O.k...i have a 2003 disco2, iknow it says premium fuel only, (93) but my brother in law says i can put reg. Fuel in it without a problem...iknow it wont damage the engine or anything like that, but has anyone here done it?? If so, what were the differences if any? Im thinking it might be a little sluggish, but at the same time, its a land rover, not a maserati...

 

The topic has been well discussed here but I'll say it again. They ECU (engine control computer) has knock sensors, lower than 91 octane gas can be used but the knock sensors will detect it and retard the timing to compensate. It is a feature that allows you to get going if you run out of gas in the middle of Zimbabwe and have to buy gas from a roadside stand in a plastic 2 liter coke bottle. Driving with the timing retarded will cost you in performance and mpg. It is not worth the few bucks you may save on a fill up. On the same topic, buying top tier gas (not Costco, not AM/PM, not 7-11, etc) will help keep your engine cleaner inside thus keeping you from spending money on fuel injectors, etc. You will notice the difference, and if you don't then something isn't right. Go ahead and shame your sister for marrying the man.

 

I've road-tripped on 89, 91, and 93. There were some mpg differences but I've forgotten which one did what, and thinking back, maybe it varied based on outside temp, too.

 

I've done trips with 87, 89, 91, and 93 octane fuel. I always do MPG on my trips and honestly I've seen no major differences. Now this was not in the mountains, and this was not pulling a trailer. This was also on an 02 D2 with 200K (now nearly 240K). In the TX Hill Country going 70-80MPH with the AC on full blast.

These engines run rich regardless. The key is to honestly drive the darn thing like you stole it. If you drive it like Mrs Daisy it's going to get full of carbon deposits, and rob all sorts of HP and MPG. I let ALL my LR V8's tach up to 4K plus when they shift and nearly 20 years later I still haven't had issues with carbon deposits. Now I've worked on plenty of 93 octane fuel only vehicles that the owners drive like Mrs Daisy and the famous LR Tech test = leave it in 1st gear and take off. When it hits the rev limiter if you loose all view of the road out the back to a pillow of black smoke = carbon deposits galore. I've then worked on LR's where the the owner uses whatever fuel they can afford, but they drive it like it's a rental and the engines were not full of carbon deposits. Also using a good fuel system cleaner at every oil change = great idea.

Now if I was fully loaded down with heavy gear/cargo, pulling a trailer, or in the mountains yes I'd go with the highest octane fuel available. Now if you have an older 3.5/3.9/4.2 equipped LR 93 is a must as they don't have knock sensors and they'll most certainly ping.

 

ive done this test only difference is I used 87 and 91 octane no noticeable difference in mpg and don’t notice any performance difference

drive it hard drive it often and keep it cool

 

It takes more than a few drive cycles for the ECU to fully adapt in either direction. You may not notice a difference right away, especially if your fuel system is gummed up as Best4x4 mentioned.

I am the opposite, top tier premium and Seafoam every other oil change. I can tell inferior gas within a mile of the offending station. I feel like i drive a very expensive fuel quality detector.

 

91 is all you need, based on the premium rating these were designed for but good quality matters. Cheap gas in anything is always a problem, I run 91 and my truck is very happy lots of power on the hills and flats, she zips along. Vancouver to Whistler BC I pass everything without any effort.

 

If you're worried about using lower octane fuel to save money you shouldn't be driving a rover

 

Going up the mountains or dragging a trailer? Yep, I'd tank up with higher octane otherwise just plane El'cheapo with a bottle of Techron cleaner in the tank once a month. If you really want to tell a MPG/power difference run corn free gas! 9.3 compression ratio engine in a 90's computer controlled vehicle....nothing special or delicate about it.
Just my 2 cents
YMMV

 

FYI, Costco Wholesale in the USA, Canada, and Mexico are TopTier licensed brands. BJ's and Sam's Club are not listed.