From: "Pete Read" <pete.read_at_boeing.com>
To: "Mformation" <mformation_at_halcyon.com>
Subject: Re: <E28> M5 Chasing Coolant Leak
Date: Tue, 2 Mar 1999 16:33:07 -0800
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!
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
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.
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