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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Originally Posted by 67:72
I think the thing that gets folks off-track (or maybe I'm off-track) is that that 220°F engine will attain 220° no matter what thermostat rating is installed. The stat will maintain the coolant temp at or near the stats temperature rating as long as there is enough capacity (volume of coolant) for the coolant to cool in the rad The only thing a thermostat does is restrict coolant flow up to and to maintain its design temperature. The t-stat determines the speed from start-up at which the choke will disengage (through heat transfer to the choke controls) and maintaining the efficiency of the combustion process once up to temp. Our engines (generally speaking) are not as efficient at 160°F as they are at 200°F, so you don't want a low temp thermostat in there staying open as coolant temps drop below optimum operating temperatures – plus it won't keep your engine from attaining the temp that reflects the system's heat transfer abilities anyway.
Whether the normal operating temp is maintained depends entirely on the efficiency of heat transfer to the atmosphere. Well, sorta. The stat plays a big role here as it controls the flow of the coolant and will only open when the engine temp reaches the stats temp rating. Then it will modulate its valve according to engine load to maintain the normal operating temp of say 180*F. But the rad needs to be large enough to cool the coolant sufficiently at high engine loading to prevent overheating or running at temps of say 220*F. Is coolant cycling through the radiator at the proper speed to allow transfer? Well, sorta. Coolant dwell time in the rad is what is required here. The bigger the rad, the more dwell time for the coolant to cool before re-entering the engine. Are the radiator passages fully open to transfer the coolant temp to the metal tubes? Can air pass through the radiator fins such that the tubes' heat will be "carried away"? A proper functioning rad in good condition should be expected to do this.
If the stat in my house is set at 72F and its -10 outside and the temp inside won't go above 65 then I need to add more insulation in the ceiling and walls or get a bigger hot air furnace. Same analogy for a car. If the stat is rated at 180 and the car runs at 220, then I need a bigger rad or reduce engine load, drive slower, drive on cooler days. These days, a bigger rad is the way to go.
Water boiling point is 212F, at 15 psi that boiling point is increased to 249.8F. A 50/50 mix of water and antifreeze will add 11F buffer to those number so in reality when this car pukes out the overflow the water temp is 260F or higher. Re-engineering the cooling system is not the answer, first find out why than move on to the fix.
Great info and appreciated. This weekend i gutted the thermostat just to see if i had two faulty thermostats in a row, maybe stuck closed. I drove it and the temp slowly increased (naturally much slower since there was no thermostat) to 220, then on freeway one exit it dropped back down just under 210. By the time we got home temp was back up to 220-230 when i shut it off. A minute later, the green waterfall. It has a stock, brand new rad, stock brand new GM water pump, all seals on the bottom and sides of radiator, the seal between the radiator core support and the seal between the core support and the hood. I checked the fan clutch and the fan does not spin freely....spins just between a quarter and half a turn which indicates to me it should be ok. I'd buy a gold plated one if that was the problem.
I will check and adjust the timing again and read the report. This may be the last test before i have the engine taken apart...at a loss guys.....but really,really appreciate your feedback.
If the stat in my house is set at 72F and its -10 outside and the temp inside won't go above 65 then I need to add more insulation in the ceiling and walls or get a bigger hot air furnace. Same analogy for a car. If the stat is rated at 180 and the car runs at 220, then I need a bigger rad or reduce engine load, drive slower, drive on cooler days. These days, a bigger rad is the way to go.
Not sure about the applicability of the house thermostat analogy... but I think I follow, and will add that raising your thermostat to 75F won't do anything to get your house warmer. Alternately, if it's 100F outside and your house A/C is set to 72 but only gets down to 80, lowering the t-stat to 65 won't change the situation. Similarly, if the car's stat is rated at 180, going to a 160 ain't going to do squat about lowering the 220. This concept was confirmed by Pls570 when they removed the t-stat altogether (effectively "installing" an ambient temperature rated thermostat) - engine temp still went to the overheating range. I completely agreed with you resdoggie it's the whole system that needs to operate well.
