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).]

While I do have a pressure testing kit for many different fittings, a cheap and dirty test I do with fieros is disconnect the hose to the overflow tank hose and introduce low pressure air.

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).]

Found another tester today... (Very cheaper used one)
mityvac mv4560 will test more systems and caps and are cheaper then many others.

And...

Will work w/ above adapter to work on Fiero and other w/ same T-stat house.

Based on their normal plastic vac pump and far easier to pump w/ one hand. But If the system has a lot of air, will take longer to pump vs Stant testers.

Says available @ amazon and pictures are correct but description is Way Wrong...
Stores maximum compression value for up to 12 cylinders
Backlit LC display is easy to read from any angle and in any light
Uses standard 9V battery for convenience and cost
Automatically shuts off after 3 minutes of non-use (memory is retained)
Rubber boot protects the gauge from bumps and drops

Wrong because have No LCD or bumper.

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).]