So, a while back, my sister-in-law needed to borrow a car to go down to Fort Wayne, IN for the weekend. Going against all of my protective instincts, I lent her mine. She came back complaining about the terrible mileage that it got. Well, I asked a few questions to try to figure out why she got terrible mileage, and it turns out that she never used overdrive. It was driven, on interstate highways, at 70+ mph, in drive.

For those of you who are unfamiliar with the area, it'* about a 3-hour drive, one way, all highway.

Needless to say, that freaked me out just a bit. I'd never dared to try that for 1/4 mile, let alone a three hour trip.

It'* been a few months now, and all seems well, but I still wonder if any harm was done? The engine must have been screaming (well, by 3800 I standards anyway). Any idea how fast the engine would have been turning at 70 mph? I'm pretty sure that I have the "highway gears" in her, though I can't seem to find the sticker to tell me for sure anywhere.

I just wanted to bounce this off of you guys, see what you all thought about the whole thing.

GX3 3.33 final drive was good for 2500rpm at 100km/h (60mph) in drive, for reference...

Rpm would have been higher than the normal OD, but nothing that should have done any damage or long term problems. She paid for the gas right? I might change the oil a little sooner than 3,000 just because higher revving will usually cause it to be dirty quicker.

Otherwise...laugh at her for gettting horrible gas mileage in your car and paying the price at the pump.

Oh yeah, she paid for the gas. I'm not that nice!

So aprox. 2700 in drive, eh? Not too bad I guess.

This was at least one oil change back already, but I think I did do it a bit sooner than usual. I think that there was still snow on the ground when this happened, because I was worried about her snow driving skils (or lack thereof).

And speaking of mileage, I actually got 31.5 a couple of weeks ago while on vacation. My previuos best had been 29.5, so maybe it was just an odd gas pump, or a fluke of some sort. I was still pleased.

The thing that always amazed me, is that you say you did your best mileage run while driving very fast. My car does far better at around 60-65 mph (which is what I did for the length of this 31.5 run). Wassup with that?

Prolly had a good tailwind going with you too.