Replaced leaky oem with a nice koyo direct replacement unit. Original oem has been in use for a very long time and I've read on here they have a service life of about 30kmi. Should I just replace with another oem? Looks like a lot of people use high pressure aftermarket, but mostly for looks...not the path I'd like to take. Koyo brand caps are 1.3bar which I think is too high. Does anyone know what the oem cap pressure is? 0.9bar/13psi or 1.1bar/16psi? Service manual doesnt say what its pressure is, just that it should test between 14-18psi (12psi min) before releasing...

Would like to know what most people are using, esp if you have a koyo rad too. My car is an avg bolt on making about 380whp. Avg driver too, no extreme heat conditions...thanks

 

been using the stock one for 75k miles. id stick with stock

 

Yea thats what I'm leaning on...didn't know if the koyo being solid all aluminum made a difference...thanks for the reply man

 

+1 on the stock cap. The aftermarket caps hold a higher pressure, and will make the water pump leak some. It's not worth having a leaky coolant system all for a better looking cap. I would've went back with a stock radiator if I could've found one.

 

Stock one here to with a koyo half radiator. Works fine for me.

 

Greddy works fine for me

 

FYI, OEM cap is about a half mm too wide on the spring loaded portion, and will scrape up the filler neck over time. The Koyo cap is a little narrower and fits properly, so definitely use a Koyo cap with the Koyo radiator.

 

I run the koyo direct fit full sized rad on my 2003 with the OEM cap. Works great.... Only problem with my set up is it's a little wider than the oem one so my wastegate dump tube vibrates against it and gets a bit noisy.

 

I run a Koyo cap on my Koyo rad. Higher pressure means more ability to shed heat. I've never had a leaking coolant system with a higher pressure cap.

 

Same here.

Koyo Cap for Koyo Rad
OEM Cap for OEM Rad

 

Do you guys get a little bit of a coolant smell around the Koyo radiator/cap? I've tried a couple of Koyo caps, and get a tiny bit of a smell/leak that I don't get if I use an OEM cap. As mentioned above, the OEM cap will scrape up the inside of the filler neck, so I'm looking for another one.

 

That's exactly what I'm trying to solve. I don't get any leak, but I can smell coolant pretty much anytime the car is run for an extended period. Very faint, and most people don't notice. No leaks anywhere, no change in level, reservoir stays at the same level. I've been running oem this whole time. Was hoping that a koyo cap would make a better fit...

 

Dang, you and I are in the exact same boat. I will let you know if I find another cap that fits better, I feel like either the Koyo cap does not fit snug enough (and lets out a TINY amount of coolant when the spring-loaded valve opens) or maybe because it's higher pressure when it lets go the hole/hose to the overflow tank is too small to let that much coolant flow fast enough and it lets a little escape from the cap.

I also find the smell very faint, and nobody else can smell it, but I have a very sensitive nose and it clearly is smelling. I'm not sure if my reservoir tank drop at all, it MIGHT be like 1mm over the course of a month, but it's definitely not an obvious amount.

The main problem though is that the filler neck is 1mm smaller than OEM, and pretty much every radiator cap I've been able to find will scrape up the inside lip of the neck and not provide a good seal in the radiator. The Koyo cap is 1mm smaller in diameter on that little metal valve in the middle.

 

FYI, this is what the inside lip will look like if you use a non-Koyo cap with your Koyo radiator. You can see that the bottom half of the inner neck is slightly scraped up.

 

I don't see how that slighy scraping is an issue. I have been running the stock cap on my koyo for years now with zero issues and zero coolant smell.