Mr. Dee

My 1977 C3 operates at : 190 Degrees around town... and up to 220 degrees on highway... Chicago Summer. Is this anything to cause concern ? Is 220 o.k. and Normal Highway Operating Temperature?
Thank you for any input ...

cagotzmann

What thermostat as you using ?

Usually when the highway temp exceeds city temps is due to poor air flow through the radiator (air is moving outside and not through), or the radiator doesn't have the capacity to cool the fluid.

This could be poor flow of fluid through the radiator due to plugged passages, or the water pump isn't supply enough flow.

Enough flow may also be the thermostat restricting flow.

Using a IR gun you could measure the upper rad hose vs the lower rad hose to see how well the radiator is working.

Has your gauge always displayed the same changes, or is this something new ?

HeadsU.P.

Old saying: Hot at idle is a AIR circulation issue.
Hot at speed is a WATER circulation issue.

First thing is to grab the lower rad hose and verify there is still a steel spring in there.
If not, the hose collasped at speed.
Vacuum Advance hooked up? 52* total? Retarded timing equals more heat.

mark79,80

In addition to the other suggestions I would check:
That all the radiator seals are in place. There should be seals between the radiator and the shroud. Also between the top of the shroud and the hood.

That there is a lower front spoiler below the front bumper.

That the lower radiator hose is not collapsing at speed. To check this, rev the engine in short bursts and watch the lower hose to see if it collapses.
Many of the replacement hoses do not come with a spring, and as they age, the hose gets softer.

Mr. Dee

Thank you All for your knowledge and time ... I appreciate any information that you folks are wiling to share ! Keeping this in mind, is 215 - 200 degrees Highway Driving with outdoor air temperature around 80 degrees or so, o.k. for this motor ? Also, I am running Bradd Penn 20 - 50 weight oil (Partial Syn) ... Many Thanks ... Dee

Big2Bird

200-225* is fine,normal,okay.
Don't get worried till 235

Mr. Dee

Thank you... Correction on Temperature : 215 - 220 Degrees on Highway. I recently had the plumbing including the radiator newly revamped. I will check lower hose for any deficiency ... Is 20 - 50 oil o.k ? dee

71 Vert LS1

With a good condition radiator and a 180 degree thermostat I would think at highway speeds even at 80 degrees 200 plus would be high.

My LS1 swap in my 71 with a dual pass radiator running a 160 degree thermostat struggles to get to 180 degrees at highway speeds even at 80 degrees.

Your temps seem high to me.

Big2Bird

What is your oil pressure? Ambient temps?

Mr. Dee

I am thinking the same ... maybe 200 is o.k. but a bit concerned at 210 to 220. Not sure on the Thermostat ... Oil pressure is good. Will the 20 - 50 oil cause the temperature to climb ?

Mr. Dee

What does Chevy Recommend Normal Highway Operating Temp ?

jim2527

Your not going to find that anywhere. As a reference some C5/6/7 vette fans don't turn on until 235+.

20-50 oil is fine.

jb78L-82

First question is the engine an L-82 or base engine L-48?

Assuming everything mentioned is correct and up to standards, The late 70's L-82's ran VERY hot from the factory when brand new, mostly due to emissions, the 882 factory cylinder heads which restrict coolant flow to aid in running the heads hot for more complete combustion, and poor ignition timing. My 100% stock 78 L-82 4 speed when new ran 225 normally and 235-240 with the AC on during hot days AND got hotter on the highway than idle when it was new. Same scenario with my friends brand new 79 L-82 4 speed back in 1979. In fact, GM changed the 12 o'clock position on the temp gauge in 1979 to 220 degrees from 200 degrees to quell customer complaints about the high temps. 79 L-82's with heavy duty cooling added an auxiliary electric fan inside the mechanical fan shroud in 1979 to reduce the temps some...it was a big problem!

The solution is the following:

1. Aluminum radiator
2. 180 degree thermostat
3. Stewart Stage 2 aluminum high flow water pump
4. 1979 Spoiler extension-See below-cars with heavy duty cooling had this extended spoiler for additional cooling




My rebuilt/upgraded 355 L-82 450 Gross HP never gets hotter than 180 degrees regardless of the temp outside, how hard I drive, highway driving etc............

pigfarmer

How do you even know if the gauge is accurate? I just went through this – car wasn’t displaying any signs of overheating but I notice the temp gauge has been reading 210*. I happen to have an IR thermometer and it says 180* at the thermostat housing & upper rad hose.

Just a base check before you go down the rabbit hole

Street Rat

Just purchased an IR gun and dual Spal fans for my DeWitt's radiator. The factory gauge is off at least 10 degrees on my '81. That my friend is a lot.

Mr. Dee

A BIG Thanks to ALL Contributors ~ You guys are the Best ! I will purchase an IR ~ Gun and check out a few other simple things... Thermostat * Hoses ( which are newer ) * Motor is L82 ...

I assume the IR Guns Provide an Accurate Reading ?

BIG QUESTION : Is 220 Degrees Highway o.k. ???

Dee

Street Rat

I purchased a good quality IR gun from Home Depot. Milwaukee brand.

I'm not comfortable at 220 degrees on the highway.

revitup

My L82 '77 runs between about 195 and 205 all day, no matter what kind of driving or weather. No fancy radiator, OEM thermostat (not that the thermostat would make any difference), all seals, shroud, and spoiler in place.

Wee

You might want to add a mechanical temp gauge as a double check....My 72 was showing around 220 highway so I added another gauge and it read right at 190 when the stock gauge was at 220. Checked with a IR temp gun and it confirmed the new gauge was correct. I did as the instructions with the new gauge suggested double check it with a pot of boiling water. Here where I installed the additional gauge.





Brian

Mr. Dee

Thanks to All ... Safe Travels and Happy Trails ! Dee