Engine running cooler than the T'stat?? Ideas ?

Matt Colie

Matt Colie

Well-known member
Aug 15, 2008
11,101
807
113
South East Michigan near DTW
My engine is running cooler thant the thermostat setting.

This has been going on for a while, but:
1 - I though it was my imagination.
2 - I suspected the gauge calibraion.

Well, I did the pot on stove test of the 160 and 195 T'stats and both were in spec.

I was sure I put the 195 back in. I just checked and 160 is in the parts box.

Both the panel gauge and the new Digipanel agree tht 180 is about all it gets to....
And it might not stay there.
I have had T'stats fail open and one fail closed. How this happens, I don't have a clue.
There is no solid valve in the heater circuit, but we are also not getting heat in cab.

Any Ideas??

Matt - about half past Illinois on the way to Shawnee
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Still Loving OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Matt, you have more cooling than you have heat. Big trucks have shutters to
restrict air flow. Might try some cardboard and zip ties.
Jim Hupy

> My engine is running cooler thant the thermostat setting.
>
> This has been going on for a while, but:
> 1 - I though it was my imagination.
> 2 - I suspected the gauge calibraion.
>
> Well, I did the pot on stove test of the 160 and 195 T'stats and both were
> in spec.
>
> I was sure I put the 195 back in. I just checked and 160 is in the parts
> box.
>
> Both the panel gauge and the new Digipanel agree tht 180 is about all it
> gets to....
> And it might not stay there.
> I have had T'stats fail open and one fail closed. How this happens, I
> don't have a clue.
> There is no solid valve in the heater circuit, but we are also not
> getting heat in cab.
>
> Any Ideas??
>
> Matt - about half past Illinois on the way to Shawnee
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Still Loving OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Your thermostat could be stuck open. A friend of mine had his fail in
the open position and he could not get his temperature up well at all.

> Seen this when it is cold out. Also driving into wind.
>
> Trade me? I would rather have 160 then my random getting hot.
> --
> Jon Roche
> 75 palm beach
> St. Cloud, MN
> http://lqqkatjon.blogspot.com/
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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--
Ray Erspamer
78 Royale - "The Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMCRoyale
414-484-9431
Web Site: http://ray-lisa.page.tl/
 
Try a different 195. I bet the amount of throttle opening it gives you in a static pot and in the engine with water pump fluid pressure is different.
May I suggest trying a Stant Superstat. Pintle type for better control. My Tahoe would feedback cycle overshooting and then overcooling gauge moving
up and down at steady cruise load. Superstat made it rock solid stabile temp
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Do you have the water heater hooked up to the engine?

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Matt
Colie
Sent: Tuesday, March 21, 2017 12:32 PM
To: gmclist
Subject: [GMCnet] Engine running cooler than the T'stat?? Ideas ?

My engine is running cooler thant the thermostat setting.

This has been going on for a while, but:
1 - I though it was my imagination.
2 - I suspected the gauge calibraion.

Well, I did the pot on stove test of the 160 and 195 T'stats and both were
in spec.

I was sure I put the 195 back in. I just checked and 160 is in the parts
box.

Both the panel gauge and the new Digipanel agree tht 180 is about all it
gets to....
And it might not stay there.
I have had T'stats fail open and one fail closed. How this happens, I don't
have a clue.
There is no solid valve in the heater circuit, but we are also not getting
heat in cab.

Any Ideas??

Matt - about half past Illinois on the way to Shawnee
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Still Loving OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

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GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Possibly the stat you are using is one of those stats that has bypass holes in it to keep a certain amount of coolent flowing when it is closed?
--
Roy Keen
Minden,NV
76 X Glenbrook
 
Do you think the cold ambient air and using the heater and hot water tank
heat transfer is effecting the temp.
The heater does dissipate lot of heat. There are times I use the heater to
assist in bringing down the temp on a hot day.
The heater and hot water tank allows the engine coolant to circulate even
when the thermostat is closed.

> Possibly the stat you are using is one of those stats that has bypass
> holes in it to keep a certain amount of coolent flowing when it is closed?
> --
> Roy Keen
> Minden,NV
> 76 X Glenbrook
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
I would next shoot the side tank right by the upper hose to get a reading on coolant leaving engine. If it's 180 or so the stat is not doing it's job.
The current gen of stats and rad caps are made from thinner and thinner metal to save pennys. My Jeep XJ started running at 210 yesterday while 40
outside and the overflow level was higher than I remember. I replaced the cap as the poppet valve spring had failed open allowing coolant to freely
come and go to the overflow. The thinness of the new cap was stunning. A thin metal stat that is slighly deformed from shipping and handling may be
junk though newer and working in the bench test scenario.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
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