So my thermostat went out on me…thankfully it’s stuck open. Unfortunately it’s killing my MPG. But I was looking on ZXtuner and it was the same price for the “Low Temp” and “Extra Low Temp.” Which would y’all recomend? I know they say the Extra Low is for High HP apps…which I know I don’t have, but would it hurt, or should I just stick with the Low?

  • Darron

I got a low temp one, haven’t installed it yet, but I really don’t need a new one at all, my engine isn’t that hardcore. Besides I want to get the uber low temp anyways. Rob gave me a deal on it, so if you want it Foos, its yours.

As in free, I’ll just mail it to ya.

Talk to Rob and confirm this…

I believe by adding the low temp thermostat will produce a cell. I’m almost certain, but check just in case.

According to the website, a CEL is only an issue on older (2nd gen) cars. I think I’m just gonna get the “low” not “Extra low,” just in case that is what killed my MPG last week. I think it was a combination of cold weather and bad thermo, because it’s a li’l warmer now and I seem to be getting better MPG at this point. I think the problem was the engine wasn’t able to heat up enough to function properly.

  • Darron

So you want the free thermostat? I’m serious, the current one in my car is like brand new, and I’m like 10 months away from my annual flush.

THat would be Hella tight.

  • Darron

I commute 262 miles round trip everyday in the Fanta…
I used the 170* temp for 2 days,mpg loss of 6-8 and threw a CEL…(ECT low)
I used the 180* temp next for a week… mpg came up to a 4-6mpg loss…
Engine Coolant Temp Low code is triggered @ 176* I believe

I put a stocker back in,no CEL and my mpg went back up to 36-39,ran better and heater was much warmer…

The engine and comp need a certain temp to fuction properly,
Good luck,
keep us updated…


Hmm. Well, Foos I just send you a PM, but what do you think? Willing to loose the few MPG?

btw Mac, you HAVE to upload images of the Fanta in our gallery. I love the look of an 03 front with the WW.

I did not meen to poop on nobody’s parade…

It’s something I learned the hard way…(as most of what I learn has come to me)


The MPG with the lower temp thermo’s is expected. When the engine is cold the pcm sends more gas into the cylinders to heat it up. This in turn creates more combustion in the chamber. More power is then created, that is one of the reasons a low temp thermo is good for power applications. It also lowers the engine temp(duh) allowing the engine to run harder with out the extra ware

The Zetec runs fairly cool anyways, so unless you have something that generates a lot of heat in your engine (FI), you don’t really need a cooler thermo. Mazda 6s pull timing like crazy at 200*, so you want to get a cooler thermo to keep the timing up.

I don’t know when the PCM on the Z starts pulling timing, but it doesn’t seem very drastic, and people that datalog don’t have any major issues with the PCM pulling timing, so yeah. Stock is pretty good for most applications.

You can get the 180* thermo from autozone for like 4 bucks. Also I have never had a 180* thermo through any codes. Know the 160 I had through enough that I pulled the CEl out of the cluster. :smiley: But the power was bad ass. But mac and Roush are rite about the gas millage.

I have a 1999 zx2 with 180 degress thermostat , its been in there 60,000 miles , no problems. The only thing that sucks about a low temp thermostat is that the tempature of the heat that the heatercore produces makes winter seem even colder!!! brrrrrrr.