[brimerianzan]

Engine temp runs around 160 degrees when moving, when ildling, it climbs up to over 225 plus. Is this a sign of a bad impeller? Is there other things that should be done at the same time when working in that area? Is there a difference in Mercruiser service manuals Seloc, Clymer

[mikeyt]

Very likely yes. First thing to check though is to make sure the water intake in the lower outdrive isn't blocked. If thats clear then a common indication of a faulty impeller pump is an engine running hot at idle but cools down with increased rpm. As the rubber impeller ages the vanes begin to retain their curled shape and lose their flex. As the engine is idling the curled impeller is not very efficient but as the rotational speed increases the vanes tend to return to their original shape. This along with some positive pressure on the sterndrive water inlets can provide enough additional flow to cool the engine down. If you discover parts of the impeller missing during the replacement process, you will need to look for the missing blades, they could be stuck downstream impairing the water flow. The impellers should be replaced every 2-3 yrs just to prevent this type of problem.

[brimerianzan]

Replacing impeller fixed over heating problem.

[spinks99]

Hi guys,

I had a similar problem today. Mine would overheat while underway. Idling through the channel was no problem. When the engine was up around 4000 RPM the gauge would climb over 175 and set off the alarm. The gauge seems to move all over the place. It seems to move too fast to be acurate. Do I have a faulty gauge?

Danny

[mikeyt]

Originally Posted by brimerianzan

Replacing impeller fixed over heating problem.

[mikeyt]

Originally Posted by spinks99

Hi guys,

I had a similar problem today. Mine would overheat while underway. Idling through the channel was no problem. When the engine was up around 4000 RPM the gauge would climb over 175 and set off the alarm. The gauge seems to move all over the place. It seems to move too fast to be acurate. Do I have a faulty gauge?

Danny

Possibly. You should verify the temps with an IR temp reader or a known good gauge. Did you recently replace the impeller? If so were there any missing pieces cuz that will cause a bockage with resulting overheat problems. If your engine has a water circulation pump then it could be failing. Worst case but unusual scenario is a blown head gasket.

[spinks99]

Mikey,

You are not making me feel any better. None of what you said sounds good. I just had the mechanic replace the shift cabe, rubber boot, and tune it up. I am taking it out on a river today. The lake I had it on yesterday is full of weeds and I had this problem last time I took it on there. The temp gauge is flying around like there is something wrong with it.

If it happens again today on the river, is there a way I can bypass it or unhook it?

Danny

[mikeyt]

Originally Posted by spinks99

Mikey,

You are not making me feel any better. None of what you said sounds good. I just had the mechanic replace the shift cabe, rubber boot, and tune it up. I am taking it out on a river today. The lake I had it on yesterday is full of weeds and I had this problem last time I took it on there. The temp gauge is flying around like there is something wrong with it.

If it happens again today on the river, is there a way I can bypass it or unhook it?

Danny

Since the common issue is a weedy lake then it may be nothing more than a blockage. Check the intake at the bottom of the outdrive.

[spinks99]

Hey Mikey,

The alarm was going off again today when I approached 4000 RPM. Temp hung around 160 to 175 while cruising and tubing. If I got into it a little the temp would climb past 175 and set the alarm off. I grounded the temp gauge and it pegged meaning it is working properly. I believe I have a thermostat going bad. I plan on changing it this week. Got another big boating day next Sunday.

All these repairs brings me back to my youth when I used to drive junk cars around. A few more problems and I'll be taking out a loan and buying a new boat with a 496mag and be done with it.

Danny

[spinks99]

Hey Mikey,

I replaced the thermostat to no avail. I had my mechanic install a new impeller. The boat runs beautifully with no heat problems. Thanks for the advice.

Danny