Tom, give me a couple of days to get it boxed.
We may have talked about the fan working, and in my posts I've been questioned on the fan, is wired right, and so on, but never is it working correctly. All I know, it goes in a circle and produces air movment, in this case in the right direction, but never did we discuss that you had some questionable controllers that limited the fans full potential.

Tom I seem to got your fan club up in arms, and I'm still one of them, a fan.
I'm not sure why they think I'm on your case. I guess the choice of words might be one, or there lack of reading all the information that has transpired.

In the simplist terms, my car overheated at highway speed. The fan that you sold was not working correctly. Reason we think, a deffective controller.

If this is it, end of story.

Dennis

 

Jack, I agree with you on experts. But in this case, I feel we are all right. However the buck stops with Tom, his product was the cause do to a defective controller that did not let the fan operate at it's full potential. We will not know for sure until he has a chance to look at.

My experience with Experts is that they operate with in paradigm's and never look past them.
Dennis

 

I see Tom is issuing a recall of the package. I understand that the system will be going back to him. I am building an engine run stand and had planned to use it there, not in a car. Good luck with finding the solution. I'm sure it has to be the controller.

 

Okay, I will concede this point. I was wrong about all OE electric fans not using shrouds... they probably work fine when designed properly (pressure flaps, large fans, etc).

Re the modern fans shutting off at highway speeds, I knew I wasn't imagining that. I found a few web sites to reference:

1. 4th Gen F-body site - http://www.shbox.com/1/4th_gen_tech2.html#cooling

"Also, when the car reaches sustained higher speeds, the fans may be commanded off so incoming air can flow through the radiator unimpeded and provide the cooling needed."

2. http://autos.yahoo.com/maintain/repa...ques021_2.html

"In newer vehicles with computerized engine controls, fan operation is regulated by the engine control module. Input from the coolant sensor, and in many cases the vehicle speed sensor too, is used to determine when the fan needs to be on."

I do not understand the argument that a running fan will provide more air flow when many times more air is coming through the radiator at cruising speeds. If the air flow from the moving car is spinning the fan blades faster than it could with the motor on high, why would you bother to energize the motor?

Sure, if you are only going 20 mph then the air flow might not be high enough, and the electric fan running would keep it cooler. But, at 40, 50 or more mph, no fan will ever move as much air as is coming through the grille.

 

Email me when you have it ready. tom@dewitts.com

 

Just because somebody said it on a website does not make it true. You are convinced that a non-rotating fan presents less restriction to an airstream moving through a radiator, and nothing I can do will convince you it is not so, but here goes:

As for fans turning off at "sustained highway speeds", that is because they are not needed as the cooling of the air velocity flowing through the radiator is sufficient to meet the cooling needs. I know of no cars that have the fans tied to the speed of the car., and I am familiar with many PCM logic ladders, mostly GM.

I would agree with your statement of "why would you bother to energize the fan". There is no reason to energize the fan, as the flow through the radiator is quite sufficient to meet the cooling needs. I am also not saying that having the fans on at high vehicle speed will necessarily make the car run any cooler, but I am saying that it will not make the car run any hotter as was claimed! The claim was made that running the fans at highway speed was somehow more restrictive to the air flow than having a stationary fan. This is absolutely incorrect,and anybody making this statement does not have an understanding of fan laws and dynamics.

There are only two things that govern the ammount of air flow going through an opening of a fixed crossectional area (a radiator), the total pressure across the opening and the size of the opening. A spining fan, regardless of the speed of that fan, will generate more pressure than a non-turning fan. The pressure that this fan is generating will be additive to the velocity pressure coming in the grille, and will always equate to more flow than the velocity presure by itself. Will this additional flow be of any value? Probably not since the velocity of the air from vehicle speed is quite sufficient to meet all the cooling needs. Remember, that once the thermostat start closing off then any adittional cooling generated at the radiator is wasted effort. This is one of the main reasons for electric fans on all modern cars. No sense spinning an engine driven fan around burning horespower, if it is not needed. It does not matter if it is a thermal clutch, or a flex fan, they all burn horsepower when it is not needed.

The other thing that most people do not realize is that the flow across a radiator is not directly proportional to the speed of the vehicle. Frictional losses go up by the square of the velocity and this imposes a self-limiting ammount of air that can pass through a radiator regardless of the speed of the vehicle. The faster the car goes, the less increase in air flow. Obvoiusly, the greatest increase in airflow related to vehicle speed is apparent at fairly low speeds, and the benefit of increasing flow across the radiator is a constantly diminishing return.

A proper trouble shooting process requires an understanding of how systems work and interact with each other, and to not understand the realtionship of such systems will assure a lot of wasted time and money.


Regards, John McGraw

 

I don't think that is very fair. I am not unwilling to learn something new.

I know that anyone can publish whatever they want on the internet. I was hoping to find a more definitive source to confirm the PCM shuts the fan off at speed. I don't think the F-body guy pulled that out of thin air, most of his web site is information from the factory service manual. I will check to see if the fan control parameters are in the FSM.

