I have a 1977 with L48 engine. It consistently runs between 200-220 degrees depending on the outside temperature, and hotter with the A/C on. The radiator has been re-cored and everything has been checked thoroughly. Are these operating temperatures normal? I rad about coolant treatments with "wetting agents". Are these effective in reducing coolant temperatures when using a 50/50 water-antifreeze mix? Thanks much!

 

how are you checking the temperature? On my C3 what is indicated on the stock gauges in no way indicates the actual temperature of the motor*.... that said, if the needle starts moving up, quickly, that is an accurate warning to stop doing whatever is making it hot.


*200 indicated, 170 actual and yes, I have the correct sender, the ground is fine, the connections are corrosion free....

 

The temperature was checked with a digital thermometer on the radiator hose. The guage is within 5 degrees of being accurate. The sender was replaced to insure accuracy. Thanks!

 

Normal...No. Common...Yes. These things love to run on the warm side. IMO the number one cause is air flow around the radiator instead of through it. Is your lower spoiler installed and in good condition? Are the shroud seals installed and in good condition?
Since the air flow has to be picked up from under the car instead of straight in like most (the spoiler's job). Then the air will go around the radiator if the shroud is not sealed to the core support and hood. I have a 77 L48 also and experienced the same issues. I do have an aluminum radiator now but the air flow control made the biggest difference.
Hope this helps
-Rick

 

Aftermarket senders are far from accurate. I went through three different new ones and tested the impedance on each one. None of them matched the other. I ended up using the one closest to the factory specs which I got from NAPA. Actual 185* reads 200* on my gauge.

 

Thanks Rick! Yes, all the shrouding is around the radiator and the spoiler is attached properly. I just did that hoping it would help ( the spoiler was missing 2 bolts and some of the shrouding was missing) and it made no difference at all! Very frustrating! Have you heard of any coolant treatments (Purple Ice, etc) being effective?

 

I hear the additives do help by changing the water's surface tension. What that will do is help prevent hot spots in the engine or localized boiling. It does not lower the bulk coolant temperature or change the boiling point.

Other things to check
1. Proper operation of the clutch fan
2. Engine timing(others here can better explain how this affects your engine temps)

 

when you say all shrouding is in place do you mean all core support seals are in place?

A good number of members accept the temps floating around, I don't.

If the system is working correctly it should hold the temps at T-Stat setting.

Start by checking your timing, make sure its set as it should be and that its advancing as it should.

You didn't mention anything about the T-stat, did you change it or check it to make sure its working?

Someone already mentioned verifying the gauge with an IR gun.

Have you bypassed the heater core?

I've tried the water treatments with no change in temps,

Neal

 

Does this mainly on the highway? My '77 did. I added an inch of hard rubber to the bottom of the existing spoiler to get more air up into the radiator. That fixed it.

 

I had the same issues on my 77 L48. It ran 210 to 230 with a/c off and higher with a/c on. Made many timing adjustments and recurved the timing with little to no effect.
Then I tried flushing the radiator and system. Little change.
I then sealed up around the radiator. Little more.
Then I went to electric fans. Still more, good temps at town speeds, but still hot on the highway.
I extended the spoiler by 1 1/2 inches and this dropped temps by 15 to 25 degrees depending on outside temp. But it still ran at 190 ish to 210 with a/c off on hot days. Hotter the faster I went.
Finally I got a Dewitt direct replacement aluminum radiator and that finally fixed the hot temps at highway speeds. In fact now it runs warmer at slow speeds than it does at highway speeds. Runs 180 (thermostat temp) at highway speeds a/c on or off and 195-200 in town. Very pleased with the radiator it drops the temp 30 to 50 degrees from inlet to exit just passing through! I find that astounding.

 

Yes. Normal.

You don't need them

 

Curious what your thermostat is rated at?

 

Thanks John! The t-stat is a 190.

 

First, another question. Did the car run cooler before you made the mods? What is your water level in the radiator.

So,here in Texas, it gets hot. My car is a small block, stock rad, no shroud and electric fans with temp control to come on at 160*. I have a 180* tstat and my factory gauge reads pretty close to 180.

I fought an overheating issue for a while and here are some things to check.
* Check your timing, factory timing will make her run hot by design. Advance keeps it cooler.
*I keep my idle air fuel mix at 12.5-13:1 richer = cooler
* make sure you have the correct radiator cap psi and that it is new. If you dont remember buying it, get another.
* Make sure you get all the air out and run 50/50 coolant mix with distilled water. As you are filling the radiator squeeze the upper hose to try and get the air out.
* I had a 16in elec fan and added another 11in. The additional fan really helped. You don't have electric so make sure your clutch and seals are all new.
* If you suspect a leak they sell leak detector dye that can help locate it.

All I am saying really is I agree that the water wetter products are not needed or should not be needed for a average street application. Keep searching for the culprit.

This is what level I am at.

 

I used Plumbers pipe insulation for my core support seals, it was easy to push it down around the edges of the radiator. Three pcs. of 3/4" worked wonders. Have a great one. Gene

 

What Gene said...

 

I run 160-170 at the most .I use distilled water with wetter water.I drain the coolant system when I put the car away for the winter.I run a 18 plastic flex fan with a stock shroud.I use a edelbrock water pump with a alum radiator.

 

I have always run a 160 degree thermostat and have never had the temp go over 160-165, even on the hottest days out here. I have all original equipment and it all works well. I'd f/ sure atleast go w/ a 160 degree thermostat.

 

I have a 69 Big Block with a/c. What is correct coolant level in the long style tank? I have a#15 aftermarket slant cap.

 

I'm pretty sure that your 77 was designed to run around 210.

By the late 70's, all cars were using a 190 thermostat and had a normal operating temperature around 210. This was done to help reach the Federally mandated emission levels. The higher operating temps, help burn off the emissions more thoroughly.