what fuel octane do you run in your 4.0 i6 and why?

87. It's the cheapest and the 4.0 is a 35 year old design that does not require anything higher for performance. Anything more than 87 is just wasting money.

thx for your response. i was making sure because ive heard mixed responses.

Don't use 90 octane. Just use Unleaded 87 octane. Using a higher octane fuel is only more expensive, and instead of conserving fuel, it will only burn/use it faster. The inline 6 was only meant to have 87, and it could possibly overwork your engine if you try and go higher. Besides, 87 is the cheapest... why spend more?

I was told by a mechanic to use only reg (85 OR 87 OCT) and not to use the 10% ethenol as this causes the senors to assume that the engine is running lean and will increase the fuel consumption until the 02 sensor is satisfied. I have a 99 with 83K and has not had anything but regular in it. Still runs exceptionally well.

i live in sweden and the low octane here is 95,i run my grand cherokee laredo 4,0 on this,no problems,87 or 89 octane can be had in former east europe or russia,but not in the west,95 gives you a lot of pulling and towingpower

Higher octane helps with fuel consumption unlike what some say, higher octane burns slower

4.0 has dish type pistons and lower compression. In my opinion 87 octane is perfect for a 4.0's factory compression.

I have a 2011 Grand Chrokee Laredo what type of gas should I put in it ?

All answers above do no have a reason for the recommendation. If the engine pings and is experiencing detonation more octane or less timing is required. If the timing were advanced you could run higher octane which would increase power and fuel mileage. But from what I’ve felt in our 4.0 87 it’s happy with. There’s no power to be gained on higher octane unless timing was changed. You’ll actually lose power and fuel mileage going with a higher octane and stock timing.

My 1997 Grand with the 4.0 bought new ran like crap on 87, used a lot of fuel & power was down. I have too put 89 in her or she pings, sucks fuel like krazy & low power on 87. With 89 it runs great but not with 87. My 99 doesn't seem too care what octane I put in it, KRAZY.