996 Heat Management on Track - Looking for Advice

Yo Rennlisters! I have a 99 996 with 100k on the clock. When I am on the track I am seeing temps in the 245 range, and only if I run the heat full blast do they come back to the 230, maybe a little lower. On hot days I was dangerously close to the red. I have an OBD2 bluetooth Kiwi3 so I am getting the temps directly from the ECU (and overlaid onto my track vids through Harry's LapTimer). Here are my mods for cooling/preservation: FVD Baffled oil pan (+.6L of oil capacity) Motul 8100 or Joe Gibbs 5w40 oil Distilled Water + Water Wetter CSF Center Radiator Stock side radiators LN Spin on filter adaptor (with Mag) NGK spark plugs 93 Octane Fabspeed Tune Brand New MAF O2 sensors (Bank 1) are within normal voltage range. Bank 2 are spaced because I have no cats. Catless X pipe and full exhaust I track the car with 93, and I push it hard, but even shifting at 6800rpm (my PCA instructor's recommend threshhold for longevity) we still had to run heater full on in 70-76 temps last weekend in 20 or 30 min sessions. Shop who did radiator install also made holes in under tray to let heat to escape from center radiator, and I have GT2 front bumper with the upper vent (but not the baffle behind the radiator for those familiar with the GT2 setup). Previous owner did a 160 thermostat I'm told. Compression is great, cylinders look great, everything is great overall. Now, my instructor runs the same radiator setup in his 996 Spec race car (also a 99). He does not have AC Condensers, and has a standard pulley (I have an under drive), but said at our engine speed the water pump is going to be spinning enough regardless of pulley. He was running the same day an his temps were a good 20-30 degrees lower. His car is 110lbs lighter. From my motorcycle days, we would start with one temp range colder plugs if we saw high temps and most of the time that worked. I might try that, but I am assuming the tune could be lean? I don't know that my shop cleaned my side radiators but assume they did since they had everything apart for the install of the CSF center radiator. I am considering doing the CSF side radiators as well. Car also has a custom installed motorsport AOS and all of what I mentioned was done by me in the last 10 months. Anyone have experience with this?

Wow, no, that's really not right. For comparison, I have run my '99 C4, also with a center radiator, earlier this summer I ran from sea level up to nearly 9,000 feet in nearly 100-degree ambient temps and I have never seen temps anywhere near what you're seeing; that's about 40 minutes running uphill between 5K and redline. I'm guessing your water pump is shot, you have some other issue preventing coolant from circulating properly, or maybe there is air in the system from the shop's install of the center radiator.

any chance that your radiator fans are not working correctly? check to make sure that both the low speed and the high speeds are working.

Low speed definitely works and deck lid fan does as well. High speed not sure... Can I test those with the Durametric software? The water pump def looks "original". I am very certain it was run with the pressure release on to bleed it, they know I like my track days. I appreciate the fast feedback! Doesn't seem right to me either!

Yes, there are fan activations for both speeds in Durametric. If your water pump is original, I suspect: * If you look at the shaft, you'll see some crystallized coolant and/or you will be able to wiggle the water pump pulley * If you remove it, you'll find that the impeller vanes are chipped up, probably significantly If you find missing impeller vane bits, you need to try to flush them out before another track day. Those suckers have a reputation for causing hotspots and subsequent cracks.

do some searching on here for the on/off temps of the fans speeds, i cannot recall off hand what they are. your tempos are def way too high. Ive ran the hell out of my n/a and turbo 996s in 100+ dallas heat and never got over 220.

I'd add the T-stat has to be suspect, that it is not opening fully. Let me 2nd the radiator fans suggestion. I've had two cases, make that 3 cases, where a radiator fan wasn't working right. A fan motor shaft snapped. A ballast resister failed. And in the last case while the fan motor was running the air being moved through the radiator was clearly much less than the other side. No fan stage errors but the tech found the fan motor drawing way more current than the other one and I had him replace the fan motor. But in all of the above cases even in 90F+ heat and running the A/C there was no sign of overheating. I have to also question the GT2 front bumper setup. While this works quite well on the GT2 I'm not so sure how well it works, and with some pieces missing, on the 996. Any chance the radiator plumbing got mixed up with the install of the 3rd radiator? Perhaps a radiator got bypassed?

