viewtopic.php?t=74239]This thread is worth a read. There's an analysis on page 7 that's worth a look. There aren't any real conclusions on a definite cause, but we all have an idea of several things that could potentially contribute to burnt valves. Leaky valve stem seals, incorrect coolant, and low octane fuel all seem to be possible issues. Also passive driving styles. I take every precaution necessary to avoid the issue... Zerex G-05 coolant, 93 octane fuel, and I drive my cars hard. They regularly see 6,000 RPM. Do these engines make any power up there? No, but it makes good noises! Plus it helps prevent deposits that can decrease gas mileage when driven conservatively or possibly cause problems like burned valves.Eddystone wrote: ↑Fri May 10, 2019 2:50 pmWell, the owner's manual that shipped with my 1995 S70 T5 states that 87 is the minimum octane requirement and that to obtain "optimum performance" use 91 octane or higher. I have always taken that to mean that Volvo is stating that you can use 87 octane without causing problems to your engine, either short-term or long-term and that if you want every one of those 236 horses you need to use premium. I know that we all have certain areas where factory recommendations are taken as Gospel, other areas where we know full well that they are BS of the CYA variety, and still other areas where we know it's best to EXCEED the factory recommendations.
Right now, in my area there is a $0.44 difference between regular and premium which is maybe $8.00 per tank for a small car that only reaches MPGs in the high 20's at legal highway speeds and much less around town.
I'm just asking whether or not anyone has any real evidence that a particular Volvo engine in STOCK configuration will burn valves from using 87 octane gas, or whether it's nothing more than talk. I have no problem spending the extra cash if there's any scientific basis that using less than 91 octane will damage your Volvo engine.
I'll also grant that using premium may yield something like 3% better mileage which reduces the extra cost. Still, I'll bet burned valves has more to do with how hard you push your engine. I spend most of my highway time at 2600 rpm and seldom hit 4000 rpm. Yes, I'm an old fart and get plenty excited by 4000 rpm. I have been thinking about what someone wrote about the valves not rotating on their axis until you hit 4000 rpm and that you should at least periodically run your engine at 4000 rpm for a period of three minute. I should do that, but it might be too exciting...
The way I see it is it's cheap insurance. $5 more for coolant when I buy it, a couple more bucks for gas here and there isn't going to kill me.