Here is my thinking: the difference between the powered and unpowered fan sitting in front of the radiator is one thing--an electric field. With the motor off, the fan is free to spin at whatever rpm the air will move it, within the capabilities of the bearings, etc. When the motor is energized, and the wind starts pushing it faster than the motor would normally spin it... well, now it's acting as a generator. And, as I am sure you know, this will take energy to move. I see this as a restriction to air flow.

Perhaps you can tell me this is a negligible drag on the air flow. Maybe the OEMs exploit this just for a fractional increase in economy, I don't have the facts on that.

 

Since I have an dash indicator lamp on my wonderful Derale 16 inch fan, I can tell you that at night I can see the lamp glow faintly at high speeds - and it's always bright when under power.

I had to install the lamp, because I can't hear the fan with the windows and top up or with the radio playing, or at highway speeds. My car no longer runs warmer that 170-180F even with A-C running, but I like to keep tabs on things.

I am looking for an old broken BB shroud to install a flexalite fan into - if any of you have one to sell.

 

Sorry for the tone of my post, it was a tough day in the shop!

First of all, on my Fbody LS1 PCM, the only fan control parameter is the the 2 temperature settings, the fan temp and the fan 2 temp. Of course, I believe that all GM PCM's turn the fan on when in the A/C mode regardless of temperature, and whenever the Check engine light is lit.

As to whether the fan is being spun at a rate greater than it's rated speed, I am not sure that that is happening. I am not sure that the velocity of the air coming through the radiator is sufficient to drive the fan at substantially more than it's rated speed. Even if it did, the restriction would be only at speeds greater than the full rated speed of the fan, and we know that that fan speed is sufficient to cool the engine. That being said, the flow across the radiator would be never less than the rated CFM of the cooling fan, and probably substantially more given the bypass of the fan around it.



Regards, John McGraw

 

Okay, I can certainly understand that. I know that the electric fans spin at a high rpm on their own, so you are probably right that it would not typically be spun beyond that under normal conditions.

I got some info from the service manual of a 1998 5.7L F-car (Camaro/Firebird):

"The cooling fans are turned OFF at certain vehicle speeds. Adequate airflow through the A/C condenser and radiator occurs with vehicle movement to properly cool the A/C refrigerant and engine coolant without the assistance of the cooling fans."

I have the entire page of info, if you anyone wants to see, but that's the only metion of fan control by the VSS. Of course we have already agreed that highway air speeds are enough to cool the radiator. This FSM makes no mention of efficiency or air flow, so yes, you're probably right that those kinds of speeds never affect the air flow through the fan.

That said, what could have caused Dennis' setup to block air enough to overheat? (assuming that, as stated, the fan was rotating the correct direction) If the fan spinning should play no part, maybe this was an issue with the shrouding blocking the air? Or possibly some odd air pressure difference causing the air to bypass the rad?

Dennis, does your car have all of the air dams in place?

 

Without getting too scientific about electric fan operation at speed. What do you think happens when your a/c is turned on at highway speed? Most cars I have worked on have an a/c bypass that turns the electic cooling fan on when the a/c is turned on. If the electric fans were causing an obstruction at highway speeds I think we would be seeing more new cars on the side of the road overheated.

Do you have a picture of the radiator and electric fan installed in your car?

 

That said, what could have caused Dennis' setup to block air enough to overheat? (assuming that, as stated, the fan was rotating the correct direction)


Big mystery, ain't it?

 

If you go by the way the General has the PCM set up, the air flow on the highway will keep the high side pressure below the set point, and the fans will not be turned on.

(are you asking me or Dennis for a picture?)

 

I was asking Dennis for a picture.

The car you are referring to probably does shut off. I was referring to cars that I have worked on not shutting off. Either way a running fan will not create a restriction. Even if it were running too slow by it's own abilities air pressure at the front of the radiator at highway speed would over power the limitations of the fan.

Again, not trying to over simplify. Look at a pinwheel or windmill, the stonger the wind the faster it spins. These two things do not even have a tunnel to pressurize the air going through them to keep them turning. The electric fan already has the advantage.

Really would love to see a picture.

 

There aren't factory air dams on a c2. I made one for my car and I also took care to seal the shroud mounted fan to the cradle/crossmember to prevent air recirculation around the bottom of the rad, and to keep air from coming up into the engine bay.

If the factory shroud was removed to install the electric fan, the opening below the rad that is normally blocked by 9 inches of shroud fiberglass will allow air to recirculate to the front of the car in city traffic. OEMs spend a lot of computer and wind tunnel time making sure that doesn't happen on new cars.

 

The fan may not appear to be blocking airflow, but if the motor or controller failed or was defective out-of-the-box the fan will not help with airflow at high speed.

John is correct in the initial statement, "two things govern the amount of air flow going through an opening of a fixed cross-sectional area (a radiator), the total pressure across the opening and the size of the opening (the radiator face area under the influence of the fan and shroud system)."

The catch is that the radiator is the item that defines the airflow (and heat transfer) derived from the differential pressure.

