Due to less relative wind resistance and less relative weight typically carried (relative to engine HP?)...I think personal vehicles are more sensitive to engine/driveline lube viscosities and lubricity? Maybe by a factor of 2 or 3? Just a guess....
Anecdotal stuff....
Preparing my Saturn SC2 for the "Switch"? - Bob Is The Oil Guy
Two days in, and I'm already noticing improved cold starts (don't have to hold down the key to get it to catch like I did with GTX on really cold days), and my gas mileage is up about 4.5 MPGs. 6 qts. Mobil 1 0W-30 K&N Oil Filter CHANGED FROM Castrol GTX High Mileage 5W-30
Tercel4WD.com • View topic - Slippery Slope
"So just before we took the Tercel on the 2,500 mile trek, I changed the tranaxel and rear differential over from 89-90 gear lube to Mobile 1 synthetic. First drained the units, cleaned the magnetic plug ends and flushed/cleaned with cheap ATF then drained and filled with the synthetic.
Now I had no way of comparing the improvements to mileage or much of anything for that matter until I did my coasting route down Academy Boulevard. Normally the stop light catches me a Wyoming so when I get green I accelerate to 35 mph and put him in neutral. I have a mile of downhill that only has 1 stop light that I usually cruise through. Now with the 80-90 gear lube, the Tercel would slowly gain speed and top out about 42-45 mph, just the speed limit. This would be the case in summer and in winter with the gear lube viscosity restriction, he would get to 38-39 on this stretch coasting.
Lo and behold, Now he zips right past 45 mph and I actually have to feather the brakes to stay under the speed limit. I know this is not very scientific. I don't care."
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