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Old 11-30-2012, 06:48 AM
rdl rdl is offline
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Location: Ontario, Canada
Join Date: Jun 2010
Posts: 1,767
Mein Auto: 530i 2003
Originally Posted by danmar View Post
losing coolant, not in oil or leaking. Smoke when start up and after slowing down to stop. It did over heat a bit when rad went out. Thinking head gasket but oil is clean. Any thing else to check before removing head for rebuild ? 1998 528i
Given the complexity and cost of a head gasket I'd check a few things first, perhaps with help from a repair shop with specialized equipment. Unless I could confirm a head gasket failure between coolant & combustion, I'd look hard elsewhere first. It's possible that the smoke you mention may be a second issue of oil smoke due to valve stem seals or piston rings.

If suspecting a coolant to combusion cylinder leak one can test for the presence of exhaust gases in coolant.
A) One method checks the coolant with strips or test liquid addition to a sample for colour change.
B) Use a tail pipe emissions probe in the throat of expansion tank to test for exhaust gases while engine is running, which should not be present.
C) If you have a sensitive nose, sniff for exhaust smell at the expansion tank, cap off, while the engine is warm and running. But only a few sniffs - be careful of ethylene glycol poisioning.

If chasing a slowish leak, keep in mind that smaller leaks may never leave a drip or wet deposit. The leak can be small/slow enough that the coolant evaporates/dries before forming a droplet, or open only when the system is hot & under pressure and thus lose coolant as a small jet of steam rather than a wet dribble. In either case there is very little indication of the leak point, although BMW coolant does tend to leave a white deposit.

One can use a pressure tester on the expansion tank and look for small leaks, often in a difficult to see obscure corner or hidden location. One can also add ultraviolet dye to the coolant, drive a day or two and then check for dye deposits with a UV light. Again the leak may be in a hidden corner but the UV deposit is ofter easier to find than a liquid seep.
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