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Onan 35EK Coolant Temp on Gauge Very Low


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Old 01-04-2018, 12:53:06 PM
farokh farokh is offline
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Default Onan 35EK Coolant Temp on Gauge Very Low

Hey gang, my 35EK (serial # A970627734, spec 86116D) has been showing very cool temps on the coolant gauge when I run it up here in NY. For example, yesterday, the gauge barely went up to 100 degrees. I replaced the thermostat a couple of years ago with a 185 degree unit, and I'm not sure if something went wrong with it, or if the gauge is just reading wrong.

First, where is the coolant temp sensor located? Is it on the engine side of the thermostat or on the radiator side? I looked in both the Ford engine parts manual and the Onan parts manual, and I can't seem to find where the coolant temp sensor is located.

Any thoughts?

Thanks and keep warm!
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Old 01-04-2018, 02:01:58 PM
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lokay5 lokay5 is offline
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Default Re: 35EK coolant temp on gauge very low

The temp sensor will be on the engine side of the 'stat.
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Old 01-04-2018, 03:02:39 PM
suntreemcanic suntreemcanic is offline
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Default Re: 35EK coolant temp on gauge very low

If you have a temperature gun check the block temperature at the temp sending unit. That will tell you if your engine is heating up. If you do not have a gun go to Harbor Freight and buy one for around $25. It will be the best tool investment you ever made this year. One thing they are great for is checking all your plug ins and switch boxes in your house for excessive heat created by a bad connection.
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Old 01-04-2018, 04:45:50 PM
farokh farokh is offline
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Default Re: 35EK coolant temp on gauge very low

I have one and that's something I didn't think of. I just have to figure out where the temp sensor is on the motor. Hopefully it's obvious
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Old 01-04-2018, 08:57:33 PM
pegasuspinto pegasuspinto is offline
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Default Re: 35EK coolant temp on gauge very low

You can feel the difference between 100 and 180 by hand. 100 is pleasingly warm, 180 will make you flinch off.

You will probably have 4 coolant temp sensors. One pre hi and one hi temp, for the lights and shutdown, screwed into the coolant jacket, they will look similar to one another. One low temp, it looks like a big alumiminum tylenol pill, one wire on it, it will just have a bolt run through it keeping it pressed onto the engine-often they use a bolt already in use. The last one looks unique, will be the sensor for the gauge.
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Old 01-05-2018, 11:40:15 AM
Pete Spaco Pete Spaco is offline
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Default Re: Onan 35EK Coolant Temp on Gauge Very Low

One small additional note on using the HF temp gun:
I used one a lot on my 30EK when I was cleaning out the cooling system, some years ago. I got really funny readings when I held it anywhere near the plug wires with the engine running. This was a bit of an issue because the manifolds are on the other side from the spark plugs and reading the manifolds won't tell you much about coolant temperature.

As previously mentioned, just test the temp with your fingers; "ouch" or "too hot to leave my hand on it" equals something over about 137° F, according to UL some years ago.

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Old 01-05-2018, 03:00:28 PM
farokh farokh is offline
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Default Re: Onan 35EK Coolant Temp on Gauge Very Low

OK, I tried to get some temps, and took some pictures. The temp gauge shows around 125, the oil pan around 160, the oil filter around 117. I couldn't find the set of sensors that pegasuspinto mentions. 2 of the pictures are of the sensors I found. One appears to be various oil pressure related sensors, and there's only 1 for the coolant, which is connected to piping that goes to the hot-shot block heater unit (which is long dead, and I haven't bothered to replace it).

I've blocked the output of the radiator, although it's not 100% covered, but that's how I got the temp gauge to get this high. With the radiator uncovered, it doesn't even get to 100. I'm guessing that the thermostat is warped or something and is allowing some coolant past even though it's cold. One of the bad things about have a coolant recovery tank is that you can't leave the cap off to see if there's coolant flowing without winding up with coolant spilling
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Old 01-05-2018, 04:59:59 PM
YellowLister YellowLister is offline
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Default Re: Onan 35EK Coolant Temp on Gauge Very Low

Pull the thermostat housing off and check it.. not much else you can do. Probably stuck open
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Old 01-06-2018, 03:37:12 PM
Gunny Gunny is offline
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Default Re: Onan 35EK Coolant Temp on Gauge Very Low

#1. If it used to show temperatures a lot more reasonable, then your thermostat has probably stuck open or has some trash stuck in it. Pull it out, drop it in a pan of water with a cooking thermometer, put it on the stove and see what it does and when. Do this while the wife isn't around. For some reason they get odd about us using their kitchen for this sort of thing.

#2. Some times genset manufacturers put them in the darnest places, not all of them good places.

#3. Takes them a while to get warm, especially this time of year. 10 to 15 minutes?

In the pictures you attached, one (in the Tee) is probably the hight temperature shut dow switch. The other one looks more like a pressure switch or transmitter.

If its been a couple of years, time to flush thew cooling system and replace the thermostat anyway.
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Old 01-07-2018, 02:17:21 PM
farokh farokh is offline
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Default Re: Onan 35EK Coolant Temp on Gauge Very Low

Yeah, I figured I'd just have to replace the 'stat. It's just that it's a pain to do. The coolant has to be drained and the fan has to come off, which in the tight quarters, is a pain. I'll just wait until the spring.
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