I was reading some rotary tech tips by racing beat and they mention the lower rad hose must have a coil spring in it to prevent it from collapsing at high RPM. They were talking about the fd and rx8, i was wondering does the fc have one too? if so, where because my S4 doesn't have one. my stock temp gauge rises from 1/4-1/3 to little pass 1/2 at high rpm, didn't want to push it anymore too see if it rise higher. what the temp if it little pass 1/2 anyways?

 

the lower hose doesn't have a spring in it.,
You're fine.
As far as temp,get an aftermarket gauge as the stock one obviously is useless and doesn't tell you the true temp.

 

If you are consistently running at elevated RPMs, underdrive pulleys would be your fix, not a spring in the rad hose.

 

perhaps in a zero pressure system like an evans conversion, the stock system being pressurized this sound like a load of crap to me. no RX7 or 8 ever had a coil spring in the hose, but it could be an issue at extremely high revs above 10k with stock pulleys... but who does that? perhaps you just missed the context of their article.

 

bingo! the spring is needed if you're ALWAYS running high rpm (6000+)

 

If I were to get an aftermarket temp gauge what brand would you recommend and where would you install it? Where the stock one is or somewhere else?

 

no simple answer for that, i'd just run a cheapo electronic auto meter. even the most expensive $150 gauges i have had crap out after a few years, overpriced pieces of **** like prosport i would avoid.

 

I have long used and recommend VDO gauges.
Cheap, reliable and reasonably accurate, their sending unit will go right where the original did.

 

I just installed my guage in the water hose from behind the water pump. It seems to read accurate so until I figure out what size the stock one is I can't change it. If you have the old housing like me the stock temp guage is the crush washer one, which is diff from the newer housings. Can someone clarify the two size differences?

 

RB has had this in their tech tips for years. I have one of their catalogs from around 1998 and they recommended this for high rpm operation back then. As others mentioned none of the cars had them from the factory. In theory at high rpm the hose collapses from the suction of the water pump. The spring prevents it. The under drive pulleys may help but I thought they were for preventing cavitation which is a different issue. Either way probably not going to be an issue on a street car as you don't see continuous 6000+ rpm all the time. It won't hurt anything to put one in there but it makes getting the hose on and off harder. I use an Autometer gauge. Has worked fine for the past 12 years or so. I drilled and tapped the water pump housing just below the thermostat for the sensor.