is it ok to burn 90 octane in the 2004 discovery?
brett

 

Not really, 91 is "okay." You should run 93.

 

91 is the minumum rating, use the highest octane rating that you can. You can pay alittle now or a lot later.

 

where are you finding 90 octane??? ive never seen that on a pump

 

at mohawk in canada.they sell 90 ad regular price.i run it in my 1987 xj12 that has 12.5:1 comp,with no knocking or pinging.
brett

 

the isue with discos isnt the comp ratio... its really kinda low in your 4.6, its that the combustion chmbers run hot, which will cause a ping, you probably wont get one from 90, and as long as its decent gas, you should be ok. i would say worst case will be some carbon, but itll take time, do an induction service every 10k and youll be fine

 

That is also why these trucks sludge up so bad too. Running to low of a octane gas makes the combustion temps really high and that bakes the oil and it breaks down sooner.
Using the correct octane will keep the cylinder temps down and make the oil last longer as well as the engine.
Your Jag doesnt ping because of the knock sensor, it retards the ignition timing to compensat for the lack of power in the lower octane gas.

 

You will be OK with 90, may waqnt to run a can of good gas additive twice a year just to cover your tracks.

 

The higher the altitude the lower the Octane that available.

I would always use the highest octane for the altitude.

 

i would use 93 or highest if its around 10-15 cents higher then mid grade. 90 is OK but, 89 isnt.