I shut down the engine on the straight, restarted it and continued driving. Now the CEL was off but the water temperature went up into the red region and I experienced less power in the upper rpms. Oil temp still was under 100 degrees C. I left the track to check things out in the pitlane and read out the error code. It was once again 22 (still the same that I wrote in the first post of this thread centuries ago) which means Vtec failure front cylinder bank.
Remember: My mechanic had checked and cleaned all the Vtec parts rear and front, replaced the sensors and the car ran fine and without CEL multiple times on the dyno (306 PS, which can not be achieved with unfunctional Vtec). But now we know that we may have more than one problem: Code 22 came up before any overheating, but overheating occured afterwards, so we must have an oil pressure problem and a water temp problem.
My mechanic came to the track, checked all lines, tubes and plugs, did some improvised work with the caps of the radiator and the coolant overflow bottle (don't ask my what he has done exactly, it was some scary work with rubbers seals, small tubes etc.), bleeded the coolant system, checked coolant pressure. Usualy those two caps would have been brandnew because he had ordered them before but both weren't available before the track event. You may have guessed it: The modified old caps seemed to hold the water pressure much better than the unmodified ones so these were apparantly both bad. Water temperature stayed in a reasonable region despite the high ambient temperature but after one hot lap CEL came up again.
Back in the pits we added a Liqui Moly Viscosity stabilisator to the oil and headed out again. This time no CEL but we only had about 5 minutes 'til the end of our run group time. Therefor I couldn't check the progression of the water temp for a longer time (oil temp. didn't exceed 100 degrees C the whole hot day under all conditions).
In the last 30 minutes stint of the day (my mechanic had already left) I did get the CEL and limp mode again multiple times (read out 22 once again afterwards), always restarted the engine and continued driving without overheating for most of the stint. Near the end the water temp. went near the red zone, I reduced maximum rpms to about 6000, water temp. came down and just when I entered the pitlane even the last CEL went out without restarting the engine.
Our thoughts are: We should change to a 20W50 or so race prepped oil because it's "thicker" than the recommended viscosity for the street (oil pump is okay). Oil cooler should move to the rear (right side air duct) with additional fan to maintain maximum air stream to front water radiator (which already has an additional high speed fan in front of it plus the stock fan behind). We should wait for the new caps. We should change the stock radiator fan layout from one big fan to 2 smaller fans (more surface area, just look at your car and you will see that the stock fan works only for a part of the radiator, the rest is covered by black plastic).
Just to be clear: All these issues we had and have are highly unlikely to appear at a non tracked car. We were never able to reconstruct any of these problems with my car outside the track. A german Liqui Moly engineer suspected that an engine with that much track kilometers as mine (125,000 overall, way over 20,000 on tracks without any major overhaul) may need more cooling under track conditions than a new one because of all kinds of age effects.
Real race engines don't run such a long distance - they are overhauled after some events or even replaced or, if the have to run for a long time (like the NSX-R at the 24 hours of Nuerburgring), they get a completely different cooling infrastructure than our stock cars. And even there at the Nordschleife (where cooling is usualy not as critical as on normal tracks) you can see some professional prepped cars with overheating issues sometimes.
As always, I find your comments on NSXPrime more worthy than all suspicions and thoughts of people (although they may be engineers) that don't know much about the NSX.
