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Re: Volvo md7a overheating, temperature fluctuating
OK, let's see if I can make an ass of myself here. I'm gonna bet I know your problem.
On my MD7A The water goes through the strainer, into the transmission, then through a really stupid pipe to the water pump, then to the water jacket.
The problem is the connection between the transmission and the water pump. It can be either connection or the pipe itself.
The connection to the transmission is weird and requires a compressible copper washer. You need to get a new one, get a few. The connection to the pump is just a push In kinda fitting with a fat rubber o-ring. The pump housing should have two u shaped holders to keep the pipe in place. If you don't have the right fat o-ring you can use 4 or 5 regular o-rings in series.
The pipe itself may be cracked and sucking air. I eventually cut the middle out of the damn thing and used some hose to make the connection, just keeping the bitter ends for the connections.
That FINALLY stopped the over heating. Took me forever and some help from an old codger to figure it all out.
The engine would run fine for days, then all of a sudden overheat in just a couple of minutes. The pipe didn't have the right copper washer so I didn't know I needed it. They had used silicone to make the seal, this was intermittent. It was after that that I found the copper pipe had a hairline crack in it. IIRC it had been repaired previously. Anyway, the copper pipe was a mess to fit. Once I cut it out and replaced the middle with hose life was sweet.
They don't pump much water at all, just kinda a weak splurt, then another, then another.
When you open the thru hull you should get a good steady stream of water, a little fountain, not a trickle. Stick your finger down in and see if you have some growth or sludge in it. May need to stick a pencil or something through.
Last edited by hpeer; 06-11-2014 at 11:05 PM.