Temp rating for an OEM thermostat?

otter63 · Post by **otter63** » Sat Jan 06, 2007 1:58 am

I have searched the archives, and found some discussion, but noone specifically has said what the stock thermostat temperature rating is. And the dealer's parts guy didn't know either . . .

takza · Post by **takza** » Sat Jan 06, 2007 6:17 am

I've heard 170 or 180...I have a new one (not installed) that is supposed to be a 192. They don't seem to stamp them.

otter63 · Post by **otter63** » Sat Jan 06, 2007 4:54 pm

takza wrote:I've heard 170 or 180...I have a new one (not installed) that is supposed to be a 192. They don't seem to stamp them.

Here's something I found in the archives:

I was considering trying out a 192F thermostat that should help improve MPG some, but found that the elect fan starts running at 194F and shuts off at 181F....so using a 192F thermostat would cause the fan to start going and never shut off while the car is running...since the coolant would never get below 181F.

If that's the case, I wouldn't put in the 192F thermostat.

It seems like the fan is trying to cool down the coolant to about 181F. If a 180F thermostat is used, the coolant should stabilize at between 180F and 181F. So i'm guessing that 180F is the correct temperature thermostat to install. Anybody agree, disagree, or know for sure? Thanks!

takza · Post by **takza** » Sat Jan 06, 2007 6:03 pm

I'm the one that wrote that...and it might even be true!

I have a new thermostat...so I'm hoping it isn't a 192...doesn't have anything stamped on it.

If I'm right...then 180 sounds like the one to use.

Then again...maybe 170 would more likely keep the fan from running?

I'm assuming that 170-180 is the temp where the thermostat is fully open.

otter63 · Post by **otter63** » Sat Jan 06, 2007 9:57 pm

OK, I'm back home now, and I found some specs, but they're from the Toyota 1984 Tercel Repair Manual. If anyone has the 1986 manual, please check & let me know if they're different.

Thermostat valve starts to open at: 176 - 183F
Fully open at: 203F

Note that if you look for this info in the 1985 version of the manual (posted on the tercel4wd home page), this info is actually missing due to a misprint.

So it looks like we're good to go with a 180F thermostat . . .

P.S. I also checked the fan start/stop temps you provided, and they're correct!

Post by **ARCHINSTL** » Sat Jan 06, 2007 10:03 pm

The '86 FSM has the identical info.
Tom M.

otter63 · Post by **otter63** » Sat Jan 06, 2007 10:11 pm

Thanks, everyone!

Together, we are awesome!

Jts · Post by **Jts** » Tue Jan 09, 2007 2:31 am

with the way the coolant bypass tube works, doesnt it seem that a 192F thermostat will still generally run well below 192?

takza · Post by **takza** » Tue Jan 09, 2007 5:18 am

192*.... valve starts to open at: 189 - 195F
Fully open at: 215F ?????????

I'm not sure what the bypass tube actually does. Or what effect it has.

I'd have to assume that the temps the rad sees in warmer weather are going to be around 12* higher than with a 180 thermo....so the fan is going to run more?

Typrus · Post by **Typrus** » Tue Jan 09, 2007 10:17 am

Everywhere I've seen indicates 180 is factory. Hotter and colder are available.

Any way to "trick" the fan into starting hotter/colder and turning off the same?

takza · Post by **takza** » Tue Jan 09, 2007 5:08 pm

You can add some resistance to some fan switches...the one in the Tercel defaults to ON...and if I remember right is difficult to modify.

It just switches on/off and works in a way I'd call ......... BASSACKWARDS! When there is continuity...the fan switches off.

Might unscrew it...plug the hole...epoxy it to the outside of the radiator?

neonsport · Post by **neonsport** » Fri Jan 19, 2007 2:55 pm

I could've told you last night, but I didn't write the temp down when I installed the new thermostat. It was stamped, in celsius. My heater works much better now.