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Non gmc thermostat question [message #251705]

Sat, 07 June 2014 20:18

roy1

Messages: 2126
Registered: July 2004
Location: Minden nevada

Karma: 6

Senior Member

Awhile back I installed a Robert shaw type 180 degree thermostat in my 350 Chevy powered 48 ford. This is the same thermostat most of us use in our GMC's . It mostly runs at 180 but when stopping for a light the temperature rises to 240 or more unless I rev the engine in neutral. I figured maybe the thermostat is bad but it opens normally in a pot of hot water? So I tried another new Robert shaw type thermostat. Same problem with the next thermostat. Yes it has a new radiator. I was thinking maybe I need a hi flow water pump as it only has a problem at idle. Today I took the thermostat out and checked it with out a thermostat no more problems when I slow down it stays at 170 to 180 constantly. So the 350 doesn't like the Robert shaw stat for some reason. Has anyone come across this problem with a thermostat? As much as I hate I plan on buying a Stant type thermostat to use rather then the robertshaw type unless someone can recomend a better one?? I'd hate to keep trying different style stats to fix the overheating at traffic lights

Roy Keen Minden,NV 76 X Glenbrook

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Re: Non gmc thermostat question [message #251709 is a reply to message #251705]

Sat, 07 June 2014 22:54

Bullitthead

Messages: 1411
Registered: November 2013

Karma: 5

Senior Member

It sounds like you need to enhance the flow of your system as it seems like the thermostat is a restriction overcoming the output of the pump at idle. So you can reduce the size of the pump pulley, or get a better pump. You do still have vanes on the water pump, right?...sometimes with the aftermarket pumps the metals are inferior to the engine's chemical solution and the pump vanes disappear. Remanufactured pumps have come to me from the stores with the vanes half eaten away already.

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

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Re: Non gmc thermostat question [message #251712 is a reply to message #251709]

Sat, 07 June 2014 23:16

roy1

Messages: 2126
Registered: July 2004
Location: Minden nevada

Karma: 6

Senior Member

I thought about a smaller pulley but 2" smaller is about as small as I could go. The engine is a medium duty truck crate motor with only about 10,000 miles on it I 'm sure the impeller is in good shape it is a factory pump not a rebuild. At this point I was hoping to come up with a thermostat that will allow the coolant to move thru the motor at idle better all the components are stock late 1980's. If I can't find a thermostat that will work my next step will be to replace the pump with a hi flow one from Summit and the smaller pulley. The less experimenting with parts the better. I don't want to damage the motor because I stopped for a light and forget to rev it.

Roy Keen Minden,NV 76 X Glenbrook

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Re: Non gmc thermostat question [message #251715 is a reply to message #251712]

Sun, 08 June 2014 00:16

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Most GM engines have a recirculation path to keep water circulating through the engine when the thermostat is closed. I'm thinking what little flow you have at an idle is being recirculated back to the engine and not being sent to through the radiator path due to the slight restriction of the thermostat. A different brand of thermostat may have the same problem. Does that engine have the same or similar pump to our 455s? That 455 pump was used on a lot of GM engines. If so that same casting was used but different impellers were used based on engine needs. I suggest that the impeller size may be too small and to go with a larger one. As an example the impeller on my GMC is 4 and 1/8 inches. I believe OEM was 4.25". I have seen that same pump casting used on other GM engines with impellers as small as 3.5 inches.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: Non gmc thermostat question [message #251725 is a reply to message #251705]

Sun, 08 June 2014 08:39

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

roy1 wrote on Sat, 07 June 2014 21:18

Awhile back I installed a Robert shaw type 180 degree thermostat in my 350 Chevy powered 48 ford. This is the same thermostat most of us use in our GMC's . It mostly runs at 180 but when stopping for a light the temperature rises to 240 or more unless I rev the engine in neutral. I figured maybe the thermostat is bad but it opens normally in a pot of hot water? So I tried another new Robert shaw type thermostat. Same problem with the next thermostat. Yes it has a new radiator. I was thinking maybe I need a hi flow water pump as it only has a problem at idle. Today I took the thermostat out and checked it with out a thermostat no more problems when I slow down it stays at 170 to 180 constantly. So the 350 doesn't like the Robert shaw stat for some reason. Has anyone come across this problem with a thermostat? As much as I hate I plan on buying a Stant type thermostat to use rather then the robertshaw type unless someone can recomend a better one?? I'd hate to keep trying different style stats to fix the overheating at traffic lights

Roy,

Changing the thermostat will probably not cure this. A number of Chevy SB versions had this problem. It would get real bad if the heater loop was restricted in any way. One company used to sell a block to put under the stat housing that had a place for the temp sensor and a nipple for a recirculation hose. No, I don't remember supplier.

