Weepy: The Brief Saga of Replacing the Thermostat in the ChevOldsmoBuiac

Last spring, the Girly started to complain that the 1990 Cutlass Ciera's heater wasn't keeping her warm, requiring her to arrive at work more frozen than she started, and more annoyingly, leaving defrosting as an exercise for the driver to undertake. Longer trips would eventually yield hot air, but it required a lengthy sit in traffic rather than a 4 mile lull to the office.

That seemed like a classic lazy or stuck thermostat symptom that could possibly precipitate an disasterous overheating situation. It's easy to fix by swapping the thermostat, a ~$5 part that takes about 10 minutes to replace, yet could ruin the vehicle if left unattended.

So, of course, I let it glide all summer until I had enough of a wish list to include a new one in an autoparts order. Shipping costs totally ruin the fun of buying things online, you know?

Oops.

For the record, I did fix the problem before anything bad happened, at least, beyond mild frost bite. That heals, right? Right.

The thermostat comes out by removing two bolts from the thermostat cover and pulling it back, which releases a torrent of green antifreeze from either side of the union.

I got a stant superstat instead of a standard OEM replacement. It seemed like it would get the heater rolling a little sooner and worker harder to regulate the car's temperature.

The old thermostat looked somewhat better than i imagined. The radiator has a considerable amount of white corrosion inside, but the thermostat and the housing where clean. There was some wear on the body of the old one, and a small gap between the gate and the thermostat housing, but otherwise, it looked functional.

While the parts store stocked a gasket that claimed to fit the car, the thermostat was put in with an RTV silicone gasket. I scraped off the RTV and put the loose fibre gasket on instead, since I had no RTV handy.

I refilled the antifreeze, started the car and let it got warm and the heater worked.

To check my sanity, I dropped the old thermostat in boiling water. The OEM spec is to turn at 195 C. The thermostat waited until 200-210 to turn, then waited until 150 or so to close again. Motion wasn't always smooth. Indeed, the old thermostat was the issue.

After a week of driving, a puddle of antifreeze appeared. Green goo everywhere! The fibre gasket was leaking. I first tried tightening the thermostat cover bolts. A careful exercise since the bolts are iron and the cover and housing are aluminium.

That didn't stop the leak, so I got a tube of RTV and pulled the cover again.

The fibre gasket was a hair small for the bolt pattern on the thermostat housing. When I put the bolts in, it tore the gasket just inside of the crimp line, causing the leak. RTV, obviously, doesn't suffer from these kinds of problems.

I am pleased to report the heater starts producing warm air within minutes.