Hello, and thank you to you all for the cordial welcome! My question is 'how important is it to use high octane fuel in my 3.0 X-Type? What are the consequences if I don't - after all i purchased it with 99k miles and I have no idea what the previous owner used for fuel.

 

As you've already posted an Intro, I've moved your question from New Member Area - Intro a MUST to X-Type forum. This is the place to post technical questions about your model.

Graham

 

beducator, as for the results that you will see with your car, that is hard to say. some cars seem to handle the lower octane just fine and others run like hell. So, what you may encounter is hard to say.

As for potentials to the engine. In short, the computer is going to correct for the lower octane by altering the timing of the car, resulting in less power with the lower octane. LIke I said, some people don't notice a difference, others see a big difference. With the dialing back of the timing, you will most likely also see a slight drop in mileage too (some see this, some don't).

The best advice that I can tell you when it comes to fuel is whatever you use, ensure it is a brand name. If you do decide to try running a lower octane fuel, do it in steps. For example, run a tank of premium. Then get to about 1/2 a tank and then fill the tank up with the mid grade fuel and see how the car runs on the mix. If things are good, then run the tank till it is almost empty then refill with mid grade. Keep going down until you either see negative effects or you notice that the car just doesn't seem to be running like it should. If you reach a point where things are just not fine, then you will have to suffer through some miles until you can add a few gallons of premium to get the octane back up. Adding bottles of octane booster will not cut it. While the quote these high octane numbers, reality is not what they make you think it is.

 

I actually did an un-scientific test on this when I bought my Jag in New Jersey and drove it non-stop (other than gas, hot dog, pee breaks) for 50 straight hours (~2,500 miles) back home. Couple of factors daytime/nighttime temps half the trip were 65/45, second half, very cold 30/-5 (thus heavier more oxygenated air).

Running premium car smooth no pinging at highway speeds or slower in town (to get fuel) noticed. Regular fuel not much noticed at highway speeds, but a slightly noticeable difference in "power" feel in town. Not as quick on acceleration, etc. kind of "sluggush".

I switched premium to regular to premium to regular, "feeling" the reaction. Kept meticulous mileage/mpg numbers (my on board readings (dash) on m.p.g. Btw, are off by a fairly decent margin). I got right at about a 10-12% reduction in m.p.g. Using regular in warmer or colder conditions. A bit higher m.p.g. on both in colder weather, but still real consistent difference in premium vs. regular fuel.

I run exclusively premium now (used to that w/BMW's, etc anyways).

 

A couple of weeks later, I read about this in another forum post. I've never been a fan of additives (too skeptical) & my exhaustive research has shown actual before and after valve, piston head photos of pretty much all the top additive, i.e. Seaform, gumout, plain water intake treatment (scary), Lucas, STC, Techron, etc. to me are less than impressive.
That being said, I gave this one a shot, and thus is certainly subjective and not backed by any science, but all I can say is my car started acting alot younger. Better jump off the start, better pick up on on-ramps, jumps out to pass better.