> Any chance the radiator plumbing got mixed up with the install of the 3rd radiator? Perhaps a radiator got bypassed? I was wondering the same thing, but was reluctant to suggest that OP's shop screwed the pooch.

I'll only add the Joe Gibbs 5W40 (DT40) is not meant for the track. If you want to use a Driven race oil go with either XP5 / 6 or 9.

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I assume when you say "baffle", you mean the Porsche GT2 center air duct, right? If you don't have one installed, this may be part of the problem. You need the air duct (item#13) part#99657532530 as shown in the image. From what I read about the GT2 aero bumper (with center radiator vent), it's vital to pipe air up and through the vent. If you don't have the proper air duct installed, hot air will get trapped and actually cause the radiator to be inefficient.

^That's true, but OP also indicates that the installer vented the tray area under the nose (which bothers me for an entirely different reason - venting air through the belly dicks up airflow; based on OP's description, OP now has a ram air intake that will be pushing the nose UP the faster he drives)... OP, you also listed a Fabspeed tune; I would advise against cooler plugs or anything else that can affect A/F unless you're certain that your tune will not react negatively...

^I'd cap them and install the proper center duct to funnel air upwards the way the bumper was designed. I can't see how just venting is going to promote proper air flow. I'm sure it will help it breath, but IMHO, the hot air will be trapped... and maybe cause resistance since the air is not properly vacated?

Venting and airflow aside, if it were my car I would be inclined to change water pump and TStat out as a starting point as well as inspect the coolant lines. As mentioned above the duct for the 3rd rad should be there to maximize efficiency, otherwise that 3rd rad isn't doing much.

I agree...something is not right. Start by replacing water pump and get a new low temp thermostat. Do not use an underdrive pulley on the water pump. If it is strictly a track car (or not a DD), ditch the AC condensers in front of the radiators.

It could be the venting......on my 997 I added the center rad myself. The instructions said to cut 4 vent holes on the bottom of the bumper cover. In my case the baffle that came with the kit directed the airflow down. I think in the OP's case his rad vents upward. You need that baffle because it directs the hot air upward though the "smile" duct on the top side of the bumper cover.

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Exactly. I guess it's more of an extractor. I will order that up, it's $159.00. I don't know if I need the radiator bracket from the GT2 (I recall a post where the guy was doing it, ordered a TON of parts, didn't end up needing them all.) I will definitely replace the pump and T_stat and I know there are a few coolant lines at the back that are on their last months so I'll get those out of the way as well. When we pull it apart (I may let the shop do this project) I'll ask them to inspect the impeller. There is always a chance that its not hooked up right, but I'm pretty sure it's proper since the shop is very reputable and has no C-level techs that they might ask to do a job like that. I do DD the car (weekends, cars and coffee, it's not a dedicated track car but approaching that direction) so I'd keep the AC for now. We like to take it out to dinner. Holes in the under tray- I think the need a cowling TBQH. I have a GT2 lip/diffuser, but I could see air being turbulent enough to interfere with air coming through the front and trying to find that little hole. Fun Fact- I had an 09 WRX with an FMIC but didn't do the non-turbo hood so it still had the top mount hole. At Thunderhill the front felt horrible (AST coilovers, alignment, etc etc). I ended up taping over the scoop (had a rock grille) and, boom, no more negative pressure zone straight over the front. I am not tracking the car again this year that I know of because of life schedules so I will have time to get into this a bit deeper. +1 for not swapping my brand new plugs Brad Penn oil was recommended for heavy tracking as well by my PCA guy. This is the VARSITY TEAM of responses!! I always appreciate it!! Note Temp Gauge in video overlay- You Tube Its cropped a little from the YouTube image stabilization but you can see it right there at the red.

