Thermostat and fuel mileage Options

[emerygt350]

Very interesting thing happened to me at the end of last year. I left myself a mental note about poor mpg when I parked the car last fall. Took it out just the other day and everything was great but again, I noticed mpg was just not what I am used to. Drove it in the cold yesterday, 30 degrees all day, and the oil never got warm. Maybe just on the beginning of the line but that was it. Drove it hard.through the hills, chugging on the highway in 5th, nothing would get it to warm up. It would also take forever for my high idle to come down (I thought it was a slow aar but now I am thinking it was a combination of that and this issue).

My thermostat cable (super slinky low E .048 guitar string) had finally broken. Popped a .052 low E on there today when I was changing oil. Yes, I ordered a real cable too. Engine now heats up much faster, climbs up to a reasonable temp (maybe an 1/8 of an inch past the beginning of the line). And my high idle is coming down much sooner after a cold start.

I really suspect the poor mileage was due to a cold engine. I think it probably failed after the weather had turned cold and I never noticed at that point since I figured it was just the weather keeping the engine cold. Instead of the 28 - 30 on the highway I was getting low 20s. About 18 in town instead of the 22 or so I normally get.

[Literati914]

That’s interesting. The car I put together and sold last year, I had left the thermostat cable unattached at the flapper rod, planning to go back before winter and attach it, once I got it idling and running really well. The idle was mostly higher than I liked (or could easily lower). and it took forever to warm up also. I planned to sort it out but didn’t really get around to it before it sold. It didn’t occur to me that the thermostat could be contributing to the issue. I’ll keep it in mind on this next one, thanks for posting your experience.

[emerygt350]

Even though I am a proponent of hot oil, I never really thought about the other effects of a nonfunctioning thermostat. It really does seem to affect driveability. Probably not for those that live in hot places but those of us in the temperate zone with stock fuel injection should respect the engineers that designed the type 4. It really messed with the regular operation of the motor. Even at 60-70 degrees.