One they pay for and the other they don't.

Yes, and they get paid for it as well.

First a disclaimer.. I'm an engineer and I think I'm genetically predisposed to experiment / validate things for myself... so I could not help but to do a test on this issue. For about the last 4 tank fulls I've been running regular with no audible detonation or no obvious loss of performance. Before Christmas I filled my tank at the local service station, drove a few miles, and all of a sudden I got my first "service engine soon" light. I hooked up a scanner and low and behold the error was that the "left cylinder bank" has a lean condition. So obviously the timing retard was able to prevent detonation but was not able to produce the required A/F ratio. Maybe this tank of gas has slightly lower octane.. but it is clear the 89 is running on the edge of safe. Given that I've never heard any detonation I'm not worried about damage.. but looks like it's super for this beast from now on!

Btrvalik: Pretty good seat of the pants review...not hugely scientific and there could be some coincidence or other factors involved, but decent, imo.

I've had good luck with running a tank or two of 89 on long trips where that one tank is gone, at steady high speed cruise, in less than a day. My seat of the pants and arith shows no real diff in mpg or "power", but it is a haulazz highway look. I suspect even my lil' 3.0 and espc. the V8s would not like a steady diet of 89 or <, in stop/go/city/hot weather driving.

But, an occas. tank of 89 and the majority of 91/93 seems to do fine.
Good post, there and thread...it comes up again on the Ol'JukeBox regulary, but I enjoy reading all the rationales, arm wrestles and opins!
BR,md

Good test thanks for the info. I did an MPG test with the 3 different grades. With 89 I got 2mpg less per tank than with upper grades for the same 50/50 city/highway driving. I did not notice any significant difference between the two upper grades though. I did this test twice and got the same difference twice between 89 and the other grades. I have the 4.4

Well a lot of different thoughts and opinions on fuel grades, Octane and Ron from the guys in the states and a couple from here in the UK. Wish we had your price for fuel overhere. :rolleyes:

First things first just so we know. I work for BP and I'm of the managers for Scotland for BP Oil Uk Limited retail.

4* leaded fuel is no longer available or refined here in the UK if it is sold at any sites then it is imported and crap.

Now don't be fooled your not doing youself any favours by putting the lower grade in your tank.

I can talk as a whole for grade here in the UK but it is different for the states because the quality and availabilty of fuel is different by state in the USA

Take for example here in the UK you can get Optimax or Ultimate petrol which is either 98ron or 97ron but say over in greece it is a 100ron. Always remembreing the majors market their fuel at a minium Ron. Infact you may be surprised at what goes on sometimes.

If you give me your state that your in then I can give you a complete break down of the fuel sold in that state and actual Octane or Ron.

Hey, that would be very interesting! So what's the deal in Massachusetts? Thanks Fiona!

nae probs but I need to wait until I'm back to work Monday to check it out on the "Intranet" :thumbup:

93 octane...premium...i wouldnt give my baby anything lower than that :)

Always Premium.........nothing else.