I know the Fiero needs a non-vented thermostat housing cap, but if I look at the caps at RockAuto, all I see are vented caps (16 psi or 0 psi). Or am I understanding incorrectly and are the 0 psi caps non-vented?
Stant 10232 or AC Delco 12R 16. They do show up on the Rock Auto search. The key is that these are flat caps with no spring on them.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
RockAuto has included both the thermostat cap and the radiator cap in one table, which is confusing, but yes, the caps that say '0 psi' are in fact thermostat caps and not vented.
There is actually no "Pressure rating" on the Thermostat cap; IT has no ability to release pressure (Automatically) If you look at the different caps, the radiator cap has a spring which is part of the pressure release, while the thermo cap has no spring...It does have a rivet that holds the cap-seal together. The "0" rating means it has no ability to release pressure (They should really have stated "Not Applicable")
The other thing that stands out is that the radiator cap has bumps for leverage, while the thermo cap is smooth.
The Stant number for the Thermo cap is 10232.....Here is a pic of it;
It is available on Amazon and Summit racing- but is also probably available thru your local auto parts store.
[This message has been edited by cvxjet (edited 01-30-2022).]
Yes, Thermostat Cap is "non-vent" and "0 psi" because is not connected to "overflow" outlet.
That is for Radiator Cap job. and "vent" vs "non-vent" is in my Cave, Radiator Caps
Get Stant Caps. ACdelco is likely Stant at high $ and nothing to show for this and most others. Only thing I push is ACdelco Battery cables because only ones made same as OE cables. (Not crap lead battery ends nearly all others use.)
Order 2 of each and keep second as spares.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
My car is still losing coolant but I don't see it leaking anywhere. No puddles under my car, the oil is not milky, and exhaust gas is "normal". So I am beginning to suspect either the thermostat or thermostat housing cap are defective.
Temperature fluctuates quite a bit. I'll be driving and see temps quickly go up to 230F only to drop to 175 in a matter of seconds. So I'm thinking the thermostat stays shut until pressure gets too high causing it to open, and in turn causing the coolant to violently boil, causing it to vent coolant through the thermostat cap? Looking at the top of the cap, I see rust all around the little center disc.
OE and most other T-stant Will Cause temp swinging like that. Worse in cold weather because Fiero has ~ 14qt or ~ 13l of coolant that can take a lot of driving to heat up. System May Never equalize on short trips, < ~ 20mi, or in very cold weather. Most cars and many other have only 4-7qt or 3.8-6.6l of coolant to heat up.
Stant Supertant in cave should help stop that or have less range of engine temp because may look same but temp curve is different so T-stant opens/closes slower and doesn't slug the engine w/ cold coolant.
As to leaking... You need pressure test when cold and look everywhere. See https://www.fiero.nl/forum/Forum2/HTML/145505.html Heater core can leak and unless you look at P-side floor then not going to find it leaked. L4 and V6 Engines can leak internally and may not show up in oil turning colors. Example: For L4, #4 cyl likes to suck coolant w/ bad intake gasket. To find often pull spark plugs and #4 is cleaner/different then others. V6 has coolant "pipe" in the intake and throttle body too and could have similar problems. Finding depends just what is leaking. Pulling plugs may help or not.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Originally posted by Cliff Pennock: My car is still losing coolant but I don't see it leaking anywhere. No puddles under my car, the oil is not milky, and exhaust gas is "normal". So I am beginning to suspect either the thermostat or thermostat housing cap are defective.
I would suspect the radiator cap. If it isn't sealing properly, it will allow coolant to drain out through the overflow tank, while you're driving. This has happened before, to me. When the engine warms up, it pushes coolant into the overflow bottle, until it overflows and dumps coolant onto the ground. Then when the engine cools off, it pulls the coolant (and some air) back into the cooling system. Then it gets an air bubble in the cooling system. It constantly loses coolant, because some of it drains out every time you drive.
You can check to see if this is happening. First, make sure the cooling system is full and the overflow tank is filled to the proper level (with the engine cold). Then, start up the engine and let it idle until it warms up. If the overflow tank fills up and starts overflowing, your radiator cap is bad.
If you need to replace the radiator cap, make sure to get one with a spring-loaded check valve. Some parts manuals incorrectly specify a radiator cap without the spring. That will cause the overflowing problem you're trying to fix!
Originally posted by Blacktree: I would suspect the radiator cap. If it isn't sealing properly, it will allow coolant to drain out through the overflow tank, while you're driving. This has happened before, to me. When the engine warms up, it pushes coolant into the overflow bottle, until it overflows and dumps coolant onto the ground. Then when the engine cools off, it pulls the coolant (and some air) back into the cooling system. Then it gets an air bubble in the cooling system. It constantly loses coolant, because some of it drains out every time you drive.
