Cant keep it cool

[bohntr28]

No at Idle the temp will keep climbing until i shut it down no matter what degree t-stat i use. I could not find an auto parts store that carried a high flow t-stat so i pulled mine altogether and it idled a little cooler (maybe 205*). I am going to check another store out today and see if they have any t-stats otherwise I will order a Robertshaw 180*. I think it may just be restricted water flow with a standard t-stat. Thanks again guys.

 

[Broncobowsher]

Recent find on another truck. fan was on backwards. There is a small curve to the blade. The leading edge should be flatter (parallel to the rad) and the trailing edge pointing more toward the back. Basicly scooping the air and pushing it back.

Found someone who couldn't stay cool at low speeds and the fan was mounted backwards. The rotation was correct bot he leading edge of the fan pointed at the radiator and the trailing edge was flat. The fan was hitting the air and holding it in instead of scooping the air and pushing it out. It was going to take another fan spacer to flip the fan over and make it fit.

 

[flousberg]

If you are having a problem at idle then you have an air flow issue with your fan.

 

[bohntr28]

"Recent find on another truck. fan was on backwards. There is a small curve to the blade. The leading edge should be flatter (parallel to the rad) and the trailing edge pointing more toward the back. Basicly scooping the air and pushing it back.

Found someone who couldn't stay cool at low speeds and the fan was mounted backwards. The rotation was correct bot he leading edge of the fan pointed at the radiator and the trailing edge was flat. The fan was hitting the air and holding it in instead of scooping the air and pushing it out. It was going to take another fan spacer to flip the fan over and make it fit."

Yeah Tim i'm embarrassed to say that the other truck was me. I Flipped the fan around and am still having trouble even though I'm getting aout twice the air flow.

 

[bronko69er]

I agree that a 19 lb cap will increase the boiling point, but I do not agree that it will help keep the engine cool. The specific heat of water at 212°F and 14.7 psi absolute, 0 psi guage is 4.2164 kJ/kg K. At 50 bar or 725 psi absolute, the specific heat is 4.205 kJ/kg K. The point of this is the specific heat capacity of an incompressible fluid, water, is bascially constanct at small pressure changes, even a very small change are very high pressure changes. With that being said, the heat removed from the engine is going to be conductive through the block, a film thickness on the walls of the water jackets, and the convection to the coolant. The conduction through the block will only change with the thickness of the material between the cylinders and the water jackets and the temperature generated in the combustion process, this is where timing and fuel mixture comes in. The film thick ness or fouling of the water jacket will reduce the amount of heat transferred to the coolant. This is due to rust, gunk, etc. The last thing is the temp and the mass flow of the coolant. If the radiator is not removing enough heat, the water temp going into the engine will be higher and the heat transfer from the engine to the coolant will be lower due to Q=mCp(Tfinal-Tinitial). The same things apply for the radiator, only the heat is going from the coolant to the copper/aluminum to the ambient air.

With that being said I have some other thoughts on high volume water pumps also. If you run a standard thermostat, but install a high volume pump, I do nto think you will see a significant change in engine cooling because the thermostat is the restrictive device in the system. Now, if you install a high flow thermostat and high flow water pump, your mass flow should increase and your effective heat transfer will increase. But at the same time, it is very important to use a thermostat. If you do not have a restriction in the system, it is possible the water will not contact all surfaces of the water jackets which will definately reduce the heat transfer.

In my opinion, the way to look at cooling is to maximize the flow rate of coolant through the engine to gain the highest amount of heat transfer. Then maximize the temperature drop in the water, pull as much heat as possible out of the coolant with the radiator. This means use a high flow water pump and thermostat and insure airflow through the radiator is fresh, not from the engine compartment, and maximized. If you still have a cooling issue after this, then you are creating too much heat for the heat exchanger area you have in your radiator and need either the largest, most efficient radiator you can fit in your bronco or need to reduce the heat generated by the engine.

I do not know what is in water wetter or other additives, but they are basically increasing the specific heat capacity of the fluid to increase heat transfer.

Ahh finally someone who speaks thermodynamics and heat transfer....
My feeling is that the main cause for loss in overall heat transfering ability of the system is boiling fluid. Even if the overall temp is acceptable, there can be boiling occuring on the walls of the cooling passages.

This is why some people experience a lower operating temp with a higher t-stat. the more flow restriction, the higher the fluid pressure, the higher the boiling point.I also don't quite buy into the whole faster flow velocity eqauls poorer heat transfer. I hear that a lot "if the water doesn't stay in the radiator long enough if can't cool off."

On the other hand it wont be picking up as much heat in the engine on it way through, but it will be retuning faster. Faster fluid flow acually promotes more turbulence/smaller boundary layer/ better mixing (says sir Reynolds). This is why tripple pass radiators work well , the fluid stays in the radiator the same time (Mdot in = Mdot out) but it has to travel 3x the distance so velocity tripples.There is abavoiusly a minimum flow rate to keep the system cool but I'm not convinced that incresing the flow rate decreases the heat flux.

