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: Engine over heating

11-27-2008, 09:04 AM
I wanted to share this with you all, but mainly, if someone can explain what happened I could put this one to rest.

It started with draining the coolant and taking the radiator off my 1995, 5251 Touring wagon. I had a slow but persistent transmission oil leak and it seemed to be coming from the transmission oil cooler (attached to the radiator). It turns out that the transmission cooler was good (a local radiator repair shop placed it under 70PSI pressure for about 4 hours and it did not loose any air) after a reasonable $20 fee for checking it and cleaning it, I put all parts back together, fill up the radiator and started the car.
At first it seemed peculiar that with the radiator cap off, while I reved up the engine, there was no flow of antifreeze through the radiator at all, it was still I keep the car running at idle until the temperature gauge moved close to the read line. I thought I may have an air pocket keeping the fluid from circulating and tied to pump the coolant by squishing the top and lower radiator hoses with no success.

I thought than, maybe this is a coincidence that the thermostat is now stuck closed and it just does not open the flow of coolant, even though I know that the coolant system is designed with a by past to prevent the system from building too much pressure until the thermostat opens which could cause gaskets, seals and components to fail.

I proceeded to remove the thermostat housing and noticed the degrees at which the thermostat would open 90 degrees Celsius, so I did a home test. I put a pot of water to boil, enough to cover submerge the thermostat, and used a convenient cooking thermostat to noticed if the thermostat opened at what degree it did and the result was favorable. The thermostat did open at 90 degrees.

I was able to reuse the gasket and put it all back together and refill the radiator as I did the first time around. Turned the car on and know the coolant is flowing, even before the thermostat opened.

I believe that the original issue was an air pocket; I do not know how I did not created the air pocket the second time around as I filled it in the same manner.

The car is running well and as for the oil leak, I replaced the two O-rings where the transmission hoses connect to the transmission cooler. Itís been two days and no sign of oir in that area. I should know in about 1 week.

Any thoughts, any one?

11-29-2008, 08:12 AM
What a frustrating ordeal:p
I think you probably had an air lock in the cooling system. With the convoluted hoses and passages through the heater and engine block it is VERY difficult to eliminate air traps when you refill the cooling system. Don't forget though that there will be little or no flow through the radiator until the thermostat opens, but obviously this should happen long before the temperature approaches the red zone. Sometimes it helps to raise the front of the car onto ramps so that the air gathers at the highest point in the radiator, making it easier to spot and top up. One tip for the future, never run the engine until you are sure the system is nearly full. Air makes a very poor cooling medium and you don't want to risk hot-spots or warping the cylinder head. Fill it up slowly and allow time for the air to work its way to the top. You can also reduce the likelyhood of air pockets if you loosen the top hose where it meets the radiator and fill the engine block by using a funnel to put coolant down the hose. Again do it slowly to allow time for it to get past the thermostat.

11-29-2008, 12:33 PM
Thanks for taking the time to read my threat, you are correct, I found in my Haynes manual that there is a bleeder valve I was supposed to open while I fill the radiator reservoir. It all makes sense now, I thought I was loosing mi mind. Despite the fact that working on car tend to be frustrating at time, I always fond it to be more fulfilling and even therapeutic now that I do it by choice and not as my line of work.

12-03-2008, 06:39 PM
Yeah that bleeder screw is key- One other trick that I've learned is to take off the upper radiator hose and actually fill that until it won't take any more....then clamp it back to the radiator and fill the radiator. Everybody has trouble getting air out of the E34 cooling system, but using that method I've never had any trouble at all. I usually do that, run the car up to temp and let it cool...maybe top off the coolant and good to go.