jon88se

I ordered an OEM rad cap as just routine maintenance and upon opening it there is no spring under the cap...so is it a non-pressurized cap? Do they differ between years?

Defiant FC3S

i have a 1990 rad cap and its spring pressurized. like when i push on it, it springs back

jon88se

But is it an OEM? I know some FC's have multiple caps...some on the T-stat housing AND the radiator. I ONLY have a cap on the t-stat housing and the one I ordered from Mazda (w/ the new metal neck) has no spring. Should I be using a sprung cap since it's the only cap in my system? Where's reted when ya need 'em hehe

jon88se

So, what I've gathered is that S4 cars (88 for me) use a sprung rad cap on the t-stat housing while S5 cars have a flat cap there and a sprung cap on the radiator.

Since my radiator HAS no cap, I assume I should not use the flat cap at all and just get a regular sprung cap for the t-stat housing.

My overflow bottle is just forward of the radiator and NOT at the drivers side shock tower. The overflow hose goes from the rad to the overflow bottle and has no connection to the t-stat housing. So, what should I be using? I have it all here...the OEM flat cap, a 13 psi stant cap and a 19 psi Cusco cap.

wrankin

ummm, *where* does your overflow hose hook in? your pressure relief cap (the "sprung rad cap") should vent to this hose. the overflow hose is not plumbed directly into the coolant systems but rather to the neck where the pressure relief cap goes.

do a search, this has been discussed before.

-bill

Wizz

I'm thinking, if the place you what to put the cap has an overflow, use the spring cap.

jon88se

My overflow is connected to the radiator...there is NO cap on my radiator. The only cap is on the t-stat housing.

NZConvertible

S4's have one pressure relief cap and one plain cap.

S5's have one pressure relief cap only.

Whichever neck has the nipple connected to the overflow bottle must have a pressure relief cap on it. The plain cap goes on the other neck.

86J

Whats the advantage of the 19psi cusco cap?

ilike2eatricers

Looks like you got a flat cap. Mazda offers both because s4 have a pressure cap and a flat cap.

NZConvertible

None at all. All extra pressure does is raise the boiling point. At the stock system pressure of 13psi water boils at a temp far higher than your engine should be at, why would you want to be able to go higher? All you're doing is pushing your old rubber coolant hoses closer to failure.

BlaCkPlaGUE

Just curious, but what would a higher pressure cap be viable for? A car that uses that kind of pressure stock, that was designed for that kind of coolant pressure/boiling point?

Not starting anything! don't read this wrong, im just curious

NZConvertible

I honestly have no idea. I've seen them available from Japanese aftermarket suppliers as an "upgrade", but I can't see any logical reason for doing it.

jon88se

Ok, but what if the overflow is connected to the radiator and the only cap is on the t-stat housing? Which car should be run?? I guess my system is pieced together?

jon88se

bump

jon88se

If my overflow is connected to the radiator and the radiator has no neck for any kind of cap, does that mean my overflow is essentially not working and just holding coolant?

As I said before, the only cap in my car is at the t-stat neck and my overflow is not connected there...it's connected @ the rad. As far as I can remember, it's always been like this.

jon88se

About the rad cap, I assume the increased pressure is to provide a higher limit of boil over for motors under constant load/strain like a road race car. The FD came from Mazda w/ a 1.3 bar cap then they switched back to .9

jon88se

bump - help out guys...

What happens if I run the OEM mazda flat cap on my t-stat housing even though my radiator has no place for a cap. Without a pressure rating, does that mean my cooling system is not pressurizing?

What happens if I run a sprung cap on the T-stat housing without my overflow tube hooked up to it? As it sits, my overflow is hookd up the radiator someplace.

oakback

I have the same setup. No cap on the radiator, overflow hose comes from the radiator, and a cap on the t-stat housing. Everyone who looks at my car (that knows rx-7s) always says "whoa, I've never seen that before, it must not be stock" with regards to the top of the radiator.

jon88se

Mine is just like yours...here is a pic:



See, overflow from the rad to the reservoir...no cap. Cap on the t-stat housing NO overflow connection. So, which cap should I run on the t-stat housing, flat or sprung?

NZConvertible

If there's no pressure relief cap then there's no pressure, and your cooling system will be getting close to boiling every time you drive (pressure raises boiling point). Are you sure that overflow hose connection is stock?

RotaryEvolution

iTrader: (30)

unbolt your radiator top shield and next to your RF headlight is a pressure cap/housing, some radiators did not have a cap fitting on them so they had to find a way to put a limiter into the system somehow so they merely relocated it halfway between the radiator and the overflow bottle, however they put a bolt to keep you from removing the cap so if it fails it is hard to tell unless you remove the idiotic screw...

you should have a flat cap on the thermostat filler neck, you could use a spring cap there but it would serve no extra purpose there other than being a slightly more expensive flat cap.



if there is no pressure cap housing there then you either have the wrong filler neck or wrong radiator in your car, you could fix this by placing an S4 n/a pressure cap housing between the radiator and overflow bottle.

evalutionr

i got a greddy cap, i wonder if it will work when i finally get the car running....hmmmmmmm???

NZConvertible

As long as it fits it'ill work, but I wouldn't use it if it's a higher pressure cap.

RETed

The sprung cap is only used if you're using a bypass filler neck.
So if the filler neck has a fitting going into a hose, you SHOULD use a sprung cap.

If the filler neck has NO bypass fitting / hose, you can use the plain / unsprung cap.
You can use the sprung cap in this case, but it's a waste of money.

If your car is like that pic, you can use a plain / unsprung cap.
You can use a sprung cap if you want.

Sorry about not replying ASAP - I just started a new job, so my reponses are not going to be ultra quick like before.


-Ted