasket has failed, rather than something like a simple coolant leak? I've never come across a M20 head gasket that has spontaneously failed and caused overheating, rather than overheating for some other reason that has caused a gasket to fail.
A simple compression test would be one of the first things to do, or better still, a leak down test, which would pressurise each cylinder in turn, allowing you to see the effect on the coolant level in the tank.
Thanks Brian. No, it does not make sense that it is the gasket. Coolant leak, but i can't find where. I know the cap is faulty and have new replacement ready. Will do tommorow. Are these cars tricky to bleed as they tend to give me trouble getting air locks out. As soon as my heating goes i know i have to stop very soon. Faulty cap not giving sufficent pressure, and where else is suspect for leaks not easily visible?
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Coolant leaks are not always easy to spot at all. Hoses can have a very fine pinhole leak, spraying a very fine, almost invisible stream a long way from the actual leak. I remember finding one of these only when I accidentally passed my hand through the stream. I also had a minor leak on my daily driver that took two years to pin down - a water pump that would only leak slowly when it was turning.
You're pushing your luck driving until the heating quits. By this time there's a considerable air pocket in the head, and the likelihood of the head cracking is quite high. Nothing like as high on the 2 litre as on the 2.5, but it can still happen.
A faulty cap may be the problem. It should have already been changed under safety recall, many years ago, but there are still originals out there.
A leak down tester is the way to go, where you can pressurise the cylinders with air for a while, and see if it causes the coolant tank level to rise, or a cheap coolant system pressure testing kit of off ebay can be very educational. I've found that very few cars are entirely water tight when pressurised up with one of these.
If you do use one of these, remove the spark plugs before spinning the engine. This avoids bending con rods if water has leaked into a cylinder, and also gives you the chance to see which cylinder, if any, water shoot out of.
E30s need careful bleeding, like any relatively modern car, but, as long as they're not facing downhill, usually bleed OK. If you do get an airlock, pulling off the top heater hose, then replacing it with coolant flowing from the hose and the stub, will get rid of it.
You're pushing your luck driving until the heating quits. By this time there's a considerable air pocket in the head, and the likelihood of the head cracking is quite high. Nothing like as high on the 2 litre as on the 2.5, but it can still happen.
A faulty cap may be the problem. It should have already been changed under safety recall, many years ago, but there are still originals out there.
A leak down tester is the way to go, where you can pressurise the cylinders with air for a while, and see if it causes the coolant tank level to rise, or a cheap coolant system pressure testing kit of off ebay can be very educational. I've found that very few cars are entirely water tight when pressurised up with one of these.
If you do use one of these, remove the spark plugs before spinning the engine. This avoids bending con rods if water has leaked into a cylinder, and also gives you the chance to see which cylinder, if any, water shoot out of.
E30s need careful bleeding, like any relatively modern car, but, as long as they're not facing downhill, usually bleed OK. If you do get an airlock, pulling off the top heater hose, then replacing it with coolant flowing from the hose and the stub, will get rid of it.
Thanks Brian. Improvement with new cap and more thorough bleeding, but after about 10 miles heating started to drop off, stopped and saw possible leak from radiator, and also suspect pump - but this is not old, i think i changed it relatively recently. I have an almost new spare to change if necessary, along with a good rad from previous owned E30. So i will address these 2 areas first before going into Leak down diagnosis.
Ps - just remembered that all was well till i revved the car a bit more - experimentally - and then the temp rose quickly after that. That's when i stopped an re bled. Heating back on but not for too long, alas. Coincidence re coolant loss, or symptomatic of something worse?
Howard
Ps - just remembered that all was well till i revved the car a bit more - experimentally - and then the temp rose quickly after that. That's when i stopped an re bled. Heating back on but not for too long, alas. Coincidence re coolant loss, or symptomatic of something worse?
Howard
PPS - Sometime ago in my foolishness, i thought to try the liquid gasket fix (steal seal). Seemed to have achieved a small help - but does this stuff affect the efficiency of Radiators? And how does it affect the cooling system in general? Thanks
Update: - changed Rad - no change. Removed water pump after noticing water leak below it! Aha a proper symptom! Pump quite worn by feel with lateral movement. Put on a part worn which i had in keeping - though i wanted to replace with new straight away - but my desire to get a result asap meant i did not mind possibly doing the job again if i could verify the Problem. Once bled, thermostat reinstated!, the temp on car was bang on where it should be and stayed there - getting cooler the faster i went. No Overheating. And there i was getting all over complicated about 'gasket' trouble! The engine is fine though i have had terrible worries whilst it overheating trying to maintain it within limits so to speak. Curious thing now is that the heater is on and off and this Has to be a bleed issue is it not? So i will get back to this when i fit the New water pump! And thank you again Brian
Ps - do you recommend a cool running thermostat at all?
Ps - do you recommend a cool running thermostat at all?
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Deal with the heater problem ASAP - if there is an airlock at the rear of the head, then there will be local boiling which can crack the head.
Take off the coolant tank cap with the engine off and cold, pull in the small overflow pipe that is pushed through a hole in the inner wing, take off the top heater hose at the bulkhead, put the palm of one hand flat across the top of the coolant tank to seal it, put the free end of the overflow pipe in your mouth, and blow gently. This will cause coolant to flow from the disconnected heater pipe and the stub pipe. Push the pipe back on the stub while the coolant is flowing, refit the clip, top up the coolant, etc. and the job's done.
I certainly do not recommend a cooler running thermostat! The higher temperature that an engine runs at, the more efficient it is.
The running temperature was chosen by BMW to be the maximum they could reliably get away with, while running the system at the maximum pressure they considered to be safe, to avoid local boiling at the hottest parts of the head.
Take off the coolant tank cap with the engine off and cold, pull in the small overflow pipe that is pushed through a hole in the inner wing, take off the top heater hose at the bulkhead, put the palm of one hand flat across the top of the coolant tank to seal it, put the free end of the overflow pipe in your mouth, and blow gently. This will cause coolant to flow from the disconnected heater pipe and the stub pipe. Push the pipe back on the stub while the coolant is flowing, refit the clip, top up the coolant, etc. and the job's done.
I certainly do not recommend a cooler running thermostat! The higher temperature that an engine runs at, the more efficient it is.
The running temperature was chosen by BMW to be the maximum they could reliably get away with, while running the system at the maximum pressure they considered to be safe, to avoid local boiling at the hottest parts of the head.