Topic: Can a new thermostat increase your MPG?

[ChippK8]

My F150 had been running a little on the HOT side for the past few months, not overheating, but getting kinda close tot he red.  I drive mostly on the highway, so it was really only a problem after getting of the highway and then having to wait at red lights.

So, a couple weeks ago I changed out my thermostat, did a coolant flush and added new anti-freeze. It stays consistently on the 'O' regardless now.  This may just be wishful thinking on my part, but it seems that I get about 2mpg more than I did before, even before I had the heating problems.  The most I had ever gone on a fill up before was about 500-515 miles.   I filled up last Monday and have gone 560 miles and probably still have a gallon or two left in the tank(s). 

Seems like it would make sense,  more heat means more thermal expansion of the metal and more friction. 

I may just be crazy and dreaming.     

[edbikerii]

Electric fans running all the time because the engine is running hot use electricity, which must be generated by the alternator, which runs off the engine, which uses gas.  I doubt if the electric fan is worth 2 mpg, but it certainly contributes.

Come to think if it, an old-style mechanical thermostatic clutch fan consumes more fuel when engaged, too.

My F150 had been running a little on the HOT side for the past few months, not overheating, but getting kinda close tot he red.  I drive mostly on the highway, so it was really only a problem after getting of the highway and then having to wait at red lights.

So, a couple weeks ago I changed out my thermostat, did a coolant flush and added new anti-freeze. It stays consistently on the 'O' regardless now.  This may just be wishful thinking on my part, but it seems that I get about 2mpg more than I did before, even before I had the heating problems.  The most I had ever gone on a fill up before was about 500-515 miles.   I filled up last Monday and have gone 560 miles and probably still have a gallon or two left in the tank(s). 

Seems like it would make sense,  more heat means more thermal expansion of the metal and more friction. 

I may just be crazy and dreaming.     

[333]

Come to think if it, an old-style mechanical thermostatic clutch fan consumes more fuel when engaged, too.

I had a 74 Chev that I converted to an electric fan from a clutch fan.  I neutral, you could hear it rev faster, and in driving it you could certainly feel the difference in power.

[eldar]

A clutch fan pulls a LOT of power from the engine. AN electric fan is the way to go.  Iknow a lot of trucks use clutch fans, or did anyways.

Another thing is that the hotter an engine, the hotter the compartment and the incoming air picks up this heat and becomes less dense. Well heat contributes to a lot of things, not many of which are good.

[rbmgf7]

what kind of mileage are you getting with your F150? i take it when you say "500 to a tank," you have a 80's or early 90's dual tank and you're filling up both tanks. i just use the front and i can get close to 300 miles which averages 15.5MPG. i also do a lot of highway driving. i drive 60 miles roundtrip a day from home to school. my last fillup i calculated 16.3MPG for some reason.

[TwoTired]

Yes, higher temps can mean better economy.

Fuel atomizes more readily at higher temps.  Better atomization means better oxygen pairing with the available fuel.  A temp only change really only works with adaptive fuel metering, where something monitors the exhaust and makes changes to the fuel metering to compensate for extra hydrocarbons in the exhaust.

Don't ignore the temp and humidity fed the engine though either.  Both can effect economy, as it changes the amount of oxygen in a given gulp of air.

Also, check the fuel composition.  Added alcohol can reduce fuel economy (removal, the opposite).  Imagine one tank with, and one tank without.  Or, even a % alcohol difference on a tank by tank basis.

Also, different gas pump nozzles may shut off with a different level of fuel in the tank, especially if the vehicle isn't park on a flat surface when being filled.

Things to think about...

Cheers,

[ofreen]

A quick answer is yes it can.  I have seen it mainly when the faulty thermostat has the engine running too cool.  With the computer engine management systems on cars now, it is important that the engine temperature is in the correct range.  I have gotten several vehicles that would not pass emissions tests to pass after changing the thermostat.  It has happened enough times now that it is one of the first things I look at.

[edbikerii]

Yes, TT points out fuel composition.  The fuel composition at the pumps differs between winter and summer supply in areas that have cold winters.  Do you live in such an area?  Perhaps it would explain something if you checked with the fuel supplier?