Learn Me Engine Cooling

I understand the general principles of ICE water cooling. What I don't understand is how and why certain engines reach a point where more radiator/fan/pump doesn't seem to help. The two examples right off the top of my head are 2JZs and Big Block Chevy engines. I knew a Supra owner who road raced his MK4 and he said that going over about 450 whp for a long session almost always resulted in temperature control problems. Likewise, I've heard from several folks that cooling problems are why big block Chevy's never made it into very many endurance/road racing applications. Neither seemed very sensitive to better/bigger radiators or higher flow water pumps etc. (In dumber applications like dyno queens and highway pull cooling is seemingly always a problem, though I'm not sure if those people even try to address it.)

Is this a water jacket design issue? Cylinder banks that are overly long and causing big temp differentials between cylinders? Something else?

I have not messed with that many big block Chevys, but in our small block dirt cars, we try to slow the water flow down to give it more "cooling time" in the radiator. We tried different thermostats, no t-stat, different size restrictors in place of the t-stat, aluminum radiators. Changing the size of the water jackets, and finally hit on a combination that works. We also ran Methanol for years but, about five years ago we switched to race gas and haven't had any heating problems. 

I think the big blocks make more horsepower and that means more heat. And I think the flow in the big block was not optimal. G.M. never intended for us to do what we do with them. 

I always assumed it was partly how the water jackets were designed and the vehicle itself.  If the aero of the car can't allow enough air through, nothing will help.

Big blocks are run in dirt track modifieds and don't seem to have a problem

Ours didn't.

I never had issues with the BBCs I did, but they were admittedly mild builds in the 375 hp range.

The Cadillac 472/500s would sometimes get too warm when you modded them past a certain point.  In that case it was a bottleneck/restriction in the water passage under the thermostat.  It's this convoluted passage with lots of bolt bosses and a sharp 90 degree bend to get to the water neck.  Some folks would take a grinder and "port" that passage with modest success, but after 500 hp, your best bet was to either remove the thermostat or use a remote thermostat.   Didn't matter how big you made the radiator if you couldn't get the water to it fast enough.

Flow isn't as big an issue as you might think unless you choke it down so much that the water in the block heats up faster than it can escape to be cooled.  The old "too fast" or "too slow" isn't really a thing.  As long as there is water against the jacket, it's absorbing heat.  If you go way too slow, it gets too hot.  If you go way too fast you can get cavitation/frothing, but the speed of the coolant has very little to do with anything.  If you increase the speed of the coolant, each unit of coolant will absorb less heat during its trip through the block, but there will be proportionally more units of coolant moving through the block, so it's a wash.  The inverse would happen in the radiator.  It would simply lower the difference in temperature between the radiator and the block, but the same amount of heat would get transferred.

Above a certain point there is not enough surface area within the engine to transfer the heat to the coolant. This area is always far greater than any manufacturer intended power level, but some engines are stout enough in the rotating/reciprocating mass department to exceed it with big enough turbos.

I don't really understand the too slow/too fast argument. At least in my head, too slow opens the door for potential local boiling issues at high power. I have had this problem in an engine that was notorious for slowly wearing away at the water pump impeller. It didn't take much for me to get to a point where it would spontaneously boil at sustained high power, and it would run a little warm at idle where I suspect the pump was just bypassing coolant instead of pushing everything through the radiator's flow resistance.

Slow flow also seems like it would give you a radiator that would not be used to its full potential - more heat rejection/transfer occurs with a higher temperature differential, and if the coolant is not flowing fast enough through the radiator to keep all or most of the core significantly hotter than ambient temperature, it probably isn't doing its job as well as it could. The downside to increasing flow rate to get there would be the risk of cavitating the water pump and suddenly causing loss of flow/block pressure at high engine speeds.