If a non-operating fan (or under-performing fan) is placed in-series with the radiator it will block airflow, and the resulting lower velocity through the radiator will result in a lower differential pressure across the isolated radiator core section. If the under-performing fan is located on the radiator core inlet, the result is a conversion from velocity pressure to a higher static pressure on the entering face of the radiator (not efficient, but usually not a serious problem). If the under-performing fan is located after the radiator it will raise the radiator's outlet face static pressure (bad for the needed differential pressure that drives airflow through the radiator core).

In this example (OCS1667's car) two issues raise concerns:

The first concern is the fan motor or drive control appears to have a problem. Something has limited the fan's ability to develop a pressure differential across the fan (and the radiator) with the car at speed. In my armchair opinion (IMAO) the problem is a one-in-a-hundred faulty motor or controller (not an application problem).

The photos provided expose the second concern, the lack of a shroud and the resulting reduction in radiator face area under the influence of the fan's effect. The fact this system has worked successfully in the past indicates it is adequate if the fan motor and drive controller were performing properly. Comparing the photos of this fan system to the other systems with dual fans and full face radiator shrouds reflect that there are alternatives that should work better to place the entire leaving face of the radiator under the pressure influence of the system fans.

To add support to John's comment, the radiator face area under the influence of differential pressure (the fan and shroud system effect) determines the radiator's air side heat exchange (holding comparable inlet temperatures constant). The factory shroud encloses the entire radiator, including the tanks incorporated into the heat exchanger with the stacked plate design, to gain the most heat exchange benefit from the fan and shroud system's influence.

If you reduce the heat exchanger face area under the influence of the shroud, use a less efficient radiator tank design or an unshrouded fan, you need to improve the airflow and differential pressure where the fan does have an effect (what Tom's design exploits if the fan motor and controller worked properly).

Locating a fan in the stock engine driven fan location (half out of the shroud) would retain the maximum face area influence benefit of the stock shroud system, and the resulting system could be designed without the power draw of the engine driven belt drive (with an electric fan) or without the clutch complexity (with a flex fan). We can read that one of these solutions works (the flex-fan), and we may soon read the results of an electric fan design (magicv8 ?).

 

Wait a second... I've missed something along the way. To me, it sounds like we're getting into a circular argument here.

We just had a lengthy discussion and now know that a running fan will not block air flow, no more than a freewheeling fan. If his fan is running, even half power or something slower, why would that block the air?

If the fan is not blocking the air flow, then there should have been enough air flowing at highway speeds to cool the radiator (and in theory shut the fan motor off via the thermal sensor). Being that the fan was cooling at idle, it seems safe to say that the motor was not siezed and holding the blades stationary.

My argument was that when a load is placed on the fan (windmill, turbine, etc) like an electric motor (generator), a grinding wheel, or similar, that it takes energy to move this. If a windmill is left operating in high winds, it will impede wind flow and be damaged. Yes, I know not quite the same as an electric fan, as John pointed out the rpms are very high when that happens.

 

There is one other possibility here other than the fan running BACKWARDS. The owner forgot to remove the piece of paper off the front side of his radiator to see if the fan was pulling air and it blocked off the air flow and overheated on the highway.

 

I doubt that was the problem but there is a butch of remaining unknowns. I went through the whole thread again to see if this car had AC and/or pusher fans but no mention of either one. The controllers require inital programing of the "fan on" and "fan off" points and that wasn't mention either. Initially, Spal said the factory temp guage sending unit would work as the sender for these controllers and that didn't work, so later we started sending Spals sender with controller. Factory sender or Spal sender?
The Spal fan we use on the SP020 package is 2360 cfm and honestly it's a screamer...as in pretty loud. If we get any complaints it is usually the fan noise that people don't like but that's what happens when you move a lot of air. The fact that Dennis never mention the noise tells me it never got to full speed or anywhere near it. The controller is also designed to vary motor speed and under a malfunction anything is possible. When the feedback started measuring real high temps it is possible it went nuts and actually started the motor backwards but we'll never know. Rather than test all these parts, the better test would be to pop in a new fan, and the relays, with a 195 switch and take the engine driven fan off. If it works, and it would, then we would know the controller was the problem. This is the only way to convince someone that something works.
BTW, this negative fan thread is working great. I've sold three more package today from people following this and believe what I am saying.

 

I did not take any photos of the installed elect fan/radiator.

The product from Dewitt fit fine, it was a little tricky installing the factory shroud. The fan that Tom supplies fits perfectly inside it, and looked like it was there as an original option.

In a earlier post I spoke of having my hand over the core support and shroud and noticed a large amount of air escaping from the area between them. I placed a seal in this area noticed a greater volume of air passing through the factory shroud to the front of the engine.

The news from Tom that I might have a defective controller will not be known until I return it to him for verification that is bad. As I told Tom it was moving air, how much I don't know, but one more time, the air was flowing the in the right direction.

Hamilton, others, and myself still do not understand why if everything being equal at highway speed what difference if the fan is at speed or not, or even working, shouldn't the air pass through, or is there a phenomenon that took place limiting the air flow. Stick your hand out at 70 mph and the air pressure is so strong you can't hold your hand steady, the air wants to push it all over.

All I want to say you all have been more then helpful. Elect. and or mech. I could care less, In this case the mech fan solved the problem big time.

Dennis