awsomethunder

had my 25a/t 454 mag in the water this weekend.when above 4000 rpm oil temp reads 280-300 and water temp reads 180.put a new impeller kit in and found a old piece in the inlet side.pulled all the hoses of to search for others and found nothing.this motor is all stock with stock coolers.why are my temps so high.had this problem before the new impeller also.can't run wide open and getting very frustrated.would it help if i ran with a cooler or no thermostat?i think it has a 180 in it now

synack

I have a 1997 454Mag and mine has a 160 in it. Some went as low as 140. Anyway, with the 160 I normally run about 165-170ish.

One thing to check is the oil cooler. If the impeller shreds, the pieces can plug up the holes in the oil cooler which will restrict flow. One quick way to check is to pull off the bottom hose from the oil cooler and feel up in there with your fingers to see if anything is lodged in the passages. Or pull off both hoses and shine a light up from bottom and see how many are blocked.

fbh-velocity

Exactly what happened for me few years ago! You can clean the oil cooler with compressed air. You will be amazing how much **** you will find. Including impeller shreds as Synac says. Another restriction could be the hose inside the transum that might be collapsed, but tjek your oil cooler and im pretty sure you find the problem

fbh-velocity

Mercruiser use 140* thermostat. 160* on MPI. 180* is too high and if you are in saltwater the salt will more likely crystallize in your motor.