Project Fiero Fix Up: Part 3 – Mechanical Fix Up

rear of Fiero

In the last installment we had managed to uplift the Fiero’s appearance but now it was time to move on to some of the mechanical concerns. The overhaul of the oily bits started well, then took a bit of a wild (and somewhat self inflicted) turn.

Fiero V6 engine

First up was a new battery, which our neighbor was able to source for a good price for my son. After the battery was installed we were able to test all the electrical components in depth, as well as take the car for a very brief shakedown run. Next up was an oil change which was a fairly straightforward process. My son had helped perform one on our previous Toyota Tercel so he was familiar with the basic steps. Oddly, the pile of spare parts included a brand new oil filter which did not fit the Fiero. The spark plugs and wires looked quite new so they were left alone. The engine bay was not all that dirty but was given a clean to get it better looking. I have always thought the intake manifold on these Fiero V6 engines is quite attractive.


Not my photo but sourced from

After the oil change was complete it was time to check all the other fluids. First up was coolant, which looked okay. Brake fluid was the same. Then disaster struck when checking the transmission oil level. To do this on the four speed transmission you have to unplug the electrical connection to VSS (speed sensor), unbolt it and pull it out. It contains a gear wheel and a dipstick. When I pulled out the one on the Fiero it came out with a bit of a pop and dropped the plastic gear wheel into the gearbox oil where it floated for half a second before disappearing into the depths of the box itself. Unfortunately, various grabber tools failed to retrieve it. After a bit of research I realized this had happened to a few other people as well. The general consensus was that one could either a) drop the gearbox to retrieve the gear wheel or b) buy a new one and let the plastic gear wheel be ground up by the transmission. The replacement part was said to be extremely cheap. So we went with option b) and a test drive. The gearbox oil level was just fine, as an additional insult.


The test drive ended quickly with the Fiero building up temperature before heading into the red on the gauge. After some diagnosis we determined that the coolant had been filled improperly, and the new looking thermostat was frozen shut. To properly fill the Fiero with coolant, one needs to take out the thermostat, fill the system at the thermostat housing (at the engine end), run the car for a minute, check the level at the thermostat housing repeating those steps until it stays full. The oddities of having a radiator at one end and the engine at the other, I guess. We did this with fresh coolant since it was likely due to be changed. In addition while the radiator fan would come on if I bypassed the switch, it never seemed to be triggered by the switch installed into the engine block itself. A quirk of the Fiero is that the switch does not trigger the cooling fan until it hits the red on the temperature gauge. My son’s car did not even seem to do this. There is a bit of a debate in the Fiero community if a lower temperature switch from another GM car is beneficial, with some claiming it mucks up the fuel injection computer. I ordered a slightly lower temperature switch which was more expensive than the stock one, but seemed worth it. My son sourced and installed a new thermostat that did open and close. The thermostat itself has a bit of extension on it to retrieve when passed down the neck of the housing.

Ugly and temp switch

The coolant was filled correctly and with the new thermostat this appeared to cure the general overheating issue, which was good timing as we were hit with a bit of a heat wave. I hoped the new switch would bring it back to perfect operating condition. When the new “lower temperature” switch arrived, it did work but only when the temperature was into the red range of the gauge or higher. Ugh. To fix this I wired in a manual override switch such that either this manual switch or the temperature controlled one would kick it on. Initially I used whatever I had lying around in a crude proof of concept. This worked a treat so we could buy and secure a proper switch. I suspect one of the reasons the previous owner gave up on the car was this overheating, judging by all the new cooling parts the car had including a nice looking radiator.

Getting tires

Before driving too much, we would need tires first to replace the very old and cracked ones on it. There are a limited number of places to buy 14″ tires these days so we went to a certain Canadian chain that sells tires. Unfortunately, when my son brought it home the car made a clunking sound from the rear passenger side when going around right hand corners. I did a bit of troubleshooting that led to swapping the rear tire sides. This meant the noise happened when turning around left corners now so it was obviously an issue with the tires. I also noticed a rather large and fresh scratch across our newly sourced hood. They also ripped out all my temporary (and admittedly ugly) wiring for the fan override switch for some unknown reason. Due to it being a weekend we had to wait a couple days for them to re-look at the car. Amusingly, when we picked it up the service advisor showed us some wheel weights, looked at us accusingly while stating “this was found inside the tire.” Ummm … yeah … that was exactly part of the job we paid you to do. Sigh. At least the tires were now safe to drive on. Next time they get four rims not a whole car.

Finished switch

We redid the wiring work for the switch which now looked at least 75% less ugly. I used a spare Ikea bracket for mounting it. I have previously used these brackets for motorcycle turn signal relocation and on the wing for the pig themed Toyota Tercel so they are certainly handy.

Broken gear wheel piece

I attempted to order the gear wheel but discovered it was discontinued and out of stock. A Fiero used parts yard in Michigan would have had one but sadly had flooded and closed. I certainly should have verified availability before driving. We drained the transmission oil and were able to get a single chunk out so at least I had a visual reference to compare to. The race was on to source a new gear wheel in order to get the speedometer working again.