Technical Coolant moving too fast through radiator to cool?

Best way to slow down water moving through your radiator is to increase the size of the radiator to accommodate a larger volume of water.

 

Greater pressure in the system (what the post you were replying to said) raises the temperature where the coolant turns to steam.

 

His theory is at a higher pressure in the system the contact of the coolant to the block/heads is better making picking up the heat is more efficient. Hey it's his theory and for us it works. We always pressure test every cap and have a 30psi on the system. Before this we had many coolant problems and ran some races at 240-250 degrees.

 

You are correct,I experienced a senior moment (brain fart)

There is a huge difference in fast and slow,the smaller diameter increased the water flow.thank you for pointing out my faux pas,I will correct my post. HRP

 

I've seen water pump impellors on Cummins and Cat diesel engines where the blades on the impellor were worn down to little sharp ribs. Cavitation does happen!

 

There ya go!
Simple

 

A lot of that water pump speed thing depends on where you are operating the engine. If you are having a problem in traffic, its a low RPM deal , and by going to a smaller water pump pulley you are increasing the water flow...and you are also increasing the fan speed, making it move more air while sitting still. BOTH of which should increase the heat transfer ability of the system.
I've also seen it where at high RPM the fan would be turning so fast it would be like a solid disc and air couldnt move through the radiator, it would go around and overheat. We would buy the biggest two row water pump pulley GM made and a smaller crank pulley from Moroso, to slow the fan down, and the car would run cooler on the track.
There is no hard and fast one-size-fits -all combination that will work for everybody. If there was the cheap-ass factories would only make one and put it on everything.
Sometimes people do the right thing for the wrong reason and it happens to work, and they are forever convinced that physics doesnt apply to them. Good Luck to all.

 

Can one of you guys calculate heat transfer and make time irrelevant?
I mean if slowing water down doesn't mean anything and speeding the water up apparently works better then ,,,, time doesn't matter.

Fuckit, I'm with you guys and calling BS on physics too.
As soon as I can figure out a calculation to prove heat transfer without time.

 

That's all you have to say? I nominate this for the most useless post on the H.A.M.B., probably ever.

 

water flow speed/time

 

Rusty is correct about pumps and cavitation. An easy way to see if a boat prop is cavitating is the missing paint on the back of the blades.

A couple things is that the radiator is clean and the system has a rad cap that holds the correct system pressure. The pressure keeps the boiling point down so if the cap is not holding pressure can run hot. A mix of antifreeze and water has to get to about 220 to boil and with pressure it suppresses the boiling point. The greater the trmperature difference between the coolant and air the better the heat exchange.

The thermostat acts like a valve and temperature regulates the flow when closes and allows flow when open. The thermostat is to hold the engine at a temperature for maximum engine efficiency. There is some thermostat bypass flow to prevent serious cavitation and boiling created by the pump impeller. There has to be some flow or the impeller will spin the coolant until it flashes to steam causing boil over. With no flow the fluid spins with the impeller and the friction against the pump housing makes it boil. I saw a large glycol HVAC pump that had exploded after an area maintenance shutdown in a mill. The operators forgot to open the valves on both sides of the pump before start up which caused the locked in fluid to spin until the friction caused the fluid to flash to steam. The steam pressure blew apart the pump casing, bent 8" sch 40 pipe and sent metal through a steel sandwich wall. If the impeller is spinning too fast then the vacuum created on the trailing edge will cause the fluid to cavitate which is flashing of the fluid that erodes the impeller. In large pumps it is loud popping or crackle noise. A 1" reduction or increase in the pulley diameter has a great effect on the impeller speed and its operation. The ideal water flow for efficiency is 10 - 15 ft/sec and any faster the resistance increases with velocity to where the system needs to burn a lot of hp to get no improvement. Water in the system basically sets its own max flow.

A heat exchanger like a radiator is efficient when the hot fluid & the cooling medium are going opposite directions with turbulent flow with good velocity. Down sizing the water pump and fan pulley will do two things. The faster rotation will speed up the fluid as well as the air so the heat exchange rate may or may not improve depending if the pump is operating in a healthy range. Speeding up the fan and the increased pump flow increases hp draw. The hp used in speeding up fans and pumps is not a linear amount and increases exponentially as the speed goes up. I was asked to speed up the flow in a water pump by changing the motors from 1200 rpm to 3600 that required the motor to go from 15hp to over 60hp so it received a 75hp. It defies reason but that is how the pump laws work. That may be why cars with AC have a slower pump and likely a larger rad so the power saved to drive the water pump & fan helps keep engine hp up which will be taken down with the AC so the net power is about the same as a non AC car.