Can we have some pictures of this engine bay water pump radiator and such ,, sounds like the fan is not working right or you have the wrong one or its backwards or the clutch fan is not working ,, the original clutch fans are filled with oil and if you lay them down they leak ,,,,pretty sure its a 5 blade fan ,, do you have the right size pullys for you car ,, it seems your car is not getting the flow and cooling you need
When is the last time you did a good flush? Crud builds up in there. Thermocure (same company that makes Evaporust) is a bit expensive but an amazing product. Used it on a C4 (also known for running hot) and it dropped temps 20 degrees. Did a really good flush including opening the block plugs. Incredible amount of rust/gunk came out. I would certainly do this before taking apart the engine.
Last edited by hornetball; Mar 24, 2022 at 11:13 AM.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Originally Posted by 67:72
Not sure about the applicability of the house thermostat analogy... but I think I follow, and will add that raising your thermostat to 75F won't do anything to get your house warmer. Alternately, if it's 100F outside and your house A/C is set to 72 but only gets down to 80, lowering the t-stat to 65 won't change the situation. Similarly, if the car's stat is rated at 180, going to a 160 ain't going to do squat about lowering the 220. This concept was confirmed by Pls570 when they removed the t-stat altogether (effectively "installing" an ambient temperature rated thermostat) - engine temp still went to the overheating range. I completely agreed with you resdoggie it's the whole system that needs to operate well.
My point was about cooling/heating capacity. I can lower or raise the temperature inside the house to 72*F but the cooling/heating unit must have the capacity to do so. Solution? Buy a bigger unit. Or for a car, buy a bigger radiator i.e. more capacity to hold more coolant which equates to more dwell time in the rad which will provide cooler coolant re-entering the engine.
FYI, I ordered a new fan clutch as that was the last piece that has not been replaced. This pic is before the hood and the final foam strip installed on top of the radiator support.
FYI, I ordered a new fan clutch as that was the last piece that has not been replaced. This pic is before the hood and the final foam strip installed on top of the radiator support.
The first thing that jumps out to me in this photo is you have a small block fan with a big block motor. Not sure that would be causing your issue, but there was a big block fan that had I believe an additional blade and definitely had curved ends on the blades. I have one sitting in my garage. Again, not 100% sure that would be your issue here and certainly would not contribute to at speed heat, but if you are having heating issues while idling, you might try the correct fan. Just a thought.
The first thing that jumps out to me in this photo is you have a small block fan with a big block motor. Not sure that would be causing your issue, but there was a big block fan that had I believe an additional blade and definitely had curved ends on the blades. I have one sitting in my garage. Again, not 100% sure that would be your issue here and certainly would not contribute to at speed heat, but if you are having heating issues while idling, you might try the correct fan. Just a thought.
Yup I think you are on to something. That should be a 7 blade fan on there. On second thought a non A/C car might not require a 7 blade.
Coolant flow to the Rad. could be a problem. I've seen restrictors put in the bypass and heater line to get less re-circ. and more coolant flow to the Rad. But only on heavy modded engines.
All non-AC cars, no matter the engine, came with 5-blade fans. The big blocks with AC had unusually tipped 7-blade fans.
The '70 BB, no AC, fan should be #3888366 - probably stamped into at least one of the blades.
I drove it and the temp slowly increased (naturally much slower since there was no thermostat) to 220, then on freeway one exit it dropped back down just under 210. By the time we got home temp was back up to 220-230 when i shut it off. A minute later, the green waterfall.
For starters when the temp increased to 220 that was your failure starting point in all this, what was the outside temp? How much operating time did you have to reach 220?
1) Critical that you verify the engine timing is correct.
2) Replacing the fan clutch will give you piece of mind if nothing else.
3) Coolant system flush can't hurt at this point.
Out of the box thinking if the above doesn't cool this beast down.
Temporary install a pusher fan in front of the radiator (use large zip ties to secure it), whatever size will fit and wire it to just stay on while you take car for a drive. You will most likely have to remove the hood to do this so take it for a drive without the hood installed. If it doesn't overheat install the hood and do another drive. Point of this science project is to get more air across the radiator.
1) Critical that you verify the engine timing is correct.
2) Replacing the fan clutch will give you piece of mind if nothing else.
The fan clutch could well be the issue as they only "lock up" when a temperature sensitive spring engages. Could be it's still free-wheeling at full operating temp and not moving the volume of air that it should.
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I have the same set up
