i have a 2001 es300 adn use regualr. i was wondering if i would get better milage if i use plus pr premium.
anyone know anythng about this?

 

I always use regular and just got 27 mpg avg on a 6 hr trip doing 80 half the way and passing people on a slower highway (but only did 70 ish that half of the trip) -- and the final 1.5 hrs of the trip were windy mountain switchbacks up and down hills in 2nd and 3rd gear most of the time.

I never hear any valve clatter at all, but Im not sure if the 99 is supposed to use premium or not, but it would usually say that on the inside of the gas door which it doesn't. I'm guessing 87 is fine.. If it's not fine the knock sensors will electronically pull ignition timing back to compensate for this problem where the fuel is burning completely in too little time or too quickly.. But it's better to run the right fuel if it needs 91.

A higher compression engine will call for 91 because of the higher tendency for 87 to burn, whereas 91 is more resistant to detonation and a higher comp engine (higher pressure) can more easily ignite the fuel prematurely causing "knocking" where the fuel flashes before the optimal point near top dead center and actually pushes back down against the piston before it should, and can cause damage by making the pistons/rings rattle against the cylinder wall.

This will usually happen at higher engine speeds though and not as much during light footed driving (highway cruising)...

In the case where a car calls for 87 octane fuel, there will actually be zero benefit for occasionally burning a tank of premium, and this will actually kill a few hp.. 87 is every bit as "clean" as 91, just chemically a little different (less resistant to detonation).