Generator tailpipe carbon build-up

[D. Wendal Attig]

I noticed the exhaust pipe on my Onan 7.5 kw generator has quite a build up of carbon, about 1/8" thick around the wall at the exit point.  I also notice some smoking upon initial start-up although the smoke seems to disappear once the gen has been running enough to warm up.

Questions:
1) Does this pose any fire hazard?
2) Does this diminish the performance/fuel efficiency
3) Does this represent a maintenance or tune-up issue?
4) Is there a recommended procedure for clean-out?

Thought I would ask since a search here on the forum turned up nothing previously.
Thanks for your help.

D.

[Dave Atherton]

D. Wendal, can answer some of your questions, soot build up will not pose a fire hazard,
second why carbon buildup,  high altitude non-turbo engine. Injector over fueling and injector
nozzle is carbon up. air cleaner is dirty or plugged up. Running you indicated it smoked for
while. Smoke if has  white/blue color this would indicate injector nozzle carboned up. Startup
and blowing black smoke color than air cleaner dirty or plugged, or high altitude.
Dave Atherton Retired Cat Mechanic

[D. Wendal Attig]

Is there an additive or injector cleaner I could use to free up the injectors?

[Doug Allman]

D. Wendal,
Thanks for asking that generator question. Our 12.5 does exactly the same thing and I had no idea why. Did not even think to ask the question like you did.
On a cool morning like when at the North rim of the Grand Canyon in late September I was totally embarrassed when we started the gen and the fog of blue smoke was horrendous for about 3 minutes. It wasn't a lot better when in Yellowstone NP in August mornings. I am sure the tenters were not impressed. Drive a coach of this caliber and then do that to your adjoining campers is not impressive. I was actually thinking that I would get a visit from the Park Rangers.
It will now get the maintenance of the nozzle it needs. I have either not read about this maintenance item or it is not in my manual but I am going looking again now. I do all my own maintenance and I will be with Dave Atherton in a couple of weeks so I know we will get it fixed.

[Dave Atherton]

D Wendal,  yes there is injection cleaner that will clear up the problem. First thing I would
would suggest, change out Gen Set fuel filter on the bottom, with today's fuel there is lot
Of Parafin or wax within the fuel and the little engine does not product enough heat on the
fuel return to remove all the Parafin or wax from fuel filter. Your fuel filter style is the filter used
On the chev or Gmc 6.2 earlier Engines rectangle metal filter with one size fitting for inlet
and one size fitting for outlet. Using injector clearner you would have to treat big fuel tank
That Gen Set draws from.   Dave Atherton Retired Cat Mechanic

[Gerald Farris]

D. Wendal,
There is one maintenance item that you can preform that no one has mentioned that may help your problem, and that is cleaning out the spark arrester on your generator. Most, if not all Onan diesel generators have a spark arrestor built into the generator muffler. Over time the spark arrestor can build up a heavy soot load causing a muffler restriction. Cleaning it only requires removal of a plug and running the generator under a heavy load. Instructions are in your operator's manual.

Gerald

[David T. Richelderfer]

I would agree soot buildup in your tailpipe likely will not pose a fire hazard for your coach.  But if you were to park where the exhaust pipe could flick some hot embers into dry grass, then you might start a fire.  I would guess if a chainsaw's exhaust can start a fire, then a generator could as well.  My old Bluebird generator's hot exhaust pipe started a fire once because I parked the coach over some short, dry grass.  The movie I was watching came alive with the smell of smoke!