=> There is no keystoke code for a light bulb....
The part was called a thermostat spacer. I have no idea where to get one, but google probably does.

Matt

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

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Re: Non gmc thermostat question [message #251738 is a reply to message #251725]

Sun, 08 June 2014 12:22

roy1

Messages: 2126
Registered: July 2004
Location: Minden nevada

Karma: 6

Senior Member

[
Changing the thermostat will probably not cure this. A number of Chevy SB versions had this problem. It would get real bad if the heater loop was restricted in any way. One company used to sell a block to put under the stat housing that had a place for the temp sensor and a nipple for a recirculation hose. No, I don't remember supplier.

=> There is no keystoke code for a light bulb....
The part was called a thermostat spacer. I have no idea where to get one, but google probably does.

Matt[/quote]

Matt that is a possibility I currently do not have a heater in the loop didn't have a need for one when I lived in Southern California but Nevada is a lot colder in winter I bought one to install but have been too busy to install it. The Chevy engine does not have a recirculating circuit like the olds does. I can see this could be a problem with the pump is not spinning fast at idle.

Roy Keen Minden,NV 76 X Glenbrook

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Re: Non gmc thermostat question [message #251739 is a reply to message #251715]

Sun, 08 June 2014 12:31

roy1

Messages: 2126
Registered: July 2004
Location: Minden nevada

Karma: 6

Senior Member

Ken no idea what the impeller size is but it is for a medium duty truck so it should be ok. Here again the engine is not set up for any re circulation bypass so I need to look into this as the problem and maybe get the heater and piping installed too move the water around but I don't want to circulate it thru the heater core in hot weather.

Roy Keen Minden,NV 76 X Glenbrook

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Re: Non gmc thermostat question [message #251752 is a reply to message #251739]

Sun, 08 June 2014 16:49

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Why not just throw a hose on it for now simulating the heater coolant flow.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: Non gmc thermostat question [message #251774 is a reply to message #251752]

Sun, 08 June 2014 19:29

roy1

Messages: 2126
Registered: July 2004
Location: Minden nevada

Karma: 6

Senior Member

Ken Burton wrote on Sun, 08 June 2014 14:49

Why not just throw a hose on it for now simulating the heater coolant flow.

I just got back from a 150 mile round trip rod run with 4 other street rods.temperature stayed at 180 the whole time with the thermostat removed. Two of the guys have 350 Chevy engines and no bypass just the Robert shaw type thermostat with the hole in it that we don't like. I'm going to back off a little bit before I tear into it. I should make sure that old heater i have has a good core and install it along with a ball valve so i can crack it open a little in the warm months.

Roy Keen Minden,NV 76 X Glenbrook

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Re: Non gmc thermostat question [message #251791 is a reply to message #251774]

Sun, 08 June 2014 22:10

hal kading

Messages: 642
Registered: February 2004
Location: Las Cruces NM

Karma: 4

Senior Member

Roy,

How about one of those "H" type heater valves. It should bypass with the heater off.

Hal Kading 78 Buskirk Las Cruces NM

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Re: Non gmc thermostat question [message #251800 is a reply to message #251791]

Sun, 08 June 2014 23:14

roy1

Messages: 2126
Registered: July 2004
Location: Minden nevada

Karma: 6

Senior Member

hal kading wrote on Sun, 08 June 2014 20:10

Roy,

How about one of those "H" type heater valves. It should bypass with the heater off.

Hal Kading 78 Buskirk Las Cruces NM

Good option but I'm not ready to do anything till I think on it a bit. I still think the high flow pump may move enough coolant but I do want to put the heater in it. Since it isn't having a problem with the thermostat out I don't have to do anything just yet.

