John Weese asks about E28 M5 coolant system leaks: >I read the excellent articles in the past two ///M Power Newsletters
>by Pete Read (Thanks Pete!), and I have a question relating to coolant
>loss. My stock '88 M5 is losing coolant when the car sits for awhile
>(is cool not hot). That seems like a loose hose connection to me, but
>I'm at a loss as to where to look. These M-Engines are really "packed"
>in there and it's very difficult to see all the hose connections!

John,

Sorry this response is so late, probably too late to help you, but maybe it will help someone else. Thanks also for the compliment on the M-Register newsletter articles. By the way, for those of you who subscribe, the March newsletter should be arriving in a few days. As I said in my editor's note, the delay is all my fault this time -- unfortunately I've been letting real life interfere with my automotive interests.

Your coolant loss while the car cools down sounds just like the problem that I described in the August 1998 newsletter. I was looking for the source of a slow loss of coolant. Bill Shook suggested that I pressure test the system with the engine cold. I couldn't believe how much coolant leaked out around the lower thermostat housing hose when pressurized cold -- it didn't seem to leak at all when warm. That short hose is very difficult to align and tighten properly, so it's a likely candidate, but any of the hoses can cause a problem.

Cold pressure testing is effective because the most common cooling system leaks result from slightly loose hose clamps. These small leaks are hard to find because the parts expand as the engine warms, before the system pressure increases enough to cause noticeable leakage. However, after the car is shut down and cools, the system is still pressurized. As the parts cool and contract, leakage occurs.

Pete Read
'88 M5
Arlington, VA