got some interesting data from my track day yesterday in the 928 Estate.

I installed an extra water temp gauge in the thermostat housing, so essentially it reads the hottest water that just came out of the engine on its way to the radiator.... I saw temps as high as 227F in my thermostat gauge, but the highest the factory gauge ever got was a tick over the 2nd white line......or maybe 195-200F....

So here is my question...is a 30F temp drop through the radiator good? I know my radiator is old.....but it appears to be working pretty well...

 

I do not think that the factory temp gauges in our cars have anything to do other than show trends in how hot they are.

Dead even with the top white line my car is showing 209 on the sharktuner and with a IR temp gun.

 

I found that when pushing my car hard at the track, the temps climbed high too.

Personally I prefer having the engine run a little cooler, and give myself a margin before it overheats.

My car runs perfectly fine in town, and under normal driving. Even in stop and go its fine.
I am planning on replacing the head gaskets soon. As well as I have a rad core I will rod out, and weld on some end tanks. I will then also run an external oil cooler. I know this isnt the best in stop/go traffic. But it will do much better for my normal uses.

I did notice that when I started to tune the car, if I get the AFR into a better range than factory, the car runs much cooler when pushed at the track.
But not enough for my liking.....

Also I believe that the air ducting is not suffice on the S4 for running cool when pushed. Proper ducting and air flow through the Rad will increase its efficiency greatly....

 

IR gun the entry area to the radiator and the exit area. The temp drop depends on the inlet water temp and air temp difference, other things being constant (coolant flow, air flow). So, with higher ambient air temp, the drop will be lower. And the relationship between the two is determined by the radiator/fan setup efficiency. Anyway, even if it was real hot at the track, 30 degrees is OK but not great. The engine cooling system on many 928s seems marginal to inadequate under high load (track, long uphill grades on a hot day). My car is a case in point. I haven't sorted out why. I don't suspect there is much I can do about it. My radiator is not corroded/blocked, water pump and Tstat are good and my fans work as designed. Fans do have big impact on airflow and cooling in my car, even at highway speeds and above where some people suggest airflow speeds should make fans unimportant. If one of my fans is not turning, I see much higher temps at speed.

 

Fans are extremely IMPORTANT......I thought in a race car that is moving at fairly high speed the fans don't do much.... this is NOT true....when we built the car it had two problems

1: I installed the thermostat backwards (duh)
2: Only the small pusher fan, no belt driven fan

At sears point 10 the drivers forgot to turn on the fan....and the car overheated big time....red zone on the gauge + warning lights...oil temps near 300F.....NOT GOOD....

I adjusted the pusher fan right against the radiator and we installed a 14" puller fan rated at 1800 CFM wired to a 175F thermo switch and it seems okay.....but I wonder how much better a real radiator with dual puller fans would help things...

 

I used to run no fans at all and it worked fine as long as you didn't get stuck waiting on the starting grid.
Not having anything restrictive at speed is a good thing. Maybe your pusher fan acted like a big sheet of paper stuck to the radiator.
I'll bet you'll run cooler if you throw away the pusher fan and try taking out the puller fan. Whatever you do you should ditch the pusher.

 

I thought the same thing.....that the pusher really just gets in the way.....so I did a test NOT using the pusher.......it did NOT work....using only the puller the car got super hot......once I turned on the pusher it came back to normal.....

Another factor for the Estate is the location of the massive trans cooler...its right where all the best airflow goes into the raditor....you can see it well in this picture.....

The upside is the trans barely gets up to temp...typically 150F......I did see almost 175F when the water peaked at 227F

 

what is the inside dimensions of the radiator? basically the size of the core without the end tanks?

 

Those are surprising results. Mayber what I see only applies to a lone radiator.

FYI, I once mounted an oil cooler in front of the radiator but at the top. It seemed to just be along for the ride with little effect so I moved it somewhere away from the radiator with it's own duct and then it starting working well. That does indicate that the lower part of the radiator is where the only cooling gets done at speed on a racer.
I've also ducted an airbox to the same top-front of the radiator and was surprised that it saw very little positive pressure at speed, even up to 170mph. A duct a few inches back and at the top of the radiator seemed to have more positive pressure at speed. It's as though the inside of the bumper at the top of the radiator is a stagnent zone.

 

Mike - interesting -- what does that say for the car's ability to breathe at speed? I tossed my drag coefficient flaps over a decade ago because I saw that when they closed, the engine very quickly picked up significant heat at very high cruising speeds. Opening that area up, made a real difference ... but again, that is the bottom of the radiator.

I wonder if the bellypans could help ..... I don't run those anymore but used to have a solid one all the way to the X (aka cats) ... and at about 150, the pan was sucked down onto the road!!!

 

ive done detailed tests on the pusher and puller combination and they do absolutely work. they dont get in the way, due to the fact that the air is moving at them and being electric motor based, will increase speed with air speed to impart power in the oncoming air through the radiator, and then throught puller on the inside. I also have my S4 system, that always runs middle temp, regardless of outside temp. never overheats at the track, always right in the middle. Ill put an IR gun on it next time at the track.
fans work i have two in parallel. on the hottest days, at a fast track, the single fan will come on after a lap , but half way throgh the race the temp will get hoter and by clicking on the second fan (manuaL) , the temps retuns to normal.

 

thats why the hood vents are so effective. what is actually happening, is the oncoming air is pressurizing the engine bay and it vents downward, because thats where ambient pressure is , under the car. above the car is vacuum, so the pressure would be diverted upward rather than downward and pushing on the belly pan.

 

As I recall the core is very close to 24"x18".
jp 83 S

 

I found exact measurements.....the main core is 619mm wide, 430mm tall and 42mm thick...