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Onan 6.5k baffling overheating problem...


i have an 80's style onan marine genset twin cylinder with an electric circulating pump and a great...

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Old 02-01-2009, 04:09 PM
wackedoutsurfer wackedoutsurfer is offline
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Red face Onan 6.5k baffling overheating problem...

i have an 80's style onan marine genset twin cylinder with an electric circulating pump and a great raw water pump... the generator runs great, i recently noticed carbon buildup on the spark plugs when i started up my trouble shooting... hot to the touch on the tops of the coolant lines going to the heat exchanger, and parts of the lines coming from the top are hotter on top than the lower parts of the lines to the bottom of the generator. OK TO THE POINT... HERES WHAT I DID!....

troubleshooting in this order:
-checked the raw water flow on the exhaust outlet on the outside of the boat... pretty good water flow
-i bled ALL of the air multiple times from the system, and at the same time i cant seem to find the thermostat...(manual didnt reference the generator as having one but i looked anyways)
-i ran the generator with the coolant cap off to see if there was flow.. there was some flow at first but after i topped it off, there didnt seem to be any fluid movement from what i could see.
-i pulled the electric pump off the bottom of the generator, tested it, and it runs great, impellar is healthy (its like a super hard rubber type, not like any impellar i have ever seen) and it runs strong
-i hooked it back up still no flow...
-i disconnected ALL THE LINES(one at a time) from every possible place on top, stuck a hose on the inlets of the lines, and with the cap off the heat exchanger, i got free flow..(and these lines went to the bottom of the generator so i know the whole system IS NOT clogged)
-spark plugs gapped at .030, still carbon buildup.
-i did not see any visible buildup in the heat exchanger side, but this boat was run in fresh water for its lifespan...

im thinking theres a relay or something keeping the flow for the pump from pushing the coolant through? i dont know any help please!

-oh and some weird thing that happens to my gen... when i start it, sometimes it doesnt put out any volts, but if i "chirp" the starter once of twice, it kicks right up to 130volts! WEIRD...
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Old 02-01-2009, 04:17 PM
wackedoutsurfer wackedoutsurfer is offline
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Default Re: Onan 6.5k baffling overheating problem....

I FORGOT TO ADD..... when i did run it, the side that i bleed the air from, somehow gets air in the system causing the coolant to completely push out into the overflow tank... almost 3 quarts of coolant! that after i bled all the air out of the system too... but thats only when it starts to get hot. it does have an overheat shutoff switch that is mounted at the exhaust elbow... nowhere else on the coolant side of the system from what i can see...
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Old 02-01-2009, 04:53 PM
K D Redd K D Redd is offline
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Default Re: Onan 6.5k baffling overheating problem....

First, I know little of Onans but if you getting air in the primary cooling system after it has been bleed makes me think you could have a cracked head or a blown head gasket letting combustion pressure into the cooling system.

Kent
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Old 02-01-2009, 05:12 PM
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Default Re: Onan 6.5k baffling overheating problem....

I think you have a MCCK but not sure. I have never seen or heard of Onan using an electric cooling pump. All the pumps that I know Onan used were belt driven. Both the closed water pump and the raw water pump run off of the same belt. Could you post a picture and model and serial number.
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Old 02-01-2009, 06:12 PM
wackedoutsurfer wackedoutsurfer is offline
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Default Re: Onan 6.5k baffling overheating problem....

yeah ill take a picture of it as soon as i can... right now i am standing duty here at my squadron (marines) i got called in before i could do more to it today. the pump looks almost identical to a fresh water pump kinda like a shureflow, but MINI sized... this little electric pump is only 7 inches long if that, and maybe 2 inches wide, its kinda strange. my raw water pump is still belt driven though.
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Old 02-01-2009, 06:15 PM
wackedoutsurfer wackedoutsurfer is offline
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Default Re: Onan 6.5k baffling overheating problem....

the thing is, is if it was a head problem, i would have issues with the motor running funny, i would have oil in the coolant/coolant in the oil/fuel in the oil, and i would probably have moisture on the plugs(the plugs would be clean with no residue as if they were steam cleaned with coolant)
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Old 02-01-2009, 07:37 PM
Jim Rankin Jim Rankin is offline
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Default Re: Onan 6.5k baffling overheating problem....

don't be too sure it's not a crack or gasket. I would pressure check either from the coolant side or the cylinder side. You can use a lot higher pressure on the cylinder side. Adapt an air line to the sparkplug hole and hold that piston at TDC-compression stroke while you pressurize it.

Do not take any chances with it turning under pressure! find some way to hold it securely at TDC. I recently snapped some of the cast iron fins off the centrifugal fan of a large generator when it turned from just blowing air into the spark plug holes to blow out water which had gotten into the engine through the carburetor. When the engine turned, the bar which I had been turning it with was still in the fan vanes and snapped a couple off.

Alternatively, you can get a coolant system pressurization kit and work from that side though at a lower pressure.
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Old 02-01-2009, 08:50 PM
oldtool53 oldtool53 is offline
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Default Re: Onan 6.5k baffling overheating problem....

Hi Whacked out,

What you have is an Onan model MCE. The MCE was the next model after the MCCK was discontinued. It has two thermostats. One on the top of each head at the small housing where the hose is connected. Yes, it does have an electric coolant pump. Make sure the pump is getting power when the unit is running.

