Cooling System Theory

0xDEADBEEF said:

Absolutely. On the C5 the lower air dam is even more important at speed. I believe the holes in the hood basically popped a bubble of high pressure under the hood because the car also felt a lot more planted at high speed.

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So would it be fair to say, that your cooling system is on the ragged edge of sufficient for what you are subjecting it to? And that falls in line with the expected results of what the guy in the video said would happen?

It sounds like your underhood pressure relief situation was a good one though. It killed two birds with one stone.

@Old77 Could you please put all these cooling system theory posts in a separate thread in the appropriate area, if Jnunez74 desires?

AK 99 said:

So would it be fair to say, that your cooling system is on the ragged edge of sufficient for what you are subjecting it to? And that falls in line with the expected results of what the guy in the video said would happen?

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It depends on your definition of the edge and how far away from it I was. The PCM in that car has an overtemp mode and it never went into that mode or let any steam out with a thermostat. (It did when the coolant hose popped off.) I think overtemp happens at 250F or thereabouts.

I used to have handwritten logs where I would write down stuff about a session including water and oil temps, but they are gone now.

Per request, I created a new thread with the "Cooling System theory" posts so you all can continue talking and not mess up a thread.

Thanks for requesting this and helping keep things cleaner.

Isn't the coolant in the block under a bit of pressure even with no thermostat? Meaning, the "restriction" would be the holes in the head?
Here's where my thought comes from. On the 5.9 12 valve and early 24v cummins, it is a known fact that the rear frost plug will blow out due to pressure from the water pump. This plug is below the deck surface, and some people have actually put pressure gauges in their blocks, and found it holding 80psi water pressure (obviously not at idle) before the thermostat opened. While the pressure did drop when thermostat opened, the block continued to carry significant pressure that wasn't equalled in the head (around 30psi if I'm remembering correctly).
Wouldn't there be pressure/restricted flow to the head to ensure the water doesn't flow so fast by the cylinders that doesn't take on enough heat as it flies by?
I'm no expert, just tryin ta learn here!

This is the flow restrictor made by Katech I used in place of the thermostat. Do not recommend it though!

Up to the point of cavitation, more flow removes more heat. The reason thermostats open with heat is to increase flow.

There's pretty-much no such thing as "flowing too fast to pick-up heat"; or "flowing too fast through the radiator to remove heat".

AK 99 said:

He explains why removing a thermostat will change the flow through the radiator and cause an overheating issue, but this is all based on an inefficient radiator.

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Removing a thermostat "can" cause overheating; but the common reason is that the vehicle has a downflow radiator. The radiator cap is on the hot side of the rad core, which means it's also on the higher-pressure side if the core has any restriction (and it always has some restriction)

So you remove the restriction caused by the thermostat, and now the rad cap has system pressure PLUS water-pump pressure...and at high rpm, (high water-pump pressure) it blows coolant out the overflow until there's not enough left in the cooling system to keep the engine at proper temp.

This is so much less likely on a cross-flow radiator, since the rad cap is on the cool tank--the suction side of the water pump.

AK 99 said:

He also states that most factory cooling systems are not efficient enough.

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Efficient enough? Or "big" enough?

Trucks and heavy equipment tend to have H-U-G-E radiators compared to passenger cars and light trucks. Reason being, those engines are worked at near full-capacity for hours at a time. Passenger cars/light trucks are generally run at part-throttle--lower power level, lower average heat load. When the engine is run hard, the temperature rises, and we're used to that. We think it's normal unless the temp rise is too extreme.

AK 99 said:

Horsepower makes heat.

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Exactly.

AK 99 said:

Sorry to quote such an old post, but this theory irks me. There's no such thing as coolant "flowing too fast through the radiator" because fast flowing coolant is also spending less time in the engine getting hot. It's a two way street basically, you can't have one without the other.


But anyway... this is such an awesome build! I love the drive train choice and the color choice too!

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I've seen it both ways. Once it was " oh left the thermostat out so it cools better.." Except it constantly overheated boiled over.
The other a thermostat failed , stuck open , was not getting warm enough to run properly.
It is a balancing act, depending on which part of equation is missing the result is different, and not operating as designed.

Oh joy, the debate of coolant moving too fast in a cooling loop or air flow moving to fast through a radiator.
I thought I got away from that when I stopped participating in PC watercooling forums.

This is the one of the few issues for which I will take off my safety squints, through on my nerd glasses, and pull out my mechanical engineering degree.

CLOSED COOLANT LOOP 101.
1. The more coolant flow over hot part is almost always* better given the same dimensional constraints.
2. The more fluid flow (air side or coolant side) through non-phase change heat exchanger is almost always* better given the same dimensional constraints.

*There are always caveats, these are the big three:
1: The flow rate isn't in the transition region between high laminar and low turbulent, (weird things happen here)
2: The restriction of either air or coolant isn't so high as to cause significant heating in the loop itself (friction or cavitation)
3: The pump does not impart significantly more heat into the fluid due to moving more volume (but at less pressure)

Other considerations.
1: The best non-phase change heat exchangers can only cool off the hot fluid up the ambient temperature of the incoming cold fluid
2: Car radiators are not optimally designed counter-flow annular pipe heat exchangers working with set fluid flows and inlet temperatures, but an unmixed cross-flow fin-stack that has to work under varied flows and temperatures
3: A higher transfer of thermal energy may not be optimal if a component (engine) was designed for a very specific temperature at a thermal interface (coolant jacket)

Biggest issue with a SBC is not so much the flow it is how the flow is distributed in a stock engine. Stewart Water pumps had 4 stages of GM SBC pumps at one point. Their information is in a mid 90s SBC performance book I own. The stock flow is designed around a ~250 hp engine that sees a continuous load of up to perhaps 100 hp. Simple math here, make 2x the HP you have 2x the heat. You need a pump that flows more volume as well as helps even out the flow difference bank to bank. That is also ignoring the fact the rear cylinders run hotter. High end cooling setups like nascar use added plumbing off the pump to help feed coolant flow toward the rear of the block as well as more plumbing to help promote coolant flow back to the water outlet. They spent probably 10s of 1,000s in R/D to help balance the engine temperature bank to bank and front to rear so that all they cylinders run closer to the same temperature.

The head gasket itself also helps coolant pressurization and distribution in the block.

OP, Look up 'Thermal Cycle' cooling systems, most old 1930s and prior tractors had no water pump but would run in a hot field 24/7 until the job was done. The steady state of having hot water rise and cold water sink moved the water.

My 1938 John Deere A has this cooling system, it weighs a ton with the volume of water it takes but its cool (pun) that it works so well, it will get to 190 on the gauge within 15-20 minutes and stay there.