Running warm again
 

Now the nice weather is here again I started using my vette and it's running warm. It's a 65 with 300 hp, automatic,with factory A/C. After driving about 10 minutes or so at 60-70 mph the temp gauge moves up to the 210-15 range . Slowing down it drops to about 195. I read John Hinckley's article about the vette cooling systems and I have to say it was very informative. I noticed that my fan blade was about eighty percent into the shroud opening twenty percent out of it, not the 50/50 John mentions. I put a cardboard in front of radiator and let it idle for quite awhile to get the temp up to about 230 degrees and turned engine off. Clutch fan wasn't locked up, kind of spun with very little resistance. It has GM aluminum original type radiator with 76 date code , so it's been replaced and looks new. It has a 7 blade fan 18 in. Diameter. I looked at a friends 67 300 with fact A/C and he has 5bladed fan and it never over heats. My water pump is GM with bypass plugged. Would this put the fan too deep into shroud? Any thoughts?

I have a 65 factory a/c 300 hp and I get the same temps, though it might take longer than 10 minutes at warm temps at 70 mph to get there, slowing down, it drops back down. Since gm changed the center mark on the gauge to 215 in 66 and all else stayed the same, I quit worrying about it. If it stays around 215, I'm not going any farther to troubleshoot. I would recommend if you haven't to shoot it with an IR gun to see how accurate your gauge is. Your friend with the 5 blade fan on an a/c car doesn't have the correct fan for a 65/66, not sure if 67 was the same, your's should be the 7 blade.

WAG based on limited info, your radiator needs replacing or you're low on coolant.

WAG based on limited info, your radiator needs replacing or you're low on coolant or your ac condenser or radiator is full of bugs/debris .

My 65 327- 300 with ac temp creeps up also when at speed. If I have the a/c on, the temp goes up faster and higher. 210 w/o a/c and 225 w/ a/c?
Radiator is a new Dewitt, thermostat is new and water pump rebuilt. Engine passages are clean.

You have verified your dash gauge is accurate I presume?

Yes. The ir thermometer is one of the best toys that I own.

As I said earlier, my 65 300hp a/c car runs the same temps as listed at 70 mph in warm weather. Also as I said earlier, GM changed that center mark to 215 starting in 66 with the same gauge and sensor so that owners didn't think it was running too hot

Attachment 47797192

In addition to what has already been said, the factory AC cars also had special sealing strips on the top and bottom of the radiator. Check that these are still in place, and in good condition.

A GOOD working clutch fan, with the correct lockup temperature is also needed………..especially at lower speeds/idle.

Larry

My 67 300hp base engine, factory A/C, Powerglide seems to do pretty well with A/C on in moderate traffic. 180 degree thermostat, stock parts with exception of 7-blade fan on stock fan clutch. No overheating at all even in 90 degree weather. Seems the General does do some pretty good engineering so I didn't really mess with it. Stock is the way to go. Don't forget the upper and lower radiator seals.

Tom

What temp do you run on a hot day at 70 mph sustained?

It runs about 175-180 with A/C on and interior fan speed on medium. I only use "high" to cool cabin down for entry. Then to "medium" setting for cruise on freeway. Drove 300 miles each way on a trip to Oakland from So Cal. First time out after complete A/C system rebuild back to Stock with A-6 compressor, heater shut off valve the whole deal. Took me a while due to my handicap but got it done.
It did heat up to about 220 degrees once I got into stop and go traffic which lasted about 20 miles. Then immediately cooled back down to 180-90 which made me happy.

Tom

If you have a 180 thermostat it should never get under 180 on a warm day. If it does the thermo should close and heat it back up. Either the thermo is opening sooner or the gauge or sender is off a little. Not that it's a problem, just trying to understand why yours would run cooler at high speed. I've never ridden in one or owned one that ran 180 or under at 70 or over.

I know. My thought as well but that's what the temp gage said. Only been out on one trip since the nine month interior/job creep A/C rebuild due to my disability. It was either at 180 or below slightly. Hoping to hire someone soon to finish off the rebuild/install of parts and "things" I can no longer do.

Tom

I installed the 67 upper rubber seal flap today and will be replacing the fan clutch ( mines definitely shot ). Does anyone sell a correct looking replacement fan clutch? Think I figured out why my fan is sticking inside the shroud so far. Seems like the plate on the shaft of the water pump that the fan clutch mounts to is a little to far forward . Pump was probably rebuilt. The pulley is somewhat away from the cutout by the bypass hole. From the photos I've looked at of other small blocks the pulley is just about touching near the bypass. This might be why the fan blade is in the shroud too far. The shroud is definitely the original. One step at a time!

Please post back what happens with the new fan clutch. It shouldn't make any difference at 70 mph, but I'm curious about what happens to your idle temps (which, from what I understood were ok to start with)

I wouldn't assume that a 28 year old radiator is performing as new.

Even worse, that's 38 years

I would agree with you. 38 year old radiator, could be bad. Though MYRONF changed his to a new Dewitt plus other parts with same scenario. Will be back with an update.

Running warm is apparently a commune denominator for some of us. I would never be comfortable running at 215 or above. I would check: radiator, thermostat, fan clutch, radiator foam/rubber seals, fan blade, coolant and engine timing. I don't use an electric fan, because back then it was not designed that way. But some people find that to take care of the problem. Good Luck!!