Kohler generator overheat after coolant replacement.

[Tomion]

I recently changed my impellar on my Kohler 10 EOZD genset with Yanmar engine. I also changed the coolant hoses and cleaned out heat exchanger. I ended up with an overheat auto shut down after 7 minutes. After much internet surfing I decided to try burbing air bubble out of coolant side. I had use the boat previous day without genset and when I removed coolant cap today the coolant level had gone down signifigantly. I topped it off and proceeded to run engine for an hour with out overheat shutdown. I presume the planing and wave action broke coolant bubble free saving me try to get the plug out of top of coolant resevoir which was not coming loose without a lot of effort!

[Midnight Sun]

I have a Kohler 9 EOZD also with a Yanmar engine so I assume it is similar. I have replaced several impellers on many units and never an issue but this one was different. It also overheated right from the get go after I replaced the impeller. The impeller cover was scorching hot. Turns out the impeller was not in all the way, yet the cover was easily screwed on. This caused excess friction at the cover and improper functioning of the impeller. Opened it up and found an appropriate sized socket so I could seat it properly, tapped it into place and everything was fine thereafter. Bottom line is the impeller was not seated properly. Good luck with your issue and hopefully it is as easy a fix as mine was.

[mjk1040]

Sounds like you had an air pocket after replacing the coolant. Any closed cooling system should have been burped. Also, when refilling, unit needs to be run with fluid level an inch or so below fill port for awhile to get it up to operating temp and also allowing the thermostat to open and flow coolant, this will also help get any air out of the system. If you look in the filler port you should see coolant flowing if the thermostat is open. That said you shut it down and top it off and should be good to go. No as for the impeller issue Midnight Sun discussed, that a whole different problem. Mike

[km1125]

An easy way to get air out of a closed cooling system is to vacuum it out!!

Sounds simple, or silly, but it works.

If you're refilling the system, put only enough coolant in till it gets to just above the bottom of the coolant tank. Take a vacuum (preferably a wet/dry one) and quickly hold the tube to the opening in the tank. It just takes a couple quick 'burps'. Check the coolant level. If it went down a bunch, add some and do it again. When it stops going down after you 'burp' it, then top to the correct level, put the cap on, then run the engine.

The vacuum also works great if you have work to do on the system and you want to drain all the coolant. Vacuum out the coolant reservoir, then take one of the top hoses off and vacuum the remaining coolant though that hose.