"Wet Stacking" Questions

[Gordon Bryant]

I have heard some talk about "wet stacking" I think I understand what this is. I believe it's when the fuel is not burning in it's most efficient state, do to under 65% load on the generator, thus causes a wet or oily exhaust. Please let me know if this is right.

But my main question is: What is the side affects from wet exhaust? What problems will it cause over time?

Thanks to all who have input.

 

[Suprman]

Oil builds up in the exhaust if you are not loading the gen to capacity. If you give it a good load for an hour or two it will clear it out. Sometimes it can actually blow carbon chunks out the exhaust under full load after a long period of low capacity use.

 

[Jimc]

yes that basically right. its from a diesel running too cold resulting in an inefficient burn. the unburned fuel builds and collects in the exhaust usually spewing and spitting out as a black oily carbon. over time this builds on the piston rings, valves and everything else. 65% load might be a bit much. water cooled diesels are more prone to this since they cool more efficiently. every generator will be different in load required. i have heard no less than 30% on an 004 but maybe it is 50 on another model. basically it comes down to temp. they like it hot and a diesel not under load is running cool.

 

[quickfarms]

This is more of an issue with air cooled diesels and turbocharged engines seem to bee much less susceptible.

 

[m16ty]

water cooled diesels are more prone to this since they cool more efficiently.

This is more of an issue with air cooled diesels .

So which is it? I'd think liquid cooled would be more prone.

 

[patracy]

All diesels are prone to it if load isn't applied. And it's not really oil. But rather fuel.

 

[Isaac-1]

It depends on the model to some degree, in the case of the generators we are talking about it tends to be less of a problem on the air cooled diesels, part of that may be that the MEP-004a and MEP-005a water cooled models tend to have a reputation for being very prone to this condition, the military did no one favors in oversizing the engines on those models by so much. As to the effects of wet stacking, one of the worst ones is cylinder glazing, a hard coating builds up on the cylinder walls which keeps the rings from seating correctly allowing for blow by and oil to get into the combustion chamber, which of course just adds to the problem and once it gets to a certain point the only solution is to rebuild the engine.

Ike

p.s. I did run across an interesting military report online dated from the 1980's on the MEP-004a and MEP-005a a while back regarding this trait, interestingly enough their review of maintenance records and testing did not show a systematic problem with these models and wet stacking, instead it found that some individual units are much more prone to it, the conclusion was it is caused by an unknown defect in production. I don't know if their were flaws in the study method or not, but apparently their was enough concern on these two models to do a detailed study.

 

[zout]

If you like pictures with a good explanation here ya go: http://cliffordpower.com/wp/wp-content/uploads/2011/12/IS_09_wet_Stacking_GENERAC.pdf

 

[ETN550]

All diesels are prone to it if load isn't applied. And it's not really oil. But rather fuel.

It starts off as fuel but over time the fuel washes the liners or bore and the rings loose ability to seat and then oil consumption goes way up. The oil contributes to the black goo.

When I was service manage at CAT we ran into this with a lot of low mile engines that were idled at truck stops too much. We had to supply readouts from the ECM as to how much time was idle and zero speed. If it was over a certain amount the CAT warranty guy would not warranty it.

We could tell by looking at the truck, practicly. The operator has an oil consumption complaint and the exhaust is wet or there are signs of "slobber" on the truck.

Once the oil consumption is bad then its an overhaul. Valves and valve guides don't seem to suffer. Just the bore and the rings. If oil consumption is ok then the recommended loading to keep the rings seated and burn off the slobber and carbon soot will fix it.

Carbon and soot alone should not kill a good engine. The piston, rings, valves and seats cna handle it. But if carbon fouls up an injector tip and the spray is bad then fuel can wash the bore.