The velocity through the radiator is not an issue with the rad manufacturers if sized correctly for the heat generated by the engine & climate. The pump efficiency is more critical to make the system flow properly. Fuzzy Knights experience showed that an oversized pump can be a problem. The pump likely was trying to move so much flow that the flow caused so much friction resistance that it became inefficient or it was overspeed so the impeller was inefficient. The pump has to be right sized and the flow is what it needs to be when the thermostat opens to take the temperature down. The washer instead of a thermostat likely replicates an open thermostat to regulate flow to keep the engine in an efficient flow & temperature range.

 

The velocity through the radiator is not an issue with the rad manufacturers if sized correctly for the heat generated by the engine & climate. The pump efficiency is more critical to make the system flow properly. Fuzzy Knights experience showed that an oversized pump can be a problem. The pump likely was trying to move so much flow that the flow caused so much friction resistance that it became inefficient or it was overspeed so the impeller was inefficient. The pump has to be right sized and the flow is what it needs to be when the thermostat opens to take the temperature down. The washer instead of a thermostat likely replicates an open thermostat to regulate flow to keep the engine in an efficient flow & temperature range.[/QUOTE]

WELL SAID!!! I've learned on my '57 Chevy (283 FI, 097 Duntov cam) that NOT all aftermarket replacement water pumps are created EQUAL! The engine was running hot at road speeds. Rodded out the stock (copper-brass) radiator, installed a 180 SUPERSTANT thermostant. I know that helped, but NO change on the gauge... 210-220 range. Next was a 180 ROBERTSHAW thermostant (from Steward Racing), again no change. Meanwhile, I'm reading everything I could find about cooling systems, to figure-out my next move...

Coming home one night around midnight, pulling up a long 3-4mi. grade, the gauge went to 240 before we got half-way up. By the time we dashed over to the shoulder, the gauge was headed towards 280! As we sat running the enging at 1500 to try to get the temp down, ALL the worst-case senareros ran through my head - mainly a blown head gasket, cracked head. Got the temp down to 220, checked for coolant loss - NADA, nothing, to my suprise!!! Tip-toed home with the gauge holding at 220.

A SHROUD was all I could think of next... While taking measurements to maybe bend somthing up, I bumped the fan - noticed a bit of play at the water pump. "That's NOT gonna last, before the play takes the seals out" I thought... Called around town for a GRINGO replacement, but EVERYTHING is rice from China - couldn't even locate a gringo rebuilt pump. So, I settled for a rice pump from NAPA - $27, lifetime warrenty.

Replaced the water pump, drove up the same long grade. 95 outside, the gauge NEVER went past 200!!! Never has since, and I SMILE to myself every time I glance at it...

 

Funny, i use a flex-a-lite type fan, and a Stewart high flow performance pump, i believe my pulleys are 1:1....i had issues w some higher than wanted temps especially on hot traffic days. Pulled thermostat out, same thing. Installed restrictor w 1" hole....waalaa...stays between 160-180....its a 580 hp small block in a 30 Coupe w 3 core aluminum rad

 

Is Anyone going to try heat transfer without time ?

 

On every Pontiac I've ever owned the ones with factory A/C always had a smaller diameter pulley on the water pump as compared to the cars without A/C.

Why would the engineers put a smaller diameter water pump pulley on air conditioned cars that speeds up the water pump if pumping the water faster through the engine wasn't the right thing to do to increase the cooling ability of the cooling system?

 

Because it turns the fan faster too, moving more air.

 

Actually the formula given above does refer to total heat transferred, and ignores time, and the result is in BTU's. The RATE of heat transfer ( the Q with the dot over it) is the same, except the right side of the equation is written over time, and the result is given in BTU/hr .....At least that's the way I think I remember it, but its been 30 years since I had to do all that theoretical calculation stuff, so if I'm wrong dont crucify me. But you are right, its the RATE of heat transfer that we are always trying to make better.
I think we all agree that " big radiator+big fan=no problems". Its when we try to make it smaller, lighter, and cheaper that we get ourselves in trouble. Good Luck

 

A lot of folks don't ever consider how tiny the flow port in a thermostat really is. A typical 350 SBC thermostat has a port size of 13/16 of an inch, plus it has the control valve sitting directly in the center of the flow. A "restrictor" with a 1" hole flows more coolant than most any automobile thermostat. A 13/16 inch hole has an area of 0.517848 square inches, a one inch hole has 0.785398. That's over a 50% increase in area. Plus there's not a brass valve directly in the center of the coolant flow like there is in a thermostat, so it's likely quite a bit more flow than the math suggests.

