Strange Genset Temperature Gauge Readings

Four years ago I replaced the thermostat and temperature sender on our Westerbeke 8kw genset.

Not having much use for a genset at that time I simply would run it until it warmed up and then shut it down, just to exercise it once in a while.

Not that I actually "need" it, the temperature gauge wants to hover around 140, then quickly jump to 180 before slowly working it self back down to 140. This cycle keeps repeating itself.

Checking temps on the unit itself, the top of the thermostat housing changes temperature in step with the fluctuating gauge, going from about 150, up to 180 for a few seconds before dropping to 150 for a while. This pretty much tells me the gauge isn't lying to me.

The exhaust manifold is at a constant 190.

I have tried bleeding air from the top of the thermostat multiple times with no effect and I seem to be at a loss on why this thing is running cool most of the time (or maybe it's not).

I failed out of genset school.

Does anybody have any ideas?

Dave

Greetings,
Mr. d. As unlikely as it may be, sounds like a sticky thermostat to me but I didn't do well in genset school either.

One possible cause is your thermostat is sticking then releasing. It should be opening at 180 degrees, but if it stays open it can cause a temperature drop. The 140 degree temperature reading sounds like a wide open thermostat and it should be closed at that point.

I would second the sticking thermostat. I have had the same thing happen several times with my collector cars. This Spring it was the 69 Cuda's turn. I thought it might be the gauge, but running the heater, quickly confirmed that the engine was cycling between normal and lukewarm. Flushed the coolant and changed out the thermostat and it went away.

I've often thought it might have something to do with the lack of use, the thermostat sitting there closed, bathed in cold coolant for long periods of time??

Replacing the thermostat was going to be my next "guess" as it is an inexpensive "fix".

It will have to wait a week until we get in to Annapolis. I was having a hard time visualizing this thing getting stuck open. Stuck closed I understand but not the other way around.

Thanks, guys. I won't fuss with anything else until I replace the thing.

Dave

Did it do this before you changed the thermostat last time? Is it installed backwards? My same model ran at about 140 without a thermostat, so yeah, must not be closing properly.

Swapped out the old thermostat today, it was pretty caked up. It was installed correctly (spring on the engine side).

After installing a new thermostat, the temperature on the housing varied from 160 to 180 degrees so the thermostat is doing it's job correctly. The gauge was still jumping around, but giving higher readings than before.

I guess the next thing is to replace is the gauge (or ignore the thing but I can't seem to do that).

Does caked up imply that the rest of your system is the same way and needs a good cleaning? Mine was rusty when I first got the boat which was not surprising considering what a pia it is to remove the sound cover and reach everything. Your sending unit may also need replacement or at least removal to see if it is covered with junk. I would have to look up how, but you can test the sender with a multimeter. Have fun. I also like working gauges.

I did replace the sender when I replaced the prior thermostat. You can see in the housing the business end of it when swapping out the thermostat. It is still clean and nice and shiny.

I expect that if i removed the sender and the gauge I might be able to wire them up and by putting the sender in a pan of hot water could verify the temperature reading.of the gauge.

Fixed (I think)

I realized I had three Westerbeke temperature gauges on the boat. The suspect one on the genset, and one in each of the gauge clusters for the main engine, on the lower and upper station.

I swapped the one out from the upper station, but before starting the genset decided to check the antifreeze level. The overflow bottle was full and the fluid pristine but one of my friends recounted how his genset overheated even though this overflow bottle was full. It turns out the hole that feeds it below the radiator cap was blocked.

We found exactly the same condition. Full bottle, real low on actual coolant, and had to take off the L fitting to clean out the crystallized antifreeze.

Topped of the antifreeze, started things up and the temperature readings on the gauge have stabilized. We also could see the antifreeze burping back into the overflow bottle as air worked it's way out of the system. It is obvious that the antifreeze needs changing as it is pretty disgusting looking.

Problem solved.

I wish I had been on the ball enough to pick up on that. I had the duplicate scenario with the blocked passage and the crappy antifreeze. Mine resulted in an over heat since it was coupled with a collapsing raw water suction hose. In my case antifreeze would leak out the pressure cap. I guess these generators are susceptible to the blockage. Turns out when I checked out my Lehman main it also was blocked so the bottle did nothing. Luckily it was not not loosing alot of coolant from the cap. Congratulations on the fix.