I've been losing coolant, I think from the radiator cap. Well not really the radiator, the fill neck by the t-stat, whatever the hell you call it. Mazda says they have one in stock, $22.80. What I was wanting to know is if it would be safe to get a generic one from an auto parts store, as long as it is the proper rating. ???

naw be jdm tyte and get a blitz one

Thanks for the help! oh wait, no, **** you.



Anyone have an answer? Where's banzai this morning???

You should be fine with any one that fits, and the one you have now 'should' have the rating on it.



I think yours is 16lbs?

the label wore off of mine, I'm not sure. screw it, I'm going to go to mazda and buy one.

The rating on the stock cap is .9bar, so about 13psi?

Not sure if your cooling system is the same as mine, but I suspect it is. The cap you describe should not be vented. The radiator cap is a pressure-rated cap that bleeds over to the expansion tank. The t-stat cap is just a solid cap. Mine was crap when I got the car, and I replaced it with an off-the-shelf one rated at 13 or 15 psi. It worked fine for a year or so, then started burping coolant whenever the engine got hot, particularly after I shut it off.



I replaced it just a few weeks ago with the proper cap from Mazdatrix. I think it was $18, plus a few bucks shipping. My local dealership has changed hands a lot, and the latest crew says they can't get any parts for the old rotary cars. I suspect they're just a bunch of lazy bastards. If you can get the proper cap locally, I'd go for it.

I picked up the cap from Mazda on my lunch break, $24 and change after tax. I only have 1 cap on my entire system. Any experienced rotary guy who looks under my hood notices that something is not right with my radiator. At the top of the rad there is no cap; there's the coolant level sensor thingy, and there's the overflow tube, but no cap. It looks like someone did something to it, meaning it doesn't look stock. The only cap I have is at the t-stat, and I'd rather have it vent when heating rather than have something pop. I don't know if my overflow works properly coming straight from the rad.



and I confirmed, the mazda cap does say 0.9 on it.

[quote name='Baldy' date='Apr 21 2005, 12:25 PM']I picked up the cap from Mazda on my lunch break, $24 and change after tax. I only have 1 cap on my entire system. Any experienced rotary guy who looks under my hood notices that something is not right with my radiator. At the top of the rad there is no cap; there's the coolant level sensor thingy, and there's the overflow tube, but no cap. It looks like someone did something to it, meaning it doesn't look stock. The only cap I have is at the t-stat, and I'd rather have it vent when heating rather than have something pop. I don't know if my overflow works properly coming straight from the rad.



and I confirmed, the mazda cap does say 0.9 on it.


[/quote]



Well, yeah. I guess if you have only one cap, it better be vented! https://www.nopistons.com/forums/pub...IR#>/bigok.gif

certain items are best bought OEM:



TStat

Rad Caps

are among them

Good then!

Any thoughts on if I'm in any danger with my current setup of not having a cap on the rad? With the hose coming off the rad directly to the reservoir, is it serving any purpose?

i use Stant caps there really good, just i've always had problems with the pressure release caps

[quote name='Baldy' date='Apr 21 2005, 09:25 AM']I picked up the cap from Mazda on my lunch break, $24 and change after tax. I only have 1 cap on my entire system. Any experienced rotary guy who looks under my hood notices that something is not right with my radiator. At the top of the rad there is no cap; there's the coolant level sensor thingy, and there's the overflow tube, but no cap. It looks like someone did something to it, meaning it doesn't look stock. The only cap I have is at the t-stat, and I'd rather have it vent when heating rather than have something pop. I don't know if my overflow works properly coming straight from the rad.



and I confirmed, the mazda cap does say 0.9 on it.


[/quote]



there are 4 different s4 cooling schemes.



early early: normal cap on the filler neck, no cap on the radiator, over flow by the coils



early w bulletin kit: this puts, the over flow tube thru the low coolant sensor, and a pressurized overflow in front of the radiator.



late early (middle? 87ish): over flow tank moved to the front of the radiator, normal radiator cap on the filler neck, w the overflow tube



late (88's): theres a cap on the radiator, over flow tube is also on the radiator, cap on the engine is just a filler cap.



all these parts mix and match so its possible to have an s4 fc with 3 radiator caps, 3 overflow hoses, and 2 overflow bottles. or you can go the other way and have none at all....

[quote name='Baldy' date='Apr 21 2005, 09:25 AM']I picked up the cap from Mazda on my lunch break, $24 and change after tax. I only have 1 cap on my entire system. Any experienced rotary guy who looks under my hood notices that something is not right with my radiator. At the top of the rad there is no cap; there's the coolant level sensor thingy, and there's the overflow tube, but no cap. It looks like someone did something to it, meaning it doesn't look stock. The only cap I have is at the t-stat, and I'd rather have it vent when heating rather than have something pop. I don't know if my overflow works properly coming straight from the rad.



and I confirmed, the mazda cap does say 0.9 on it.


[/quote]









I have that set up and found/fixed a leak of the upper plastic section of Thermostat housing, and the plastic pipe leading to the overflow tank was half broken. I am fixing it with epoxy.



My radiator got oxygen in itand alarmed the idiot light came and went for a couples days before I realized where the leak was.









'='

I was wrong. There is the cap by the t-stat. There is a tube from the top of the radiator that goes to something in front of the radiator that has a cap on it, there's a threaded stud that keeps you from opening this cap. Then from there a hose goes to the overflow bottle.



So what's with the cap that's blocked from opening, should I change that cap as well?

The cap in front is the overflow. It comes off the top of the rad to help vent air from the rad. This one is probably blocked from opening because that isnt where you are supposed to fill the system. If the system isnt pressurizing normally, you should probably change that cap though. The flat cap on the water pump neck shouldnt have a pressure rating. It shouldnt have a spring on it at all.

So I guess I can take my new pressure-rated cap, put it on the overflows thingy, and get a flat cap for the fill neck?

[quote name='Baldy' date='Apr 22 2005, 12:18 PM']So I guess I can take my new pressure-rated cap, put it on the overflows thingy, and get a flat cap for the fill neck?


[/quote]



I would say yes. Put the pressure release cap at the overflow location and put a flat cap at the filler neck. You don't want the pressure release cap at a location that doesn't have a provision for overflow, or you'll just lose coolant.

Cool. Yeah, evidently that's exactly what had happened.

someone make this a faq, or remind me.



odd cooling system part numbers:



86-88 t stat: 8af1-15-171a-9u (the 9u stands for they went to kragen)

86-88 water pump: 8af1-15-100b, although they are swtiching to a shitty reman

86-88 o ring between filler cap and thermostat cover: n326-15-174

86-88 filler cap adaptor with overflow: n326-15-17ya

86-88 filler cap adaptor without overflow: n323-15-17y

aluminum filler cap adaptor without over flow: n3c1-15-175

86-88 upper radiator hose: n326-15-186b

86-88 lower radiator hose: n326-15-185b



89-91 thermostat housing: n350-15-172

86-91 thermostat : 8af6-15-171

89-91 upper radiator hose: n350-15-186

89-91 lower hose : n350-15-185





heater hose under oil filter: fb03-61-211 or fb01-61-211c, same hose 2 part numbers.

firewall to heater pipe: fb01-61-212b

heater pipe to radiator: fb01-61-213

Yes, I'm a FNG...



Can you use the S4 thermostat housing on S% iron? I prefer the fill cap at the top of the neck here, rather than just at the overflow tank...

gotta ask, getting ready to put in new motor and would like to swap if possible