Ok well I redoing my coolant fan wiring setup and while I'm there I need to take my t-stat housing off and tap for a temp switch . So I got a new t-stat and also wanted to get new pressure caps . Then I got to thinking . On my previous 2 s4's I only had 1 cap on the t-stat housing and none on the radiator . Or block off type of plate on the housing and one cap on the middle of the radiator . Well on this one I have one in each location . Is this normal and if so just by two radiator caps or should I make a block of plate for the engine one and keep the radiator . I fill from the top one cause it doesn't spill out but if I have to loose it I well . Thanks guys for and info or tips

I just bought 2 caps. They're not that expensive. I've also never had problems with air in the system by squeezing the top and bottom rad hoses as I was fillling. Not just once or twice but a bunch of times while filling the system.

Its best and easier to keep them both, especially when you are refilling the coolant system, the one on the Thermo house is best to leave open to "burp" the air out've system since its the highest point

install a pressure cap where the overflow tank is connected and a dummy cap at the other location (you dont want that one relieving pressure).

^ This is what the other posters missed. The dummy one should be where there's NO hose to the coolant overflow tank. The real one goes where there is one.

the S4's had a couple of different cooling system configurations.

the early cars had a single cap on the thermostat housing, and the overflow was by the fuse box.

a bit later they moved the overflow to the front, its larger.

the next variation is to move the pressure cap to the radiator, and then the one on the thermostat housing is just a flat cap.

then there was a service kit for cars with problems, this puts a flat cap on the thermostat housing, and puts the pressure cap on a bracket by the overflow tank. the overflow hose is then routed to the coolant level sensor, which in this kit had a pipe through it.

add 30 years of mixing and matching parts and you could have all kinds of odd variations

Well its been setup in my car for 8 yrs with the two caps . The the overflow res. is connected to the radiator and the t-stat over flow port is capped off . So now I guess I need to find the cap that goes to the t-stat then to replace the pressure cap there . It's never had problems with over heating or anything . Just doing some rewiring to the fan so it controlled by the E6k and figured I'd ask before I put it all together . If anything I'll make one if I can't find one . Thanks guys for your quick reply's

I've got mine set up now with a Flat cap and NO Nipple on the thermostat neck.The rad has the Pressure cap with the hose to reservoir.
Previously I have run 2 pressure caps and hoses from both locations and Tee'd the hose into the Reservoir also.
Both setups served me well with no issue.
You can get a NO nipple neck piece off an FD setup.(alumimum,just elongate the holes a bit to fit) use a Flat cap...Or Mazdtrix sells the part for about 30 bucks.

One more variation. On my rad, there are no nipples or caps, just the level sensor. The Tstat cover has the pressure cap and nipple for the reservoir hose. It's an 86. I'm in Canada.

I will most likely make a cap here at work then or find a fd . I like being able to fill there though since it's the highest spot .also going to move my temp gauge sender down to the front iron and install my thermal switch for the fan in the t-stat housing

Also have a build thread going in the build section if anyone cares

You honestly do not have to make a cap.
Just bring in the pressurized spring cap into a parts store and ask for a Flat cap the same size.
They are fairly common.
Holy Crap!..Mazdatrix wants 36 bucks for the Filler and flat cap!
I'm rich!..I got like 2-3 of em!..lol.

Meh..make one.heh!!!

Does anyone know what the pressure cap is for in the very front left between the intake snorkel and the front nose? it says don't open or something on it, so i never did. This thread just reminded me that I should know what its for.

http://i58.tinypic.com/vrrmo9.jpg

Radiator cap (It's just not physically on the radiator but same thing).

So as I'm putting the cooling system back together . I got to thinking about temps . What's the average temps I should be looking at now that my temp sensor will be in the front iron . I've had my 18" Jeep Liberty fan wired key on and temps never would leave 160-170ish . Now I'm putting a 170 t-stat (Texas heat, no heater in car ) and a 185 temp switch for fan control . I have custom lower panel and can stick a $1 up to the fmic and it gets stuck so it pulls air for sure lol

S4's are goofy. There's two types of coolant level sensor, one that's just a plastic bolt with a metal tip that contacts the coolant and one that's a brass bolt with an elbow-bend hose nipple like the one pictured. That hose goes to the weird cap up front by the headlight.

If you install an all-metal radiator, you'll have to switch to the plastic type and re-arrange the overflow hose to someplace else or the level sensor will short out to the metal radiator and make your coolant light never come on no matter how low it is.

Whenever I change fluids like oil or coolant, I like to turn the key on after draining it (don't start it!) just to make sure the light and buzzer work properly. These things are nearly 30 years old now... :)

you have the early cooling system with the service kit. they added that second radiator cap to help it bleed air out better

Cool thanks guys. I thought it might be that just kept forgetting to find out. I have drained and refilled coolant on this 7 and have had less trouble getting the air out. But I thinks it cause I've done It multiple times. Now how would I incorporate this radiator cap in the process or should I just not mess with it like previously?

I know it's an old thread, but it had a lot of good information that is related to my current problem. I think I have what is referred to as the "service package": one cap on the thermostat, no cap on the radiator, an overflow line running from the coolant sensor to the overflow bottle, and then a cap (2nd one overall) on the overflow bottle.

Currently, it is set up according to the attached pictures. It looks like I have a pressured cap on the thermostat housing neck. Also, the one on the overflow bottle, is that 0.9 bars of pressure aka 13 psi? So do I have a pressured cap on both?

Thank you in advance.

I wish my memory was as good as when I was younger,as I recall threads about how to get rid of that system.
Ya,it looks like 2 pressurized caps.

So I need a dummy, pressureless cap on the thermostat housing?

whoa that something new to me! does that mean the coolant overflow gets pressurized?? likely to blow out when they rot.

The one by the overflow tank is not factory or dealer add on that I have ever seen. The mismatched hardware looks like a DIY job.

The S4 had two different radiator cap setups. 86-87 had one cap on the thermostat housing with the overflow nipple coming from that location. The 88 has a non-pressurized filler cap at the thermostat housing and overflow coming from the pressurized cap on the radiator.

87 TII

https://cimg9.ibsrv.net/gimg/www.rx7...a784e57304.jpg

88 TII

https://cimg3.ibsrv.net/gimg/www.rx7...197001b8af.jpg

My car (the pictures attached earlier) is an 87 TII and has neither of those setups.

Edit: the reason I am asking is because my coolant buzzer is going off. Could it be because the (improper) pressure cap at the thermostat is causing an air pocket somewhere?

Post a picture of your radiator, I am guessing it looks like the one posted in 2015 which is a 86 radiator. I have seen this type of radiator but not with the additional service pressure cap add on. Since these cars are now nearly 30 years old, it is hard to tell who did what.

If your add coolant buzzer is going off, it either needs coolant or the sensor is bad. You can unplug the sensor and connect the harness wire to ground to test the circuit, the buzzer should stop.

I'll post an engine bay shot this weekend, but, if I recall correctly, it looks identical to j9fd3s's.