454 Overheating at higher rpm? Operating temp?
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454 Overheating at higher rpm? Operating temp?
Have an 1988 Merc 454, Bravo I combo. Replaced the raw water impeller, but now seems to be slightly overheating at cruise. Gets up to 160-180 at 3200-3400 rpm. Didn't let get any hotter. Runs nice at and cool at idle.
Always remember ran around 150 -160 max. Any thoughts? Maybe the thermostat? Checked the water flow and seems good.
Thanks
Always remember ran around 150 -160 max. Any thoughts? Maybe the thermostat? Checked the water flow and seems good.
Thanks
#2
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Re: 454 Overheating at higher rpm? Operating temp?
What shape are the manifolds in. If over 5-7 years, they might be getting plugged up. And not to be mean............was it running hot before the new impellers? If not you might have gotten the wrong impeller.
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Re: 454 Overheating at higher rpm? Operating temp?
Were any of the blades missing on the old impeller? If so you will need to make sure they are not restricting the water flow. Try to back flush.
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Re: 454 Overheating at higher rpm? Operating temp?
I had same problem, it would only start to overheat at cruising and WOT. I replaced everything. Ended up cracking the head from the heat. After that is when I found the problem. It was the small hose that goes through the transom in the gimbal. Big time corrosion inside the hose. Many others had the same problem. It is the hose that attaches to the big hose that connects to your sea water pump at the transom. If you check everything else I bet you anything that is your problem.
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Re: 454 Overheating at higher rpm? Operating temp?
I had the same problems last year. Turned out that when this one shop replaced the impeller for the previous owner, they never thoroughly flushed/cleaned the system and I had a handfull of impeller bits clogging the oil cooler. Check that 1st before you spend money on anything else.
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Re: 454 Overheating at higher rpm? Operating temp?
Originally Posted by vandeano
I had same problem, it would only start to overheat at cruising and WOT. I replaced everything. Ended up cracking the head from the heat. After that is when I found the problem. It was the small hose that goes through the transom in the gimbal. Big time corrosion inside the hose. Many others had the same problem. It is the hose that attaches to the big hose that connects to your sea water pump at the transom. If you check everything else I bet you anything that is your problem.
#9
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Re: 454 Overheating at higher rpm? Operating temp?
thermostat ............ quickest test ... take it out and run it ...
but after reading the post again ... does look like blockage ..the thermostat problem will generally let the motor run cool at idle or slow speed but the motor will overheat if you run it at normal speed ....
but after reading the post again ... does look like blockage ..the thermostat problem will generally let the motor run cool at idle or slow speed but the motor will overheat if you run it at normal speed ....
Last edited by offthefront; 04-16-2006 at 06:56 AM.
#10
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Re: 454 Overheating at higher rpm? Operating temp?
1) Pieces of old impeller in the oil cooler.
2) Collapsing water inlet hose, at that age the inside can separate from the wire and collapse.
3) Thermostat
2) Collapsing water inlet hose, at that age the inside can separate from the wire and collapse.
3) Thermostat