Koyo radiator rad leak thin quality issue
 

So I have been rockin a Koyo radiator for almost 10 years and the radiator cap flange has worn out. Not a bad run, but still is a pain in my ass. I had a coolant bubble issue in the past that was fixed by a new cap, but I think it didn't fix the root of my issues.

Has anyone else had this issue? How did you fix this?

I was thinking about chopping the neck off and welding in a plug, or getting a CXracing radiator. They are nothing special but the 2.5" 63.5mm core is huge (Koyo is 53mm).

Has anyone used a CXRacing radiator? I haven't found any bad reviews for other rx7s or other cars.

Any way let me know what you think.

Thanks
Supercharged fc

Why not buy a new cap flange from Summitt Racing and have a local shop weld it on for you?

not only are the necks rather weak and flimsy, the end tank cores are as well. one good overheat and the koyo gives it up. not a huge fan of them personally as far as upgrades go but they work well as it is a direct bolt in replacement upgrade, one of only a few.

I have a CX racing copper/brass radiator. I haven't had any issues.

How does a flange wear out? Are you saying a leak developed at the weld, or that the metal surface has ground down to the point that the cap can't seal? If metal was lost, electrolysis may be to blame.

The first thing I did to my S4 Koyo was cut the flange off and weld a small piece of aluminum sheet over the hole. If you've already got a radiator cap on the thermostat cover, there's no point in having a second one. From your description you have an S5 version with a long metal neck by the battery? I can't speak to the quality of that version, but the flange on the S4 one (top/middle of the rad) is fairly stout. Or at least on those built more recently (mine is about 1 year old now). The weld quality on mine is actually very good.

Yes I have an S5 but I added a surge tank with a cap so I no longer need the neck, but I would like a radiator with a higher capacity.

I have the battery behind the passenger seat so it not an issue.

The lip of the and cup of the radiator cap based show signs of wear and fatigue. The lip is very thin and definetly will wear over time. If you don't work on your car all the time it would not be an issue, but it's an rx7 so you will be working on it all the time.

I would say the weld quality is good but I aslo agree with Karack. The Koyo performed the same as the stock one and the metal is too thin.

Any more people using CXracing radiator?

Thanks

brass vs aluminum radiators are a hotly debated issue

The CXracing radiator is aluminum and so is the Koyo so it should be an apples to apples comparison.

http://www.cxracing.com/mm5/merchant...gory_Code=RDMD

Quote from website

Aluminum Radiator For 86-92 2nd Gen Mazda RX-7 RX7 FC with Manual Transmission, Big Core. High Cooling Efficiency.

Radiator:
- Overall Size: 25"x21"x2.5"
- Core Size: 20"x19"x2.5"
- 1.5" Inlet & Outlet
- 2 Rows

From what I've seen they've actually been pretty stout. I've had quite a few modified here and there (either moving the inlet/adding/removing bungs, and have one that was given to me that landed on a jack when the car slipped off, drilled a hole and pulled it out/welded and pressure tested it, haven't had any issues in years.

I've not seen any failures of them either.

I wouldn't go with CXracing. I'm not a fan of their products. Mishimoto should be putting out a RX7 radiator soon (I think I remember reading that somewhere here).

Do you have a reason why? I'm looking for feed back.

Thanks

i've had 2 cars that were severely overheated with koyo's that were barely over a year old, they both boiled straight through the core right by the endtanks.

know how easy it is to tell someone their brand new $350 radiator is toast? believe me it's not easy.

Been there done that :lol:

Here's what I did, I got an aluminum filler neck, and had a pro weld it over the koyo radiator neck. I've been rocking it like that for almost a decade, and haven't had any other issues with it.

http://static.summitracing.com/globa...r-80-092_w.jpg

http://www.summitracing.com/parts/CTR-80-092/?rtype=10

Fixin time
 

I desided to try and fix the Koyo for now. The over flow nipple ripped when I removed the hose so I when ahead and cut the whole "cup" part off. My welder said he could put a bung in for me, but that he didn't like to tig weld old aluminium radiators because the coolant soaks into the metal. I'll get it back Monday or Tuesday.

Here a pic of the thin metal that I pulled off the neck.

https://www.rx7club.com/attachment.p...1&d=1267898740

https://www.rx7club.com/attachment.p...1&d=1267898740

Update
 

So here is the final setup using the Koyo radiator, and switching to an s4 waterneck with aluminum cap flange (no vent). I have a 16 psi (1.1 bar) cap on the water neck and 13 psi (0.9 bar) caps on the remote tank with a pressure cap to self regulate the coolant level. I was so nice to not top off the system for weeks to get the bubbles out, like the original setup.
https://www.rx7club.com/attachment.p...1&d=1269701929
https://www.rx7club.com/attachment.p...1&d=1269701929

Not much of a debate.
While copper/brass conduct heat better than aluminum, the overall superior strength of aluminum allow it to be extruded into far more efficient shapes than can be achieved with copper/brass, which improves the efficiency of the aluminum core above that of copper/brass.
Couple that with the lower weight of aluminum, and from a performance stand-point, there is no reason to go with copper/brass.
The only caveat is ensuring the core your manufacturer uses actually makes use of the aluminum properties in its extrusions.