Onan carburetor Icing

[gene]

I did not keep it, but there was a discussion several months ago about a
mod that could be made to heat the carb air. I had the impression it was
described in the Onan book, but I cannot remember the details...

Some one here will remember, if not you could search the archives.

gene

>During the past few months I've become aware that my
>Onan's carburetor will ice up whenever the temperature is
>below about 50. Being a pilot I know a little about carburetor
>ice in carburated aircraft engines. In the plane we can turn on
>carburetor heat whenever conditions are favorable for icing etc.
>The Onan does not have such a control.
>
>I have to think this is a common problem with Onan generators
>and their use during cold weather. The dreaded PO of my coach
>said he never experienced ice. But then he never used the coach
>between September and May.
>
>Before I "reinvent the wheel" and build a carburetor heat unit,
>I'm wondering if anyone out there has experienced icing in
>their Onan and if they have, what was done about it? I hate to
>cobble something together that's "half-assed" when someone
>knows of a better way.
>
>Richard Waters '76 PB, Troy, MI
>
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/

 

[richard waters]

> I did not keep it, but there was a discussion several months ago about a
> mod that could be made to heat the carb air. I had the impression it was
> described in the Onan book, but I cannot remember the details...
>
> Some one here will remember, if not you could search the archives.
>
> gene
>

> >During the past few months I've become aware that my
> >Onan's carburetor will ice up whenever the temperature is
> >below about 50. Being a pilot I know a little about carburetor
> >ice in carburated aircraft engines. In the plane we can turn on
> >carburetor heat whenever conditions are favorable for icing etc.
> >The Onan does not have such a control.

Gene,
Thanks for the reply.

I can't find anything in the archives about carb heat.

I also remember something in all the material that the PO gave me
there was something about building a carburetor heat unit.
Unfortunately, I've not been able to find it.

There is no mention in all of the Onan stuff that I have about carb heat.
In fact in the "Trouble Shooting Guide" section of the manual that I
have does not mention carb icing as a "Cause" for "Engine Stops."

The icing condition that I've experienced is pretty severe. Under
certain circumstances it will kill the engine after about 10 minutes
of operation. I know that its ice because I can see it form. What
I've done is to pull the Onan out. I'll start it and watch the carburetor.
After a few minutes I can see frost start to form near the venturi.
After 5 minutes or so the engine will start to run rough and then
finally it will stop. I can wait a few minutes for the ice to melt and then
it will start up just fine and run or another 5-10 minutes. The cycle will
repeat. This seems to happen when the temperature is under about
50 and the humidity is pretty high. I have to think this is a pretty
common condition for those of us in cold climates.
Richard

 

[peter brandt]

Richard,

This is what I found in my "archives".

Peter
77 Eleganza II
Colorado

> Carburetor Ice! I think that explains a lot of my recent problems. I
think
> there is a kit or something that can be made to heat the intake air
during
> cold weather. Anyone have any suggestions?

Richard,
There was a kit to shroud the air cleaner and pick up warm air from
around
the exhaust. It is not in the 78Z parts book, but was reported in a service
bulletin (76-IM-16, July 1976), Part # 2018248 for 6KW Onan, # 2018249 for
4KW. Had to be "partially removed" above 50 deg. F. When I inquired of
Cinnabar about it a couple years ago, they said it was no longer available.
I can barely make out what it looked like from my faded Xeroxed service
bulletin, but this might be a good project for one of our sheet metal
wizards. ??

Rick Staples
'75 Eleganza
Louisville, CO

Hi All
My Onan has a cold weather kit installed on it. I had to get a replacement
hose so it would not ice up on New Years eve.

The air cleaner is covered with a cylinder that has a 1.5 inch hose fitting.
There is a hose between the air cleaner fitting and a scoop that fastens on
the engine baffle. I don't think it picks up exhaust heat. It looks like it
may pick up cylinder head heat or cooling air or ?? There is a decal saying
to remove the hose above 50 degrees. I used flexible exhaust pipe for a
hose but I will be ordering some SCAT tubing as soon as I get a chance.

I didn't pay that much attention and I have not looked that closely at a
standard Onan When I get a chance I will try and get some pictures. I may
need a cold weather kit for myself before I do that .

Dave Mumert
dave

- ----- Original Message -----
From: "gene"
To:
Sent: Saturday, February 12, 2000 5:58 AM
Subject: Re: GMC: Onan carburetor Icing

>
> I did not keep it, but there was a discussion several months ago about a
> mod that could be made to heat the carb air. I had the impression it was
> described in the Onan book, but I cannot remember the details...
>
> Some one here will remember, if not you could search the archives.
>
> gene
>

> >During the past few months I've become aware that my
> >Onan's carburetor will ice up whenever the temperature is
> >below about 50. Being a pilot I know a little about carburetor
> >ice in carburated aircraft engines. In the plane we can turn on
> >carburetor heat whenever conditions are favorable for icing etc.
> >The Onan does not have such a control.
> >
> >I have to think this is a common problem with Onan generators
> >and their use during cold weather. The dreaded PO of my coach
> >said he never experienced ice. But then he never used the coach
> >between September and May.
> >
> >Before I "reinvent the wheel" and build a carburetor heat unit,
> >I'm wondering if anyone out there has experienced icing in
> >their Onan and if they have, what was done about it? I hate to
> >cobble something together that's "half-assed" when someone
> >knows of a better way.
> >
> >Richard Waters '76 PB, Troy, MI
> >
> >
> Genef -- 77PB/ore/ca
> GMC MOTORHOME INFORMATION
> mr.erf
> http://www.california.com/~eagle/
>

 

[john szalay]

>During the past few months I've become aware that my
>Onan's carburetor will ice up whenever the temperature is
>below about 50.
>The Onan does not have such a control.
>
>

Later Onan models do have that feature, I replaced the Powertray
model on our 73 with a Onan Emerald. it has a tube coming off the
heatsink fins into the carb air intake with a selector lever for
winter/summer.

 

[richard waters]

> Richard,
> GM Service Bulletin 76-IM-16, July 1976, describes the installation of
> carburetor preheater kits to prevent icing. I checked with Cinnabar a year
> or two ago, and they said the kits were no longer available. There was some
> discussion here in the past about this topic, and I believe someone had made
> up their own preheat shroud.
> BTW, the Service Bulletin stresses the need to disconnect the preheater
> above 50F to prevent engine damage.
>

Rick,
I knew I saw something about carb heat somewhere in all the stuff
I had. I never thought to look in the "Service Bulletin" binder that
the PO gave me. Now I have some pictures and text to help me
make a carb heat unit myself.

I'm thinking of making a unit to fit around the air cleaner with a small
coffee can and use some hose routed to a pickup on the head.
Richard