Renault 8HP diesel overheating

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Tom Milke

Hi All, I have a new (to me) 1980 Hunter 27 with an 8HP Renault diesel. Following no apparent pattern, the engine stops passing cooling water. For example, on the way out last Sunday (my first real sail) it ran fine for 1/2 hour with the needle pegged in the cold (120 degree) position. Several hours later when I started it up again to head back in, the engine overheated and I could tell by the sound that no water was coming out the exhaust. I pulled the water pump outlet line and it was putting out water OK, but nothing coming out of the engine! The engine has two paths to the exhaust, one thru the block and a second path that appears to be some kind of by-pass. There doesn't appear to be a thermostat of any kind. I have previously backflushed the engine and examined the water pump impeller, which is fine. I backflushed it again last night, and it ran cool as could be. I have no doubt that it's going to overheat again as it's happened multiple times. Wazzup wit dat? Would appreciate any and all comments/suggestions that don't involve pulling the engine and throwing it over the rail. (I have back problems and couldn't lift it). :cool: Tom Milke
 
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Pat McCartin

Tom,

Being raw water cooled that engine is designed to run no hotter than 140 deg F. If this is an intermitent problem you might have picked up some trash that blocked the cooling passage in the motor. About the only help I can be is to recomend an intake water strainer. Make sure you back flush completly. Pat
 
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D. Prior

Cooling water

Tom I have a larger Hunter but had the same problem once. It turned out to be the exhaust riser elbow was rusted on the inside and the cooling water could not exit hence overheating. Once I found the cause it was easy to fix. Subsequently I have replaced the riser elbow every five years. Also check the manifold-to-exhaust water inlet for corrosion. On my Yanmar this is just a 3/4" (?) brass elbow. It corrodes on the inside and gets smaller until the water flow is reduced again causing overheating. Hard (and expensive) lessons on my part but once you know it is not too bad. Fair winds.
 
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Tom Milke

Thanks for the tip on the outlet elbow...

Hi "D.", The exhaust has been recently replaced and I reamed it out anyway (it was clean), but I didn't look at the other location that you mentioned. I'll pull it on Saturday. One of the puzzling things about this is that it's a bit of a binary state. Either the engine is cool or the engine is overheated (NO water circulating). There's not much of a middle ground. Thanks for your comment. Tom
 
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j Cianflone

rc8

Check the t connection that screws into the back of the engine. I have had to work shell material out of it before. I also had bits of rusted metal jammed up in the t connection that would stop the flow once in a while. Be careful of the plastic tee breaking as I now have one made of metal. The rc8 has no thermostat.
 
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