A few days ago I posted asking if my temp sending unit may be going bad. I was advised to check the temp with an IR gun which I did today. The sending unit seems to be fine. Here are the numbers after a warm up drive:
Temp at T stat housing - 238
At upper radiator hose just past T stat housing - 205
At upper radiator hose at radiator inlet - 185
At lower radiator hose at radiator outlet - 135

Gauge in car reads just below the red "Hot" zone - consistent with reading from T stat housing. Temp is pretty constant whether running at 40 mph or idling at light. The ambient outside temp here today is 100 (Phoenix). Earlier in the year when the outside temps were in the 70s, the gauge would hold right around the first mark (180?). Now, with 30* more ambient heat, the car is running ~ 50* hotter. The car in question is a '66 with L79 and factory A/C.

Any ideas as to why I'm getting such high temps? The radiator (after market copper/brass) seems to be doing its job (50* drop in temp inlet to outlet). Would timing cause this much heat gain (I don't have a working timing light so can't report timing at the moment). What else to look at? I know it is missing the upper radiator seal (and maybe the lower, too) but the temp doesn't drop even at speed.
I hate overheating issues!
- Jeff

 

I think you need the correct radiator. Dewitts aluminum correct unit. Dennis

 

Jeff:

I had been having similar problems with my '65 327/365. I also have AC. I live in LA and our temps are somewhat like yours usually. My lower radiator shroud seal was missing. I was encouraged to get one (Powershift recommended getting it from Dr. Rebuild). I did get it, installed it today, and saw a big improvement in temp. If you are missing yours I suggest you install one.

 

Especially for a factory air car in Arizona in the summer. Plus the special AC upper and lower radiator seals and lower shroud extension and a good working fan clutch are also required even with the DeWitts restoration radiator.

I don't understand the significant temperature difference between the thermostat housing (238 F) and the upper radiator hose at the radiator inlet (185 F). The IR gun may be having issues with the different reflective surfaces of the metal and rubber.

I would also shoot the temperature sending unit with the IR gun and also get a resistance (ohm) reading from this sending unit at the same time.

Larry

 

Thank you for your responses. Now that I know about the A/C seals, I will be ordering them. However, if my IR readings can be beleived, I'm getting a respectable temp drop between inlet and outlet (both taken on the hoses). I will try shooting the temp sending unit and get an ohm reading and let you know what I find.
I'm still wondering if timing and air/fuel mix could raise the temp that much. The car idles and runs fine but I don't have readings for either. What else could generate that much heat internally?
- Jeff

 

Plugged water jackets. Have you ever removed the lower block plugs and done a thorough flushing?

Gary

 

I would consider doing a chemical flush of the cooling system, as it is easier than pulling freeze plugs, at least as a first attempt at cleaning up potentially clogged cooling passenges. The stuff works great if you have softer oxides of iron slugging up your water jackets.

Prestone makes a weak morpholine solution used for flushing cooling systems that is very effective. Just follow the directions, and take a look at the color of your coolant after flushing with it. I do not recommend leaving it in for days as others may have done.

Know that if you have corroded-over cooling system micro-leaks that it may cause those to fail, starting a leak, but they would have gone sooner or later anyway, and usually not at a time and place of your choosing.

 

I have a lower radiator seal new in the bag from Zip (327 w/AC) Their P/N ZWS-474
http://www.zip-corvette.com/catalog/...category/6092/
- you are welcome to it.
Kurt in Tempe.

 

Has the motor been bored out excessively?

 

Kurt,
That is very kind of you. Yes, I would be glad to take it off your hands and pay you as well. I'll send a PM to ask about where to pick it up.
- Jeff

 

Tom,
As far as I know, the motor is untouched (I have receipts back to 1981 and it hasn't been touched since then). 62K miles as of now.

I got a suggestion that the t-stat may be partially closed. I may pull it and see what difference that makes.
- Jeff

 

Check your email, please.

 

Just a thought, were you using the A/C also when the temp was in the 70's? I would think you were while driving when the temp was 100.
The hot air coming from the condenser has to go thru the radiator and is much higher than the ambient.
Also there were a few problems caused by over charged A/C systems. If the A/C is over charged with either oil or gas it will cause the condenser to get much hotter and that hot air has to go thru the radiator.
Just a thought.

Dom

 

No, I wasn't using the A/C either time. I have the t-stat out but can't convince the wife to let me use one of her pots to test it.
I may just button the car back up without one and see how it goes. That, or go buy a cheap pot (and a thermometer - I'm sure she'll object to me using that, too).
- Jeff

 

Jeff,

If you run the motor without a stat it will overheat. The coolant will move too quickly through the radiator. Better just buy a new one as they are cheap and be done with that question.

Steve

 

Hmmm, I had a 180* in there, should I stick with that or go to 160* to give myself a little margin? I guess if everything else is working properly, it wouldn't matter.
- Jeff

 

Either will work for you. I would probably install the 180 F .

Larry

 

160 is too cool in cooler months and it will not make problems disappear in the Summer either. And it's bad for the oil / engine to run too cool. Like you said if it works it works.

Steve

 

I had to laugh when I read this comment. A number of years ago I made the same comment on the Forum in an attempt to be helpful to a fellow with a problem. One of the Hot Shots, who is no longer on here, chose to ridicule my reply as not possible. I took the time to explain the theory behind applying restriction to flow to no avail. (We old Hot Rodders learned a few things the Hard Way, Back in the Day.) LOL. Al W.

 

Stick with the 180...its matches the design spec for operating temperature...