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Sneaky, that's why they cut the vents I guess. Basically I bought the GT3 kit but upgraded to the CSF radiator instead of the stock one. I think the GT2 kit (based on research last night) might have different brackets to tilt the rad forward? I haven't pulled the bumper to look. Daily driving temps are "normal". The 8 in 180 or maybe the 0. A different shop I brought the car to replaced a tranny output shaft seal and agreed that with a 160 and functioning system it should be much cooler as well. I might bring it back there. Both shops have 4.5+ star review locally here in the Philly area.

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The underdrive pulley is a crank pulley that underdrives all of the accessories. I ran a UD pulley on my 986 and for the first couple of years I had my 996 and had no issues with cooling. M96 lore is that the UD pulley is better for the water pump on tracked cars because it theoretically reduces the chance of cavitation when the car is near/at redline; I don't know if there's any fact behind that particular UD pulley claim. The ONLY issue I ever had with the u/d pulley was a very occasional low voltage situations when sitting in traffic evidenced by the PSM/ABS warning light combo (I am aware that there are other potential causes for that issue, but I have not had a recurrence since reverting to the stock crank pulley).

A friend of mine with a 986 Boxster (same up front as your 996) put on a GT2 style aftermarket bumper and suffered overheating even after several attempts of opening vents and cutting holes. After he got too hot and burped out some coolant onto his back tire and had a big spin, he went back to stock and it is solved for him now. I hated it for him because the bumper looked sooooo good.

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He probably just changed the bumper and left the OEM duct work that matched the previous bumper which could be a problem when tracking the car obviously.

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Super! Let us know how it turns out. Pictures would also be most appreciated!

You can always do the fan mod and hard wire to go on high speed.

For what it is worth the Turbo center rad vents down.

^Indeed. The GT3 center radiator (and if you have a center radiator fitted on any street 996 aside from GT3 RS and GT2) all vent down. That said, the venting up is supposed to be beneficial for a few reasons, chiefly downforce. You’ll need to tilt the radiator to do this. Anyway, Porsche claims to have achieved superior cooling with the MK2 cars, by changing just the front bumper shape. You can see how the ducts channel/force more air into the side radiators. I would suspect the problem in your case may have to do with the air ducts to the side radiators , are they nicely sealed against the radiators AND the bumper? Remember your car has different radiators than the ones that came on the turbo/GT2... The radiator fans should not have an effect once the car is moving. There many people running 996s without radiator fans. The GT3s only came with one fan for example. I’ve tracked an early 996 into triple digit heat, on very hot days even running the A/C without over heating issues on track.

Notice the wind tunnel tests and you'll see the GT2's ability to funnel air through the center vents.

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I removed the plastic housing in the back of the side radiators that forces air downwards. It was essentially a log jam for air flow. And, when I pulled them, I put in GT3 brake cooling ducts. On my 996, it made a difference in air flow, which improved temps as well. -td

Heres a pic of the car... Don't even mention the drag from the intercooler inlets that go to, well, the inside of the fenders. =)

I spoke with one of the 2 shops today here outside of Philly. He feels like when we pull the water pump we will likely find impeller issues. Either way, it's beyond time to replace that and I'm getting a new LN thermostat as well. He also recommended using an IR gauge thing to get actual temps of the radiators, heads and expansion tank to make sure the temp gauge is correct. (And the temp gauge and OBD2 would be feeding off of the same data/sensor, so the only thing I can verify is the gauge and the OBD2 are reading the same - so the gauge isn't broken). The downside of all of this: I won't be able to get the car back on track anytime soon to test it because of my schedule...

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Where do the GT3 brake ducts pick up air? I have the plastic GT3 ones that snap on the LCA, did you get those or something more legitimate?

They are more legit. The ducts pass air that comes through the radiators/condensers. And (as I mentioned) the air has much better flow without the downward fender inserts. Here's an old thread from my build on this point. https://rennlist.com/forums/996-foru...-mod-pics.html -td

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Sharp machine you got there buddy! Let me know how my suggestion with the air duct works out. I'm willing to bet you it will make huge difference. Rerouting the air on the back side of the side rads should help too. That was good advice. Porsche design to funnel the air downward on the side rad doesn't make much sense for track use. Let us know! Cheers!

