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M30 Losing Coolant

jkishel

New member
M30 runs at 185 degrees F, system doesn't pressurize (after an hour no pressure). Heat exchange stack was just replaced, no coolant in oil, no visible leaks. After one hour run time, up to a gallon of coolant is lost. Thoughts?
 
I don't know your system, but if coolant is not going into the bilge or the oil then it must be going into the raw water flow or the exhaust (both of which probably go into the ocean out the same hole). I would look first for a pinhole leak in your new heat exchanger. Keep in mind that when the coolant expands it will be forced out into the raw water, and when the engine cools sea water will be sucked into the engine cooling system. Not a good thing if you let it go. If the heat exchanger is tight then it could be an engine problem such as a head gasket that is letting coolant out of the exhaust.

CaboJohn
 
Thank you. I suspect that the original heat exchanger wasn't a problem either (previous owner replaced it). Since system never pressurizes, seems like it has to be either head gasket or one or both of the boot seals. Otherwise engine runs great, lots of power, lots of revs, so I'm cautiously optimistic that it's not a head gasket issue.
 
OK, pressure tested as follows:

1) Pressurize system, losing pressure therefore there is a leak.

2) Loosen rear heatex seal and rotate 90 degrees. Also remove exhaust hose from mixing elbow.

3) Pressure test again, coolant running out heatex seal means heatex stack is cracked. Coolant running out mixing elbow means exhaust manifold/tank is cracked.

In my case, tank was cracked. Mixing elbow was also a mess. Parts $600 but problem solved.
 
Any more I look at $600 as getting off easy. At least you had the satisfaction of finding and fixing yourself. Don't forget to flush and change coolant if you think there is any chance it was contaminated.
 
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