Does replacing the thermostat increase MPG?

[radlynx]

Did anyone replaced their thermostat and noticed an increase in MPG? I have 2005 4runner v6 and I used to get 20-21MPG and now it's down to 17.5 mpg. I have around 95000 miles and the coolant was never replaced since it was new including the thermostat.

please post if you have previously did this. So far, i replaced the air filter, spark plugs, and to no avail. everything is stock with the car. Thank you in advance. I need some advice please.

 

[MikeInNH]

If you put a cooler thermostat then what the standard thermostat is...then yes it can effect gas mileage.

 

[Ventil8]

I have the V6, and also USED to get around 20-21mpg, I'm getting about the same as you now, around 17.5, hand calculated. I've done spark plugs, air filter, sea foam, cleaned the mass airflow sensor to no avail. I'm stuck. My 4runner is pretty stock, with the exception of spidertraxx spacers which have been on for about 10 months and I've been at the same mpg before the spacers went on. I've done all the scheduled maintenance, I'm figuring she's just getting old.

 

[nevada]

that's typical for the winter.

 

[A10GAC]

A thermostat that is bypassing or stuck open will affect mileage. The thermostat in my car had a bad seal, coolant was able to bypass the closed thermostat allowing nearly full flow to the radiator; with the winter temps, the motor wasn't able to come up to temp and ran rich...the result was a 4mpg loss. Replacing the thermostat solved the issue and mileage is back to normal.

A 10%ish loss in mpg isn't unheard of with the combination of "winter blend" gas they switch to here in New England and added time spent defrosting the vehicle.

 

[littlehandegan]

Is there a way to tell, or check to see if a thermostat is bad?

 

[daka320]

Just replaced my thermostat along with a new radiator and external transmission cooler. Beefing up the girl to tow a 5000 lb travel trailer. Been thru a few tanks of gas and do not notice any difference.

I use a OBD 2 reader and the Torque android app to monitor various parameters while towing. One of those I monitor is the coolant temperature. Normally around 195-200 degrees Fahrenheit. App is less than $5 (get the pro) and the reader off of Amazon is less than $20. Cheap insurance for me to see what is going on!!!

 

[Troymclure]

Is there a way to tell, or check to see if a thermostat is bad?

Your truck will run very cold, and wont get up to normal operating temp. It will most likely stay within the first 1/3 of the gauge from the cold side.

 

[Sungod]

Is there a way to tell, or check to see if a thermostat is bad?

Take it out and put it in hot water. At that point you might as well replace it.

 

[radlynx]

Thank you for the info. I appreciate it. What I knew before is that even in the winter time, my MPG was always constant 20-21 MPG. I don't warm up my car at all, I just start and drive normally. I'll try this in a couple of weeks and report back the progress for everyones' info.

A thermostat that is bypassing or stuck open will affect mileage. The thermostat in my car had a bad seal, coolant was able to bypass the closed thermostat allowing nearly full flow to the radiator; with the winter temps, the motor wasn't able to come up to temp and ran rich...the result was a 4mpg loss. Replacing the thermostat solved the issue and mileage is back to normal.

A 10%ish loss in mpg isn't unheard of with the combination of "winter blend" gas they switch to here in New England and added time spent defrosting the vehicle.

 

[littlehandegan]

Just replaced my thermostat along with a new radiator and external transmission cooler. Beefing up the girl to tow a 5000 lb travel trailer. Been thru a few tanks of gas and do not notice any difference.

I use a OBD 2 reader and the Torque android app to monitor various parameters while towing. One of those I monitor is the coolant temperature. Normally around 195-200 degrees Fahrenheit. App is less than $5 (get the pro) and the reader off of Amazon is less than $20. Cheap insurance for me to see what is going on!!!

Care to share what OBD 2 reader you use from amazon?

Thanks!

 

[daka320]

Care to share what OBD 2 reader you use from amazon?

Thanks!

LYL® Vgate ELM327 v1.5 Bluetooth Mini Small Interface OBD2 Scanner Adapter Torque Android

Sells for $12. Works good. Figured I would try a cheap one to see if it works instead of investing $$$ in an expensive one. Reviews on it are good.

 

[Supersonic]

Found a couple of post here that relate to Toyota Readiness DTC p0125 -coolant temp too low, seems my temp may be operating low by 10 degrees and my gauge does stay in the bottom 1/3 of the normal range indicated by the widening line on the gauge. I'm sure I've seen other post that say around 185 is normal so I'll keep looking into that.

One of those I monitor is the coolant temperature. Normally around 195-200 degrees Fahrenheit.

Your truck will run very cold, and wont get up to normal operating temp. It will most likely stay within the first 1/3 of the gauge from the cold side.