64 Cooling Temp Question

[Kevin B.]

I have a very original #'s matching 64 with 35K miles, 327-300, purchased from a well-known corvette person. Driving the car in the fall in FL( outside temps of low 80's) I noticed the temp gauge creeping up into the 220-230 range. This was true even when the car was moving. It would also run in the 220 range on a day in the low to mid 70's. I get these cars tend to run warm as designed. My mechanic replaced the original radiator with a Dewitt's period correct, date coded radiator. Also replaced fan clutch, belt, thermostat, sending unit and water pump. Replaced all hoses with period correct GM hoses including spring type lower hose. Used Dewitt's pre-mixed coolant. Car has never overheated or purged fluid. Expansion tank is 65 date coded- no issues. Since completing these repairs, the car has been running at 185 consistently. Attended a cruise in yesterday (65 degree Temps) where it took 90 mins to go 3 miles. Lots of idling. Temp creeped up to 230 again. Turned the heater fan on and temp gradually declined to 200 range. Heater core was by-passed by a previous owner. After the cruise-in, Temp was again 185 for rest of my day under normal driving conditions. Thoughts on why the Temp increased so much under long idle condition, but in cool temps? Is that "normal"? Maybe the gauge is wrong? I'm not a DYI guy but baffled at this point. Car felt warm even at the base of the shifter stalk.

[Gary C.]

Re: 64 Cooling Temp Question

best to use a Robert Shaw thermostat and Flow Kooler high volume water pump

Gary
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[Duke W.]

Re: 64 Cooling Temp Question

Most guys don't understand that the spark advance map has a lot to do with EGT and heat rejection from the engine. At idle the 300 HP engine needs low to mid twenties total spark advance, and this value is achieved by the combination of vacuum and initial advance.

The first thing you need to do is verify that it still has an OE type camshaft by checking idle vacuum, which should be about 18" Hg at 500 in neutral. Report your results, and also state whether manual or PG trans and whether or not it has AC.

Also report the data stamped on the VAC bracket (You may have to loosen and move the dist. cap.) and use a Mighty Vac or equivalent to report the start and stop points of the pin.

BTW, if you have not already done so, you need to procure and 1963 Corvette Shop Manual, 1964 Supplement, 1964 AIM, and download the 1964 Corvette vehicle information package from GMHeritage.com

Duke

[Kevin B.]

Re: 64 Cooling Temp Question

Not sure about the brand of thermostat or water pump(although I believe it was a high volume pump). Got both from Zip Corvette. I'll check.

[Kevin B.]

Re: 64 Cooling Temp Question

It is a Muncie 4 speed. No AC. I believe it has OE camshaft but I will check. Definitely will look into the shop manual/ info. Car had Petronix ignition conversion done prior to acquiring it

[Kevin B.]

Re: 64 Cooling Temp Question

Runs great, smooth with no pinging. Ignition timing too advanced?

[Bob R.]

[Owen L.]

Re: 64 Cooling Temp Question

Most guys don't understand that the spark advance map has a lot to do with EGT and heat rejection from the engine. At idle the 300 HP engine needs low to mid twenties total spark advance, and this value is achieved by the combination of vacuum and initial advance.
Duke

Runs great, smooth with no pinging. Ignition timing too advanced?

I believe what Duke is suggesting is that your timing is not advanced enough. (Retarded timing will run hotter than advanced timing.) You should go through the timing process to determine max. timing and the 2" vacuum can rule. Duke and Lars Grimsrud have extensive papers on the process to set optimal timing. Email Lars at <v8fastcars@msn.com> and ask for the basic timing and vacuum papers.

Temp creeped up to 230 again. Turned the heater fan on and temp gradually declined to 200 range. Heater core was by-passed by a previous owner.

Just an aside... this doesn't make sense. If the core (mini-radiator) was bypassed, turning on the fan wouldn't do anything to help coolant temps.

[Kevin B.]

Re: 64 Cooling Temp Question

That was my thought as well. The air was lukewarm at best. My mechanic told me the core had been bypassed( by the previous owner) when he replaced the radiator. Could have been unrelated that the gauge showed moderating temp during that time. I will definitely look into the timing.

[Dan B.]

Re: 64 Cooling Temp Question

Has anyone checked what your temp gage is saying with an IR gun? Likely the temps are not what you think especially with a new sending unit.