Hi Years ago in my Lotus Elise we had overheating problems similar to what you're describing here. We sourced an electric water pump system that was just amazing. http://daviescraig.com.au/electric-water-pumps With two electric fans and a variable water flow regardless of engine speed we could almost dial in the temp desired and the auto thermostat would keep it there regardless of how hard the car was being driven - and it was driven hard, very hard. Plus after a hard run with the engine off, the water pump keeps operating to cool the system down quickly and this also avoids "heat soak" I'm told... An additional bonus is the slight increase in power as the parasitic drain is removed... May be worth a look at...? Good luck! Rgd's AT

My Boxste' was cooking at the track this weekend. Outside air temps were in the upper 90s. By the end of the 4th session, coolant was bumping 250 degrees. Melted the rear bumper cover. Going to install 3rd rad, low temp therm., new water pump, and manual fan switch.

The oil is running too hot, the coolant soaks up *some* of this heat via the heat exchanger... Install a stand alone oil temperature gauge with the sender in the sump. Also, the earlier poster is correct- DT40 was never developed for a track oil, it is not designed with a high viscosity index for operation with exceptionally high oil temperatures. A huge issue is the bumper. I see high coolant temps all the time from aftermarket, and OEM bumper covers that have the wrong angle of attack for the air to enter into the radiators. All the air stacks into the outboard corners of the radiators, and often it stagnates there. I have seen many cars with these bum,per come in with cracked heads, and upon repair we have to add a CSF 3rd radiator just to get the coolant temps back down to where they are supposed to be stock (on the street). Looks kills. Keep that front bumper stock.

Unless they custom mounted the center radiator the GT2 ducts won't affect it. Your car shouldn't be running that hot even without a center rad. Especially if you are running Water Wetter. As stated water pump and t-stat seems like the biggest culprits. I would also have them clean the radiators and condensers and ensure you have a good air path all the way through. DT40 will ruin these engines with heavy track use. XP9 seem to work really well on the track but like all race oils, won't last as many miles.

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Slakker, I agree that there are other contributors to the overheating problem, but are you really sure the OEM upward air duct won't have any affect on cooling the car??? Please explain. Please correct me if I'm wrong, but if air is push straight through the center radiator and not vacated properly, then air will get trapped and actually cause un wanted resistance on the car. Doesn't the upward flow of air also contribute to improved down force on the car too?

Relegate, Did you reused the existed side air ducts that were designed for the OEM base bumper on your car when you installed the GT2 style bumper cover? If so, this may also be another problem especially when tracking the car. You need the GT2 side air ducts which match the bumper's side inlets. They are larger and funnel *all* of the air properly across the rads. If you reuse the base bumpers air ducts (which are smaller and designed for the Carrera lower inlets), air will actually flow above the base air ducts which will cause the air to get trapped in the corners and cause your rads to not be as efficient. I personally learned this the hard way when I upgrade my base bumper to the TT style bumper.

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I saw a thread somewhere a few years ago (not on here, maybe on Pelican or Planet-9) where Jake was talking about a possible XP9 that could last 2500 miles for folks that drove their cars to and from the track, but I guess it never made it into production, as last time I talked with Lake Speed Jr he said the interval was still around 750 miles. I wish it would bump up to 2500, that would be perfect for me

If they didn't dam up the bottom then all they did was create two exit paths. If they left the radiator tilting up then the vents shouldn't have any affect. If they reversed and tilted the radiator down, which requires some customization, then as long as they matched the intake flow from the bumper to the radiator, it still should provide good additive cooling. As for creating downforce, yes this would benefit aero but not cooling. That's where adding the GT2 exhaust duct and damming up the bottom becomes advantageous. I looked at doing this yesterday but bumped it to my winter list due to the amount of time it will take. I'm already pushing it to have my current list done for next weekends race. +1!!!!