Roy Keen Minden,NV 76 X Glenbrook

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Re: Non gmc thermostat question [message #251802 is a reply to message #251705]

Mon, 09 June 2014 01:53

Chris Tyler

Messages: 458
Registered: September 2013
Location: Odessa FL

Karma: 7

Senior Member

I had that problem when I was young and dumb...somehow managed to put the thermostat in backwards. Embarassed

Embarassed

I dont think you can get a real Robert shaw Stat anymore, they are chinese.
I used to swear by them. They would stick open if they failed.
You can dril 3 1/8" holes around the base of a conventional stat to let it bypass some before it opens.
Previous poster mentioned using a hose to check flow. You might be able to see how the flow is at idle with the cap removed.
What type fan do you run? How far offf, and do you have a shroud?
I have yet to find a flex fan that cooled well at idle
Couple other esoteric things to check: very leal idle mixture or retarded timing at idle. Or trapped air pocket.

76 Glenbrook

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Re: [GMCnet] Non gmc thermostat question [message #251803 is a reply to message #251802]

Mon, 09 June 2014 02:04

Mr ERFisher

Messages: 7117
Registered: August 2005

Karma: 2

Senior Member

Mondello would only warranty my rebuilt engine if I only use a washer
instead of a thermostat. They still sell them.

The only function of a thermostat. Is to heat up an engine and they are an
engine killer

Erf

On Sunday, June 8, 2014, Chris Tyler wrote:

> I had that problem when I was young and dumb...somehow managed to put the
> thermostat in backwards. :blush:
> I dont think you can get a real Robert shaw Stat ll them, se, they are
> chinese.
> I used to swear by them. They would stick open if they failed.
> You can dril 3 1/8" holes around the base of a conventional stat to let it
> bypass some before it opens.
> Previous poster mentioned using a hose to check flow. You might be able to
> see how the flow is at idle with the cap removed.
> What type fan do you run? How far offf, and do you have a shroud?
> I have yet to find a flex fan that cooled well at idle
> Couple other esoteric things to check: very leal idle mixture or retarded
> timing at idle. Or trapped air pocket.
> --
> 76 Glenbrook
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> GMCnet mailing list
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>

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Re: Non gmc thermostat question [message #251823 is a reply to message #251802]

Mon, 09 June 2014 14:06

midlf

Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)

Karma: 1

Senior Member

I had a car that did the exact same thing. Drilled a small hole in the thermostat, That solved the problem. I think the hole was 1/16"

Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI

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Re: Non gmc thermostat question [message #251828 is a reply to message #251705]

Mon, 09 June 2014 14:47

roy1

Messages: 2126
Registered: July 2004
Location: Minden nevada

Karma: 6

Senior Member

OEM flex fan don 't have room for a clutch fan and don't like electric fans but the radiator cooling isn't a problem stays cool without the thermostat. The Robert shaw type can be readily obtained from Summit they carry Mr Gasket Millodian and another clone that appear the same. The one I have has a 1/16" hole in it . The fan is quite close to the new aluminum radiator a shroud couldn't hurt but won't help the lack of circulation a flow rater washer probably would fix it but it would be a problem in 25 degree temperatures since I left California.

Roy Keen Minden,NV 76 X Glenbrook

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Re: Non gmc thermostat question [message #251831 is a reply to message #251828]

Mon, 09 June 2014 15:58

midlf

Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)

Karma: 1

Senior Member

roy1 wrote on Mon, 09 June 2014 14:47

OEM flex fan don 't have room for a clutch fan and don't like electric fans but the radiator cooling isn't a problem stays cool without the thermostat. The Robert shaw type can be readily obtained from Summit they carry Mr Gasket Millodian and another clone that appear the same. The one I have has a 1/16" hole in it . The fan is quite close to the new aluminum radiator a shroud couldn't hurt but won't help the lack of circulation a flow rater washer probably would fix it but it would be a problem in 25 degree temperatures since I left California.

Try bigger holes. More/bigger holes looks more like the Mondello washer.

Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI

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Re: Non gmc thermostat question [message #251928 is a reply to message #251705]

Wed, 11 June 2014 06:27

MIGUEL MENDEZ

Messages: 179
Registered: August 2004
Location: Montclair, California

Karma: 3

Senior Member

Just a thought, but, I have run into a few customer who purchased super high flow water pumps, after checking into it, and learned that, super high flow water pumps just push the coolant through the rad way to fast to allow it to cool off enough to keep the engine cool, and more so at idle, may not be your problem, but after changing those pumps back to stock, the problem was fixed, but again, just a thought

Miguel

1978 Royale Pain in the %$@, side bath w/ a 403 that i love.

GMC name : The other woman

http://www.mgmgmc.com

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