LEOSOPHIE

Are any of you running regular 87 unleaded in your gas versions? I have 220000 miles on my navigator which requires 91 with no problems. I have yet to run my 550 on 87. I am guessing the only problem would be reduced performance ? In California that would be a savings of 19% compared to diesel.

a2j

Reduced performance should be the least of your worries. I also used to own a vehicle (acura) that required premium, and that is what I've been filling it up with. Others reported that they've been filing theirs (same acura) with regular and no issues. So it might work for you. But when manufacturer says you need to use premium, its not because exxon and mobil1 gas station owner wants you to but more because the engine was designed to use that fuel. If I'm not mistaken, timing and compression ratio will dictate your fuel type. Yes, higher compression ratio and more aggressive timing is what makes more power. But that does not mean you can just fill it up with regular and have reduced power and save some $. We are talking about possible engine damage because of "knock" or predetonation. That's when your fuel ignites before the intake valves close. Think about that for a moment. Regular gas is more easily ignited vs premium gas, but even premium has its limits. That is why I run my red turbo car on E85, but that's a different subject.
So, in your case, bad things (like blown engine) might not happen from using regular. But if engine has a turbocharger, I'd say don't even think about it.
Correct me if I'm wrong.

amdeutsch

This post makes no sense to me. Comparing a 10+ year old technology (engine older) Ford product with a newer MB product and then trying to justify cost savings with diesel versus regular pricing instead of the regular versus premium pricing.

alx

you bought a 550 and you want to feed it 87 to save money?

it will work as long as you dont push the truck especially in hot weather.

but... your priorities need some calibrating imo

eric_in_sd

It's crazy how MB owners scold each other about saving money. It's almost like there is a masochism - the more they suffer, the more they spend, the better they feel.

First of all, the octane difference between regular and premium is pretty minimal. This isn't like the good old days, where you could get 104 octane at the pump, and cars like my old Volvo demanded it. 87 to 91 octane just isn't that big of a spread.

I tried 87 octane in my 07 GL. It didn't cause any audible knocking at any throttle or rpm range, except in the oddest point: brief and mild knock at part throttle, low rpm, when the transmission was just getting ready to downshift. If nothing else, this is about as benign of a knock as you can get.

I did a bunch of extended gas mileage tests between premium and regular. I measured tank refill volumes and mileage driven over 1,000 to 1,500 mile ranges. In other words, I calculated the accumulated mileage over several tanks full. There was no difference whatsoever in the mileage.

If the 87 octane were causing knock, and the knock sensors were retarding the timing to stop it, the mileage should have suffered. Because the mileage was the same, I can conclude that either the knock sensors aren't doing anything, and the engine is suffering inaudible knock, or the engine doesn't actually need 91 octane.

This is in southern california, so mild weather may have helped.

For what it's worth, that old Volvo had some pretty insane knock problems. I lost track of it but last I heard the car finally gave up somewhere around 160K miles. I have the feeling that the minor crap going wrong on this thing will take it down long before knock induced bearing wear will.