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Topic: Onan generator oil drain plug leaking

Posted By: MrTravelDecal on 09/01/09 09:15pm

Hi I have an Onan Microlite 4KY generator. It has a drain plug that always leaks. I have tried 2 wraps of teflon tape on the tapered brass oil drain plug when I change the oil each time but I always get oil dripping/seeping passed the plug. The last time I changed the oil I tried cleaning the plug and threaded hole as best that I could and used a little Hondabond semi-drying sealant on the threads but it still leaks.

Is there another way to keep the oil IN the crankcase? I hate the leakage that occurs as it seems to blow oil mist all over inside the generator cover which in turn coats everything including wiring harness, electrical connections, bottom pan, etc.

Any suggestions?


Posted By: wny_pat on 09/01/09 11:23pm

New plug and rubber gasket?


“All journeys have secret destinations of which the traveler is unaware.”


Posted By: J Walker on 09/02/09 08:57am

I hope a new plug works, but after using Teflon tape and thread sealant I have some doubts. I would look closely for a crack caused by too much tightening. I truly hope that is not the problem though.


Jim Walker
2014 Thor Palazzo 33.2, 6.7 Cummins, 2100 Allison
2009 Malibu



Posted By: MrTravelDecal on 09/02/09 11:20am

I let the oil drain all night long and have just returned from inspecting the drain hole. I dont see any cracks around the threaded hole. There is a flat machined surface That a washer style drain plug (without a taper to the threads) could seal against.

In my mind I am concerned that a drain bolt with a copper sealing washer would not tighten up enough to crush the copper washer BEFORE it stripped out the threads of the aluminum crankcase. I dont see how a rubber washer could hold up to the job without deforming/cracking, either.

I dont believe that I have over tightened the brass drain plug as I am concious of the consequences of it (it is hollow and brass) twisting off.

Any more thoughts? I am going to town today to visit a cummins onan parts store and a NAPA store.


Posted By: MrTravelDecal on 09/01/09 11:29pm

Yeah perhaps a new plug would cure it. Next time I see a Cummins dealer I will pick one up

what would I do with the rubber gasket as the drain plug is not the type with a washer/flanged head?


Posted By: 67Airstreamer on 09/02/09 05:28am

How about getting a non-factory plug which will accommodate a gasket.


Posted By: J Walker on 09/02/09 12:58pm

You may have lost a gasket. If you can find an O ring large enough it might act as a gasket and keep the oil in. Relative to Teflon tape, it can seal some threads but not others. It depends on the tolerances. In gas fittings it seals threads very well and some water fittings as well. I keep pipe thread sealer handy when Teflon tape does not work.


Posted By: LittleBill on 09/02/09 12:44pm

MrTravelDecal wrote:

I let the oil drain all night long and have just returned from inspecting the drain hole. I dont see any cracks around the threaded hole. There is a flat machined surface That a washer style drain plug (without a taper to the threads) could seal against.

In my mind I am concerned that a drain bolt with a copper sealing washer would not tighten up enough to crush the copper washer BEFORE it stripped out the threads of the aluminum crankcase. I dont see how a rubber washer could hold up to the job without deforming/cracking, either.

I dont believe that I have over tightened the brass drain plug as I am concious of the consequences of it (it is hollow and brass) twisting off.

Any more thoughts? I am going to town today to visit a cummins onan parts store and a NAPA store.


use permatex used on ford oil pans, can be put on the plug screwed in and the oil can be added, no reason to wait. i use this stuff everywhere gaskets used to be






Posted By: donn0128 on 09/02/09 12:49pm

It probably requires a gasket under the plug. Teflon tape is NOT a thread sealant. It is a lubricant used when installing threads to help prevent galling.


Don,Lorri,Max (The Rescue Flat Coat Retriever?)
The Other Dallas



Posted By: knparker on 09/02/09 06:26pm

I was going to say try a new plug. Ours is a pipe thread plug so all the sealing is done with the threads. I use a couple wraps of Teflon tape and a dab of pipe sealer and it works fine. A new plug might have deeper threads and go into the case farther giving you a better seal.


'05 Bigfoot 30MH24DB
'07 Subaru Forester toad


Posted By: MrTravelDecal on 09/02/09 05:51pm

I am not sure as to where to find a different style drain plug. One that would allow a sealing washer underneath. Are all Onan generator oil drain plugs the same?

I called the RV place that was 30 miles away and listed as a dealer on the cummins/onan site. They didnt have the replacement drain plug but could order it for $2.XX plus $12 dollars shipping. I stopped by NAPA to get the oil to refill the crankcase and had the original drain plug with me. NAPA had a duplicate brass plug for $1.49 so I picked it up and came back and wrapped one wrap of teflon tape on it and torqued it to 21ft/lbs as the manual states. This plug seems to go in farther(all the way to the head), so we'll see if the oil seepage stops. Unfortunately it could be a while before I can tell. If it doesnt work I will try to find a drain plug that has a head on it where I can use a copper Oring under it. If this new one leaks, and I cannot find the different style which uses a sealing washer, I will try the Permatex gasket sealant next time that LittleBill recommends.

I looked in the Onan manual and it doesnt mention/show a sealing washer in the text/diagram. I cannot imagine that this style of plug (hollow brass bolt) uses a washer under its head as there is not enough of a bolt head to keep it retained when it is tightened.

Do any of you Members here have a 4000 Microlite or Microquiet generator? If so, do you recall what the oil drain plug on your genny looks like?

Thanks and I appreciate all of the suggestions.


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