You can check to see if this is happening. First, make sure the cooling system is full and the overflow tank is filled to the proper level (with the engine cold). Then, start up the engine and let it idle until it warms up. If the overflow tank fills up and starts overflowing, your radiator cap is bad.
If you need to replace the radiator cap, make sure to get one with a spring-loaded check valve. Some parts manuals incorrectly specify a radiator cap without the spring. That will cause the overflowing problem you're trying to fix!
Not Quite right... 1. The system is made so when hot, coolant and air Will flow out to the overflow tank. When cool again, Will suck coolant Back and Without Air. (And why "burping air out" during filling is pointless.) 100% of vehicles with O-tanks work the same way.
2. Fill lines on the O-tank is for checking Hot coolant systems for Fiero and Many Other Models and Brands. Note that a Hot system may still have a cool/cold O-tank. So don't bother w/ actual temp of coolant in the O-tank. Do Not over fill when system is cold. When cold, treat Add line as Full line then check again when system is Hot. In Winter, that can be hard for same reasons OE type thermostat making gauge swinging I posted above.
If system have issues... System Can suck Air back in. With or Without leaking coolant out. Iffy hose joint(s), WP Seal, T-stat cap, O-tank tube or Rad cap can all do this. Even the engine and parts bolted to in can do this because sucking air is way easier then sucking coolant for O-tank.
If you think have air leaks and O-tank isn't Full line or higher when cold... Mark the tank and see if level charges cold to hot then cold again. If level doesn't change then system has air leak problem and can't purge air out and radiator and maybe more have air trapped.
Worse if level gets lower after heat cycling because w/o obvious leaks, Engine has likely Internal leaks covered above.
At any rate... I recommend Both caps need replacing and why said order 2 each to have spares. Maybe 3 T-stat caps because often get "wrecked" because of rust "eat" the housing flange. I coat the entire flange w/ Permatex Brake Grease and rust still tries to eat this part. Maybe because mild steel housing w/ SS cap body cause dissimilar metal rot. And replace T'stat w/ Stant Supertat See my Cave, Radiator Caps and Thermostat
[This message has been edited by theogre (edited 01-31-2022).]
I described a problem I had with the cooling system in my Fiero, and how I fixed it. I offered that story, because Cliff's problem sounds familiar. He can easily test his car, to see if it has the same problem.
If you want to nit-pick minutiae, that's up to you. Have a nice day.
It's quite different from the old cap. The old cap seals 100%, it has no pressure release valve or anything:
The new cap however, has a middle part that moves up and down. Meaning it doesn't seal at all. It is indeed a 0psi cap. So it is a vented cap. Also, since the thermostat pushes up on the cap, the middle part is always open.
So which cap is the proper one? My old or the new cap?
The one you just received is the Thermostat housing cap, in the engine compartment. Your old cap you pictured is a radiator cap in the front of the car.
Oh shoot my apologies I was looking at it on my TV across the room and wasn't paying close attention. The one you ordered with the spring is a 'non-vented' cap and the correct radiator cap. The one you're replacing without the spring is a vented radiator cap and not the correct cap.
I just looked it up in the official Fiero parts list, and the RC40 (my old cap) is the car´s original cap. my new cap (Stant 10232) is an open vent cap.
I also looked up several threads here on PFF about the cap and just about everyone is using the Stant 10232 which is the wrong cap. I'm guessing that if you use the open vent cap, you're losing a lot of coolant as steam and the radiator cap never opens.
Okay if your new cap is a 10232, doesn't have a spring, then it isn't the correct cap to my knowledge.
The caps I buy for restoration Fiero's that I flip for resale are #10230 caps (i believe is original P/N # and are hard to find these days) and also #10409635 (which is current last I checked) and I never have issues. These caps have a noticeable spring installed on the underside, but are considered 'non-vented' caps.
I think you're talking about the radiator cap, since the 10230 is a radiator cap and not a thermostat housing cap. The thermostat housing cap doesn't have a spring so it's either a closed cap, or an open vent cap. A closed cap is what is required, an open vent cap is the incorrect one. The Stant 10232 is an open vent cap.
I probably need something like the Gates 31313 since that looks like a closed cap.
The Thermo cap should not vent at all- that central rivet should be TIGHT. You may have a bad one (Defective) There would be NO reason for any cooling system cap to vent at 0 psi- you want the cooling system under pressure. Send that cap back and have them send you another.
I want to add that the Gates 31313 is the correct diameter; 2.86" as stated on the Jegs website, and I measured mine (Stant)
[This message has been edited by cvxjet (edited 02-05-2022).]
The middle parts (arrows) can move up and down. I can actually blow air through it. Like I said, I remember reading somewhere it is supposed to work that way.
Someone else here with a Stant 10232 who can confirm the middle part is moving?
