Onan 7.5 Quiet Diesel Issue

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New member
Jan 1, 2007
I am looking for some help on a problem that I am experiencing with my generator. When I start the generator in the cold weather (30 degrees and lower) to exercise it while in storage, it only appears to run on two cylinders ( I believe that it has three). Symptoms are rough running. It idles and responds to load increases in a normal manner but with quite a bit of vibration. I usually shut it down after 30 seconds or so as I don't think it is good for it to run that way. When the weather is warmer it runs fine, very smooth with no vibration. I am guessing that one of the glow plugs isn't working but any other ideas would be welcome. If it is a glow plug, has anyone had any experience with replacing one and how difficult it is?
Thanks in advance for any info.
Model HDKAJ11451H Spec H
I have a copy of the service manual for this unit, but surprisingly, it does not show the glow plug location.  You are correct in that it is a 3-cylinder engine.  Looking at the various drawings in the manual, I would think the glow plugs would be on the right side as you face the unit from the front where the control panel is.  There is an access cover in the center of the top panel that has 4-screws holding it in place.  Once removed, and using a mirror, you may be able to see the glow plugs.  The entire top panel comes off by removing the screws around the perimeter.  On the front corner by the control panel, the 3-screws are a different length than all the others in the panel.  They also support the coolant recovery tank.  Make sure you reinstall these 3-screws in the same location rather than any of the others in the top panel.  Once the panel is removed, the engine will be exposed and you should be able to locate the glow plugs.

Hope this helps,

If it's just a glow plug, I would think the engine would smooth out within 30-60 seconds. The glow plug is to aid in cold starting and the other cylinder should begin to fire as the engine warms up from the two working ones.  How did you conclude that just one cylinder is not firing? Could just as easily be all of them running poorly, could it not?

Is their a cold weather switch or adjustment on this genset? Most of them have some provision for cold weather or high altitudes, with the accompanying change in air mass from the norm.
Thanks for your help. I guess I believe that it is running on two cylinders in that it just feels unbalanced. Maybe I am not letting it run long enough to warm up the dead cylinder but I hesitate to let it run too long due to the imbalance and the possible wear due to cylinder washdown from the unbutnt fuel air mix. I do not know of any switch of adjustment to compensate for cold weather. I will pop the top and check out the glow plugs.
Thanks again.
There is a cold weather lever on / around the air filter.  This is on my Gas Onan 6.5.  I do have to adjust this lever for summer/winter of it runs rough with black smoke from exhaust(running too rich)
Sorry, I'm no help on the Diesel.

Thanks for all your help. I have determined that it was a shorted glow plug. Apparently I was not running it long enough to waqrm up the cylinder with the faulty plug. I tested the three plugs and found one shorted. As I was in there, I replaced all three. Unit runs fine now.


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