Anyway, it's nice to bounce thesse theories off someone who understands....

 

[Broncobowsher]

"Recent find on another truck. fan was on backwards. There is a small curve to the blade. The leading edge should be flatter (parallel to the rad) and the trailing edge pointing more toward the back. Basicly scooping the air and pushing it back.

Found someone who couldn't stay cool at low speeds and the fan was mounted backwards. The rotation was correct bot he leading edge of the fan pointed at the radiator and the trailing edge was flat. The fan was hitting the air and holding it in instead of scooping the air and pushing it out. It was going to take another fan spacer to flip the fan over and make it fit."

Yeah Tim i'm embarrassed to say that the other truck was me. I Flipped the fan around and am still having trouble even though I'm getting aout twice the air flow.

good to hear that the fan flipped worked for more airflow. I was willing to leave you out of this, but since you spoke up...
Did you ever find another set of pulleys to spin the waterpump a touch faster?

 

[flousberg]

Ahh finally someone who speaks thermodynamics and heat transfer....
My feeling is that the main cause for loss in overall heat transfering ability of the system is boiling fluid. Even if the overall temp is acceptable, there can be boiling occuring on the walls of the cooling passages.

This is why some people experience a lower operating temp with a higher t-stat. the more flow restriction, the higher the fluid pressure, the higher the boiling point.I also don't quite buy into the whole faster flow velocity eqauls poorer heat transfer. I hear that a lot "if the water doesn't stay in the radiator long enough if can't cool off."

On the other hand it wont be picking up as much heat in the engine on it way through, but it will be retuning faster. Faster fluid flow acually promotes more turbulence/smaller boundary layer/ better mixing (says sir Reynolds). This is why tripple pass radiators work well , the fluid stays in the radiator the same time (Mdot in = Mdot out) but it has to travel 3x the distance so velocity tripples.There is abavoiusly a minimum flow rate to keep the system cool but I'm not convinced that incresing the flow rate decreases the heat flux.

Anyway, it's nice to bounce thesse theories off someone who understands....

I agree about the boiling point and boundary layer. I think it is safe to say that the coolant is going to be in turbulent flow. The only variables in heat transfer are mass flow, heat capacity, and temperature difference. With that said, if there is not significant backpressure from the thermostat, it is quite possible that the higher points in the water jackets are boiling. Once this occurs, the specific heat of saturated steam is minimal compared to water/coolant so the temperature will rise dramatically, but the heat absorbed will be minimal. If you can't change the temperature differential at the radiator where heat is being given off to the atmosphere, the you must increase the mass flow of either the coolant or the air. If these are fixed, the only way to dissapate the heat is with a larger heat exchanger area.

 

[bohntr28]

good to hear that the fan flipped worked for more airflow. I was willing to leave you out of this, but since you spoke up...
Did you ever find another set of pulleys to spin the waterpump a touch faster?

Yeah, I did. Yhe crank pulley is about 7" and the water pump pulley is about 5". In my defense the directions that came with the fan were contradicting. According to them, both sides of the fan should have been facing the engine. Oh well, live and learn.

 

[bronko69er]

I agree about the boiling point and boundary layer. I think it is safe to say that the coolant is going to be in turbulent flow. The only variables in heat transfer are mass flow, heat capacity, and temperature difference. With that said, if there is not significant backpressure from the thermostat, it is quite possible that the higher points in the water jackets are boiling. Once this occurs, the specific heat of saturated steam is minimal compared to water/coolant so the temperature will rise dramatically, but the heat absorbed will be minimal. If you can't change the temperature differential at the radiator where heat is being given off to the atmosphere, the you must increase the mass flow of either the coolant or the air. If these are fixed, the only way to dissapate the heat is with a larger heat exchanger area.

I understand how increasing the mass flow of the air would help since that half (heat sink of the atmosphere) of the equation is not a closed system, no matter the mass flow, T1 will always be the same. I'm still trying to understand how increasing the mass flow of the closed system (coolant) would increase the system'ss ability to dissipate heat. It would seem to me that incresing the coolant's mass flow would decrease delta T between the engine and the radiator. If this is the case, smaller delta T means slower rate of heat transfer..... I better stop b4 I logic myself down the wrong past. I think I might be missing something. I'll have to ponder some more.

 

[chuck]

I think coolent moving too fast is bad but how fast is too fast? I think the stock pumps allow too much water to pass around the impellors so enough coolent does not flow through the engine. The hi flow pumps move more coolent per RPM. Turn them a little faster and they move more coolent while the stock pumps may not. Also the flow limiter is the t-stat.
so because the hi flow pump will build more pressure than the stock pump it will move more water.

 

[Mark]

Last year there was a thread about cooling and we came up with over 20 things to check that could cause overheating. You might do a search and have a look. I don't remember who started the thread, I added to it.

This one?

http://www.classicbroncos.com/forums/showthread.php?p=586651