As covered in some PFF pages using many current Coolant Pressure Testers on Fiero have problems because has no room to use them with the hood on.
You can find Stant ST255 and ST270 that will attach to the Fiero Radiator on Ebay etc.

But also find Stant 12453 Cooling System Adapter, AKA GM 4 Cylinder System Testing Adapter
I see new ones cost as low as ~ $15 (plus S&H depending on "store.")
You can find it used and New on Rockauto and many more. If used make sure it has the rubber gasket.

Why?
It's the adapter to fit the Thermostat housing.
Ignore Many Descriptions/Doc's by Stant and others only says will fit J and X body cars but in the manual for my ST270 does list Fiero L4 and V6.

I found one at a flea market today to see against T-stant cover to make sure they match.

⚠️ Warning: when you use this adapter... Your max pressure is limited by the radiator cap. If you try to reach Test PSI marked on most tester gauges 1. You can't reach that mark. 2. Your pushing coolant into the overflow tank then on the ground/floor.

Caution: Stant 12450 Cooling System Adapter, Truck Pressure Tester Adapter Kit, looks to have the adapter as well but without right thin gasket.
(Grayed out "A" size Rad Cap test part that come with many complete Stant tester kits on ebay etc.)

Notes:
If you find ST255 with bad hose, test "cap" or gauge... Can upgrade to work as ST270 with 12701 Update Kit. This upgrade may fit other old testers because made by Stant and rebrand for GM AC-Delco or based on Stant design.

If Gauge drops slow or fast and coolant doesn't leak... look for air leaks including in the tester. Tester has a check valve that gets dirty or wear out. To clean/fix that need to take apart "bottom" of the pump body.

While Stant has stopped making some testers or parts you can still get most or all because Stant made Millions of them over 50+ years.

I think you can use other testers w/ same adapter. Setup them as if run on Fiero radiator neck but connected to the adapter. That way you could get "universal" tester from loader tools at AZ etc. and only buy the adapter.

------------------
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

[This message has been edited by theogre (edited 04-30-2024).]

Yes there are "other ways" to pressure test the system....
One problem is Often no way to watch pressure. Common 15-16 psi systems can have "fatal" fails when push to 20psi or more. If doesn't blow out right then, the stress cause by over pressure will be there forever and weaken the system.

The hand pump testers can start seeing many leaks well below the full operation pressure. Often just 1 to 3 psi and many leaks start dripping.
System full of water or coolant mix doesn't take many pumps on the tester to reach full pressure.

Stant and some others also test the caps. Both kits above include "standard" cap test adapter. GM Ford and others use same cap/neck format on millions of vehicles even if many look different to buyers for several Decades.

Some Old Stant/AC you take rad test part off of the pump to test the cap... One I have...


Very Old Stant testers had the pump is directly connected to the Rad. Works but having the pump loaded on the neck can cause problems even tho make before plastic rad tanks because Dumb users pump only w/ one hand etc. Oldest example I know of is Stant T250
https://www.jalopyjournal.c...h-case-sold.1079193/

[This message has been edited by theogre (edited 09-28-2021).]

Stant 12552 Cap Adapter to test Stant 10230 & other "A size" Radiator Caps attach to ST270 tester...


Note that the Adapter can be used either way & have no soft seals.
The cap & tester end often need some clean water to seal the middles.

Top Seals will Not seal because of 2 "notches" to prevent False passing of a test.

[This message has been edited by theogre (edited 04-30-2024).]

Here is the gauge w/ a New Stant 10230 under test... (actually test @ ~ 16PSI but had dry seals so leak some before get a pic.)


Important Notes:
● Some system tests overlap others like 13-14 and 15-16 PSI system zones. That's part of why the Arrows next to the PSI scale. Those arrows are the Maximum PSI allowed to test that system.
● You should Never Reach that Maximum using 12453 Cooling System Adapter as the Radiator cap "pops off" @ 14-16 PSI. The Adapter is to help looking to find leaks under pressure but not be a full test of coolant system.
● Some may think can "force" the cap close by pinching overflow etc often won't work & can damage the hose that never expect to have pressure.
● The "upper" cap seal are not design to have system pressure & "Fail" if you force a test. Only there to control flow to & from the Overflow Tank.

I posted this mainly because many buy used tools & manual is very bad or missing. Others have no clue what marks are or have missing marks on some gauges. This is the ST270 above that many copies the gauge but have a crap manual.

⚠️ Warning: Some Tester kits have "cheap" gauges that are "label wrong" making people think to test > 20PSI. Again, the system may "pass" a test like that but stress cause by them can bit you.
Example w/ warning:


You need a system that handle a bit above the cap "pop off" value but only a bit. not > 18psi as those "cheap" gauges that people think is fine.

[This message has been edited by theogre (edited 05-06-2024).]