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PCM 351 overheating

essikr

New member
My 351 PCM starboard engine overheated. Zebra mussels (lake Erie) plugged the oil cooler water inlet causing a water pump impeller failure . I replaced the impeller and cleaned out the damaged impeller piece's. Took the boat out on the lake at cruising speed temp climbed to 180,had to stay under 2000 rpm to keep it at 160. I checked the output of the water pump and it looked good. I took the thermostat out and tried again. The temp stayed at 140 at cruising same as the port engine. Do you need to have the thermostat? Can I continue to run without it? Any ideas on what's going on?
 
My 351 PCM starboard engine overheated. Zebra mussels (lake Erie) plugged the oil cooler water inlet causing a water pump impeller failure . I replaced the impeller and cleaned out the damaged impeller piece's. Took the boat out on the lake at cruising speed temp climbed to 180,had to stay under 2000 rpm to keep it at 160. I checked the output of the water pump and it looked good. I took the thermostat out and tried again. The temp stayed at 140 at cruising same as the port engine. Do you need to have the thermostat? Can I continue to run without it? Any ideas on what's going on?
I need to add that I tested the thermostat and it worked OK
 
I would encourage you to fix the original issue and put the thermostat back in....your engine will be better off in the long run.

Its very possible one of the pieces is blocking the flow further down the raw water path....may want to try flushing things out 'backwards'.

As far as pump output goes, the only definitive way of assessing it is to measure it - eyeballing it isn't the same thing....

May also want to measure the temps of the elbows; if their outlet (mixing) ports into the exhaust stream get plugged, they will get hot and induce a broader temperature rise.....they have finite lifetimes....
 
Thanks for the reply. I'm not sure what I have to do to backflush. I want to do that. What is the normal output of the water pump and at what RPM ? This is a 1984 engine. I was planning on measuring the exhaust elbow temps with infrared sensor next trip up . The pieces I removed were less than 1/4 " in size and I'm really not sure I removed all of them. I would appreciate any suggestions you can offer,thanks.
 
Oil coolers are the big items...not one method.....many disconnect the inlet and outlet hoses and then use a piece of soft vinyl hose on the outlet side and use a garden hose the flush....sometimes adapters are readily available where you get the vinyl.....

an alternative is to remove the suspected pieces and take them to a radiator shop to be 'boiled out' (usually in an acid bath)....just be mindful that if the parts are real old, it may make more sense to just replace them....
 
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