Lots of good info here… let me add what I have learned.
As I see people become better racers and/or push their cars harder in terms of constant high RPM, the NSX starts to over heat. Then add higher performing engines and you have permanent cooling problems with heavy track use.
An oil cooler is defiantly a good idea.
20/50 oil is a must, but make sure you bring it up to temp.
I agree with insulating the front header near the oil pan.
The radiator needs to have shrouding from the front to the radiator or any resistance can cause turbulence in front of the radiator.
Run good coolant.
ARP studs.
Take the time to bleed the radiator system by the book… all of the bleed locations!
Target 200 degrees as max.
RTR had similar issues to solve, they ultimately ran with a hollowed out thermostat and welded shut the ~1” hole in the back of the housing… But they also ran a 3k+ and 7” thick worth of radiator that was sealed to vent out the largest hole you have ever seen in an NSX hood. And they still had high temps in 95+ degree days. They removed their electric fans (Like most race cars) to improve the airflow when the car is moving.
Other notes to help with your problem solving:
The OE NSX fan is especially restrictive.
In one case I had a blown head gasket that leak down tested perfectly, but when it got Race hot the combustion would blow air into the cooling system causing an air pocket and over heating. It would run forever without a problem if I kept the temps down. In addition the water stayed out of the cylinder and didn’t burn water.
High RPM causes heat exponentially. 5000 rpm to 6000 rpm might only be a 10 degree difference, but 6000 to 7000 might be 40 degrees, and 7000 to 8000 can increase 100 degrees (For example). In a race we lost coolant from a radiator that was damaged from the race before, the engine overheated and blew a head gasket. Some other cars had dropped out, so we decided to refill the coolant and go back out. After 3 laps of running hard and shifting above 8000 we overheated and came back in. We still needed 4 or 5 more laps to earn another position so we added water changed drivers and went out again. I needed more then 3 laps like last time so we collectively decided to short shift at 7000, after 5 laps we decided to stay out and go after the next drop out. The point is that at 7000 rpm we kept the car cool enough to finish the race and at 8000 rpm we could only get 3 laps.
At a point in my life I was a race engine builder who got some useful experience from our shop that built engines for many famous cars/drivers. In the Buick Grand National days we use to make some great power from the boosted V6, but the OE block only had 4 bolts per cylinder compared to most other HP engines with 5 or 6. We first went to ARP studs that helped but we still needed more so we went from 7/16” studs to ½” in the Iron block. If you needed even more power, you needed to go to the stage II block and heads with more bolts. Now going to ½” on the NSX wont likely help because aluminum wont likely handle any more torque, but the point is that 4 bolts per cylinder is not enough… especially with floating cylinders and lame gasket choices. A closed deck design will help eliminate cylinder shift that aids in the gasket letting go. This paragraph doesn’t solve your heating problem but may become useful in the future.
Many people have had gasket problems on the NSX. You have a few choices OE 3.0 (Worst), OE 3.2, Cometic steel shim, and Racers use copper with O-rings in the block or heads. But a better technology exists… Felpro and others build great gaskets for much higher performing engines, the difference is that they incorporate an O-ring into the gasket for combustion, and have “Print-a-seal” for the water. Its like having rubber o-rings around each water passage. Problem is that no company wants to tool up for the NSX engine. I finally found one that will and I will use them on my next engine.
Back to the heating-
Some race engines require additional hosing to rout more water to the heads.
I purchased one of those new vacuum radiator bleeders to 100% verify a good bleed. The dealers are starting to use them.
I have used the OE radiator, then a custom radiator that gave us some improvement, and then a Ron Davis radiator that had no gains over the previous. None of them solved the problem so I called multiple radiator builders to hear their advice. The common response was that since the larger radiator didn’t improve my temps, the radiator simply wasn’t getting enough air or possibly enough water flow.
During one of my over heating sessions I put a new normal thermostat back in and the over heating got worse. I changed back to the cut out one and cooling got better.
This said, I don’t think that having too much water flow is your problem; I think it’s just the opposite. Have you ever looked at the OE water pump? It’s pitifully small, especially for having to pump a system as long distance as in the NSX. Having too high of flow would only hurt you in slow moving conditions with minimal airflow. When moving high speed, the airflow should be so phenomenally high that it should have no problem cooling the volume from the 1-1/4” tubing below your car. Another note, the pump is driven by the back of the timing belt that wasn’t designed to drive anything. It’s possible that it might be slipping under a heavy load like high rpm.
My latest project is better ducting to the radiator and out the hood. Using the latest gaskets. Using the bleeding tool. Adding a 16” fan that flows better at high speeds. And most important- Adding an electric water pump to aid in the flow. I’m debating the elimination of the OE water pump to save 10-15 hp and possibly any problem causing affects it might have. But electric pumps aren’t that good, so it’s a flip of the coin, with major work needed to change it later.
Hope this helps, were all fighting the same problem but working together we can solve the problem quicker.
