Thermostat: 180 or 195?
 

My Metro's G10 seems to be lacking a thermostat as it will not heat up, so I went out and bought one. I got a 195 degree model on the theory that the engine would run more efficiently at a higher temperature. However, this does have me wondering if I am correct? Would the 180 have been the better choice? I'm curious if anyone has ever done A-B-A testing on this before and if it makes any real difference at all.

The 190° thermostat would be the right choice.

My 1994 FSM calls out for a 190°. Always use the correct one for the cooling system design wherever possible.

The XFI used a 197°F thermostat. That is likely the "Replacement" you got.

180° is not appropriate. Fuel consumption will be higher, and power lower running at a lower temperature.

The 195° thermostat will likely work just fine.

CJ

i changed my thermostat a while back to a hotter one and ive noticed it got a little bit better fuel economy and some tiny bit more power. no a-b testing though sorry but can try if you want

Sadly I have no real A to speak of or I would try to quantify the change myself. I know my car should pick up a substantial amount of FE because without the thermostat the engine would not warm up sufficiently for the ECU to go into closed loop operation. Thus, no O2 sensor data and a constant limp home mode. I am hoping to see another 5 mpg when the car goes back into service next week ( $250 cars tend to need a bit of help to become reliable!)

For mpg, warmer is better. For power, warmer engine with cold air is best.

They make a 205* t-stat for V8 chevys, I used to run one in my 4.3L S-10year round up here in Wi. w/ no problems. You might be able to adapt that for winter use w/ alittle grinding on the stat.

from the drag racer book-of-rules-of-thumb: colder thermostat= more power/worse FE. warmer=more FE/less power. Run stock unless you've got a good reason otherwise. unless that reason is other mods, fix the problem making you do something other than correct.

In many cases, that's true. However, if you can up the t-stat temp without increasing air intake temps (dependent on manifold design), you get even better power due to keeping the dense air charge and increasing the engine's thermal efficiency.

i went from a 205 thermostat to a 180 because i had a overheating problem and that took care of it, and from what i understand you don't need a lower thermostat because your engine isn't getting to temperature anyway. on the other side i think i'm going to go with a 165 degree thermostat cause i'm going to add a electric fan to my jeep and set it for 190 on 180 off

p.s. I read that for every 10 degrees in engine temperature decrease is another 1/4 to 1/3 a compression ratio increase you can get with the same unleaded fuel(to a point of course) and every 8 degree decrease in intake temperature is one point decrease in octane level required for increased CR

Stovie - Stock t-stat in your Jeep is a 195*. Going colder than a 180* will most likely trip a CEL for running too cold, and isn't good (nor is there any benefit). If you do an e-fan conversion, set it to kick on around 200* and off around 190* with the 180* t-stat.

Also, dropping to a colder t-stat doesn't fix an overheating problem unless the old stat was bad. It can simply band-aid it by allowing more time before it overheats, which typically allows time to get moving again (if it's an issue in traffic). ZJs are known for running hot in traffic, particularly with the A/C on. As long as it's no more than 1 tick mark to the right of center (just over 220*), it's not even a slight concern. If it hits the 3/4 mark (235*), then it's time to worry.

For comparison, with a 195* t-stat, mine runs 200* when cruising, up to 205* in hot weather. It'll hit 210 - 215* in traffic in the winter (mine's an e-fan, being a 5.9, so the fan cycles). In the summer, however, when the A/C is on and trips the fan sooner when stopped, it runs under 210*. It barely touched the 210* mark when climbing a hill last summer in 105* weather. It stayed around 205* when crusing, 207 - 209* when in traffic. Keep in mind that I'm putting the heat of a much bigger engine through the same sized radiator that you have. If your cooling system is up to par, it should have no issues, and shouldn't get over 215 - 220* idling in traffic with the A/C on, even in 100* weather with the mechanical fan.