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I've been experiencing overheating during the races and have been making changes to improve cooling effectiveness.  After doing NORC-2021 at 135 I installed a large  aftermarket aluminum radiator, 165 thermostat and oil cooler, but the car (Pontiac Trans AM) is still running hot. This past May I ran NORC at 145 and going north it was running even hotter.

For Sept, I've switched over to using Water Wetter, have funneled more air to radiator and installed a hood louvre.

I'm also looking at my electric cooling fans.  They come on based on temp so they come on at approximately 200 and will stay on.

Do the fans being on at these speeds help or do they obstruct air flow?

Do folks know if their fans are on or off at the higher speeds?

Thank you for any feedback,


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My '02 Camaro is a "bottom feeder" for air into and through the radiator ...

The faster I went (150 class) the more air the front of the car aerodynamically "packed" and the hotter it would run.

I did some creative routing of air through the fog light holes (I don't have lights) in to the bottom radiator feed, also a 160 thermostat, water wetter, and Mobil 0W40 oil. It got warm on the North run, but manageable.

Following this closely.  My Dodge Challenger RT is running warmer than before the new cam and exhaust manifolds were installed. Not horrible, but hotter than before.  In the May race, I hit 230 at the end of the second leg of the race. Prior to the upgrade, end of race temp was 210. BTW, I run in the 120 mph class. I am trying water wetter in the September race and plan on swapping the stock plastic radiator for a two core aluminum unit with better fans.  I want to run in the 135 class,  but will not do it until I think the temp issue is under control.

Our fans do not seem to slow air through the radiator at speeds. we could never get enough air through the radiator from under the car and ended up putting a grill in front of the radiator. Not an option for all, I understand. Make sure you are not running lean. Lean always built a lot of heat for us. In the beginning our car would hit 250 degrees every time we ran it even at 130 mph. Now we run 180 mph with temps between 180 and 210 depending on air temp. Now we are hoping that continues at higher speeds. Rocket

Last edited by Rocket

Andy, Dave, All,

I have to preface my comments and suggestions that my Pantera is not a race car. I drive it on the street.

At 150-165 Mph and the engine red lined at 6500 R's or 180 Mph at SSCC and other ORR's operating temps are 180F Water and 200F temp oil. They do not go higher. Back in the day my best record was a 168 MPH Average but as I get older I realize I am not immortal and have slowed down to 140-150 averages. Will probably drop down even slower this year because yea I am gulp old like most of you guys.

What I learned about cooling design on mid-engine automobiles like the Pantera, etc would fill a small book of "lessons-learned".  My mentors 25 years ago were the infamous Junior Wilson and the equally infamous Mike Cook of Bonneville fame and they both shared what works and what doesn't at least for Pantera's and Ford powered race cars.

On cooling changes we added a Griffith brass 4-pass heavy duty radiator with large tubes. Yes, you can do the same thing with aluminum but do not be fooled by all the claims about how much more efficient alum rads are. Yea they are lighter but make sure when you spec your brass or aluminum radiator that you talk to other street/ORR racers who own similar cars and have similar lessons find out exactly what you need because most salesman won't know but will claim they do.  I say that because we added a Fluidyne Alum radiator about 10 years ago and operating temps ran higher....I went back to the Griffith brass. But that is me. I was told by a fluidyne salesman that the alum rad used a 3-pass radiator and I would not need a 4-pass. He was wrong.

Secondly, we went with the usual all roller engine, nothing special HV water pump, re-routed the water lines, and other then when I am in "heavy" traffic downtown creeping along at 5 mph the fan never comes on until I reach 220F on water temp.  We also added a taller ring gear and a taller 5th so we changed from a 4.22 to a 3.77 and a taller .655 5th. I only did this 25 years ago because I knew I wanted to run ALL the ORR's so the Daytona gearing made allot of sense. And my engine builders promise was he would warrant his engine a full year assuming I made the usual cooling modifications.

I will be in Ely this weekend for SS if you want to look at or discuss what we have done I'd be glad to help. We normally stay at the Hotel Nevada's overflow lot so come on by.  Most Pantera's are still running a stock 4.22 ring gear and stock radiators. They all work just fine with goal speeds under 140 in a Pantera even if the owners know going slower is allot less risk.

