Onan genset, overheat after coolant change

[smlranger]

I just did a cooling system drain, flush and refill on my 10KW Onan generator. I followed the procedure in the manual precisely. I was also able to get all of the required 6 guarts of new coolant back into the beast.

However, it runs for about 10 minutes, shuts down and does the slow single flash which is the code for overheat. I figure there must still be some trapped air in the system. I have left it alone overnight and will try again today.

Other than removing the pressure cap and running it until the T stat opens, are there other tricks? I do hope I do not now have the dreaded Onan temp sensor failure.

[Archie_Kravitz]

Does your 10 have belts on the front you can't see? My 12.5 did. What a nightmare.

[bounder39zman]

Do you have Onan 10KW with earlier Izusu or later Kubota engine?
usually when gen runs 10 min or so then shuts off with overheat code it
is an air flow issue. I assume you checked water pump/fan belt condition and tightness? Is the Radiator core clean? Also the service access door must be installed or air will not pass thru rad. core and unit will overheat

[NRALIFR]

A Coolant Lift is a handy shop tool for those that do their own cooling system maintenance. It removes all the air pockets from the cooling system, and can be used to check for leaks.

On a large engine with a complex cooling system it might be necessary to leave the lift in place after filling and run the engine with the system under vacuum to get all the air out. On a small system like your genny, I would think the lift could get all the air out just by using it for the fill.

:):)

[palehorse89]

Good for you! Thanks for the update, safe travels to ya.....

[smlranger]

Thanks for all the suggestions.

I went back this AM and, after sitting overnight and cooling down, it had sucked more coolant from the reservoir. I topped it off, removed the pressure cap, started it up, let it run for about a minute, put cap back on, closed access door. It ran for about 30 minutes with no issues.

Its all good now.

[smlranger]

Thanks for all the suggestions.

I went back this AM and, after sitting overnight and cooling down, it had sucked more coolant from the reservoir. I topped it off, removed the pressure cap, started it up, let it run for about a minute, put cap back on, closed access door. It ran for about 30 minutes with no issues.

Its all good now.

[RedG]

Were you running it with the cover still off?
If so, it will overheat because the fan will not push enough air through the radiator.
If so, put it all back together and try again. I bet you'll be fine.
I found this out the hard way myself....

[JackMS]

On my 8kw I did like ivy log suggested except that I ran it with the hoses extended out like that to get the air out. It seems like if you got all the water in it should be ok but I got all my water in and still ran hot until I pulled the hoses out. I had my genset out for repairs and replaced some hoses so I blamed it on kinks, but that is a lot of hoses stuffed down into a small space- easy to kink even at the factory.

[Ivylog]

From a old post by Caymann on how to change that his manual did not include. If you did not do it this way you may need to drain and start over. I also read where you need to refill slowly or the air will not come out. This is a Onan 10kW with Isuzu 3LD1 engine.
If you open that cover, you will see a 13lbs rated pressure cap.
There are three tubes attached underneath the cap.
The top one goes to overflow tank.
The middle one is of interest. It goes straight to the top of the
engine where the water pump and thermostat is located.
The bottom tube is where all the coolant goes.
Raise this assembly of tubes and pressure cap, above the engine.
Use a funnel to pour coolant into the bottom tube.
As coolant fills up, air is expelled through the second tube.
At some point you will see the coolant coming out through the second tube and third tube together. Cover this with a new pressure cap (preferably).
Now lower this tube assembly below the bottom of the coolant overflow tank. Any air trapped will now come out the overflow tank.
Assemble it the way you found it.

[John_S_]

Yup sounds like air trapped. Do you have a IR temp gun. Run the beam over the radiator and see if there is a temp differential.

[palehorse89]

Sounds like you may have air trapped, try running it with the cap off.