Mother-in-law has normal S-70 regular engine. She says owners manual states requirement for Premium gas. She doesn't want to pay price so car sits in garage and she drives old Olds,we want her in the safer car. Would there be a problem if she ran plus?? I have a 94 850 and it runs great on 87 regular. Have tried plus and only difference is in final price for gas.

If you check the owners manual, I think you will find the minimum octane rating is for "research" octane number (or "RON"). However, the octane at the pump is the average of RON and "motor" octane number ("MON"). The pump should say "(R+N)/2" or something like that to incidate it is the average. Since RON is typically at least 8 to 10 numbers higher than MON, a gasoline with a pump octane of 87 should be at least 91 RON. The bottom line: 87 should work just fine for a NA engine. That said, IMHO the T5 engine runs noticably better, both in terms of performance and fuel economy, on premium gasoline.

Octane is a measure of the resistance of the fuel to explode--higher octane, less explosiveness. Higher octane fuel actually produces less energy than regular gas, but allows engines to run at higher compression ratios which results in more power. Bottom line, try running a tank of regular and see if the engine knocks (sounds like a bunch of BBs rattling around in a coffee can). If it knocks, try plus, but i highly doubt it will. Our 850 runs great on regular and has the same engine as the S-70. Keep the extra money in your pocket.

Tom

96 850 base model 91K

Terry, tel the MIL to read the maual carefully. In my 98 manual it clearly says 87 is the minimum. I have a N/A (non-turbo) S70 and have been feeding it 87 (regular in these parts) since new. No issues at all (almost 23K miles on the clock new). I, like youself, tried super and the biggest difference I felt was in my wallet. I do run fuel injector cleaner now and again to make up for fewer detergents in regular gas. Oh, I also drive the car rather hard (it loves being above 4K RPM).

I have '97 855(Canadina, my manual just say recommend 87 octane. I always use 87 only, as you do. So far 60k km, not much of damage, as I know the engine has knock sensor. As I know S7 2000 use the same engine, so I would suggest you to double check the manual. For me the safer is better car, even with a broken engine.

Peter