After much searching, several wrong vented caps from the various chain auto parts stores,(and spending several hours in parking lots waiting for the car to cool off enough to put more water in the cooling system :P), I found a local source for the proper non vented radiator cap at Napa. I didn't find this in the numerous threads in searches, although it wouldn't be the first time I've missed it somewhere.

Part number 703-1698, 16lb non vented cap, boxed (as opposed to the shrink pack hanging package). This is actually listed on Stant's website as an equivalent cap to the 10230 (with the 11230 being the same cap, only in the hanging card packaging instead).

I previously had a Murray/Motorad 7616 cap from Oreilly's on the car, which is listed as a "16lb standard" cap, and has "16V" stamped into the cap. Worked fine around town, although I did notice that it didn't seem to hold a steady temp....would cycle between a little below to a little above the 1/4 mark on the guage, back and forth. But a longer freeway trip, like the few I took to the other side of the valley, about 30 mins at 65-70mph resulted in the temp gauge seeming normal on the freeway, but as soon as I stopped at the end of an exit ramp, the gauge very quickly went to the 1/2 way mark, but came back down just as quickly once I got moving again. Both trips were equal - approx 5 mins of surface streets after the freeway, then the car getting well past the 1/2 mark within a couple minutes of slowly cruising through a parking lot, followed by coolant overflows from the recovery bottle. Once the car cooled down, I'd be about a gallon low on coolant.

I also noticed that the cap spun on and off the radiator (radiator new a couple months ago) fairly easily. Didn't really take a notice to it until today when I installed the Napa cap, that took a bit more effort to get it past the first "notch" so to speak. I haven't driven the car yet with this cap, but given that Stant lists it on their site, I'm confident that I finally have the right cap.

I hope you fill and burp the coolant system properly (for a Fiero). This of course entails filling up the system using the thermostat cap opening. Proper filling procedure can be found easily enough here if you don't know it.

quote Originally posted by Patrick: I hope you fill and burp the coolant system properly (for a Fiero). This of course entails filling up the system using the thermostat cap opening. Proper filling procedure can be found easily enough here if you don't know it.

Wait...so I'm not supposed to assume that I know better than the guys who designed and built the car, thus ignorning that label on the decklid that says the car has a special coolant fill procedure?!?!?!? :P

You DO know better! Those guys are all disgraced and have become consultants at Kia....or was it Chery?

[This message has been edited by Gall757 (edited 12-10-2012).]

Quickie update - Ran the car down the freeway last night, approx 35 miles each way, at 75-80mph the whole way. Gas mileage SUCKED (guess I should have gotten a car with a 5 speed instead of the automatic, lol), but not a lick of problems from the cooling system