Generator smokes, what kind of oil should be used?

[Dave1210]

Sent: 9/19/2002 

I bought out my partner, in July, on a 72 Indian and have been fixing up stuff that he would use but once it broke would never fix. Today I began fooling around w/ the generator (Onan 4kw) and finally got it started (weak battery, dirty plug, and cleaned the fuel filter got it going) but it smokes bad, like oil burning. I checked the oil and it is well over the full mark and is not thick (viscous) at all, almost like water.

Could over filling it cause this smoke? We have changed the oil 2 times in 2.5 years and it is always watery, I am using Valvoline 30wt. Should I switch to heavier oil, what kind? I hope changing the oil and putting it to the correct level will cure the smoking. Any insight on this would be appreciated.

[denisondc]

Sent: 9/19/2002

     Don't know much about gens, but on old cars, if the (old) mechanical fuel pump bladder had a small crack in the rubber, it could still pump fuel okay, but some of the fuel would be squirting through the bladder and into the crankcase via the base of the fuel pump.  This would thin down the oil, and if it got too thin could damage the piston rings.  On the other hand, you might just have stuck piston rings from using the generator only for short periods, or with dirty oil.  I would advise a compression check, except on an air cooled engine this might only show you that the valves were leaky.  Let us know what you find.     Denison

[HAL]

Sent: 9/19/2002

Hal here. I use 20/50 Valvoline oil in my generator.  I checked the paperwork and the owner has always used 20/50. He had it servced at an RV shop, so it was easy to find out what all had been done.  Talked to an RV shop here and they recommend 20/50 also.

[Homer Simpson]

Sent: 10/11/2002

In my manual it states to use a detergent oil and a specific weight depending on the weather around the area. I use Penzoil 30HD (I am in Fort Myers, Florida - South West Florida) and have not had a problem. I was also told that not using a detergent oil can cause it to smoke, I don't know if that is true or not. Hope I could help.
Homer Simpson

[Dave1210]

Sent: 10/20/2002 

My last posting was about why the generator oil was overfilled and the oil was very thin. It turns out that there was gas in the oil (thanks for the tip) so I decided to drain the oil and clean the carb to prevent the gas from flowing into the engine, my guess is that this gradually occurred during starting because the fuel pump still ran even when the carb should have been full, stuck float. After I did that I tested it, it starts up fine but smokes badly (white smoke). I ran it for about 2 minutes and it did not clear up, actually it got worse, however it runs fine, no internal engine noices or sputtering.

Does anyone have any ideas on what is wrong? I am guessing it is time for a rebuild since it ran for a long time w/ gas in the oil. If so does the whole thing have to be gone through, top end and bottom end? It is an Onan 4kw CCK series from a 72 Indian.  Thanks for any tips.

[jhuey]

Sent: 10/21/2002 

You might not have run it long enough to rid the muffler of un- burned oil/gas/condensation mixture.

You said it got worse, thats telling me that the heat is building and burning off the wet deposits in the muffler. Two minutes isn't a very long time, if it all looks and sounds ok, put a good load on it (A/C and anything that will make the gen work harder) and run it for 15 to 20 minutes you should see the smoke diminish.

If this does't seem like it's working run a compression check to see if any damage was done to the cylinder or piston rings. I don't know what the normal compression is, you would have to get that from the Onan dealer or tech pub on your model.
joe

[denisondc]

Sent: 10/21/2002 

    I would try doing a compression check, and would try running it for longer than minutes.  Just as a desparate hope that the white smoke is from oil puddled in the muffler.  But I can't think of any reason it would still be smoking after 20 minutes which would not require a teardown to fix.  Damaged rings, scored cylinder walls & pistons would be the expected cause.  By the time you are looking at the insides of the cylinder walls wouldn't you want to do a full rebuild anyway?  In which case a lot of us will want to know your story on getting engine parts.   denison

[Dave1210]

Sent: 10/21/2002

Thanks for the help, I actually ran it about 3 more times last night  at 2 minute intervals before I took the MH back to its storage lot. It seemed to run better, less smoke, and it kinda has a weird smell like burnt oil and something else mixed together, not like a typical oil burning engine. So maybe there is hope. I am eager to try it again but the storage lot closes at 5pm so it is hard to make it there in time after work. I will keep you all posted.

[Dave1210]

Sent: 10/22/2002

I ran the gen under a load for 15 minutes today and the smoke cleared out (it was pretty bad at times) and it ran fine w/ AC on.

Thanks for the tips guys. I was really bummed out when I first saw all that smoke cuz I thought I was going to have to replace or repair the gen. You guys probably saved me a lot of money, maybe some mechanic would told me it needed a rebuild or at the minimum I would have had to pay around 65 for their evaluation fees. Thanks again. Now on to other things.

[denisondc]

Sent: 10/22/2002

Stll, I would advise draining the oil from the generator right after you had been running it, and catching some of it in a clear plastic bottle. Then let it settle for a couple of days and check how much stuff you find on the bottom of the bottle. What you Don't Want To See is called "gold dust" - that would be aluminum piston shavings. A few black flakes of varnish/carbon film are to be expected. If you see much, then frequent changes of oil are indicated until you get much residual.