Just Snooping Around Under the Hood
- Thread starter 32witha409
- Start date
No fan clutch but I want to add a clutch and correct fan to reduce losses and belt squeal while pushing it.
I was thinking because its only at ~70 mph or higher that it might be insufficient airflow or not enough timing,what is your rpm's at 70 and if less than 3000 what is the advance at that rpm?It seems to me that because its fine at slower speeds even under heavy load that radiator capacity and water flow are good unless you have something weird going on with the water pump like cavitation or something that causes flow to drop off at higher rpm's.I would really be looking at airflow,if the fixed fan has been swapped for one from a low capacity application or if its a low blade count flex fan and you have close clearances in your shroud it could actually be restricting airflow thru the radiator.If you have a flex fan throw it in the trash,and if you have a fixed fan and don't want to convert to clutch,make sure it has a minimum of 5 blades preferably 6 or 7,while it will be noisier that means your moving more air.Unfortunately that also means your using more power to turn that fan.Best choice would be a clutch fan with 6,7 or 8 blades,but that maybe a challenge finding one that will work with your shroud and may not look original if that matters to you.Fixed fans from a small low power engine will sometimes have a low pitch fan to keep parasitic loss down so make sure one of those hasn't found its way on your car.
Have you had your radiator cleaned out, heating up at higher speeds can also indicate not enough radiator (or partly blocked).
Might check pulley diameter. If pump turning to to fast the waters not in radiator long enough to cool properly.
If you have belt squeal the fan/water pump are not turning the rpm they should. Double pulleys and an idler would help that.
Thanks for the advice. Radiator is absolutely pristine. The fan is oem 18-1/4 dia 6 or 7 blade high pitch (looked at it last weekend measured but forgot what I counted) and direct drive with GM shroud. Pulley drive ratio is 1-1 or very close to that.
@ Scott In any system heat transfer capacity is dictated by Delta T, surface area and in this case air volume. The hotter the radiator the more heat is dissipated to the air, thus more BTU transferred from the system. water velocity other than keeping the radiator hot to maximize Delta T is not one of the variables.
@ Scott In any system heat transfer capacity is dictated by Delta T, surface area and in this case air volume. The hotter the radiator the more heat is dissipated to the air, thus more BTU transferred from the system. water velocity other than keeping the radiator hot to maximize Delta T is not one of the variables.
This thought did cross my mind. I was going to go there next after the thermostat.
What was OEM on these cars with the 348? Did they have double belts to drive the fan?
Over all of the 348's I have seen, single groove WP pulleys are common. Some AC cars have a double arrangement.
I have mine as tight as I feel is necessary. I think it would make a good guitar. I'm planning to review belt size and groove engagement this weekend.
A 6 blade fixed sounds like it would be adequate.Scott is right though,while you are also right in that the variables of heat transfer are delta T,surface area,heat transfer coefficient of exchanger material,and flow of both mediums, in liquid to air heat exchangers dwell time inside the exchanger is also a factor.
Phil he said the water could be going to fast to transfer enough heat to keep temps down.
The general function of a heat exchanger is to transfer heat from one fluid to another.
Again, the laws/formulas that dictate the thermal capacity of a heat exchanger are known and available in your basic thermodynamics classroom book. In non of them does dwell time reverse the formulas outcome. Further more in no case will increasing the flow of heated fluid (decreasing its dwell time) reduce the total thermal transfer of heat energy. The system will eventually bottom out and not improve, but it will not start going the other way. You will only thermally saturate the cooling fluid to the point that it can no longer absorb anymore heat.
Example below:
You have two radiators with all variables the same with the exception of the volume/velocity of heated fluid flowing through the core, one is 50% the other is 100% of the systems capacity. In the 50% low example, the mean coolant temperature across the core is 150* the other 100% example is
example the mean coolant temperature is 195*. Which example will transfer more heat energy out of the system? The 100% flow example because the mean Delta T is greater between the two fluids is greater.
Sorry to preach but these are basic system fundamentals, and I'm fine if we agree to disagree, this won't change my initial question. Off to work and then out to the garage.
Again, the laws/formulas that dictate the thermal capacity of a heat exchanger are known and available in your basic thermodynamics classroom book. In non of them does dwell time reverse the formulas outcome. Further more in no case will increasing the flow of heated fluid (decreasing its dwell time) reduce the total thermal transfer of heat energy. The system will eventually bottom out and not improve, but it will not start going the other way. You will only thermally saturate the cooling fluid to the point that it can no longer absorb anymore heat.
Example below:
You have two radiators with all variables the same with the exception of the volume/velocity of heated fluid flowing through the core, one is 50% the other is 100% of the systems capacity. In the 50% low example, the mean coolant temperature across the core is 150* the other 100% example is
example the mean coolant temperature is 195*. Which example will transfer more heat energy out of the system? The 100% flow example because the mean Delta T is greater between the two fluids is greater.
Sorry to preach but these are basic system fundamentals, and I'm fine if we agree to disagree, this won't change my initial question. Off to work and then out to the garage.
32 you are correct that a heat exchangers function is to transfer heat between fluids which includes both liquids and gas/vapor,these different forms of fluids can have very different heat absorbtion rates.You are correct in stating that 2 liquids passing thru a heat exchanger with similar physical properties will maintain a rate of heat transfer based on delta T and flow up to rated capacity assuming no degradation of surfaces.When dealing with 2 fluids of very different physical properties the rate of heat transfer is not so straightforward.Even with the example of 2 similar fluids if you increase the flow of the 2 liquids to the point of exceeding the rated capacity of the heat exchanger the exit temp of the hot liquid will increase.
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We'll agree to disagree.