OK, I stated that wrong..... (archive)

I went back and read and noticed I wasnt real clear. No, I do not get any pressure escaping when the engine is cold and I unscrew the cap, just as the coolant level does not rise up right away when it is cold. When the pressure comes out, thats the same time the coolant level rises, and that is while the system is warm. I guess my point is that I read in the manual that the clear expansion tank is just for that reason, to check level without remvoing the cap. It says not to unscrew the cap unless you are filling the coolant level because they system is pressurized. Im just wondering if Im checking this coolant level wrong and if maybe Im not topping it off where it should be or something....as Im not familiar with this expansion tank. Tomorrow Ill check for hose leaks and Im gonna fill the coolant level to where it should be and bleed the screw, etc. like it should be done.

e in the cooling system. If you put the cap on at atmospheric pressure heat the system up and then cool it down, it should still be at atmosperic when completely cool or even a slight vacum if it pushed any pressure out the overflow. Usually if you have a substantial amount of pressure when cold that is an indicator of a head gasket leak. It means higher pressure combustion gases are escaping into the cooling system. Easily checked with a cooling system pressure tester. On the wires the only sensor i can think of is the auxillary fan switch and it has 3 wires on it. Its up near the top of the radiator on the passenger side. I believe one wire is for the lower speed setting and another for the high speed setting and the third is the usual german brown for ground.
2 for bill. Alex, that is a good idea, Ive been thinking of a way to see for sure if its leaking while Im driving, I will try that.
Bill, the mechanic also noticed a wire had been cut off going to the radiator, possibly to a sensor. The sensor had 3 or 4 wires going to it, any idea what this may be? Also, I have just realized how important it is that the system is pressurized. Whenever I check my coolant level, yes the car is off and engine cold, but I unscrew the cap, thus letting out all the pressure. Could that be effecting anything. Thanks ALex and Bill.

Matt,
I was about to bring my 89 525 to the shop for the same problem. Not a large amount of fluid loss but enough to trigger the light and need more fluid. I went under the car with a flashlight sure enough it was a hose which expanded once it got hot and fluid leaked out - majority evaporating in the other hot components. The smell is very recognizable. Place some cardboard after a ride around the block and before you depart once again take a look for drops and try to determine after looking underneath where its coming from.

This really saved me some bucks. As you can tell both top and bottom hoses are pretty simple to replace. However would suggest get the original BMW equipment, it has the ridges inside and the quality is also much better than the aftermarket stuff.
Good luck,

Alex

Bill, I took my car to a mechanic today, strictly independant, because Ive had somewhat of a coolant leak since I bought the car. When I originally bought it, the check coolant light was on and when I checked it, it was probably at the lowest point possible in the expansion tank. Well I accidentally filled it to the cap, as I couldnt see the cold start line without taking off a hose. Anyway, the coolant light went off after I filled it. 2 days later,I chcked the level and it was under the cold start line by a little, maybe a notch. I assume that since I overfilled it and coolant rises when hot, that excess ran out the excess tube. Anyway, the level drops a little whenever the car is ran. I drove about 600 miles total after I bought the car, but its been parked for the winter the last 3 weeks, and Ive only ran the engine, not driven it. I have noticed it still dropping alittle though. There are no leaks on the ground. Anyway, the mechanic was gonna test the antifreeze for carbon monoxide but he could not becasue the system is pressurized. He pulled the spark plugs and they all look fine. I have no other symptoms of head gasket problems. There is some smoke that comes from the tailpipe but I think its due to carb cleaner I cleaned ICV with and I havent had time to drive the car to get it out of the system. He said if i had a gasket leak, it was so small that it could not cause that smoke. What do you think.....do you think it might be a hose somewhere near the engine that may be dissolving the coolant before it hits the ground? Or even a leaky hose? The guy says to just keep driving it.

I guess my theory is that if the coolant loss was due to a head gasket problem, that there would be at least some eveidence of antifreeze on the plugs. Reason is, even if its small, that would continue to clean the sparkplug no matter what, so the plug would be clean after a period of time.

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