 

So...the water pump doesn't affect pressure in different parts of the system?

 

Ok, I've had first hand experience with this, even tho it's been poo-poo'd. I had a 49 ford pickup with a '67 mustang 289/cruiso. The truck had the original 4.27 rear gear in it. It ran cool up to about 40MPH when the temp would climb until the radiator boiled over...gauge said 240.
I removed the T'stat housing to find no thermostat at all.......put a 180 degree thermostat in it and never again had a cooling problem. That tells me the coolant flow was too fast. Jus' sayin

 

Everybody can post all the theories and formulas about cooling they want...but in 1964 on my first gasser I didn't use a thermostat in the cooling system on my SBC..it ran hot every run, very hot...someone suggested that I might need to restrict the water flow, I placed a body washer with a 3/4 in. hole in the thermostat housing to slow the water flow and from that time on the engine stayed in it's proper operating temperature. Right or wrong, I don't know...but this worked for me for over 20 years of drag racing.

 

After several problems with cheap LPS thermostats not working as intended I started using the Milodon Balance Sleeve thermo especially if I have up graded the water pump..........................

 

Only if the motor is running, and the belt is on.

 

Here's a graph showing the temp drop vs flow rate.
A bit different than our car cooling systems and thus eliminating variables zeroing in on flow rate alone thru the "heat shedding" end of things. The parameters for this were 180* water temp entering a radiator type devise, the rate of flow went from 0.5 Gpm up to 8 Gpm.

As you can see when the rate of flow was 0.5 Gpm the drop in temp was 55 degrees
At 8 Gpm the temp dropped just about 6 degrees

 

I totally agree with what you say about what is really a "blanket formula" by some laboratory test. It means nothing in "our" world

Each one of our custom builds are different! Fans, engine block wall thickness, radiator design, front end sheetmetal and grill flow rates/restrictions...etc etc

Keep experimenting with a given build, and you can work around any limitations of our unique cars.


That's what we do on every part of our builds.
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Also remember that for example a 180 degree thermostat STARTS opening around 180.
At this temp it is barely open with very little flow and it stays that way unless temp increases.
Then the thermostat opens wider allowing more flow and trying to bring temp back down to the thermostat rating, so it can almost close again for normal operation.


As the engine's coolant warms up, the increase in heat causes the wax to melt and expand. The wax pushes against a piston inside a rubber boot. This forces the piston outward to open the thermostat. Within 3 or 4 degrees F. of the thermostat preset/rated temperature which is usually marked on the thermostat, the thermostat begins to unseat so coolant can start to circulate between the engine and radiator. It continues to open until engine cooling requirements are satisfied. It is fully open about 15-20 degrees above its rated temperature. If the temperature of the circulating coolant begins to drop, the wax element contracts, allowing spring tension to close the thermostat, thus decreasing coolant flow through the radiator.


Put a thermostat in almost boiling water with a thermometer and you can compare valve lift per temp.
It should be open widest around 200 degrees with a 180 rated thermostat.
Subtract 20 degrees for a 160 rating.
Add 20 degrees for a 195 rating.

 

So...in one minute, you either have

0.5 gallons x 55 degree drop = 27.5 "gallon degrees" drop

or

8 gallons x 6 degrees drop = 42 "gallon degrees" drop.

which is gonna take more heat out of the engine?

 

I'd like to add something to that theory, or at least what actually happens at 180.

I just put a 32 on the road. All old parts, and a early big Olds motor. Stock original 32 unpressurized radiator.

I overheated on first time road test. Never had a Stat, so I added one. Still same boil-over. Found out from a hamber on my build thread, on how to "time" the flow of a early Ford radiator by pulling lower hose. Ok, it was plugged up a bit; fixed that and then ran it with cap off.

As soon as the stat opened, (a brand new top brand 180) there was a large column of water pushed right out like a boil-over.......but it was still Ok on gauge and thermometer in filler neck!

It did this several times while refill/watching gauge, still "saw" the needle movement to "see" each Stat "cycle".

Ok.. Pulled Stat back out and problem is gone. When it first opens, the water pump pressure is trapped under the Stat, then it over-runs the very small top tank on the 32 tank. If cap was on, I bet it would be OK.

But my car runs cool, with or without....it's just the warm up that takes longer without a Stat.
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The length of the warm up (or whether or not it ever warms up) will affect the life of the engine....but only if you plan to put a bunch of miles on it. If you are a typical modern hot rod owner, you can run the engine cold and it will far outlive you.

It's only the guys who put a lot of miles on their car, that really need a thermostat.