Thermostat housing cap, which is the proper one? (Page 1/4)
Cliff Pennock JAN 30, 09:16 AM
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?

Thermostat housing caps: https://www.rockauto.com/en...em,radiator+cap,2068
Dennis LaGrua JAN 30, 10:35 AM
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.

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Gall757 JAN 30, 10:59 AM
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.
Cliff Pennock JAN 30, 11:14 AM
But aren't 0 psi caps not just that? That they prevent pressure to build up in the cooling system?
cvxjet JAN 30, 11:42 AM
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).]

theogre JAN 30, 03:40 PM
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.

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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)

The Ogre's Fiero Cave

Cliff Pennock JAN 31, 04:31 AM
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.
theogre JAN 31, 05:42 AM
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 http://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.

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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)

The Ogre's Fiero Cave

Blacktree JAN 31, 10:08 AM

quote
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!
theogre JAN 31, 11:49 AM

quote
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).]