Just bought a 1990 GTU, and it had been sitting for a while, so I decided to replace all the hoses and belts. The coolant had rust particles in it, so we did a flush when I replaced the radiator and heater hoses. Unfortunately, when reattaching the upper radiator hose, that portion of the radiator crumbled in my hands.

I'm told this is a common problem, but if it's so common, why are the hose connectors still made out of plastic? Is there an aftermarket radiator that doesn't suffer from this problem (preferably one that requires few modifications to install)? The stock radiator looks like it was already replaced once, since the radiator I had wasn't a mazda part (at least, it didn't match any of the diagrams in the haynes manual). I'd rather pay the extra money than get another substandard part.

Also, any suggestions for diagnosing where the rust is coming from? It seems to be behind the thermostat, as the rust particles didn't float to the top when we were refilling the car with coolant until after the thermostat opened up.

It's possible we just didn't get a complete flush, so we're going to try that again when we replace the radiator.

 

There are many rad replacements available. Most parts stores will carry a stock aftermarket replacement. Those generally come all metal.

If you want an upgraded aftermarket unit, the Koyo and Fluidyne both bolt right in.

As for the rust, since the engine is made of aluminum and cast iron, the rust is probably coming from the block itself. It may take several flushes and some driving to clean all the gunk out if the engine has been sitting.

 

Thanks, Aaron.

I've read about people having problems with the Koyo not fitting well, but those were mainly with 3rd gen turbos (and one person with an S4). Are there any fitting problems with the Koyo on the S5 (NA)?

The Koyo is a good price for all-aluminum, but given that my daily driver is out of commission at the moment (timing belt tensioner on an interference engine, sigh), I'd rather not spend the extra time fussing with the install.

 

I got my aftermarket radiator for $110 I believe it was from radiators.com . All metal, I think its brass. Works great.

There is no reliability reason to buy a fluidyne or Koyo if your engine is not pushing a good amount of HP.

 

I don't believe there are any fitment problems with the Koyo on the S5.

 

I ended up going with the fluidyne. Got a good price from abosluteradiator.com. Might be a bit of money up front, but I do plan on pushing more power once I get the car running well (it was left to sit for a while and needs some TLC).

The only problem was that the fan shroud didn't attach quite right (but drill a few new holes and it fits just fine). Am I right in believing that I do actually want to keep the shroud on?

The filler cap is also in a different spot, and gets in the way of the stock intake system. I guess most people with this radiator are using either open air or cold air intakes rather than the stock air box? I guess I'll be there eventually, but I'd rather not make too many changes at once (and from browsing the archives, it seems most people can't agree on what type of intake is best anyway).

 

As long as you run the stock thermoclutch fan yes, you have to keep the shroud.

Where is the Fluidyne's fill cap located that it interferes with the stock intake?

 

Hmm, reading what I wrote, that's not what I meant to write. It doesn't interfere with the intake, but the presence of the intake makes it harder to remove the cap. It's in the center of the radiator rather than sticking out of the filler neck like the stock one.

Not a big deal, just an extra step to remove the cap.