A Few More Basic Questions

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Well-known member
May 29, 2006
Poulsbo WA
I recently posted about the generator on our MH and how it was running for a bit and then just dying. Started right up again and then stop 10-15 minutes. Tonight I noticed a little switch on the generator. It says "pre heated air" and the switch has two positions - winter and summer. It was on summer. I switched it to winter and it ran until I shut it off. Hmmmmm - any help?

Stupid question #1 - is the term "genset" same as generator?

Stupid question #2 - what is delamination? I have a rough idea (from this forum) and Googled it but I'll get a better explanation from someone here.

Thanks, y'all!

Poulsbo WA

Yes, 'genset' is slang or short for 'generator'. More correctly 'generator and motor set'. A generator can't produce electricity unless/until it turns which, in the case of the generators we talk about, is where the motor part comes in.

Delamination is the separation of one or more layers of a material from each other. If you've seen the glued layers in plywood separate (caused by failure of the glue that holds them together), you've seen delamination. When we talk about delamination in terms of RVs, we're often talking about fiberglass separating. It may be layers of (fiber)glass separating, or the topmost layer gel coat layer separating from the actual fiberglass. Various causes can cause either of these situations, which I'll leave for a separate message/topic.

I forgot to mention that we have an illustrated Glossary of RV terms in our library. The Glossary was compiled/edited by the late Don Jordan, a long time forum member and staffer.

Don did a great job of pulling together the inputs and suggestions from other staffers and several folks contributed the photos. Next time I see fiberglass delamination (hopefully, not on my coach or boat), I'll try to remember to snap a photo to add to the Glossary.
Tonight I noticed a little switch on the generator. It says "pre heated air" and the switch has two positions - winter and summer. It was on summer. I switched it to winter and it ran until I shut it off. Hmmmmm - any help?

Check your generator's operating manual. The general Onan recommendation (per Cummins/Onan Midwest Service) is that the switch should be in the "winter" position when ambient temperatures are below 55 degrees. Other brands may be different.

If ambient temps are not at least "chilly", you should not have to switch to the winter position and something is wrong if you do.
I've never heard of a winter/summer setting on an engine.  What does it do? Change the air/fuel mixture like a choke or something?
If it's a diesel, from the description it sounds like it turns an intake air preheater on for use in colder temps.  Most diesel have them, but on the larger engines such as we have for propulsion, it's automatic.  On his genset it's manual.
The Onan Marquis gas genset on our 96 Southwind had a winter/summer switch. It was never clear to me what it did, but the operator manual was specific about using it in cold weather. Didn't say what "cold" meant, however.

The density of the air charge increases substantially with colder temps.  Maybe it adjusts the air/fuel ratio, perhaps by closing a baffle in the air intake? 
It does indeed re-route the incoming air and, in my case, sucks a bit of heated air from the motor in with it. You're problem may indicate a weak fuel pump, clogged fuel filter, or carb in need of a cleaning/rebuild; the increased vacuum in the winter position may be helping overcome a fuel starvation problem somewhere.
Karl (and all) -

Thanks for the great answers!

I haven't messed with the generator but I'm guessing I do oil/oil filter/plug myself. Is replacing a fuel pump difficult? How about rebuilding a carb? I'm assuming I can find parts online. There were no manuals with anything, incluiding the generator.

I monkeyed with the choke settings on a tiller once and never did get it right again - had to take it into the shop. If I can do a basic genset rebuild/tune-up myself, I'd like to do it.

The fuel pump is electric, and replacing it is not difficult. There are carb rebuild kits at most rv repair/supply places. They're a little tricky to do and adjust properly after the rebuild, but if you have patience, it shouldn't be that difficult. Hardest part will be setting the governor linkage properly to avoid 'hunting', but after a few tries you should get it o.k. Make sure you don't stretch the spring! Yes, plugs, oil, filter are things to do yourself. Have plenty of old rags ready 'cause removing the filter can be messy.   
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