Hey Wes? This Stu guy just showed up and is trying to hijack this thread. Can you chastise him?
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Your bravo comment is not correct.This sure sounds like an impeller problem to me. Easy to go after if the boat is on a trailer. Thermostat would be a less likely choice. BTW: Although rated to last longer, my mechanic recommends replacing impellers (need it or not) every two seasons.
I hear the point about the risers and manifolds getting hot after slowing down. Could even be true, but that is not where the temperature sensors are located on my 5.7 engine: They are right at the thermostat housing. That cools really, really quick.
As for the I/O drives: The Alpha 1 drives pick up water through the I/O unit. The bravo's use a through hull. The Alpha 1 does not have a forward facing scoop by any stretch of the imagination. There are slots on the sides that allow water to flow into the unit.
.....I hear the point about the risers and manifolds getting hot after slowing down. Could even be true, but that is not where the temperature sensors are located on my 5.7 engine: They are right at the thermostat housing. That cools really, really quick....
Your bravo comment is not correct.
Useing this thread as an example.....The OP states his engine "usually runs around 145 degrees" and your response is "if the temps stay under 180-190F, I wouldn't loose sleep over it". Why shouldn't a 30% increase over normal gauge readings(pick any guage) be reason for concern? What would be the point in having gauges or even ever looking at them? Not throwing red at you, just sitting here thinking.I am not quite sure this explanation is on target.
First, what engine do you have? Most mercruiser's have TWO temperature sensors, one wired to the temperature gauge and the other wired to the engine temperature alarm. If you peg the gauge, but the alarm doesn't go off. . .then there is a good chance it is a sensor.
But I would not rule out a bad sensor AND an overheat problem.
I would think the first things to check are the sensors and thermostat -> just because they are easy. Impellers would be the next thing to check. I forget where the BIII impellers are located. They can be replaced with the boat in the water right? Only the Alpha drives have the impellers in the "drive" and require the boat out of the water.
On my boat, once the engines warm up I NEVER see the temperature gauges move. The thermostats control the engine temperatures throught out the operating range, and control them well.
If you are seeing the gauges move during some part of the operation of the boat, then I would suggest that either the thermostats are being slow to respond OR the cooling system is not adequate in some way. Regardless. . .if the temps stay under 180-190F, I would not loose sleep over it.