I've got a nipple for a hose to goto the overflow on both my filler neck cap holder and my radiator cap holder, I'm not sure why??

Car is 87 turbo

Ive.got a flat cap on the filler neck so I see no reason to have a hose connection to goto my overflow when the radiator already has one...I think it may be causing me.to lose coolant pressure idk.

I'm going to go ahead and put.a cap holder without the overflow tube on my filler neck...just wonder why it has an overflow tube on it?

Anyways, hopefully this alleviates any problems it could have been causong my coolant system....two pressure caps.is.certainly unneeded.

I'm running stock pressure cap on the radiator and flat cap on the filler neck...both from mazdatrix

Rotary > Pistons

Yeah I have the same situation with my 87. I blocked off the filler neck nipple since it seemed redundant and it kind of just gets in the way anyways.

I got 2 overflows and no problem for 4 years now.
Just too lazy to change the top one to a flat cap and no nipple setup.

You should use whichever one is the highest in the system for the overflow hose.

Idk which is the highest ??

Should where the overflow hose.is connected have the pressure cap or does it not matter?

I was gonna keep the flat cap on the filler neck for thermostat etc and put the cap holder with no overflow on it.

Coolant system just doesn't feel like its getting pressurized and its been a concern, I take it for the normal weak drive for breakin and it stays running cool and around 1/4 on gauge .. 4 krpm Max shifts, I have to bleed/burp.the system
..I'm wondering if its just running cool.

the add coolant light came on , I'm.gonna refill/burp/bleed it asap

Rotary > Pistons

oh and engine has like 100 miles

Rotary > Pistons

The S4 thermostat neck that has the nipple is made of metal, and is stronger than the plastic s5 thermostat neck that does not have the nipple. I would either cap off the lowest nipple, or leave them both routed to the overflow bin. There is nothing wrong with that setup. Factory is good sometimes.

S5 are completely different, no cap on the t-stat neck.

s4 has 3 types: aluminum w/o overflow nipple, plastic w/overflow and without.

the best method is to run the overflow from the radiator neck and cap off the nipple on top. this is because the plastic housings tend to warp and not seal 100%.

i run the aluminum cap housing, because it is bulletproof where i have seen the plastic ones leak due to the above in more than one way. it is a superseded part and the same one found on the FD3S.

^ what he said, the S4 has two styles, just pick one.

the early 86-87.5 cars have the overflow tube on the thermostat neck, late 87.5-88 cars add a radiator cap on the radiator, and just a fill cap on the engine.

neither one seems to work any better than the other, so just pick one. if you have some mix of both, you're going to have weird problems

the one I bought from the junkard is plastic w/out an overflow nipple and the one currently on it that has an overflow nipple is plastic as well.

swapping on the plastic one w/out the overflow nipple might cause leaks?

I'd get an aluminum one but I can't until I get some money to buy one off mazdatrix.

what should I do ? >.<

I'll take some pics , I don't know exactly how I should have this setup if I have it right or wrong.
The parts did come from a mixture of cars.

I'm gonna most likely block off or swap the thermo neck cap to be blocked off from the overflow and have the flat cap and then the overflow hooked up to.the nipple on the radiator cap with overflow tube and have the pressure cap on the radiator.


the 86-87.5 cars only had one place to fill.coolant?
Rotary > Pistons

every time i take one of the plastic necks off and put it back on it bows up in the center now matter how evenly i torque it down. 25 year old plastic ftl.

food for thought.



i've seen about 6 different FC cooling system variants, it seems as if there was little rhyme or reason why some had oddball configurations. some even had no pressure port cap on the radiator OR engine, but placed it just inside of the RF headlight housing by the evap receiver dryer(filling was done by the flat cap on top of the engine), the radiator just has a port off it to feed pressure to the remote cap.

ya my 86 sport had that setup with the overflow tank by the leading coil pack.

the fill neck isn't plastic, just the piece that bolts onto it where the cap goes.

Rotary > Pistons

Yup, I'd go ahead and find a replacement for that. My plastic one leaks at the moment as well and I'm searching for a metal replacement

Just get the aluminum FD cap assembly, we have been installing them on FC's for 10+ years.

is that the same one as this?

listed on mazdatrix for 87-88

http://mazdatrix.com/getprice.asp?partnum=15-17Y0-N323



Attachment 504426

Rotary > Pistons

Yes.

36 dollars us broke fc owners cant afford expensive fd parts!

https://www.rx7club.com/2nd-generati...992-parts-194/

FC owners just don't buy it new