steepsnow

Hi All,

I have been experiencing overheating problems at the track on days over 90 degrees (very bad over 95).

I clean the radiators with the bumper removal process each yr. That does help, but it does not eliminate the problem. Thus, I am considering adding the third, center radiator as a (hopefully) permanent solution. This requires using a duct for the opening in the bumper to the new radiator.

I am also considering an MK1 Aero Kit conversion for my 1999 C4.

My primary question:
Is the bumper duct the same for the Aero kit as the standard bumper?

Secondary Question:
For those of you that have done the 3rd radiator upgrade, did it make a major difference? With 122K miles on the car, could the original radiators just be "tired" and just need to be replaced?


Thanks!
Douglas

steepsnow

One more Question:
Is there an advantage to the Aero kit at the track?
...of is it really just cosmetic?

Thanks again!
Douglas

Tbred911

the 3rd radiator is a good mod for the track... and I would also do the "fan mod" that allows you to turn on your high speed fans and bleed off heat.... if your tracking in hot temps then some good 50 weight oil will also work better than the 40 weight many use on the cars...

OZ951

Yes the duct is the same and yes the radiator helps, when combined with the low temp thermostat.

When the rad gets tired they leak but they don't lose cooling efficiency.

Aftermarket rads may also have fewer cooling rows than Porsche rads.

steepsnow

Do they get any type of sludge that forms inside them?
Are they more prone to failure, cracking, etc from age, semi-abuse at the track?
They have 125K miles, but overall seem to do a good job.

Perhaps it is not necessary to replace them...maybe jut the hoses and rubber parts while installing the Center. That would save some money.

NZ951

You can use radiator flush, but really leaking is not there only issue, fin damage would also be a consideration, but you would have seen that when your bumper was off. They would need to be quite bad to effect the cooling efficiency.

Ubermensch

I'm also in a C4, and did add the aero kit, third radiator, and low temp thermostat. On the highway, coolant temperatures are much lower with this combination. On the track they're a little lower, but not a huge difference. I still get moderately high temperatures just as I end a run (104-106C).

Scale inside heat exchangers (radiators) is a common cause for reduced efficiency but I don't think it's much of a concern in a closed system with DI water a coolant. Your more likely to loss efficiency from damage to the fins and random debris that collects in them. I doubt our normal cleaning and vacuuming removes everything lodge between the fins. I have heard of people seeing improvement in track temperatures with new radiators, but I haven't gone this route yet.

The aero kit does a nice job of reducing lift and the consequential "floating" sensation you get in stock cars at moderate speeds. I definitely like it at the track.

chsu74

Radiator Fan mod > 3rd radiator IMHO and much cheaper. Its about how much air you flow through your radiator at the end of the day. I never had my coolant temp exceed 93 C via climate control read out after a 30 min session on a 90 F day in my old aero at WGI. This is one of the best mods for 1st gen 996s.

I would make sure the radiator fans are kicking up to high speed properly on both sides. Relays go bad on them.

mglobe

I'm not sure about the rocker panels, but the wing and front bumper combined do make a difference on the track. I've run both without it, and with it.

As far as the radiator mod vs fans, I doubt very much that the fans do much at speed. Fans are for cooling in traffic and idling. Many racers completely remove the fans.

steepsnow

Regarding the Aero Kit and track use, what is the "trade-off" related to down-force vs horsepower/torque.

It makes sense that there would be less "lift" as mentioned, which would affect "grip." However, does the down-force make the car "heavier," thus a little slower with the same horsepower/torque?

OZ951

No.

mglobe

Absolutely not. I'd say the kit is worth about 1/2 second. I put the Getty Spec 996 wing on my car (basically a cup car wing), and it was worth about 1 1/2 secs. These cars need less lift to really perform.

Ubermensch

Well, in theory less lift does mean more drag. On most tracks you're limited more by grip than by power. The additional downforce will get you around most tracks faster but if you were to do a top speed run you might find you lost a couple of mph relative to a car without the it. Top speed is rarely a concern for most DEs...

gieseja

Be sure to change your oil every 3-4 track days.

steepsnow

Any thoughts on what speeds the Aero kit starts to give an advantage?
Here in Denver, our local track (High Plains) is not a very "fast" track; lots of fun with elevation changes, etc. ...but not much time over 100mph and couple tight slower turns.