I have to go with Tweaked on this one - the thermostat is the key component to controlling the cooling of the engine. The water pump circulates the coolant, but the t-stat is what regulates its flow through the engine and allows the car to be cooled properly. You're taking your engine's life in some shaky hands.

 

Interesting the range of opinions on this (almost as bad as "What octane should I use, and MUST I use 91?"). Removing the t-stat is an old racers trick. They did this to keep the temperature low by NOT allowing the block/heads to heat up. It is not helpful to cool the block that you have a t-stat in there. The thermostat ensures the block maintains a minimum temperature; "regulates" the temps as Jeremy said. But once it opens, it is full flow to the radiator, and it should alternate open/closed right around the set point of the t-stat to maintain the proper engine coolant temp. So I guess, essentially, I disagree with BOTH sides of this argument, as both sides have flaws in their theory.

Without the thermostat installed, the engine will not reach proper operating temperature quickly. This means that the computer will adjust the fuel mixture to deal with the low temps and this will cause long term issues. This was not a problem with the old racers, as they would adjust their carbs (anyone remember those things??) to get the proper A/F ratio at the cold temps. Here, it is a problem long term. So, yes, TLN, you do need a thermostat for longevity.

The thermostat opens fully at the set temperature and allows full coolant flow through to the radiator. It will NOT help to COOL the engine whether it is present and open 100% or just outright missing. The flow restriction of having it there is not enough that the absence of the restriction allows a greater flow, and therefore becomes less efficient at cooling (no one tried this argument, but let's put it aside before someone tries to use what sounds like a "possibly" decent theory). So, no TLN, you do not need a t-stat to help cool the engine.

So, you you need it? Yes. And No. Do you want your car to perform as it should and behave as it should, and last as long as it should? The answer to this matches the answer to the question about whether it should be there. And using the "I live in AZ and we don't need heat" is masking the REAL reason the thermostat is there in the first place. Combustion happens best at specific temperatures, and for a daily driver (regular car) that means at the temperature designed by the motor manufacturer, which can only be maintained by the correct thermostat.

So put it back in.

 

Thanks for the back-up guys.

I will point out that I did make a mistake in a previous post. I wrote "overheat" instead of "overcool." It's been edited. Your car will overcool and run poorly, especially in a hot climate such as AZ. As Mlaubach pointed out, it will cause the car to run rich; when mixed with hot air, it will be a very noticeable difference.

 

Not to mention it will fry both cats from being grossly over fueled, what a knuckle head. Put your thermostat in.

 

Furthermore, excess fuel will wash the cylinder walls of needed oil. Lack of oil increases wear and increases lifespanm (see my comments above).

 

Not for nothing, you posted this thread because you had a problem... tweaked and everyone else are trying to help you. He and everyone else could have just passed this thread by and you would still be wondering how to find TDC on your car. If someone gives you advice take it constructively, don't jump all over them.. and try to prove them wrong, wait for a few more opinions and then do whatever you want.. Just put the thermostat back in.

 

Well said.