Flow geometry can also be a problem in some engines, especially older ones. I work for an engine company, and I know as we have increased the power density in some engines based on older designs, we have run into strange cooling problems during validation that ultimately turned out to be parts of the water jacket that would become completely stagnant in some conditions. It wouldn't surprise me if some of our favorite pre-CFD engines have the same problems. No amount of larger cooling system or higher water pump flow would fix the issue, either. It was just a wall we would hit at a certain power level that required water jacket design changes (including casting changes) to fix.

No such thing as too fast unless you cavitate the pump or have another issue that shows up at high flow rates. I have done full pwm controlled water pumps with no thermostat and it's amazing how well you can control the temperature and heat transfer just with the speed. More flow always = cooler temps as long the rad is big enough. The only radiator that's too big is the one that doesn't fit, also true for intercoolers 

For starters we should address the plastic/rubbery air dams and ducting that either rots away or nearly everyone foolishly throws in the trash when they work on a car....Yes I'm speaking from experience. This is because a large number of overheating problems I've ever dealt with had to do with air supply THROUGH the radiator. Just air to the radiator isn't good enough. It needs to be forced to go through. This was highlighted for me last year when I traveled to PPIR for a race and had my car setup with no cooling problems....at nearly 5000ft lower elevation. Overheating in couple laps was fixed by taping up any gap in sheet metal and shrouds that was in front of the radiator. Even jabbed a towel in underneath the radiator to seal the gap that the rubber isolators held the radiator up from the core support.

Another massively overlooked cause is the tune. An engine with too much timing (at cruise or under throttle) or a lean air/fuel ratio is just waiting to overheat. This is especially evident with older carburetted cars that never get properly tuned. Know a guy who just slaps stuff together and "is so good" he tunes timing by ear...yea his overheating is likely a E36 M3 tune. I can't drive this point home enough...Just check it so that you KNOW! A great example here is a car with a great radiator/fan setup and only overheats when cruising after an hour or so, or sitting in traffic (which lack of airflow also contributes to). This particular engine when dyno'd was ok on timing but was near 17:1 AFR...even at wide open. After some tuning adjustments the engine gained 28HP, started easier, ran cooler, and was all around made for a much better car.

Hard parts...Is the system clean of gunk, rust, debris? If you experience overheating after hard pulls...you sure the water pump is working? I've seen an impeller get loose on the shaft when hot and quit pumping! Leaks? Kinked hoses? Restrictions? T-stat working? Head gasket blown? 

Ready for system design yet? I've been looking into this recently. So there is the "closed system" style with cap that vents fluid/pressure into a catch can. Works well and used for decades but not the most effective. Then we move up to more modern style of "pressurized" or "recovery" in which there is a recovery tank with intentional air pocket that acts as a spring in the system. Here the goal is for the system to never let coolant or pressure out unless it exceeds the cap rating. All modern cars are designed like this OEM and it is a much better system. Again....how many people just rip all this "unnecessary" stuff off a car when building it for performance? An explanation here between the two before someone says "but the closed system is pressurized"...yes but in the closed system you often see the coolant level when cold is a few inches down in the radiator. Collapsed hoses is another symptom of this too. The pressurized system with the recovery tank air spring is to keep the radiator full at all times and even when dead cold have zero or positive pressure still in the system. This is evident on newer cars when opening the cap when cold and getting a pressure releasing hiss. These are more efficient due to the coolant being "full" all the time and the maintaining of pressure in the system.

Pressure: Here it is widely agreed that higher pressure makes the system more efficient and raise the boiling point. Over a few hours of searching I couldn't find any real word data on how much efficiency increases or what that means for temps during cruise or on track. Only the increase in boiling point could be found. Some racing runs over 50psi but it obviously takes a very dedicated and properly built system to handle that.

As for the original question of 2JZ and Big Block Chevy i'd bet my money on little or no shrouding and poor tunes.

Adding to what has been said. Exhaust valve opening timing, exhaust valve seat width, exhaust valve lash, piston ring thickness can all have effects on cooling. 
 