So unless you are planning to run some high endurance speeds. Yea, like SS you do not need to do much. If you already have a heavy-duty radiator like most all the Corvettes and Porsche's etc have disregard all this advise or buy one.

And BTW my Pantera is 4-SALE because after 25 years of racing I need something docile that even an old man can drive.  So if you want a totally sorted out and fast mine.

It's for sale!

Qualifer: Notice I did not get into air flow dynamics and engineering but my first bad advise was "forget about racing the Pantera. Your never going to flow enough air to cool the beast. I think that was my drag racing brother. hahaha


Last edited by Dennis Antenucci

Regarding the original question, running fans while the vehicle is at speed will absolutely create additional turbulence that will reduce cooling effectiveness and increase the drag of your vehicle.  You want orderly flow through any cooling core and a running fan will induce excessive turbulence.  It would be detrimental to cooling and vehicle drag.  Also, the internal drag  created by air for cooling is substantial.  Whenever possible, the internal path of cooling air should be ducted.

Moreso than adding a surfectant like Watter Wetter, increasing the ratio of water to coolant will improve cooling effectiveness even more.  I would do both.

Randall Bramstedt

2013 Mini Cooper S

Randall, Thanks for the feedback on the fans & water wetter.  I went with 1 bottle of Water Wetter, 1 gallon antifreeze and then topped off with water to get ~30/70.

To see if my mods were effective, my race profile had me getting up into the 160s at mile 4 thru 10.
I maxed out at 239 coolant & 169 engine oil
When I slowed down to high 140s the temps dropped to 232 & 168

The cooling improvements had modest, but noticeable positive impact.
The needle on gauge was always close to top line, and just barely over.
In May, needle was almost out of range and service light was on.

Decision now was whether to stay with the Race Profile that had me trying for checkpoint challenge or back off and only go for Finish.
The temps seemed reasonable enough, but I decided to ditch the checkpoint  profile, because the car did not seem responsive enough.

Plan B was to average ~152 up to the narrows and then be in the low 150s post narrows which worked out well.

Temps popped up Coolant-240.8 and Oil-172 and 300.2-rear diff when I had throttle at 80-90%, I assume going uphill at ~23 minutes into race

After that, temps went down to 217 and then ranged for Coolant: 217 to 237, Oil: 168 to 173, rear diff: 280s-300 and maxed out at 304 at end/finish where I had 100% throttle again briefly.

Intake air ranged from 70-77 and didn’t seem to have a relationship to speed.
I measured the air flow with an air speed indicator and an absolute pressure sensor and the data didn’t point to any noticeable back pressure.

I monitored the Coolant fan activity by measuring voltage at positive side of fan 2.
If the voltage is half of battery voltage, then the fans are in low speed mode.
If the voltage is full battery voltage, then the fans are in high speed mode.

The fans started out in low speed and when I reached 120 MPH and coolant temp of 205, they kicked in to high speed and stayed that way until ~2 minutes past the finish when the coolant temp was 199.
They went off ~3 and a half minutes after finish when coolant temp was 195

I've attached the HPTuner Coolant Fan params.
The shop that does most of the work on my car had made some tuning adjustments based on some mods and they provided me with a snapshot of the Coolant Fan params.

Dave, the tuning mods look similar to yours so I don't know why the fans are still on.

There was a head wind and I heard others also complained of some performance issues.

I am also wondering if I might have limited air to engine by my trying to force more air to radiator.
I might change some of the ducting to see if more air will flow up to air intake.
I will also try to block off any air from escaping the air intake & radiator area.

End result was car ran cooler and I made it to finish OK so I was happy.



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  • HPTuner Fan Params

Nice work Andy.   The coolant mixture you mentioned is 30% anti-freeze.  You can safely go down to 10-15% anti-freeze.  You only need a small amount for water pump lubrication and corrosion protection.   This will further improve the specific heat of the mixture in your cooling system.  Just don't park it for extended periods in below freezing conditions.

You have a very methodical approach and good data points.  However, with your fans still engaging at speed, you most certainly are losing cooling capacity when you need it most.   The only exception to that would be if your cooling intakes are obstructed or extremely inefficient to the point that the fans provide improved air flow through the radiator core.  By the way, make sure all of your fans are shrouded.