Mark
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Old 02-01-2009, 09:13 PM
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Default Re: Onan 6.5k baffling overheating problem....

i did a human pressure check a while back... maybe a month ago... i blew into the purge valve and held the pressure with my mouth to hear if there were bubbles.(stupid i know but i have been running out of other ideas) no bubbles and no noticable leaks. ill try that pressure check with the cylinders... anything else i should also look for? maybe the plugs are too hot for it? i dunno..... ill get a pressure kit from advanced auto or something tomorrow
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Old 02-01-2009, 09:23 PM
wackedoutsurfer wackedoutsurfer is offline
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Default Re: Onan 6.5k baffling overheating problem....

the pump is definately getting power, because thats how i tested it. i plugged it back in after disassembling it, and it turns strong and is healthy. impellar is good too... as for the thermostats, if im looking down upon the generator, am i going to have to take off the heat exchanger? looking down at the head, it looks like the heat exchanger sits literally right on top of it... that would be the only place i can think of where a thermostat might be.. then again im not used to working on tiny engines like this so i really dont know how small the thermostat would be lol...
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Old 02-01-2009, 09:26 PM
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Default Re: Onan 6.5k baffling overheating problem....

i have a feeling i am going to have to tear apart the whole topside.... i mean i have worked on plenty of engines but this darn thing has got me stumped!
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Old 02-01-2009, 09:37 PM
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Default Re: Onan 6.5k baffling overheating problem....

YET ANOTHER THOUGHT...... when i unplugged a couple of the lines to feed hose water in the topside, and the water cam through the other side of the system, SO!...it shouldnt be a thermostat problem correct? when i filled the system the first time, i let the water run into the lines with maybe just a little pressure, and with the filler cap off, water came back up the other side very easily... it might be the pump... maybe it cuts off or something because all the lines running down the sides are cool halfway down and the tops of the lines are very hot to touch.... AND THESE ARE THE LINES I TESTED and they are all good! hmmmmm.....

LINES ARENT CLOGGED, PUMP WORKED WHEN I PLUGGED IT IN... BUT THERE IS STILL NO CIRCULATION... oh! and the first couple times i did refill it, when i turned the generator, all the bubbles from below came to the top... maybe i got a lazy pump that only works when it feels like it, BUT im still going to check for thermostats again...
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Old 02-01-2009, 09:52 PM
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Default Re: Onan 6.5k baffling overheating problem....

If it is the MCE. That one came along after I was taken out of the boat section(THANK GOD). I do have a manual for it so we can work through it. Boats
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Old 02-01-2009, 10:02 PM
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Default Re: Onan 6.5k baffling overheating problem....

i looked it up and the manual for this unit looks very fimiliar... THE MCE manual i was looking at online and im 99% sure this is the exact one i got... thanks billy! i got the factory manuals... and the Parts Breakdown lists, and stuff... yeah any help would be great though!
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Old 02-01-2009, 10:13 PM
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Default Re: Onan 6.5k baffling overheating problem....

thanks to you too mark... for some reason i didnt think of looking for manuals online to see if my specific model falls under it or not... THATS WHY I HAVE ALL YOU OUT THERE IN THE CYBER WORLD TO KEEP ME STRAIGHT!
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Old 02-01-2009, 10:39 PM
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Default Re: Onan 6.5k baffling overheating problem....

<--- my water circulating pump
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Old 02-02-2009, 08:34 AM
K D Redd K D Redd is offline
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Default Re: Onan 6.5k baffling overheating problem....

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Originally Posted by wackedoutsurfer View Post
i did a human pressure check a while back... maybe a month ago... i blew into the purge valve and held the pressure with my mouth to hear if there were bubbles.(stupid i know but i have been running out of other ideas) no bubbles and no noticable leaks. ill try that pressure check with the cylinders... anything else i should also look for? maybe the plugs are too hot for it? i dunno..... ill get a pressure kit from advanced auto or something tomorrow
You know that most people can not blow, no matter how windy they are, over ONE PSI. I thought I was a very windy person, but I found I was not. I have an in/oz gauge for setting LP regulators and I could not blow 16 in/oz on it. You need a better compressor than your lungs.

Kent
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Old 02-02-2009, 03:15 PM
RSlifkin RSlifkin is offline
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Default Re: Onan 6.5k baffling overheating problem....

I wouldn't rule out a head gasket problem. I've seen them leak where they push air into the coolant, but barely (if at all) get anything in the cylinders.
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Old 02-02-2009, 05:32 PM
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Default Re: Onan 6.5k baffling overheating problem....

The thermostats are on top of the heads. You might try removing them and then see if it cools ok. I would also flush out the heat exchanger on the closed system side just to make sure it is clear. How many hours on this unit.
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Old 02-02-2009, 05:38 PM
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Default Re: Onan 6.5k baffling overheating problem....

OK SO HERES MY QUESTION TO EVERYONE... if i had a slightly cracked head or anything like that, i should still see coolant flowing around the filler cap area right????
when you look into your filler cap, and its topped off, and you run the generator, you see the coolant moving or no? i mean hot or cold too... i do not see coolant moving at all when the generator is running. im just trying to rule out everything else before i start tearing into everything and taking everything off... i have a history of breaking things unintentionally when i try to "improve" or fix something that doesn't need to be torn apart or fixed...

if i dont find the thermostats where i think they might be, im going to start taking everything apart bit by bit and inspecting them. i might as well sand blast everything and repaint them before i put them back on too... make it like new again. everyone keeps saying head/ head gasket so im going to work from there i guess... pressure testing the cylinders first of course!
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