Fuel

[Kellsonm]

Hey everyone, I just got my first R50 last week so I'm still learning about the car. It's a 2001 QX4 with 155k miles. I bought it from a friend who owned it for 12 years and at some point switched from 91 premium fuel to regular 85 unleaded. Should I continue using 85 or switch to 91? Will my fuel economy be affected? Right now I'm getting about 15mpg mixed driving. Also should I use fuel system cleaner on these engines?
Thanks!

[szh]

If the manual says that 87 is okay, then you can use it. Mostly likely, using 91 (for a car that normally uses 87) will be imperceptible - no real gain in mileage probably.

However 85 seems wrong - does that gas even exist? I have never seen it around here in California and we are notorious for not making 93 available. If 85 existed, I am sure our wonderful politicians here would be insisting all cars use it.

Of course, if the manual says that 91 is required then you should not drop below that. Otherwise you will see some engine drivability problems. Yeah, you may not hear anything wrong since the engine management electronics will attempt to compensate for the reduced octane. it will mostly be successful at this, but it has to detect low levels of knock first - this "silent pinging" can damage engine longevity, even if you are not hearing anything seriously amiss.

Z

[nickelghandi]

I think the 2001's have the VQ35 which does recommend premium fuel. However it does have a knock sensor that allows it to run 87 octane without issue. When I say without issue, I only mean that it shouldn't damage the car. The fuel economy may be a little worse, and the performance will definitely be a bit worse. I average 16.83mpg on 91 octane and average 14.97mpg on 87 octane. For me that boost in mileage and (possibly placebo) boost in performance makes it worth the extra cost at the pump. As far as 85 octane, I have never seen it either. If you really do have 85 octane where you live, I would stay away from it with your engine.

[atraudes]

I switched to premium about a year after I bought mine, and did notice that it idled and ran smoother overall. No comment on mileage since I wasn't tracking it and had other factors playing into it being horrible. I haven't switched back despite the extra cost. Some people here say they don't notice a difference, some do. Regardless, you'll need to give it a number of fill-ups before you notice a difference, though. The engine will adjust to the different combustion as you put some miles on it.