Also, a lot of 2jz are run with reduced timing and the effect is that a fresher flame is flowing right out the exhaust valve opening. Hot valve = hot coolant!

asphalt_gundam said:

For starters we should address the plastic/rubbery air dams and ducting that either rots away or nearly everyone foolishly throws in the trash when they work on a car....Yes I'm speaking from experience. This is because a large number of overheating problems I've ever dealt with had to do with air supply THROUGH the radiator. Just air to the radiator isn't good enough. It needs to be forced to go through. This was highlighted for me last year when I traveled to PPIR for a race and had my car setup with no cooling problems....at nearly 5000ft lower elevation. Overheating in couple laps was fixed by taping up any gap in sheet metal and shrouds that was in front of the radiator. Even jabbed a towel in underneath the radiator to seal the gap that the rubber isolators held the radiator up from the core support.

Another massively overlooked cause is the tune. An engine with too much timing (at cruise or under throttle) or a lean air/fuel ratio is just waiting to overheat. This is especially evident with older carburetted cars that never get properly tuned. Know a guy who just slaps stuff together and "is so good" he tunes timing by ear...yea his overheating is likely a E36 M3 tune. I can't drive this point home enough...Just check it so that you KNOW! A great example here is a car with a great radiator/fan setup and only overheats when cruising after an hour or so, or sitting in traffic (which lack of airflow also contributes to). This particular engine when dyno'd was ok on timing but was near 17:1 AFR...even at wide open. After some tuning adjustments the engine gained 28HP, started easier, ran cooler, and was all around made for a much better car.

Hard parts...Is the system clean of gunk, rust, debris? If you experience overheating after hard pulls...you sure the water pump is working? I've seen an impeller get loose on the shaft when hot and quit pumping! Leaks? Kinked hoses? Restrictions? T-stat working? Head gasket blown? 

Ready for system design yet? I've been looking into this recently. So there is the "closed system" style with cap that vents fluid/pressure into a catch can. Works well and used for decades but not the most effective. Then we move up to more modern style of "pressurized" or "recovery" in which there is a recovery tank with intentional air pocket that acts as a spring in the system. Here the goal is for the system to never let coolant or pressure out unless it exceeds the cap rating. All modern cars are designed like this OEM and it is a much better system. Again....how many people just rip all this "unnecessary" stuff off a car when building it for performance? An explanation here between the two before someone says "but the closed system is pressurized"...yes but in the closed system you often see the coolant level when cold is a few inches down in the radiator. Collapsed hoses is another symptom of this too. The pressurized system with the recovery tank air spring is to keep the radiator full at all times and even when dead cold have zero or positive pressure still in the system. This is evident on newer cars when opening the cap when cold and getting a pressure releasing hiss. These are more efficient due to the coolant being "full" all the time and the maintaining of pressure in the system.

Pressure: Here it is widely agreed that higher pressure makes the system more efficient and raise the boiling point. Over a few hours of searching I couldn't find any real word data on how much efficiency increases or what that means for temps during cruise or on track. Only the increase in boiling point could be found. Some racing runs over 50psi but it obviously takes a very dedicated and properly built system to handle that.

As for the original question of 2JZ and Big Block Chevy i'd bet my money on little or no shrouding and poor tunes.

I see. At what point do you think it simply becomes a question of the engine itself? I'm thinking specifically of the dyno queens and highway nonsense that immediately overheats on shows like "Sorted."

Vipers, R8s, 911s, stuff that would seem to have good cooling systems and at least reasonable tunes. At what point does a Viper just have too much turbo, etc?

Curtis73 (Forum Supporter) said:

I always assumed it was partly how the water jackets were designed and the vehicle itself.  If the aero of the car can't allow enough air through, nothing will help.

Makes me wonder.  I know most of the cooling of an engine is through the radiator, but there's a non negligible amount of cooling that comes from radiation and convection of the surface area of an engine.  Does make me wonder how much that amount is.

i like using   ' evens waterless coolent '  not vapor in the head. little tiny bubbles bursting in the engine, chewing away at the block/ head.. works for me.. i live in sacramento,, a 100 to 112 days are not uncommon in the summer.. but temp gauge always stays in the safe zone..and it warms up faster in the winter...