Can overheating a motor damage the thermostat

[motion30]

I have an 8 KW westerbeke generator. I recently installed a new thermostat. Everything has been fine and it has run at a hundred and eighty degrees. Last night I have a small 3/8 bypass hose blow and the motor got hot due to loss of coolant and the generator shut itself down. When it cooled off it started just as normal. I repaired the hose and refilled with new antifreeze now it is seems to be running hotter closer to 200° if run for a long time. Yes I have check the coolant level and bled air out the vent. So my question is can overheating the motor damage the thermostat?

[motion30]

Just to be clear these generators have a high temperature switch that will shut the motor off if overheated. Oil level is fine and. Oil is clear. I ran the unit for an hour and it did not shut off just the temperature is 15 to 20 degrees hotter than it was yesterday

[a64pilot]

Understood, however you should know that all the temperature Murphy switches I have ever seen measure coolant temp, if the coolant is missing say from a leak, they will not shut the motor down, cause they don’t sense an overheat condition.
Likely you got lucky and it did before the level dropped to the point that the Murphy switch wasn’t in coolant.
Overheating shouldn’t harm a thermostat.
However I’d keep looking, and a thermostat is easy to test, just put it in a pot of water on the stove with a thermometer.
Realize of course that it will begin to open at x temp and be fully open at a higher temp. I assume but do not know the fully open is the rated temp.

However I’d go through the cooling system, and verify the gauge, by placing it in the pot of hot water, likely have to walk the pot over to the generator of course.

[motion30]

Yes thanks. The reason I am suspecting the thermostat is when the gauge gets the full temperature the gauge is cycling back and forth between 185 and 200. Seems odd to me before it had held the steady temperature

[Delfin]

Originally Posted by motion30

Yes thanks. The reason I am suspecting the thermostat is when the gauge gets the full temperature the gauge is cycling back and forth between 185 and 200. Seems odd to me before it had held the steady temperature

Unfortunately, coolant temperature lags block temperature, and I believe the murphy switch is based on coolant. So things might have gotten a bit hotter than you think, but that shouldn't affect cooling now if the stat is working properly. The cycling suggests that the stat isn't opening cleanly, so I think I would replace it.

[motion30]

Yea. The thermostat is only like a week old. But I think I will pick a new one up tomorrow. I checked the sea strainer it was clean and I put an infrared gun at the radiator cap and the temperature indicated around 200 degrees. Other parts of the motor are much cooler including the heat exchanger. The water coming out of the exhaust it's cool enough you can come from play put your hand in it. I have it running right now and the temperature seems to have stabilized around 185 or 190. I'm going to let it run a while and see how it goes

[captstu]

Take the old one out.

My engine’s thermostat failed closed after an overheat incident.

Took it out and fixed the primary cause. Without the thermostat it takes longer to get to 195 but runs at the same ultimate temperature,

The thermostat is unneeded on a steady high load application such as a generator.

[motion30]

Originally Posted by captstu

Take the old one out.

My engine’s thermostat failed closed after an overheat incident.

Took it out and fixed the primary cause. Without the thermostat it takes longer to get to 195 but runs at the same ultimate temperature,

The thermostat is unneeded on a steady high load application such as a generator.

Well with the old tstat Temp only reached 120 degrees

[Kita]

Originally Posted by captstu

Take the old one out.

My engine’s thermostat failed closed after an overheat incident.

Took it out and fixed the primary cause. Without the thermostat it takes longer to get to 195 but runs at the same ultimate temperature,

The thermostat is unneeded on a steady high load application such as a generator.

Some engines you can get away with this, leaving the thermostat out I mean. On other engines you can't because what happens is the water or coolant never spends enough time in the radiator. So for short runs it's all good, but on a long run we're maybe you would leave it run overnight it could be a problem because the water is cycling too fast and never spends enough time in the radiator to actually cool off so progressively it gets a little hotter until eventually there's a problem. I have taken thermostats out and remove the centerpiece of the thermostat so that it acts like a restrictor but does not open and close in emergency cases and that seemed to work very well.

[a64pilot]

The dirt track boys and I assume NASCAR run with a washer in place of the thermostat to act as a restrictor. They don’t run thermostats only because they see it as a possible failure, and of course their engines aren’t in service very long either.

However for any other reason you need a thermostat, it’s there for a reason, that reason is to maintain the engines temp, without the thermostat, the temp will vary with load, that’s not optimal.

[Wulf]

Originally Posted by a64pilot

The dirt track boys and I assume NASCAR run with a washer in place of the thermostat to act as a restrictor. They don’t run thermostats only because they see it as a possible failure, and of course their engines aren’t in service very long either.

However for any other reason you need a thermostat, it’s there for a reason, that reason is to maintain the engines temp, without the thermostat, the temp will vary with load, that’s not optimal.

Running without some form of restrictor (washer, thermostat with guts removed etc) will result in coolant flowing too fast to effectively shed heat through a heat exchanger AND results in localized hotspots within the engine as it doesn’t effectively transfer heat from the surrounding metal. Folks who elect to run without any restriction are fooling themselves by possibly doing away with a symptom, yet the root cause is not being addressed.

[Kenomac]

Check your raw water impeller immediately. Overheating even one short time will destroy the impeller sending small chunks of the broken off fins into the heat exchanger tubing which will in turn cause the engine to run increasingly hotter.

[P3sailor]

Change the thermostat, it's a cheap fix and may eliminate a lot of stress!!

[transmitterdan]

When you say “bypass hose” do you mean something in the freshwater circuit leaked out antifreeze coolant?

In that case there could be damage to the engine block or head. The high temp cutout works based on coolant temp. So without coolant flow the temp of the block and head can get very high before the thermal shutdown kicks in. In such a case it is possible the shutdown was initiated by low oil pressure caused by excessive block or head temperature.

When you replaced the bypass hose did you replace it with exactly the same size and length hose? If this is the hose I am thinking about its purpose is to let water flow around the thermostat so as to not starve the freshwater impeller for water. If this bypass is larger or smaller than before then it might cause the coolant temperature to fluctuate more.

[Mike Banks]

Yes--almost certainly the thermostats has been compromised. Early types had a liquid or gas filled bellows that opened the valve at specific ranges of temperatures but held the engine to about 180 degrees Fahrenheit. If these fail the valve locks shut and the engine will run hotter because only the bypass to the thermostat will be allowing coolant to pass. Some thermostats instead of an engine-provided bypass simply have a hole drilled in the valve--crude but effective most of the time. There almost always has to be a bypass of some kind to allow hot water to reach the bellows. These thermostats do not usually latch open in the event of engine overheating and thermostat failure.

More modern types use a wax system and are much smaller and cheaper to make--and if they overheat--once the thermostat reaches the fully opened position, (when the engine is overheated) they are not able to close again because of a latching system holding the valve open so that coolant from the radiator or heat exchanger is always at full volume.

On restart your engine would fail to reach operating temperature. I suspect your thermostat in not of the latch-open type and is damaged and needs replacement.

The only way to find out for sure is to remove it and put it into a container of water at 190 degrees Fahrenheit. The thermostat should begin to open, and open fully if the water remains at the temperature. Do not test them with boiling water--even a faulty one is likely to open if heated to excess.