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Why is it that aftermarket thermostats don't work properly in our cars?

I don't think they don't work properly; it's probably more a quality control issue. Some third-party thermostats don't open or close as far as OEM, or they do so at a slightly different temperature, or the jiggle valve doesn't operate quite as well, or when they eventually fail they fail closed instead of open, or they don't fit perfectly in the boss, or ... stuff like that.

I think the consensus is you'd probably be okay with an aftermarket thermostat, but it's not clear that the slight change you wouldn't is worth the ~5 dollar savings.

they don't work because most of the ones I've seen are a completely different shape then the OEM units. They are not as deep, do not have the jiggle valve, etc.

The aftermarket ones may have gotten better or more like the OEM ones since I tried one back in 95-96, but that's my experience....

Thank you both for your answers. I didn't realize the aftermarket thermostats would be so different from the original design.

Ummm, I got thinking about the "jiggle valve." Where is it on the thermostat and what does it do?

It's a little metal piece on the outside rim of the thermostat that "jiggles" in its hole, hence the name.

I've always put it facing towards the back of the water pump (close to the engine). I dunno if that's the right location, but I've never had any problems putting it there.

They definitely have a different design. The OEM one looks much beefier and looks to have a larger opening with less restriction, among other things.





I would definitely go with OEM.

Andrew

Definitely OEM. I had three aftermarkets go bad after a few weeks (when they even fit at all). I paid less than $20 at the dealer and they last a long time.

Steve

Thanks everyone for all that info! It really helped!

Yesterday I went to BAP Import Parts and looked at their thermostat for my car, then went to the dealer. Boy, what a big difference! One thing I wanted to add to all the info you've given is that the weight of the Subaru thermostat is about 2 to 3 times heavier than the aftermarket. In fact, I remember having this grin on my face musing that the OEM thermostat is going to take away from the handling of my car.

BTW, before going to BAP I already made up my mind (based on all of your input) that I was going to get an OEM unit. But BAP usually sells better quality parts than other chain auto parts stores and based on Josh's comment and Andrew's photos I wanted to see how close the latest aftermarket unit came to the OEM unit. The thermostat BAP had seemed better (deeper and bigger opening) than the aftermarket unit in the photo but still the OEM unit is clearly a better unit.

I just have two more questions, What is the jiggle valve for and should should the thermostat be installed with the jiggle valve facing in any particular direction for maximum efficiency?

The Jiggle valve is there to help let trapped air out.

As for circular orientation/position of the jiggle valve, I don't think it matters.

As I stated above the T-stat will only work one way. The housing won't fit if you install it backwards.

Molto gratzi!