Is this what the OP should be aiming for regarding air ducts?

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Are your fans properly connected or have the wires been misconnected so that the fans are turning in reverse direction and inhibiting air flow rather than helping it. I had this happen with a 308 I owned. The PO had removed the radiator fans and when reconnecting them, reversed the wires on one of them.

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We are doing something about those inside fenders before our next track day together. I will cut them out while you sleep if I have to lol.

Yes, that will should improve front end aero significantly. FYI, fans are irrelevant on the track unless you are sitting for a period of time.

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Thanks Jake! I'll need to find a stock bumper and test it, car came WYSYG. I'll pull the part numbers off of the ducts that are on there. The center is GT3 OEM (I ordered all of the parts from the Fiche and then subbed the factory radiator for a CSF). There is no ducting behind the radiator... Is there an external oil cooler that is preferred? I have the LN Spin-on adaptor and I know a sandwich adaptor plate can be installed.

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This. The amount of air those fans can move compared to the CFM of air getting stuffed into the inlets due to the ram air effect is insignificant.

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Better be careful. I've been in high ambient temperature (~116F) conditions with my Boxster that had the coolant temperature to 226F and the radiator fans running high speed even when moving down the freeway at speed. And even in less severe ambient temperature conditions (~90F) when pushed hard (on mountain roads, pushed similarly to how it would be pushed on a track) the coolant temperature climbed to 226F and the radiator fans ran on high. While it is probably true the 996 -- at least models newer than my 2002 Boxster -- have better aerodynamics and thus better flow through the radiator ducts when underway I'd be darn sure the fans work properly at all times.

Where is the best place on the sump to attach an oil temp sensor. I take it you would have to drill it?

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I understand...your car has fans that are controlled thermostatically; when the coolant gets hot, the fans go on. You would probably flow significantly more air @ 70MPH if the fans were removed than having the fans in place and running; consider how much of the radiator surface area is blocked by the hub and frame of the fan. OP is seeing overheating in situations where it doesn't make sense; an otherwise stock 996 with no fans should still be capable of dumping adequate heat once the car is moving sufficiently quickly for the CFM to exceed whatever flow the fans are rated at. I'm not suggesting that OP should rip out his fans; I'm saying I believe that even without the fans, the stock 996 cooling system should be capable of doing a better job than OP's car appears to be. Since OP has the fans AND has the center radiator installed, something is very wrong.

Wednesday we are going to install water pump and LN 160 T stat. I am also ordering GT2 ducts and will try those out. I am aware that the turbo/GT2 radiators are larger than the C2/4/GT3 but I am certain I will be able to make everything work within some reasonable % of perfect. I've been scouring for a 996 Aero front bumper and OEM ones are 1/7th of what my entire car cost... so I will have to look to the aftermarket. (Mashaw or Getty). Lastly, I did find Duraflex offers a GT2 duct for C2 conversions. I assume the idea is the opening at the front to "match" their GT2 bumper while the radiator side is the smaller C2/4/GT3 size. Hoping to get the car on track on Saturday at NJMP to test the T-stat/water pump and maybe some new ducts.

Quick update- Getty is making ducts for me to fit the 996 radiators and the GT2 bumper. Will be finished next week.

Center radiator also?

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Could you tell me the price they quoted you for the side air ducts? I was interest in updated mine since I put the upper end TT bumper on my car. The car doesn't overheat, but the thought of trapped air in the corners concerns. I would be interested in updated them the next time I clean my radiators.

Slakker- I'm going to investigate the proper GT2 center position this winter. In the mean time I am going DIY a small extension to the bumper opening out of plastic sheet from Speedway and make some other improvements. The real lift/drag is the side rad ducts it seems. B3freak- $299 I am hoping they are close enough that we can use them with maybe a slight addition of plastic or garage door strip. (This isn't a show car but you won't see it ) Oh, and a step ladder blew over into my wing at a coffee shop yesterday and chipped/cracked that.