1967 Chevrolet Chevelle Overheating big block Chevy

Tiny
MPRAT
  • MEMBER
  • 1967 CHEVROLET CHEVELLE
  • V8
  • 2WD
  • MANUAL
I have an overheating problem I have been fighting for a year now. I have a 67 chevelle with a '90 model 454 stroked to 496, .060 bore w/10.2 compression, with aluminum pro comp heads. Everything is brand new in this engine. It has a March single pulley system up front. The water pump is Edelbrock which came with system and not reverse flow. It was first installed with a 3 core aluminum radiator with 2 -12" fans w/shroud, pullers set to come on at 175deg. And they work fine and are the right direction. The thermostat is a 185deg w/1/8" hole drilled. Now taking the car out and getting it up to warm up, it does not stop, from 190deg up the more I drive the more it will heat up, I will usually try and have it home by the time it reaches 220, at which point it will fill the over flow tank with water. No matter it sitting or driving it will still overheat. I have tried different deg of thermostats, tried no thermostat. No matter what I do it has the same effect still overheats. The water flows when I watched it without a thermostat, so the pump is working. Tried every aspect of getting the air out of the system. Nothing changes.
Now during this experience the 454 ate a lifter with not even 100 miles on it. So I chose this time to pull the engine and make sure all water passages were clear, re checked everything new cam and lifters. Reinstalled and the same thing over again it overheated again. I did a check for exhaust gases in water, there was none detected. Still this thing overheats. Last result I installed a 4 core radiator, with the 2 -12" fans but had to lose the shroud and put fans straight to radiator due to clearance problems but I got er in there. It seemed to help a little but it still overheats. I drove it to a car show which was maybe 5 miles, only two quick stops then all freeway driving, while driving only 60mph, still when I parked the car it was at 220deg and puked water out on the ground. Since it was at night on the way home it did run cooler, the days were in the 90deg range when test driving. That night after getting it home it was around 205, I pulled it into the garage put a large fan in front to see what would happen and it still reached 230 when I shut it off. I have no idea how to proceed. I changed temp gauges, just to make sure. This car is equipped with air cond. I cant even turn that on, or figure out what to do next. I know how every thing works, this should not be overheating. I am so frustrated at what to do next. Please help with something I have missed. Thanks so much.
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Wednesday, June 25th, 2014 AT 3:56 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
I can offer a couple of things to consider. First, you need some type of shroud. Without one, the fan could be blowing a lot of air around, but not through the radiator. Next, check for holes in the core support. If an optional item wasn't used at the factory, they bolted a plate over any hole that was created. By not plugging or blocking a hole, the air that went through the radiator can blow around back through it, and heated air will go back through the radiator repeatedly and it will just get hotter and hotter. Blocking a 6" diameter hole solved an overheating problem I had on a '73 Dodge Challenger race car many years ago.

Check the rubber seals along the front and rear edges of the hood. A missing front one will let cool air go over the top and bypass the radiator. Next, be sure there's enough water in the coolant. Antifreeze doesn't hold as many BTUs of heat and it does a very poor job of moving heat from the engine to the radiator. A 50/ 50 mix is best, but for summer driving you can increase the percentage of water a little.

Do you have the heater hooked up and working? The heater hose circuit is involved in cooling the engine on GM cars. If it is blocked or capped off, it changes something about coolant circulation, but I don't remember what or why. Try running the heater and fan on high. If you get burning hot air from the heater and the temperature on the gauge comes down a little, the radiator isn't giving up the heat, either due to air flow blockage or poor coolant circulation. If you get just warm air, and there's little change in the gauge reading, there's not enough coolant circulation. Look at the diameter of the various pulleys. If the water pump pulley is too big, it may not be spinning fast enough to move enough coolant. If the pulley is too small, it can make the pump spin real fast leading to "cavitation", meaning the coolant just goes around and around with the vanes, and doesn't flow out to the radiator.
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Wednesday, June 25th, 2014 AT 4:47 PM
Tiny
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I finally got around to doing another test drive. There are no openings in the core support and all the rubber parts are there and new. I got it on the highway and turned on the heater and it was hot air and it did cause the radiator temp to drop. The pulley on the crank is 7.5" in diameter. There is no way to have a shroud with the 4 core. But it did have one with the three core but it made no difference with than without overheated the same. I do not want to pour more money in it if I do not know the cause. I know Be cool radiators are supposed to cool better but hate to purchase one if still the problem. They swear their two core 1" tubes will cool like a four core. I did try without the thermostat to see how the water flowed and it seemed to flow good, but still overheated even without the thermostat, but I knew it would. Seems if the temperature outside is cooler it will seem to operate much better, but it would never support any kind of traffic stops or even turning on the air cond I have never been able to turn on. Frustrating, seems to be a ghost I cannot figure out.
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Saturday, July 12th, 2014 AT 6:50 PM
Tiny
CARADIODOC
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There has to be a shroud, even if there are other unidentified causes yet. I don't think more radiator is the answer. You need more air flow through it. Years ago when removing the shrouds were fairly easy to do, doing so caused a lot of overheating issues that owners and a lot of mechanics didn't understand or associate with doing that.
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Saturday, July 12th, 2014 AT 8:22 PM

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