It's done like that cliff it's to be able to compress it to pass the thermostat housing lock and not break the cap gasket Try it on the thermostat housing and when it is screwed in place you will find that the rivet on the top of the cap no longer moves, it is compressed and there is no leak. It is the correct cap that you have Stant 10232 0 pressure means that it does not open under pressure A radiator cap ex: 16 lbs means that it will open at 16 lbs to let the pressure out of the radiator so as not to blow the radiator
Originally posted by Cliff Pennock: I also looked up several threads here on PFF about the cap and just about everyone is using the Stant 10232 which is the wrong cap. I'm guessing that if you use the open vent cap, you're losing a lot of coolant as steam and the radiator cap never opens.
No. Is Not the Wrong part and you Won't leak Coolant using it. (Unless the T-stat Housing is damaged...)
Stant 10232 is the T-stat cap and is 0PSI and "Non vented" but those terms Does Not Apply to this Cap. Those entries Only likely to fill in spaces in the databases to make Stant Catalogs but Mean Nothing to this cap.
GM RC40 Is T-stat cap. Old one is make so nothing will move/rotate means made to an old design. And often easy to get damage because seal fights you turning the cap on/off.
Nearly All Stant "Radiator" Caps including 10232 are made so the "guts" including all seal(s) can rotate relative to the top to make them easier to install and remove. Stant sell this feature under "SWIV-EL®" logo/brand and that Trademark is often on Older box/package.
Old Blister packs had it too.
Stant "SWIV-EL®" feature Has Nothing To Do with a Cap is Vented or Non-vented.
GM RC40 Is T-stat cap. Old one is make so nothing will move/rotate means made to an old design. And often easy to get damage because seal fights you turning the cap on/off.
Oh man, those old thermostat caps were awful! The rubber seal would practically bond with the top of the thermostat housing, and because the cap couldn't rotate independently of the seal, they were a total b!tch to remove. That's when the big ol' pipe wrench would need to come out.
[This message has been edited by Patrick (edited 02-06-2022).]
Many keep small oil filter or other band/strap wrench for that.
Even w/ Stant "SWIV-EL®" T-stat cap can be hard to remove and/or install. More so for people install them without coating the flange with silicone or permatex brake grease.
Rust love attacking there because SS cap and mild steel T-stat house and no clearance so seize up easy.
Do Not use other oils/grease for same reason don't use on brake parts.
E2A---> Stant new web site and recent packages seems to drop SWIV-EL marks. I have both caps bought 5+ years ago w/o the mark. I look at then today to get a better pic then above. Stant web is useless and parts lookup doesn't work when you find that thru google. Stant was sold a few year back. Many think Motorad took but few sources should know said no but different private group. (Motorad makes nearly all "store brand" caps and own label too. Rad caps are ok. "Fiero type" T-stat would fit some T-stat housings.)
[This message has been edited by theogre (edited 02-06-2022).]
The Stant SWIV-EL® radiator cap design allows the cap to be installed and removed much easier than conventional radiator caps, because the shell of the cap rotates independently from the upper sealing gasket, stem and bottom plate. The octagonal shape is easier to grip than the round OEM design, too.
Stant SWIV-EL radiator caps have been designed to function on older open cooling systems and overflow reservoir type systems.
Note that shape often isn't octagonal but "standard" shapes as other types. Even the "SWIV-EL® Radiator Caps" DL shows a "standard" top.
While doesn't show on recent packages... SWIV-EL is a Live TM at USPTO... uspto.gov trademark, search, Word Mark SWIV-EL Registration Date March 19, 1991 Renewal 3RD RENEWAL 20210622 Live/Dead Indicator LIVE
Originally posted by theogre: Old one is make so nothing will move/rotate means made to an old design. And often easy to get damage because seal fights you turning the cap on/off.
Nearly All Stant "Radiator" Caps including 10232 are made so the "guts" including all seal(s) can rotate relative to the top to make them easier to install and remove. Stant sell this feature under "SWIV-EL®" logo/brand and that Trademark is often on Older box/package.
Awesome. Makes a lot of sense. I'll reinstall it. 😊
1985 Pontiac Fiero Service Manual, Section 6B, page 2, states " A pressure-vent cap is used on the cross-flow radiator to allow a buildup of 103 kPa (15 psi)
Originally posted by wilberto: 1985 Pontiac Fiero Service Manual, Section 6B, page 2, states " A pressure-vent cap is used on the cross-flow radiator to allow a buildup of 103 kPa (15 psi)
is irreverent here as is not the radiator cap he replaced a week ago...
I don't think I've ever seen a thread here with so much confusion involving thermostat housing and radiator caps! It's knee deep in erroneous comments. lol
That's when the big ol' pipe wrench would need to come out. 
lol
