Is My Mercruiser Running hot?

[andym84]

I have a 2000 Sea Ray 180 powered by a 3.0 Mercruiser of the same year and am concerned it could be running hot as a result of the last outing. The boat hasn?t been used for about 3 years so had it professionally serviced by a marine engineer that included changing the impellor and water pump amongst a whole host of other things.

Whilst the boat was idling and at slow speed/revs, the temperature gauge indicated approximately 80?C (176?F) and whilst up on the plane, about 90?C (194?F). I have tried to diagnose the fault today using an IR temperature gun and whilst running the boat on muffs. I noticed when the temperature gauge was indicating 80?C, the temperature on the thermostat housing was approximately 60?C (140?F) and the temperature on the exhaust riser/elbow was about 40?C (104?F).

I couldn?t get the engine any hotter to replicate the 90?C reading I had whilst out on the water as I wasn?t reluctant to run the boat at high revs without a load on the prop.

The manual states my thermostat is 71?C (160?F) so to me, it would appear my engine is running at the correct temperature and the fault is somewhere else. Possibly the temperature sender and/or gauge?

So my first question would be, do you agree with my thoughts as I have little mechanical knowledge and after my horrendous servicing bill, need to resolve this one at minimal cost?!?! If so, how would I test the sender and gauge?

Hope I have chosen the right section of this forum.

Thank you in advance.

Andy

 

[Dekker500]

I'm not familiar with that engine, but I'm not sure I see the problem... Is it simply a concern that your engine is running hot?

Your thermostat is set to 71?C, so it won't start to cool until it reaches that temp.

You were seeing temperatures of 80?C at idle and 90?C at WOT on the gauge.

What I'd be worried about is if the temperature consistently stayed at the max. If you run at WOT and it climbs to 90?C, when you drop back down to idle for a few minutes, does it return to 80?C? If it does, everything looks good.

I'd ensure, though, that you are getting good flow from the tell-tale, and verify the water is not scalding hot. If it is, or the flow looks weak, then something is still not right with the impeller/pump/tubes.

BUT

Having written all that, I dug into the issue some more, and I'd recommend changing the thermostat... or verifying they changed the thermostat with the correct one...

 

[Chris1956]

Yes, the thermostats are a maintenance item, unfortunately. They usually open at 140*F. Overheat can be caused by insufficient circulation thru the manifold and riser. If you are boating in saltwater, it might be the time to change them, if they are salt water cooled.

Running the motor without a load proves nothing, as the load is what causes the heat. That action can also cause engine damage.

 

[andym84]

My concern upon seeing the temperature gauge reading 90?C was that the engine wasn't suppose to run that hot. Or at least I didn't think it so. Can anyone tell me the correct temperature range?

Having done a little testing with an IR thermometer it would appear my temperature gauge is out by about 20?C. How can I tell if the gauge or sender is at fault?

I seem to have a reasonable flow of water cycling through but it does exit hot although not steaming.

 

[andym84]

What I'd be worried about is if the temperature consistently stayed at the max. If you run at WOT and it climbs to 90?C, when you drop back down to idle for a few minutes, does it return to 80?C? If it does, everything looks good.

Yes, temperature drops back down to 80?C 80

 

[Alumarine]

It does sound like the gauge might be out.
The temperature sender is right under the thermostat housing I believe and has one wire going to it.
You could check the temperature with your IR gun at that point.
I would hook up a different sender and gauge to verify. But then I have an old car one lying around.

Not sure where you're located but it might help if you refer to temperatures in C and F for us fahrenheit guys.

It would be better if this was in the mercruiser forum.
Perhaps one of the mods could move it.

 

[andym84]

I did try a IR gun at the thermostat housing where the temperature sender hits and there was a huge difference between the gun and my boats gauge.

I'm guessing it's more likely the sender is failing as appose to the gauge?

Please do move to correct forum, my mistake.

 

[andym84]

By way of comparison these two photos illustrate the difference in temperature readings and were taken within seconds of each other. The temperature gun was taken from the thermostat housing where the sender is located.

The guns reading in Fahrenheit is 134.

 

[andym84]

Mods - can this be moved to the mercruiser section please? Apologies for the error.