I just bought a 86 rx-7 n/a. The previous owner had installed a new koyo radiator. My question concerns that and how the hoses are supposed to be routed because I don't know how it looked when it was stock. Someone had told me it wasn't the one for this car, but I could make it work. There is a hose that goes from the overflow up to the radiator filler neck. There is another elbow hose on the other side of the overflow. The radiator itself also has a cap with a small pipe that protrudes out from the cap neck on the radiator. I was told that I could just close up that little pipe and all would work ok. Because now, coolant will flow into the overflow but not back out. And I have a feeling it has to do with how these hoses are routed. Anyone know how to solve this? I'd appreciate it, thanks.

 

I plugged the one on the Koyo radiator and left the original one on the thermostat housing in place as if came from the factory.

Seems to me you need to cap off one or the other. Or install a cap that does not relieve pressure on one or the other.

 

Not quite sure I get how your hoses are run, but I think I can give you an answer.

Since you have an '86, your stock overflow hose will go to the rad cap on top of the water neck on the engine. Make sure that hose is proper secured at both ends (no leaks!) and that the hose is in good shape...Actually, just replace it and use small clamps to hold it on each side. If that hose has pinholes, it will suck air back into the cooling system instead of coolant. Also replace the rad cap as it can wear over time.

The extra nipple on the radiator can be capped.

 

What could I use to cap it? Could I just stuff something in there? Is there something specific I could buy?

 

would any non-pressure radiator cap work?

 

Most auto parts stores sell vacuum caps. Get one of thick rubber. If there is a threaded port on the Koyo with a nipple screwed in, remove the nipple and use the approprite size pipe plug (1/16" or 1/8").