GMCforum
For enthusiast of the Classic GMC Motorhome built from 1973 to 1978. A web-based mirror of the GMCnet mailing list.

Home » Public Forums » GMCnet » Thermostat update and non thermal fan clutch
Thermostat update and non thermal fan clutch [message #331038] Tue, 17 April 2018 07:51 Go to next message
C Boyd is currently offline  C Boyd   United States
Messages: 2629
Registered: April 2006
Karma: 18
Senior Member
The 180 Mr Gasket thermostat worked as it should on our trip to S.C. Stayed right on 180 till we hit Saluda mt. Stayed on 55 mph going up and temp did rise to ~190 but not hot enough to engage fan clutch. I had found the new fan clutch I was running was a non thermal unit? It looks the same as the thermal unit I replaced it with, small spring and all. So what's the deal with a non thermal fan clutch? I never heard the non thermal kick on with the old thermostat even with temps running in the 200 range. Didn't even hear it on initial start up. Now that I have a proper working thermostat I can hear the new Delco clutch on initial start up and it quietness down as it should.


C. Boyd
76 Crestmont
East Tennessee
Re: Thermostat update and non thermal fan clutch [message #331042 is a reply to message #331038] Tue, 17 April 2018 08:13 Go to previous messageGo to next message
jhbridges is currently offline  jhbridges   United States
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
Senior Member
If it runs at startup and then slowly stops, it is distributing the working fluid properly for a disengaged clutch. If you only got to ~~190, it probably never saw enough hot air to fully engage.

--johnny


Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons. Braselton, Ga. I forgive them all, save those who hurt the dogs. They must answer to me in hell
Re: Thermostat update and non thermal fan clutch [message #331046 is a reply to message #331038] Tue, 17 April 2018 10:54 Go to previous messageGo to next message
Bullitthead is currently offline  Bullitthead   United States
Messages: 1411
Registered: November 2013
Karma: 5
Senior Member
Maybe your previous t-stat did not flow as much at 200 degrees as the new one does, and the radiator was doing a good job of cooling that lower flow rate, so the fan clutch 'stat never got hot enough to fully engage and the engine ran warm. At least, according to your gauge that senses the coolant in the engine, instead of the radiator airflow being sensed by the fan clutch thermostat.

Terry Kelpien ASE Master Technician 73 Glacier 260 Smithfield, Va.

[Updated on: Tue, 17 April 2018 10:55]

Report message to a moderator

Re: Thermostat update and non thermal fan clutch [message #331047 is a reply to message #331038] Tue, 17 April 2018 10:58 Go to previous messageGo to next message
roy1 is currently offline  roy1   United States
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
Senior Member
Are you saying you removed a thermal clutch fan and replaced it with a non thermal unit? If this is the case a non thermal fan will not move as much air it is designed to be much quieter . It may be ok on the flat lands but it would be a bad idea to have it if you are in the mountains out west especially if you are towing anything.

Roy Keen Minden,NV 76 X Glenbrook
Re: [GMCnet] Thermostat update and non thermal fan clutch [message #331048 is a reply to message #331046] Tue, 17 April 2018 11:04 Go to previous message
James Hupy is currently offline  James Hupy   United States
Messages: 6806
Registered: May 2010
Karma: -62
Senior Member
Many people miss the fact that the fan clutch is activated by hot air from
the radiator flowing over the thermostatic coil spring on the clutch. NOT
FROM THE RADIATOR COOLANT. Those are two different things. Engine coolant
is in a very precise closed environment, pressure controlled, and not
subject to many outside influences. The air flow over the radiator, no
control at all. Ground speed, solar heat gain, headwind vs tailwind, and
many other factors influence the air temp over and around the radiator. So,
expect that there is going to be a different result each time you drive the
coach.
Jim Hupy
Salem, OR
78 GMC Royale 403

On Tue, Apr 17, 2018 at 8:54 AM, Terry wrote:

> Maybe your previous t-stat did not flow as much at 200 degrees as the new
> one does, and the radiator was doing a good job of cooling that lower flow
> rate, so the fan clutch 'stat never got hot enough to fully engage and the
> engine ran warm. At least, according to your gauge that senses the coolant
> in the engine, instead of the radiator airflow being sensed by the fan
> clutch thermostst.
> --
> Terry Kelpien
>
> ASE Master Technician
>
> 73 Glacier 260
>
> Smithfield, Va.
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

Previous Topic: Intro and some questions!
Next Topic: Onan new fuel hose pump to carb
Goto Forum:
  


Current Time: Fri Sep 06 11:55:52 CDT 2024

Total time taken to generate the page: 0.01797 seconds