William Buckley

On my '66 coupe, 327/300, with auto tranny, power brakes, power steering, when I turn the AC on, I get an increase in motor temperature to the 210 range in hot weather. New fan clutch with no leaks around the fan shroud. Are you people seeing the same thing with your AC cars? It seems that the AC compressor puts an abnormal load on the motor in stop and go traffic. Not so much on the highway. Thanks for your responses.

65tripleblack

Normal for cars of that vintage. You must be too young to remember the amount of cars pulled to the side of the road with steam coming from under their hoods during traffic jams in hot weather.

There are three reasons why that no longer happens:

1. Modern radiators have more excess cooling capacity than did vintage radiators.
2. Better airflow through those radiators because of electric fans using better/tighter shrouding.
3. More heat rejection capacity of modern condensers enable use of less powerful compressors thereby eliminating excessive pulldown of engine speed.

firstgear

Maybe a DeWitts radiator would help!

Easy Rhino

I have had new cars in the last 20 years that exhibited coolant temperature increases while sitting in stop and go traffic in the hot sun in the humid south with all accessories running, including AC on full blast, so it's not just older cars.

First, I would validate the temperature gage against actuals to ensure you're seeing a real indication.

Second, I would search and find the JohnZ article about cooling systems - it's great and a very useful guide on making sure that these systems are working correctly.

Third, I would consider convection heat transfer where Q" = mc (Th-Tc), which states that as the temperature (Th) increases, the amount of heat rejected (transferred by the cooling system to the air) increases. So, in a heat balance, the hotter it gets, the more heat it's rejecting - in short this may be entirely normal.


Lastly, I would keep a sharp eye on it, until I confirmed it was okay (particularly if I had any aluminum engine parts).

Easy Rhino

BeatinTheHeatRestorerArticle.pdf

Tried to attach the JohnZ "Beating the Heat" article.

65tripleblack

Maybe you should drive better cars. I haven't had that problem nor have I seen any overheated cars in the last 40 years.

Easy Rhino

Two were new Chevys.

William Buckley

Harrison aluminum radiator, new thermostat, new fan clutch, shroud intact, and new radiator hoses. On the road with AC, 180 in hot weather. In stop and go with AC on, 210 and beyond. Temp gauge is accurate ..... confirmed by IR temp gun. I seem to get a vibration when I turn the AC on, but everything looks and sounds fine. Just wish I had no overheating problems with AC in hot weather.

65tripleblack

Aha!!!! Thought so.

65tripleblack

It's factory air I assume. Modern compressors don't load the engine the way antique compressors do. Although 250/300 HP 327s should be able to handle it better than a 350 or 365 HP engine. Read my post above.

It's possible that the system is overcharged, or the dryer is contaminated. Those conditions would cause the compressor to load the engine to a greater extent than normal.

I'd recommend you replace the radiator with a new DeWitts. First check it for hot spots with your palm. The upper part of the rad should be noticeably hotter than the bottom, with a smooth transition in between. Is the upper rubber baffle in place between the hood underside and the radiator? Seal ALL the gaps between the rad and the fan shroud with weatherstripping.

AS LONG AS IT'S NOT ACTUALLY BOILING OVER, than a significant temperature rise is normal.

65GGvert

If it only goes up to 210 you've got a real winner there. People that have a dash light have no idea how much the temperature goes up and down.

SWCDuke

The normal operating temperarture for your car is 180-230F, same as a modern car.

With a proper 15 psi cap and 50/50 glycol-water coolant blend the boilover temperature is 265F.

Coolant temperature over 200 in hot weather slow speed driving with the AC on is perfectly normal.

Duke

65GGvert

I will add that if you spend any money trying to keep the temperature below 210 with AC on a hot day, you'll soon be separated from your money. I'm sure you know the saying I'm talking about. 210 is not overheating

domenic tallarita

For what it's worth, I did a thread a few years ago on that. All the advice here is good but I found that if your system is over charged, it will cause the engine to overheat.
I charged my system and didn't pay attention to the pressure, high side, just got it pumping cold and decided to use the rest of the can. Couldn't drive in the heat here in Palm springs.
My son who does A/C checked my charge and said I was way over charged. He reduced the charge and I was good in the heat. Over charged oil will do that also. There is a procedure to remove the excess oil without loosing your system charge that use the A6 compressor.
Newer compressors don't have a oil pan and it's more like a 2 cycle oils its bearings. The A6 has a oil pump that oils 4 bearings and the front seal.
The garage air compressor will heat up air. the more pressure the more heat. That's what can happen to your A/C system. The condenser is in front of the radiator and the over pressure will cause the condencer to get real hot and that air has to go thru it then thru your radiator.
Check your high & low side pressure, and if it's not cooling good you might have to reduce the oil in the compressor.

Dom

pop23235

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jet-tech

I had the same overtime issues when I installed a VA system on my 66 300 hp car, 220* plus temps. Like others have done I replaced the old radiator with a Dewitts unit, a larger fan & heavy duty fan clutch. Even with the high temps here in Dallas, my engine always stays in normal temp range and rarely gets over 200*.

65tripleblack

All of the cars I have owned over the last 35 years or so have had temp gauges. On every one of those cars, the gauge did NOT climb, at all, with the A/C on, in traffic in very hot weather.

Vettrocious

R6T7

My experience with factory A/C midyears (I currently own three of them) is exactly the same as yours. They will run under 210 degrees on the highway, but in stop and go in high ambient temps they will soon overheat and start boiling coolant. On my '67 300HP coupe which we drive all over the US, I fixed the problem by adding a 16" Spal puller fan with a switch mounted under the instrument cluster. While I rarely use it, in those conditions when the coolant temps start to rise, that fan will move enough air through the radiator to keep coolant under 210. My functional test after I installed it was turn A/C to max, park the car in the driveway in 110 degree weather and let it idle for 20 minutes. Coolant stayed under 210. (By the way, I live in So Cal desert where summer temps are well over 100 degrees.)

Bob

William Buckley

Thanks for your comments. I just would like to stay stock without the electric fan installation, but I may have no other choice. Not sure about to temp in traffic, as I turn the AC off when it goes past 210 headed toward the orange area. I've put enough money in this sucker without having to rebuild the engine.