Smoking generator

Graham Boyd

My Onan MDKDP 6.5, was unused for about 6 months. Now, on start up and before any load is applied it produces large amounts of white smoke (the smell tells me this is unburnt fuel). This smoke persists even when the engine is warm.As soon as I apply load to the generator (aircon etc) the level of smoke drops drastically and becomes slight darker. My thoughts are this is probably a fuel supply or pump problem as the injectors have already been changed.

Any thoughts or similar first hand experience?


SM140 Sula

Hong Kong

ps full rebuilds in this town are rarely cost effective!

Alan Leslie

Yes...white smoke is most likely unburnt fuel...or less likely, water vapour in the exhaust.
Put your hands over the exhaust ...if it smells of diesel , it's unburnt fuel 
If that is the case, then perhaps one cylinder is not should be able to hear / feel that...
OR if the weather is cold when you start the engine and it goes away as the engine warms up, then you've got a compression problem...piston rings / valve seats....
Elyse SM437


As has already been suggested, I'd start with a compression test.  

A bit of corrosion, or a stuck ring after 6 months of inactivity could be the problem.  If the compression test is good, AND the injectors are good (which might be different than "new"), then the next place to look is the injection pump.

If the compression test is bad...  then you have a decision to make as to how far into the engine you dig to try to solve it.  Might be valves (not too expensive) might be rings or cylinder walls (much more expensive).

Bill Kinney
SM#160 Harmonie
La Parguera, Puerto Rico