Fitting a center radiator to a 996 4S

I wanted to fit a center radiator to my 02 4S, however, I was not able to find much info on Google as to which radiators/hoses I would need. I wanted to share my experience so that if someone else was looking to do this with their car, they would have a reference for some part numbers. I got this kit off of ECS Tuning along with a CSF equivalent radiator (instead of the stock one that was listed in the kit). Please note, this kit is that it comes with the Turbo center radiator and not the NA one that is listed for this application on other sites. I found to plumb this in (with Porsche parts) you'll need in addition to a center radiator kit, the following hoses from a turbo, parts diagram below. 99610672474 - left side coolant hose with center radiator outlet (6) 99610672874 - right side coolant hose with center radiator outlet (11) 99610672511 - left side hard line to radiator (26) 99610673071 - right side hard line to radiator (27) NOTES: I think the NA radiator(along with appropriate brackets) would be a better fit as the turbo one with the supplied brackets did not fit perfectly and had to be flipped with inlet and outlet on the bottom. A short run of hose from the hard line to the radiator inlet and outlet. With the turbo radiator, since i had to put the outlet and inlet on the bottom, the hoses were still ~1"-2" short so I had to use a 1" metal coupler and radiator hose to bridge the gap.

A friendly word of warning - there is a problem creating the right amount of radiator area for both driving around at 30 mph on a cold day and racing round a track close behind another car on a hot one. The thermostats only control flow and if the radiator area is too much for any given situation the flow is minimal. Because the engine only allows about 10% of the coolant to enter the cylinder block (the rest goes straight into and out of the cylinder heads) low flow can allow the cylinders to run very hot internally. You do not notice this because the coolant is mixed together again before it passes the temperature sensor or travels back to the radiators but low flow overall results in unbalanced cooling to the cylinders. Because that makes the oil between the pistons and the cylinder walls hotter it also makes the viscosity thinner and then any free silicon particles that have become loose from the cylinder wall can impinge more on the piston coatings resulting in premature scoring. So in conditions when you didn't need an extra radiator (which is most of the time) it can be contributing to cylinder scoring and not preventing it. The extra radiator is only beneficial in those conditions when the standard thermostat is wide open and the engine is still getting hotter. To sort this we made a housing that fits between the feed to the third radiator to house a thermostat set at a slightly higher temperature than the main LT thermostat so it only opens when the engine would have started to get too hot anyway. All this proven with multiple tests in different conditions - that revealed that in most normal conditions and driving - one radiator would be sufficient. However we have not yet managed to productionise this additional thermostat for retailing but while you are figuring out how to connect them - you could allow a hose to bend away and fit to our 996 third radiator system before joining to the centre radiator and achieve the same outcome (or simply make one yourself or fit a proprietory one). On our race cars we actually went further and split the outlet from each bank (because bank 1 ran cooler) and made a "Y" outlet housing to hold 2 thermostats (throwing the original single thermostat away) to make sure each bank ran at the same temperature and then fitted another thermostat before the third radiator and that covered all conditions maintaining good cylinder temperatures and hence reliability. Baz

Thanks for the insight Baz, It is much appreciated! I'll look for an inline thermostat to toss in for the feed for the center radiator. Would you by chance have a suggestion for a thermostat/inline thermostat housing for the ~1" ID hoses for the center radiator?

Just curious, are you doing this so you can track the car?

why do this? In over a dozen years of tracking my car (southern california, nonetheless), i have NEVER come close to the halfway mark on the coolant temp. Even in the severe hot track days at Thunderhill and Buttonwillow where it can easily hit 100 degrees ambient air temp. the 996 C4s has the turbo radiators, which are thicker and have more cooling capacity but without the added heat of the turbo, and it keeps it super cool. In fact, you would be wasting money on the 3rd radiator. Plus the aforementioned warming capacity of the engine when cold. The system is optimized for the heat generation. i can understand a third radiator for a C2 (which the GT3 is based on), which has smaller bumper intakes and volume than the larger intake of the C4s/turbo. That's why also, if your radiator leaks, you would spend $300 on the turbo radiator as a direct OE replacement than the $100 996 C2 radiator. Just do regular coolant flushes to keep the system clean and optimized.

RngTrtl: Yes I hope to participate more at the track. Jyoteen: Thanks for your input, I do agree in stock form the turbo radiators would more than adequate and are optimized. However, my engine has increased displacement to 4L and I had assumed made more heat, as it did run a bit warmer than I remember. For me this is a precaution and I think with the addition of an inline thermostat, this setup would a benefit if things did run hot for whatever reason.

Many, many track days in my C4S in all types of weather including 100 degree days. Haven't had one single heat issue other than greasy tires on hot days late in sessions and wheel speed sensors getting cooked causing ABS faults. The larger C4S radiators are more than adequate in current form. If I was to add a center radiator - it'd be connected to a blower. That being said - this couldn't hurt but you may be creating other problems. You'll also want to make sure you've got the right air flow through the front bumper and radiator. If the airflow goes down under the car instead of up like on the GT2 - you're going to create high speed lift.

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Thanks Baz, does the same go for a 996 C2 MK2? My car is in Australia so it can get hot here but also winter is cold but not extremely cold. My MK2 doesn't have an overheating problem so i'm in two minds about this mod and if its even necessary. I just like the idea of the 3rd radiator!