OEM 82* Thermostat and engine temps

[Flank]

As a precursor, this is NOT a "my engine runs too hot" thread. Actually the opposite.

Prior to my radiator swap last year from 20year old OEM to new Koyo OEM clone, my average engine temp on my "permanently" installed Scangauge was 186* to 190*. After the radiator swap and new OEM thermostat, I have been regularly getting engine temps lingering in the high 170s for a while, until settling around 181* during warmed up normal driving. To me this has always seemed too low. A recent conversation with Mike from Frisbee offroad about a possible engine rebuild or swap brought up fuel mileage and engine temps led to the question as to whether running this cooler temp could make the engine run rich to attempt to warm it up more, and lead to reduced fuel mileage.

Suspecting that the t-stat was the culprit, I swapped out my thermostat this weekend while replacing my heater valve and noticed that the thermostats (new OEM and old OEM) have 82* (C) stamped on them, which equates to 179.5* F or basically 180*. This coincides with my current engine temps, but is contrary to my previous temps and expectations due to on Mud.

The only other variable is the koyo radiator. Seldom have I heard the complaint that the rad is running "too cool" and the t stat should take care of that anyway. I'm wondering if I need to switch to a higher temp t-stat.

 

[inkpot]

What numbers were on the old OEM thermostat?

 

[Flank]

82*, same as new. Did not look for part number, but it matched the new perfectly. It was less than a year old.

 

[Tools R Us]

The thermostat controls intake temp, under load the motor will run warmer. When cold, little load, especially with heater use, it can run cooler than thermostat temp.

 

[Elbert]

in general in the winter....engine should run approx the temp rating of the thermostat, all things equal and working properly.....key word "approx".. Depending on where you take temp reading from.....can be some variation. 180F would be in the "normal" range, assuming the Yota OEM thermostat is rated the same or similar.

 

[Flank]

So are you guys saying that there is no need for concern that my engine averages 5* to 9* cooler than what I had thought was nominal, and that that condition won't cause it to run rich?

 

[NLXTACY]

NEW OEM thermostat doesn't match its specs

Yeah I'd say its normal. There have been times my truck runs at 178º if I don't mash on the skinny pedal. My typical right now seems to be 182º. I HAVE noticed that when its this cold the truck does run a little richer because I can smell it.

 

[jeffro109]

As a precursor, this is NOT a "my engine runs too hot" thread. Actually the opposite.

Prior to my radiator swap last year from 20year old OEM to new Koyo OEM clone, my average engine temp on my "permanently" installed Scangauge was 186* to 190*. After the radiator swap and new OEM thermostat, I have been regularly getting engine temps lingering in the high 170s for a while, until settling around 181* during warmed up normal driving. ....

I've noticed the same trend after changing out to a new water pump, replacement of a ~5 year old t.stat, and new hoses, swap to green coolant, etc. Temps were always 186-191 and now about 181 or lower. I'm sure in the summer it will be higher.

 

[NLXTACY]

Been driving for past 20 or so minutes. It's about 40deg outside. Stopped at a red light where the temp just ticked up to 177deg even though it didn't go past 175 the past 20mins.

 

[e9999]

The temp stamp is I believe the opening temp of the thermostat. So the operating temp should tend to stick there until it is fully open, with a band of operation of sorts at relatively constant temperature. If it were a few degrees F below nominal that would not be too surprising, these thermostats are hardly precision instruments. Either you are running just below opening or the combination of low outside temp and given engine load placed the cooling system just smack in the partially open thermostat state. I would not worry about it, I can't believe it would affect your mpg greatly.

 

[Flank]

Up Date / Follow up on this from the original post - The recently replaced (new) thermostat returns temps at 184-186 normally. So my conclusion is the other thermostat returning the 181* temps was bad out of the box.

 

[Flank]

2nd Update: Mileage. I have been averaging 10-11 mpg for the last year or so. With the thermostat change, my last two tanks have been 11.5 and 12 MPG. I have not seen 12 MPG once during the last t-stat. Pulled my 12 ft trailer for work on this tank as well. I'm convinced.

 

[luke 8603]

I have a similar issue after replacing the radiator rarely hitting 175-177 this time of year. Replaced the thermostat when doing the radiator (crappy replacement from advance) I have a flexalite syclone fan which I haven't used in 1-2 months even after sitting at idle for 20 min I barely hit 190 I'm going to replace the thermostat again with oem this weekend and see where I get with that

 

[luke 8603]

It also takes FOREVER for my 97 to get warm

 

[red mud fj]

Been through same as others questing running temperature & replaced thermostats

many times just to see little change.
Just pulled a used one off the shelf and tested it.
It's a 88 C or (88×1.8)+32 = 190 F thermostat .
It started to open at 190, at 205 it was fully open.