Koyo Radiator

SupraTrbo89

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This past weekend I was under my car while it was running trying to diagnose a power steering leak and noticed my Koyo radiator had a slow drip at the very bottom right in the middle. I believe there has been a slow coolant leak for a few years now but was never able to determine where it was coming from because I had never laid under the car while it was running. The leak is very minimal and I can drive the car for a full year without having to add coolant to the overflow. I only drive the car ~2K miles/ year. The car is an 89 turbo 5 speed and the Koyo radiator was one of the first things I purchased for the car when I bought it ~10 years ago.

My questions are --

1. Can this be repaired?
2. Is this typical as radiators get old?
3. If I buy another one should I get a Koyo or Mishimoto. I know the Koyo's are about $50 more expensive.
4. Is it beneficial to switch to electric fans while replacing the radiator? (Thermostat and water pump are relatively new -- a few years old). The car has no overheating issues currently.
 

plaaya69

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I would double check to make sure your leak is not from any of the coolant hoses on the radiator (especially the small one going to the overflow tank). You can also go to AutoZone and use the cooling system pressure tester kit they have from the loan-a-tool program to see where it can be leaking from.

Do you have a performance aluminum Koyo radiator or the stock replacement style with the plastic ends?
 

JDMMA70

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If its an aluminum id stick with a Koyo over a mishimoto. They fit better
 

SupraTrbo89

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Thanks guys. I checked the upper and lower rad hoses and they are not leaking. Didnt think about the small overflow hose. I'll check that. And I have the good koyo one all aluminum which fits perfect. If I dont see any hose leaks ill get the pressure tester.
 

plaaya69

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If you have a older all aluminum Koyo radiator then it is probably worth fixing.

The last 10 years a lot of common radiator brands went down hill and failure rates seem to gone up (especially with the mk4 Supra guys reporting their problems). I made this thread when I was looking for a radiator replacement and did some research then:

http://www.supramania.com/forum/threads/lets-talk-aftermarket-aluminum-radiators-in-2018.247966/

I ended up going with a Mishimoto radiator mainly because of the lifetime warranty (with supposedly very good support on that). The Mishimoto radiator is larger so it is a tight fit when assembling the whole fan, shroud and radiator assembly but once in place everything bolted right up like oem. My only complaint was the Mishimoto radiator cap that came with it, I tossed it and put the original 87 radiator cap on it. Coolant temps are very constant and run about 15 degrees cooler than my old Koyo radiator but that one was just a factory replacement style with the plastic ends.
 

SupraTrbo89

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I just read through your thread. Good info. The Koyo rad did not come with a cap so I am using the OEM one. I would agree that my supra runs slightly cooler with the Koyo unit when compared to OEM. The only thing that was a pain when I installed the Koyo was I had to find a screw to plug the bung at the bottom of the radiator which I believe is used if you have an auto. It also has the standard drain bung with a valve. No fitment issues with the top brackets or posts at the bottom. Anyways I will recheck for leaks this weekend and go from there.