Low temp thermostat affect milage?

[Cheesetoast]

would putting a low temp thermostat in a 93 vw golf 1.9td affect the fuel economy positively or negatively?  I think mine has one in it, temp stays at 75 most of the time, should i switch to a regular one?

[VWRacer]

To me 75 sounds too low. Both my '85 1.6TD and my '02 Golf TDi run at 95. Folks typically install a 75 thinking it will lower overall engine coolant temp, but it rarely works that simply. I'd try a 95. If the engine runs too hot, fix the real reason -- don't install a lower thermostat as a stop-gap.

My 2-cents (Canadian... :wink: )

[Cheesetoast]

it's always been running that low since i got it.  is it affecting my fuel economy or anything?  i could go buy a regular one and switch, but should i bother?

[VWRacer]

I doubt it make a great deal of difference to fuel economy in a daily driver, though it will make a very small dent in the economy and power of the engine. Whether you could see it even in back-to-back testing in the real world is problematical, though.

[farkman]

Cheesetoast

My 94 Golf does the same thing. The gauge only moves between 70-80 degrees. But I think that this isn't the actual temperature of the coolant in the engine. I think the reading is  from somewhere else like the radiator because I have the cooling fan schematics and it says that the fan turns on at 95 degrees. When I park in the garage and shut the engine off, the cooling fans are running even though the gauge is at about 75-80. So if the cooling fans turn on when you shut the engine off I think your car is running normally.

Take care.