There are parts on a GT-R that seem like they should be simple. The radiator cap is one of them. It sits on top of the radiator, it holds pressure, it opens when pressure gets too high, it closes again. How complicated can it be? More complicated than most people realise, and more important than its modest price tag suggests.

The cooling system on an RB26DETT runs at a pressure determined by the radiator cap's spring rating. This pressure is what allows the coolant to reach temperatures above 100°C without boiling — which it needs to do during hard driving without creating steam pockets in the system that cause localised overheating. A cap rated too low lets the system open prematurely, dropping pressure and lowering the coolant's effective boiling point. A worn or degraded cap does the same thing.

Why the NISMO Cap Matters

The NISMO Radiator Cap (21430-RS013) is rated for higher operating pressure than the factory cap — specifically calibrated for the heat loads a driven, and often modified, GT-R generates. The seal material maintains integrity at higher temperatures and through more thermal cycles than the rubber in a standard cap, which degrades and loses its sealing ability over time. An old cap on an old GT-R is almost certainly not holding the pressure it was rated for when new.

Fits the Skyline GT-R BNR32, BCNR33, BNR34, as well as the 180SX S13, S14, 300ZX Z32, and 350Z Z33. One part, genuinely useful across the JDM range.

The symptom of a failing radiator cap is subtle until it becomes dramatic: coolant temperature running slightly higher than normal, occasional coolant loss from the overflow tank without apparent cause, and — in severe cases — overheating under hard use. Replace the cap on any GT-R that hasn't had it done recently. The NISMO Radiator Cap is the correct replacement. At ¥3,456 it's among the cheapest meaningful upgrades available for these cars.