While testing my built S2000 on the Nurburgring in Germany, the car consistently overheats after 10km of racing. So no way it's going to finish the 21km.

The system is perfectly bled and while driving normally to hard on the autobahn there is no problem. The coolant will rise till 203F (95C) but no further. And that's driving 200+km/h consistently but without much boost.
Under normal driving it will be between 176F(80C) and 194F (90C).

But when racing, and under boost most of the time, the temperature will rise fast to about 221F (105C) and after a while it will rise again to 230-240F. After 221F it's time to get off the throttle.

When I open the hood there is alot of coolant over the engine, the overflow tank is filled completely and that's where all the coolant is coming out from.
So it's just squirting all it's coolant out.

Has anybody has this same issue?

I checked the radiator cap (J's 1.3 bar), works fine.
Radiator is filled, doesn't leak.
Hoses don't leak.
Thermostat opens correctly since it works under normal circumstances.

Could it be the water pump failing under pressure? I haven't replaced that yet.
The overflow tank (PFabrications made for me) is a bit small I think. It's that black tank near the radiator. The connection is at the bottom of the tank, I think it should be at the top but don't know for sure.
Also it's at a lower point than the radiator. Actually the radiator is now at a lower point. We had to reroute the hose over the engine to the radiator because of the supercharger. Filling and bleeding the coolant has to be done from a small opening on this rail.

Any ideas?

setup

 

I had a similar problem on another car - coolant overflowing from the bottle. It was a bad rad cap

 

Once coolant temp is at operating temp (179°F+), squeeze a radiator hose to feel if the cooling system is holding pressure. If there is no pressure, replace radiator cap. I have had brand new radiator caps be bad. I have also had a radiator cap not work immediately after having worked fine for years. Happened on my Subaru Impreza a month ago. It was good, I flushed cooling system and it was faulty upon reinstalling. Cap was visibly fine.

Use a maximum of 30% coolant. I run primarily distilled water with approximately 25% Honda coolant. Worked fine at Sebring in the middle of summer.

Vent your hood.

Duct the radiator very well. Looking at the pic, you have a lot of gaps where air can easily leak around the radiator. I stuffed all the crevices around my radiator with foam rubber from a crafts shop.

 

Some very good advise, thanks!
The hoses are under pressure when hot, so I think the cap is good. Though I am using 100% coolant, would that be an issue?

The hood is vented. You're right about the gaps, i've done nothing to seal those off. Very good idea to close them off.

If the coolant is getting too hot then the cap will open. I think it stays open and keeps filling up the overflow tank till it overflows itself.

 

As the coolant expands, Charles's law says that it will expand.

The only coolants that are designed to be used without water are propylene glycol based coolants such as Evans coolant. They do not have the specific heat capacity of water therefore I would recommend using distilled water.

The cap is pressure based therefore it opens when pressure exceeds the rated pressure, which is caused by a rise in temperature or a headgasket issue.

If this is a track only car, it would be advisable to use only water for coolant. Most tracks require it here stateside simply because a coolant leak on track will make the track very slick and it will take a long time to clean it up. If you have a full loss of coolant on track, it is typically a two hour plus ordeal. I would not want to be the cause of that.LoL

 

Good point. I'll change over to distilled water and check the headgasket too.

 

I would check you're not getting cavitation on the water pump at high rpms too. That's something we often see with the racers as we tend to see masses of high load, high rpm but low airflow situations, often it's as simple as a bigger pulley on the waterpump, sometimes making a pump with proper curved impellers is a better option.

 

Are there any replacement water pumps on the market with better performance then oem?

Cavitation could be an issue since i've also got the supercharger on an extra belt. That isn't really good for stability ofcourse.

 

Do you have an oil cooler?

 

Yes that was one of my first updates.
Oil temp rarely get's to 130C. (sorry no converter available at the moment)