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671 TIB Overheating

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maverick4415

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I have 671 TIBs (485 hp) in a 44' sportfish...port engine is overheating...just cleaned out raw water side of cooling system and replaced hoses and impellers - no leaks when done and plenty of water flow out exhaust...bring boat up on plane, and it runs at 178 for a couple of minutes, then creeps north of 180, and within seconds starts climbing up over 200...as soon as it goes over 190, I start bringing it back down to idle and it comes back to 180...I'm thinking because of how quickly it climbs, I have a thermostat that's sticking closed...don't think it would have hovered at 178 at all if it wasn't getting enough raw water through system....BTW - a couple of years ago I had a thermostat problem on the other engine except, in that case, it was stuck open and running too cold...thoughts from the forum??
 
You could very well be right about the thermostat. That's where I would go first since it is quick and cheap and fairly easy.

However, if this were in a truck (where most of my expertise lies) I would say that you MIGHT have an inefficient radiator. This is a sort of classic symptom of poor heat exchange due to either the radiator being internally plugged or scaled to the extent it just can't absorb heat past a given point. As the engine load goes up and more fuel is burned, it just can't "keep up". I suppose the exact same thing could be said for heat exchangers on boats but, again, my experience is with big rig trucks.

My understanding is that the 6-71TIB 485hp is at the edge of the envelope for this power platform and keeping the temp in check is no mean feat when everything is A OK. So, something in your cooling system just a bit out of kilter here ie: water pump vanes worn or slipping, thermostat hanging, scale build up or heat exchanger blockage could produce this sort of trouble.

But, by all means, go with your gut and do the thermostat and see if it doesn't improve.
 
Thanks Jgmo...since the heat exchanger was off and send out for cleaning in the spring, and I just cleaned the oil coolers and the rest of the raw water side, I'm convinced it's on the freshwater side...will swap out thermostat and make sure coolant is topped off and see where that takes me....Btw - I've had these motors for 6 years and they've never run warmer than 178, even before cleaning the system and replacing impellers
 
Well, I've heard it said, and I agree, it isn't the amount of hours that an engine has on it that dictates it's lifespan........
It's the maintenance.
Sounds like you are in the habit of taking care of your stuff.
Good luck with the old girl.
 
Thanks Chris...that would result in leaking coolant at that site though, correct? I have not seen any coolant or raw water anywhere in the engine beds, which is why I'm thinking internal...your thoughts?
 
As a follow-up, discovered coolant in engine beds and finally found leak on 5/16" hose between heat exchanger and water manifold...Repaired, topped-off coolant and now running 170 degrees at cruise...thanks for the comments all
 
maverick4415 said:
Thanks Jgmo...since the heat exchanger was off and send out for cleaning in the spring, and I just cleaned the oil coolers and the rest of the raw water side, I'm convinced it's on the freshwater side...will swap out thermostat and make sure coolant is topped off and see where that takes me....Btw - I've had these motors for 6 years and they've never run warmer than 178, even before cleaning the system and replacing impellers
Click to expand...
I'm having the exact problem and I am going to replace my thermostat. Did replacing yours fix the problem?
 
seacane,
Read post #8 of this thread. He says he found a small leak in a hose. He had previously stated that he saw no leaks so it must have been pretty small. A thorough visual inspection is crucial in the beginning to find an overheat problem. Do that and if you continue to have issues, I advise you to start a new thread to attract as many readers as possible.
Good luck.
 
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