My 99 Volvo S80 T6 starts better on 87 octane than 91/92. I'm in Hawaii, and it's all 10-15% ethanol. I know a place where I can get ethanol free gas, but haven't tried it yet. Want to wait until I pass it with empty or near empty tank.

If I put high octane in it, it sometimes takes 2 attempted starts before it cranks up in the morning.

What would be the reason for this? At first I thought it was injector o-rings, or maybe just needed a new fuel filter, but neither would make sense now that I figure out the low octane trick. Nothing else has changed. The engine runs great, better with high octane, but not much difference with low octane, about the same mpg.

Thanks for reading, I did some searching before, but found nothing.

 

Well higher octane gas resists detonation, but im not sure why it starts better for you on 87,,

i am actually going to ask you something unrelated, can you please talk some more about the difference you feel between 87 and 91 ? i am considering switching to 87 , but im afraid to harm the turbos , i know how the system works and had cars in the past that too premium, but neither of them had turbos. Just wondering if its all a placebo effect or if you actually can tell the difference...

 

I think there is something wrong with the 92 that I buy. The 87 seems to give it more torque while the 92 seems to give it more high rpm power. I admittedly rag my car out a good bit but prefer the low end power to get it spun up more quickly.

I will test different high octane and repost but I'm happy with the 87 just wanted to know why it starts better. Want to fix it so it starts better no matter the grade.

 

But I would say that the timing will advance and get a better burn with high octane. The computer will adjust ... so far I think the engine liking 87 octane either means the high grade fuel I buy is phoney or its a sign of problems to come.

 

I'm going with the latter...

These cars are designed to run on 91 or higher octane, this isn't a matter of running a car designed for 87 and running 91, which will have no effect.

In essence, you are getting pre-detonation, but the car has retarded the timing to adjust for the lower octane. But there is a reason your car is not running right with the designed specification of fuel.

 

maybe a bad knock sensor ? even if you may not show a check engine light there still may be a code set in the ecu, i would get the car scanned

 

ya my lexus can also run on either on low or higher octane. I mean its a lexus so nothing about performance so i choose lower octane. It runs fine. no problems hardly notice any slow performance. But on a Volvo higher the better. So i have been putting a "medium" octane. Like 89

 

You should be running at least 91 in the Volvo.

 

But is there a problem if i switch between octanes ..like one gas fill up i fill 91 and maybe next time i fill up its 87..maybe because lets say that day gas prices for 91 are ridiculously high$$..will changing octanes every fill harm the engine.?

 

That's an excellent suggestion. I should have though about knock sensor. I have a scanner and plugged it up but no codes...nothing.

I bought some new plugs, the ones in Volvo package. Maybe that will help. I want to run the higher octane but want the starting issues to go away.

 

also has the fuel filter ever been changed ? its easy to change and it could be full of sediment,

thats funny, i want to use lower octane to same money

 

You really shouldn't use less then 91 octane, if you move between 93 and 91, sure, whatever, you're just wasting your money on 93. But dropping below, although the car will retard the timing to prevent predetonation, is not really good for the car. Performance will be impacted and if you use too low of fuel, the car won't be able to avoid pre-detonation.

I'm all for saving money, when it's logical. You're better off driving slower, avoiding jack-rabbiting, keeping the car in proper running order (ie. proper maintnenance and keeping the tires properly inflated) then using lower then recommended octane.

 

I guess Volvo original OEM batteries are actually pretty awesome. It must have been the original battery from 1999. I replaced the battery, and thought 'hmmm, I'll try high octane since it's near empty' and wouldn't you know it? It starts up just fine. Soooo... long story short, after several replies and lots of time, it just needed a new battery. Probably had a dead cell. Sometimes it's just the simple stuff... but, now I got a coolant problem, gonna start a new thread.