The problem is semantics in isolating where the effect of the non-operational fan motor occurs, and comparing apples to oranges.

At speed in a modern car (the C4 Camaro F-Body - an apple) the under hood pressure or lift extracts airflow through the radiator. The fan does not need to operate to have the radiator achieve a pressure differential and airflow across the radiator core. Drive the C4 F-body at speed and the front end stays low to the ground and stable, and the same suction that keeps the front end stable is also working to extract airflow through the radiator core. The suction under the hood is so efficient that the fan drag is not an issue (the generator effect you observed).

At speed in a C2 Sting Ray (the orange) the aerodynamics build boundary layer under-hood pressure and lift, and pressure resistance that the fan must overcome to motivate a differential pressure and airflow through the radiator. The fan needs to develop a minimum pressure to overcome the lack of space-age aerodynamic pressure control. If the fan system is compromised (weak clutch, weak electric motor or controller, missing shroud & seals, etc.) the system may fail to achieve enough differential pressure across the radiator core. It will fail to reject the waste heat generated by the engine operating under load at a higher than idle rpm. The compromised fan may not be blocking airflow, but it's also not overcoming the aerodynamic pressure generated under the hood (with a similar result... reduced differential pressure and airflow across the radiator core).

In a stock C2 fan and shroud system the aerodynamic under-hood pressure only acts against the face area of the fan located in the shroud. There is no chance of the aerodynamic pressure acting directly against the radiator core (unless the seals are missing).

In the electric fan and shroud system that generated this thread, the aerodynamic under-hood pressure can restrict airflow through the radiator core in the unshrouded area surrounding the electric fan. A little math would be needed to model the effect, but eventually the heat rejection lost due to the compromised differential pressure across the radiator core area not benefiting from the unshrouded fan's influence will become a problem (and it will only occur at speed when the aerodynamic pressure builds).

The point to take to the bank is that a quality fan shroud system is much more critical in older car designs with poor aerodynamics that create lift under the hood. The last thing the cooling system needs is under-hood aerodynamic pressure compromising the pressure differential and airflow across the radiator core.

I just read Tom's most recent post. He is probably right (99% confidence, IMAO) that a replacement fan motor and controller would have resolved the overheating problem. I still want to see a cooling system with an envelope shroud & electric fan that captures as much of the radiator face area as the factory system (the result may not be space efficient, or cheap, but it would reject the heat off the factory radiator).

 

Thank you for the thorough explination, I think I understand the problem much better now.

I do follow the idea that modern cars, with all their air dams and spoilers, create a high pressure area in front of the car, and low pressure behind/under, creating very efficient flow through the grille.

I'm not sure I understand how the C2 doesn't work... are you saying that the non-aerodynamic design allows the high pressure to build in the engine compartment? I can see how that would absolutly require a fan to keep air flowing through the radiator.

 

Ok, now I'm getting closer to the problem. I remember you telling me about this air coming out between the core support and the shroud. Which was weird but what didn't make since was that packing that area made it run cooler. I get it now...
The car has AC and pusher fans in front of the radiator. That was never mentioned above and it's kind of important because the pusher fan will make your paper stick to the radiator as if it is being sucked onto it. Typically you do not want a good seal between the condensor and the radiator because the heat from the condensor needs a place to escape or it will be transfered directly to the radiator.
I now think the Spal fans were running backwards or Spal mislabled the puller as a pusher. The two fans were supplying air directly against each other and a bunch of it was blowing out of the gaps. At lower temperatures, the PWM controller ran the fan slower (albiet the wrong direction) and the pusher supplied most of the air, making it appear to be flowing in the right direction. When the car was driven faster, more heat was generated, the controller told the Spal to run faster, which it did, pushing more air in the wrong way, making it run hotter, telling the Spal to run even faster, making the problem even worse.
I wasn't buying into the fan restriction, block the air flow, etc but a fan blowing 2360 in the wrong direction will definately not work.

 

Tom I removed the condenser fans over a month ago and it made no difference.

As I've said I tried eveything.
Dennis

 

and you tried the paper test again, without the pusher?

 

Tom, yes I did and it stuck to the front of the condensor.

Believe me Tom, I tried everything including a test to make sure I did not have a head gasket problem.

Dennis

 

I must respectfully disagree with this. I may have been wrong about the fan blocking the air flow, but I have done enough a/c work to know that this is not true.

Condenser heat will transfer to the radiator, that's why the cooling system is often upgraded for use with a/c. Yes, I know that for 50 years OEMs did not seal the gap between the condenser and the radiator. But, anyone who has retrofit an R12 system to R134 without updating the condenser knows that all those gaps should be sealed for maximum efficiency. The better OEM systems do have the gap sealed between the condenser and rad, in addition to proper sealing between the heat exchangers and core support.

Another very good reason to seal the gap is so that the engine fan will not pull hot air from the engine compartment back through the radiator.

 

Tom,
You have an e-mail from me about same problems. Glenn

 

I just spoke to a friend and told him I had resolved the heating problem.

No no sense rehashing what we spoke of earlier, so I'm not going there.

He and I spoke of the design of the car and the fact that the front end to include the bumpers probably inhibit the air flow to some extent through the grill, especially if the fan was not working at 100%, it more then likley could not get enough air to cool the radiator.

Know here I think it gets interesting, He has a 67 BB w/air and powerglide with the factory condensers and trans. cooler. He told me that GM must have recognized the air flow problem through the front of the grill. GM moved the license on his car from the center of the grill to below the grill and to one side letting the maxium amount of air pass through.


Dennis

 

Whatever

 

totally true

 

I laughed at this as I have a couple of 'T' shirts with that word emblazoned across the front that I frequently use.

Very appropriate for many situations. ....

 

Ok, you dragged me back in again.

Not true, here is why...

He said the AC added a load onto the radiator and that's right. So you have a choice, add 100% of the AC load to the radiator, or allow some to escape. I'd go the escape route. You will also pick up some new air for the radiator, which will also help.

 

Okay, I can take a hint.

 

I've been reading this thread for last week and I want you to know
........................................ ........................................ ............
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I've also been educated in art of Hot Air removal which might be helpful when the boss comes at me
and
I saved a lot of money with Geico
Thanks go out to Tom and the Gecko

 

Very interesting thread .. Any verdict on the controller, yet?

 

Dennis,

Please post the part numbers for the GM flex fan and spacers you used. I know there are a lot of mid-year owners who would like to have that information. If its already included in this thread I apologize, but I couldn't find it. Thanks

 

I feel fortunate that my original system never overheats.

 

I feel that you never drive with A-C running on 100F plus days

 

My A/C is not hooked up but, I driven my car alot on 100 degree days stuck in traffic and never had a problem.