Overheating Question = Answer?

RXTbone · Apr 21, 2008

I stopped in to pick up a set of electric fan ties today - and got into a conversation with a track guy about Mustangs and overheating. He stated the following - something I've never heard before about overheating:

He said the problem is due to the lower pulley on the 302's were too large (thus operating the water pump too quickly) - the cooling system is so efficient in moving water through the radiator that it actually doesn't have time to cool.

My thoughts are that the system is under constant pressure - and if it's moving fast through the radiator, then it's moving fast through the engine. The only thing you can change is surface volume on the radiator, and air volume over it.

Anyone heard of this track guys "theory"?

STSFCTN67 · Apr 21, 2008

I have heard of that happening when boneheads take out the thermostats. But you can't make a generalization that all 302's have to large of lower pulleys. Overheating issuse can be so numerous and specific to each application.

biggyfan1 · Apr 21, 2008

the water only moves when the stat opens. it might move through the little pin hole that some stats come with but thats not going to make it move to fast. thats what i think

66Runt · Apr 24, 2008

He may or may not be correct, in your specific application. But the theory is definitely correct.
It takes time to get heat out of the coolant. If it passes through the core too quickly, it can't transfer enough heat. An easy way to tell is to compare the tank temperature top versus bottom. Too much flow, and there won't be a large differential. Correct flow for the circumstance, and you can see upwards of 40*F difference in temperature between the two tanks.

D.Hearne · Apr 25, 2008

If anything at all, the radiators in the 65-70 Stangs were much too small. And the fans were inefficient. He's wrong.

rbohm · Apr 25, 2008

while there is some truth to using a smaller pulley to slow coolant flow through the radiator, but radiator efficiency is also a major factor, as is fan efficiency.

Sicarius428 · Apr 25, 2008

Typically if you are stopped and your car is overheating, your fan is the culprit and cannot pull enough air to cool the motor. If you are at speed and your car is overheating, your radiator cannot reject enough heat to keep your motor cool. Granted there is a balance in there but the thermostat should regulate the water flow. There are some water pumps that just don't flow enough at lower rpms(my Milidon didn't on my 5.0) and at a stop the temp would slowly rise. Underdrive pullies don't help either.
Kevin

blown65 · Apr 25, 2008

Thats gotta be pretty tuff to do with a stock thermostat. I highly doubt turning your waterpump a tad faster on a mustang is going to effect much as to cooling as long as the stat is there.

I would say the #1 reason they over heat is the lack of a fan shroud. How many Mustangs do ya see with shrouds on them.

ForceFed70 · Apr 25, 2008

Your gut fealing is correct (sorry 66Runt).

The speed in which the coolant moves through the cooling system has very little effect on cooling system efficiency.

Often you hear people say "The coolant doesn't have time to cool down in the radiator". By that same logic "The coolant doesn't have time to get hot in the engine".

Cooling system efficiency is a direct result of 4 factors:
- temperature difference between ambient temp and coolant temp
- surface area of radiator
- efficiency of radiator (fin design, material, etc)
- amount of airflow through the radiator.

Clearly you can see that the circulation speed will not effect any of these factors.

66Runt · Apr 25, 2008

Actually you're incorrect 70 bottle fed.
The temperature differential between the cylinder bores, heads and coolant passages is far greater than the air-tube-water correlation. Heat saturation is dependant on pressure, and absorbtion slows as it reaches that peak.
I've spent a lot of time with this issue working for a manufacturer. There is a lot of engineering calculations to get the proper flow rates.
The key is to get enough flow to create turbulence, without creating so much turbulence that you restrict flow.

henry_v · Apr 25, 2008

Engine Cooling Tech

I believe the idea is to move the water at a high enough pressure at a great enough velocity through an efficient enough heat exchanger and expose it to a great enough (and cool enough) air flow. The use of a surge tank and/or swirl pot may be of advantage.

Check out tech from the Corner-Carvers Forum:
http://corner-carvers.com/forums/showthread.php?t=34424&highlight=thermodynamics

Good luck,
Henry V

mustangdave · Apr 26, 2008

Didn't read any reponses, but BS on that comment. It is theorectically possible but not common to these engines: in fact, I have never had an overheating problem with any 302/351W enigine, no matter what cam/head combo as long as I used a stock rad. and shroud combo.

CraigMBA · Apr 26, 2008

henry_v said:
I believe the idea is to move the water at a high enough pressure at a great enough velocity through an efficient enough heat exchanger and expose it to a great enough (and cool enough) air flow. The use of a surge tank and/or swirl pot may be of advantage.

Check out tech from the Corner-Carvers Forum:
http://corner-carvers.com/forums/showthread.php?t=34424&highlight=thermodynamics

Good luck,
Henry V

Be careful Henry. This is a 'Stang forum and can be tech adverse.

Y'all ought to check out Henry's car.

henry_v · Apr 27, 2008

All Cooling Myths Dispelled

RXTbone,

Here is your answer, rather tech heavy:
http://www.corner-carvers.com/forums/showpost.php?p=343405&postcount=36

Henry V
http://www.cardomain.com/ride/703052

c24sc · Apr 28, 2008

my 68 302 in my 66 was overheating. Tested water pump, flushed block, new lower hose, installed new electric fan, new lower thermostat and replaced read cap. Still didn't fix the problem. The rad looked didnt leak and looked good, but I replaced it and that fixed the problem. I must have had a lot of corrossion inside that was too tough to clean when flushing. Just used a new thicker stock brass replacement. cool as a clam now.

nate

carefact0rzero · Apr 28, 2008

i fought mine for at least two years... it'd run fine for a month then start overheating again. it'd go away and come back. i changed everything, water pump, radiatior (stock style), thermostat, the housing, heater core, hoses... everything. then i just got pissed and got what must be an 9 foot thick fluidyne aluminum radiator. works like a freakin' charm. only problem i have now is it runs too damn cool, no heat in the winter! gotta figure that one out now

Hack · Apr 29, 2008

ForceFed70 said:
Your gut fealing is correct (sorry 66Runt).

The speed in which the coolant moves through the cooling system has very little effect on cooling system efficiency.

Often you hear people say "The coolant doesn't have time to cool down in the radiator". By that same logic "The coolant doesn't have time to get hot in the engine".

Cooling system efficiency is a direct result of 4 factors:
- temperature difference between ambient temp and coolant temp
- surface area of radiator
- efficiency of radiator (fin design, material, etc)
- amount of airflow through the radiator.

Clearly you can see that the circulation speed will not effect any of these factors.

Yes, that is well said.

It is not true that water can move too fast through the cooling system and thus not cool the engine.

01ragtop · Apr 29, 2008

henry_v said:
RXTbone,

Here is your answer, rather tech heavy:
http://www.corner-carvers.com/forums/showpost.php?p=343405&postcount=36

Henry V
http://www.cardomain.com/ride/703052

+1 on the tech, and

Awesome car Henry!!!!

Overheating Question = Answer?

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That's why they call it "dope"

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