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Joined: Mar 2010
Posts: 10,289
You are completely dead in the water without a heat control valve in the manifold. Some are comfortable with a stuck valve as long as it is stuck in the fully warmed up position. I am not comfortable with that scenario, but is better than nothing, which is what you have.
Chevrolet didn't include a cab heater from the assembly line for these trucks to keep the sale price down. Wouldn't one think that they could have saved money on the sale price by not spending money on a heat valve in the manifold? Must be it is there for a very important purpose, like preventing liquid gasoline from pouring down into the cylinder when the intake is cold, washing away the oil on the cylinders, creating premature engine wear.
In the case of the OP's scenario, heat is being applied to the intake manifold all of the time. That is not good either. It is likely the cause of the overheating issue.

Last edited by 52Carl; Tue Sep 20 2022 01:47 AM.
Joined: Nov 2014
Posts: 21
52Carl - Thanks for your response, insight and guidance. I wish I knew the decision behind removing it. My curiosity is that it's been about 18 years since the engine/truck was rebuilt, so what failed/triggered this issue now.

Otto - Thank you. I have a friend who has the thermometer and I'll be meeting up with him later in the week and see what we find out.
As a side note, you had previously written your comments about the series. I re-confirmed that this truck is a 2nd series and when I read the reason for the conclusion (from a local antique car buff) is that is has an open rear-end on it.

Joined: Nov 2014
Posts: 21
Update on engine temperature readings.

Drove truck to a shop about 3 miles away. By the time I arrived, the temp gauge read H.

I had to wait about 30 mins to use the thermometer. We took initial readings - above the TS housing and below, radiator, upper/lower hose, front and back of engine. At that point the engine readings were 135 in the front and 140 in the back. Checked the temp gauge and it was at H. So, that tells me there is an issue with the sending unit or gauge.

Started the engine, revved it up to raise the temp. Focused on the TS housing and engine, we observed that at 181 degrees the TS opened and then the above and below temps on the housing read the same. The engine temp continued to increase, and the rear got up to 210 and stayed steady there. The front of the engine read 205. Had consistent temp readings on the hoses and radiator.

In summary, there is a 5 - 10-degree difference in temp between the front and rear of the engine. Interestingly, as I drove home the temp gauge started to move from H back to C but it only moved back a little and then went back to H.

So, I'll be doing some tests (or just replace) the sensor and gauge. I wanted to Thank everyone for your guidance and input, thank you Oz for staying on the thread. I am planning to rebuild or replace this engine in about a year or two. I will definitely make sure the heat riser valve is a part of that.

Joined: Jun 2011
Posts: 4,655
Make sure to clean out any sludge at the bottom of the water system on the engine accessed by block drain with a stiff piece of wire!


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
Joined: Oct 2021
Posts: 1,163
None of your temperatures sound like "overheating'. Keep monitoring them but if water isn't blowing out of your radiator cap, I think you're OK.

210 isn't even boiling, of course.

Of course the temp gauge will drop as you're driving. Fresh cool air flowing through the radiator as you drive will have that effect.

1939 Packard Standard Eight Coupe (The Phantom)
1950 Chevrolet 3100 (Ol' Roy)
1956 Cadillac Coupe de Ville (The Bismarck)
1966 Oldsmobile Toronado (The Purple Knif)
1966 Ford Mustang (Little Red)
1964 Ford Galaxie 500 coupe
1979 Ford F-100
1976 Ford F-150 (Big Red)
1995 Ford F-150 (Newt)
Joined: Sep 2020
Posts: 120
If you are using a infrared thermometer (pyrometer) be aware they often misread on shiny or semi shiny surfaces, a piece of black electrical tape on the shiny surface and the reading will be good, as mentioned before a cheap digital meat thermometer from the hardware or bbq store is great to put into the radiator, and also to confirm the infrared readings, btw infrareds do work well pointed at water, at least it does when it’s coming out of a faucet.

Hank: 46 Chev 1/2ton shortbed
2018 Miata RF
Joined: Feb 2000
Posts: 4,566
Not surprising it's hotter at the back. Water flows through the block then turns upwards into the head, across the head to the t-stat housing. Along the way through the block there are holes between the head and block which allows some water to rise and exit, the holes are sized so most of the water stays in the block, they progressively get bigger as you go back. Water exiting the thermostat is what you want to check, that will be actual temperature. Depending on the amount of crude build up, it could be hotter then normal due to no thermo transfer, and less coolant. If it stays around 200 you will be OK till you get time to clean it properly with a rebuild. Block temps vary a lot due to the thickness of the iron and how it was cast, core plugs are good place to check, they are thin and touch coolant.

Joined: Dec 2017
Posts: 1,183
I dont want to sound critical, but you are spitballing with the thermometer. Consider purchasing an under dash aftermarket temp guage. Electric or mechanicl, both styles are pretty accurate these days. Lets see what the water temp is by guage reading. Then you will know for certain whether you are having an issue or not. The factory temp guages are notorious for not being all that acurate.

Joined: Nov 2014
Posts: 21
Thank you all again for your insights and guidance.

Adding an aftermarket gauge would definitely helping in always knowing the temp. I would prefer to have it in a temporary capacity as I do want to keep the truck an all of its original parts as possible.

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