Do you really need to use premium gasoline in Discovery II, 4.6 engine, or can you somehow get by with just regular unleaded? Regular is expensive enough as it is, so can't these engines be tuned to suit the regular gas we all now see at our gas stations, without resorting to paying for the more expensive premium higher octane fuel?

 

Premium is about $5 more for a full tank fill up. If you are that broke you probably should just sell your Rover now and get a Toyota.

There are several threads here on the subject but the consensus is if you have ethanol in all of your choices you should run premium. If you have non ethanol available lower octane will work if you must.

The computer controlling your engine retards the timing when you lower the octane. With E in the fuel you will get worse mileage and performance.

If you don't mind even worse mileage and performance then sure go for it. Otherwise you should follow the advice of the manufacturer. It's no accident that they spec premium. It is by design for best operation of the vehicle.

I'm guessing you've already tried? What has your experience been?

 

I've seen people run it with mixed results. Some don't notice a difference at all.

I take it as no one really knows but it's bad karma if you don't run premium. I don't want to give my Rover another excuse to crap out on me.

 

FWIW, I have used regular unleaded in my 2001 DII (4.0) for the last 6 years with no problems. Years ago I filled up with premium for a few tanks in a row and didn't notice much of a difference, if any, in either performance or MPGs. Come to your own conclusion about performance and MPGs, but your Disco will be fine with regular.

 

That is certainly not my experience.

Is it possible the 4.0 and 4.6 are different in this regard?

 

These engines have fairly high compression and like higher octane to avoid detonation. That being said, I saw a show on testing gasoline at the pumps and the 89 octane tested well above 90. Apparently, this is pretty typical. I've been running 89 in mine, and ran it in a P38 I owned previously as well with no problems.

 

Simple answer? No, you don't.

...and ethanol has no effect on this. 87 octane with ethanol is still 87 octane.

 

The engines have knock sensors so I believe they are able to adjust to the lower octane fuels. Someone correct me if I'm wrong. I however always run 93

 

I switched to a "top tier" supplier and 89 octane. I did the math the old fashioned way, before I had a Scan Gauge, and figured I was ahead. In other words, the increase cost percentage was less than the increase miles per gallon percentage. Your results may vary.

 

I can't tell a difference in my 99 of whether it is regular or 93, but the motor is louder after a tank of ethanol mix regardless of octane for some reason. Now my 04 runs better on 93 without a doubt.

Everyone is going to feel different in some way though due to their experience, but after driving a number of D2's I feel like each one sorta has its own personality. Kinda crazy I know, but rarely have I driven one that drives like another. Which could also be because the youngest D2 is 9 years old, and we've all seen that like gravity age will also take its toll on some of prettiest of equipment.

Only a few extra dollars a tank I always run 93 non-ethanol in both of them. Just a little peace of mind.