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oliverquibbl · 10-05-2021, 11:00 AM

What is the fix in a gas motorhome that has gray smoke coming out of one exhaust only on acceleration?
It's a 2006 8100 Vortex GM engine on Workhorse Chassie.
Mileage 73k.

Before I take it to a shop, I'd like to hear suggestions from this group rather relying solely on a repair shop.
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Skip426 · 10-05-2021, 11:24 AM

Is the smoke visible continually on acceleration ( eg. long uphill ) or momentary , 10>20 sec then clear ?

CountryB · 10-05-2021, 11:30 AM

Grey (I think you mean Blue) smoke is oil burning. Usually means the piston rings are worn and/or cylinder walls are glazed, and is letting too much oil get into the combustion chamber. Worn valve guides usually smoke more at startup and then clear up. Worn or stuck piston rings will bypass more oil under load. Do you see any smoke/pressure coming out the oil fill cap with the engine idling?

A cylinder "leak down test" will tell if that is the problem.

Black smoke is too much fuel (unburned fuel) from faulty/incomplete combustion, can be weak ignition/spark plug/ wires, lack of air (dirty air cleaner, bad turbo, etc.)

White smoke is water getting in the combustion chamber (leaking head gasket, cracked head, etc.).

There really isn't a "Grey" smoke.

inthepines · 10-05-2021, 11:38 AM

it could also be a bad transmission vacuum modulator and its allowing trans fluid to be sucked into engine and burnt.

jeanluc001 · 10-05-2021, 12:26 PM

Add a couple bottles of mystery oil and cross your fingers.

AKIQPilot · 10-05-2021, 02:02 PM

Gray/whitish smoke is caused by water, moisture or antifreeze. Does it go away after 10 minutes or so of driving or is it there any time you load the engine like going down the highway. Many workhorse chassis coaches have the mufflers orientated in a way that condensation will build up in the lower part of the muffler. It takes a long time to burn this condensation out after initial start up.

If your smoke never goes away then you may have more serious issues. Head gaskets can be an issue if the coach was over heated. Intake manifold gaskets can also be an issue and can also allow coolant into the intake tract and cylinder.

edgray · 10-05-2021, 03:31 PM

Most of the Workhorse chassis have true dual exhaust, so whatever the problem is, it is likely only on that side of the engine. Without seeing the actual “smoke”, I’m betting on a head gasket leaking antifreeze into the combustion chamber(s). I think you could confirm if that is the problem by observation of the level in the radiator going down. Don’t rely only on the level showing in the “overflow” tank. Good luck.

TimmyB · 10-05-2021, 03:41 PM

Quote:

Originally Posted by inthepines

it could also be a bad transmission vacuum modulator and its allowing trans fluid to be sucked into engine and burnt.

Good call! Sadly, this being the culprit (and missed TWICE by the shop I was using) cost me about $600 on my Chevelle back in 1978, which was a lot of money back then for a college kid! It was a $20 part and a super easy fix, but they swore it was something else. Twice. Only when I was driving back to campus and my transmission started missing (and the smoke occurring again) did we put two and two together.

Ray,IN · 10-05-2021, 06:24 PM

I second CountryB's leak-down cooling system test comment, and add a compression pressure test. Without diagnostic testing everything else is a EWAG.

cadillac_al · 10-05-2021, 06:46 PM

Gray smoke could just be carbon burning out. I never suspect head gaskets in cast iron engines. I would just monitor the situation and look for a pattern of when it happens and make sure the smoke isn't black or blue. The black and blue smoke is easier to diagnose.

LETMGROW · 10-06-2021, 11:16 AM

Quote:

Originally Posted by TimmyB

Good call! Sadly, this being the culprit (and missed TWICE by the shop I was using) cost me about $600 on my Chevelle back in 1978, which was a lot of money back then for a college kid! It was a $20 part and a super easy fix, but they swore it was something else. Twice. Only when I was driving back to campus and my transmission started missing (and the smoke occurring again) did we put two and two together.

Bad call. Show me where a vacuum modulator is on an Allison trans.

GypsyR · 10-06-2021, 11:53 AM

To be sure. Modulators can let ATF be inhaled which usually makes a white smoke. Unfortunately the vehicle under discussion is not equipped with one of those. Vacuum modulators disappeared years ago.

TimmyB · 10-06-2021, 12:07 PM

And, we see the two ways of handling the situation, right there. One, explaining the situation properly (with manners) and educating others; the other, the all-knowing wise one, putting others back in their place.