There are books on the internal aerodynamics of cooling systems that discuss efficiency.   I have a reference if you wish.

Though I am not an expert on your particular system,  I would try increasing your "fan enable" temps for both fans to at least 220 degrees F  to more closely match the temperature setting when the ignition is OFF.   This would allow the normal air flow through the radiator to do its job without interference from the fans.

The other thing is that the "fan enable" speed should be set lower.  Fans are intended to be used at low vehicle speeds and the current setting of 30 mph seems too high.

In general, fans are not intended to run at high vehicle speed or to provide solutions for other systemic high speed cooling problems.   You may be dealing with an issue of overall insufficient flow to the radiator core.   You should not need any fans at speed whatsoever.  Check the condition of your radiator core as well.

I saw your Trans Am at Nardi's and commented to my friend how much I like it.   In times back, I owned an IROC Z Camaro and loved it.   There some thoughts I have on your power situation, but I will save that for future discussion.

Randy Bramstedt

2013 Mini Cooper S

I think fan on/off at speed, coolant blend and to some extent the path/ducting of air exiting the radiator is secondary. In line with Rocket's comment, I'd take a look at the engine tune first before fine tuning the secondary items. Can you share your RPMs, AFR and spark advance for the steady state at 140, 150 and during the 80-90% throttle pull? Either actual numbers or just the targets in your tune might give some ideas as to whether a richer AFR or adjusted timing would be beneficial. Trying to cruise at 80% throttle and 13.0:1 AFR (gas) will make more heat than 12.5:1 or 12.0:1 for sure and I wouldn't be surprised to see a tune that is 13.0:1 or higher at loads less than WOT. Many ECUs support 'High Power Time Enrichment' that can lower the target AFR when you are above a certain throttle/MAP/load level for an amount of time. I think I remember Cadillac Northstars dropping to 11.8:1 under high power time enrichment.

I'm using a pretty mild HPTE, ramping the AFR target down .2 for loads above 90% and rpm above 3500 ( load = manifold pressure / barometric pressure in my case). But, I have a target AFR down at 12.7 starting as low as 55% load.


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  • mceclip0

Yes, Fans are shrouded - Factory setup

I've been working thru various (relatively clean) options on how I might disable the fans, either thru the engine's PCM or via my race tablet.

My 1st approach was removing the fan relays and just running without, or to use my own relays to control the fans, but the PCM threw a Coolant Fan service engine fault when I removed the relays, and since I didn't know if the PCM would then go into some reduced performance mode, I backed out of that option.

I'm currently looking at getting the proper connectors to insert a relay after the car's relays and before the fans.

I'm not adverse to seeing if there's a brass radiator that fits my car per Dennis's recommendation, but I did drop some $s on a new DeWitts radiator last year.

I tried ducting, but the duct needed to be below my splitter in order to get same/bigger amount of air into the radiator & intake. Even with driving really, really carefully, I was scraping the front of the duct and then there was the potential to do damage to splitter so I backed out of that.

The closest thing that jumps out at me for AFR is "Oxygen sensor voltage, Short term fuel trim", but that really can't be reliably converted to AFR. If anyone knows if the LS1 provides a readable AFR value, or point me to a sensor that I can install and then read via my race tablet, then that would be appreciated.

At 161, throttle ~84, advance was 24, ~4920 RPM
AT 159, throttle ~81, advance was 24-24.5, ~4850 RPM
At 147, throttle 55-60, advance was 25-26.5, ~4500 RPM
No steady state below 147

I'll be bringing up the tuning relative to AFR and load/throttle to the shop that does most of the work on my car.


Heh Andy,

FWIW, before you try a brass radiator keep in mind my 4-pass brass radiator was never the end all solution to cooling on the midship Pantera I call “lessons-learned”.  The  incremental changes to improved cooling, including adding a Fluidyne heat exchanger, larger water lines. a larger capacity oil system, reducing engine compression, and gearing etc.

I am certain  you will find exactly what you need for your ride that balances out your street/race goals. Keep us in the loop on the final results.

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