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Old 05-17-2010, 04:12 PM   #1
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Onan 8 K Generator Coolant?

I just flushed my cooling system on my ISL400 and my Onan 8 K generator and changed to ES Optimax OAT coolant in both. The generator now shuts off and the hi temp light flashes even though it only runs a minute. Is this a sensor problem with the new coolant? I ran the 400 for 15 minutes with no problem.

Any help would be appriciated.
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Old 05-17-2010, 08:41 PM   #2
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Would suggest reading your operators manual and/or contacting Cummins/Onan service tech for help
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Old 05-17-2010, 10:14 PM   #3
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Your fan belt on the generator could be loose.
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Old 05-17-2010, 11:06 PM   #4
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hardy1000.....I had the same issue when I changed mine. The generator has an air lock and won't accept the coolant....thus it gets hot and shuts down. You have add the coolant very slowly because the vent tube is at the top of the reservoir.

I panicked on mine and pulled the cover. I removed the radiator hose and filled it that way. You don't have a problem, other than the system isn't accepting the fluid.

I read an article/post once about this issue, but couldn't find it. You might want to check the gen manual.

Like I said....don't panic......you just have to get the air out of the system. It might have even bled down some since you last started it.
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Old 05-18-2010, 06:56 AM   #5
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Quote:
Originally Posted by Diplomat Don View Post
hardy1000.....I had the same issue when I changed mine. The generator has an air lock and won't accept the coolant....thus it gets hot and shuts down. You have add the coolant very slowly because the vent tube is at the top of the reservoir.

I panicked on mine and pulled the cover. I removed the radiator hose and filled it that way. You don't have a problem, other than the system isn't accepting the fluid.

I read an article/post once about this issue, but couldn't find it. You might want to check the gen manual.

Like I said....don't panic......you just have to get the air out of the system. It might have even bled down some since you last started it.
Thanks Don, I am going to start it again this morning. I read the manual and it says to fill the coolant tank and then the radiator. Well, I did just the opisite, I filled the radiator and then the tank, I guess I should have read the manual first. Thanks again for your reply Don it did save me from a slight panic because Im getting ready to leave to go fishin.
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Old 05-18-2010, 06:56 AM   #6
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Thanks all,
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Old 05-18-2010, 12:24 PM   #7
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Quote:
Originally Posted by Diplomat Don View Post
hardy1000.....I had the same issue when I changed mine. The generator has an air lock and won't accept the coolant....thus it gets hot and shuts down. You have add the coolant very slowly because the vent tube is at the top of the reservoir.

I panicked on mine and pulled the cover. I removed the radiator hose and filled it that way. You don't have a problem, other than the system isn't accepting the fluid.

I read an article/post once about this issue, but couldn't find it. You might want to check the gen manual.

Like I said....don't panic......you just have to get the air out of the system. It might have even bled down some since you last started it.
Don,

It took about 5 starts to get the air out and it works perfectly now...thanks again, goin fishin now.
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Old 05-18-2010, 10:44 PM   #8
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Don I don't why I didn't think of that as many times as I've done it myself. I just had a overheat problem with my generator and it turned out to be a loose belt and that was the first thing that came to mind. Air pockets will definitely cause one to over heat.
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Old 05-18-2010, 11:48 PM   #9
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It was fresh in my mind because I really started to panic when mine wouldn't run. I've got to say......taking that generator shroud off is not a simple task.....but it was cool to look in at that little motor......felt pretty dumb after I got it running.
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Old 06-14-2010, 10:17 AM   #10
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I'm going to flush and fill my Onan Quiet Diesel 8k soon. I haven't looked it over too close yet. I'm guessing there is a drain valve on the bottom somewhere? I looked at the diagram on the Onan site but can't spot the drain valve. I'm moderately competent with a wrench so I should find it. I was planning on flushing with clear water. Then drain and fill with 50/50 mix of coolant/water? Looks like it has a 1 gallon coolant capacity. I'll use distilled water for the mix. Is there some trick to avoid the air lock thing you're talking about here? On my Chevy I add the required amount of coolant and top off with water, then start the engine and run it with the cover off the radiator and when the thermostat opens up I start adding the water. That allows the air to escape while it's circulating. Will that work on this Onan? Or does it require a bunch of starts and stops? Not trying to hijack but I found this thread when I searched for Onan Coolant so thought it would be good to get the whole procedure down here. Also, does Onan require special coolant or is Prestone all types good? Thank you.
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Old 06-14-2010, 01:28 PM   #11
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Bob....The coolant drain is a metal cap that screws on. It looks like something off of a can of liquid metal polish. These generators fill really s l o w. It takes awhile to get the coolant back into them. Looking back now, I probably could have helped my situation by cracking the drain cap a little and allowing some air back in.
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Old 06-14-2010, 04:31 PM   #12
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Thanks Don, I'll try to remember to bring my camera when I do it and take a picture of that drain plug. I keep my rig at my storage condo 35 minutes from my house so have to make the time.
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Old 06-14-2010, 04:45 PM   #13
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When I change the coolant I pull out the radiator cap hose and take off the cap. Then I pour the coolant in very slowly and wait a few minutes for air bubbles to work out. With the cap still off I run the generator about five minutes to let more bubbles work out and then I top it off. After I run it a while I check the level again and make sure it is to the top of the radiator cap and about an inch of coolant in the overflow tank.

Sometimes I get an error code when I first start the generator after the first fill. The code says the coolant is low and shuts it down. I just restart the generator and it alwaays runs OK after that.
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Old 06-15-2010, 10:29 AM   #14
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Thanks Norm, I'll try that. Prestone universal coolant okay? 50/50 mix.
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