myronf

I have the original recently rebuilt 327-300 in my 65. The temp is 180 ish up to 50 mph. At 70 it climbs to 210. New Dewitt aluminum radiator. Am I ok? Could the fan clutch be bad. Does the fan really make any difference at 70 mph? any ideas? What should the temp drop be across the radiator (or rise across the engine be.) If it's too great, it's not enuf flow - yes? Then is it the thermostat not opening all of the way?

Myron

capevettes

Have you confirmed the accuracy of your gauge with an IR gun near the thermostat housing? Heating up at speed is usually an indication of poor air flow or a radiator issue. Is your radiator shroud and seals in place? You have the right radiator in there. It certainly wouldn't hurt to change out the thermostat.

65GGvert

I have confirmed my temp with IR gun and the temps match yours exactly. If I drive at 70 for more than 10 minutes, I also get to around 210 on a hot day.

capevettes

My 65 350 horse runs 180 even on a warm day with a Dewitt's aluminum radiator. With a new Dewitt's aluminum I wouldn't expect to see 210 on the highway. Even my big block runs under 200 on the highway.

65GGvert

Both myronf's and my 65 have air. I believe that the temp runs a little higher at speed due to the a/c condenser reducing flow through the radiator. I also believe that 210 is not too hot. GM changed the center reading on the temp gauge to 210 (from 180 in 65) in 66 and changed nothing else in the cooling system.

Addition: The condenser also causes the temp of the air moving across the radiator to be higher than a car without an a/c condenser warming the air as it passes.

Bluestripe67

How recent is the rebuild, how many miles on it? If low numbers, your still breaking in the motor. Did you fill the system via the thermostat opening (air pocket in system?) What is the jetting on the carb, you could be running lean/leaner as speed increases. Dennis

Frankie the Fink

I know this freaks people out but its straight from the 6K section of the 1967 Chevrolet Chassis Manual:

Bluestripe67

Your right Frankie it did, it does and will continue to. Dennis

SDVette

I see the same thing on my '61 (350 LT-1, aluminum radiator).

180 when cruising around.. 210 at freeway speeds on a hot day (85 here yesterday)
I was blissfully unaware until I recently fixed the temp gauge!

All seems fine though!

Powershift

If you guys are running the AC AND cruising at 70 MPH on a 90 F day I can see the engine temp running around 200-210 F.

If however you are running with the AC off, then I would expect a normal 180 F temperature (assuming you have a 180 F thermostat installed).

I have a 1967 327/350 HP factory air convertible, and my comments are based on my experience here in the Deep South.

Larry

MikeM

Running the engine at the temperature listed in the '67 Service Manual was probably okay in 1967. Today, when your gasoline turns to vapor, it could cause no engine operation at all. Isn't that why you have those plywood shims under your carburetors?

65GGvert

Nope, air off. If you can run 210 or under at 70, congratulations, you're in the minority.

myronf

Answers to questions:

Rebuilt engine has 500 mi on it
Yes temp was checked with an ir gun. One of the best toys I own.
Yes the car is a/c 210 is with the a/c off
thermostat is 180

Do you guys agree that if it is a high speed issue that the fan clutch has nothing to do with it?

Frankie the Fink

Agree (for the most part) but if 247 was OK back then I think 210 is not beyond a reasonable running temp....especially with a nearly freshly rebuilt engine. I'd drive it another 1,000 miles and then see where things stand....

JohnZ

The fan and clutch have nothing whatever to do with cooling at highway speeds; the fan can actually become a restriction to airflow if the clutch locks up. I'd pay attention to sealing the fan shroud to the radiator and the radiator to the radiator support so all the incoming air is forced through the radiator, not around it.

1snake

My 65 runs right at 180° regardless of speed or outside temp. but we don't get above 85°. This is confirmed with an IR gun. Everything is new - engine, water pump, DeWitt's rad., rebuilt fan clutch etc.

Jim

steampunk c1

Check timeing and jetting lean or retarded timeing will increase temp as engine speed goes up. Also maybe try a additive to coolant to improve heat transfer in the radiator.

magicv8

You can block your hood open a couple of inches and tie it down at the latches for a test ride, to see if increased air flow is what's needed.

myronf

Just pulled thermostat housing - coolant up to the top and then some. No air pockets - While at it I changed the thermostat. Temp is the same.

Timing is 6 degrees btdc

Carb was "professionally rebuilt" I don't know what jets I have in it. Is there an easy way to tell if the mixture is too lean?

1snake

Make sure the mechanical and vacuum advance are working correctly.

Jim