What sort of grade of gasoline to use? 87, 89, 91 octane. Read why below:?

Question

I've been putting 87 octane (I believe based on the [R+M]/2 method: R = research octane, M = motor octane) into my car (Toyota Corolla).
But I recently re-read the owners manual, where I noticed that it states, "Fuel selection: Use only UNLEADED fuel: Research Octane No. 91 (Octane Rating 87) or higher."
Now, I'm wondering whether I should be putting in 91 octane or 89 octane. Do the words "Octane Rating 87" refer to Motor octane or the octane I get at the pump, which is the average of the two.
Would putting in higher octane now cause problems with the engine? The car has 195K miles on it, and other than a small oil leak, the engine runs fine most of the time. About once every 6 months, I do get a strange starting problem: after driving in hot weather on short trips, if I turn off the engine, the car won't start, and I have to wait about 5-10 minutes before the car starts. I attribute this to letting the engine cool, although the temperature gauge never gets above 45% of max.

As far as the every-6-month-starting problem described above, my mechainic can find nothing wrong with the engine. I've taken the car to two other mechanics with similar results.

BTW, the engine is a 1.6L fuel injection 4 cylinder.

Answer 1

It basically says to use 87 octane but you can use 89, I would stay with the 87 as it's cheaper and any of the problems you are having are not caused by the gas your using.

Answer 2

D@mn, you read to much into things. Dont waste your money, with that many miles you wont see a different. I have to run 91 because I have a factory performance engine in my Jeep and if I ran anything else it will have spark knock that can cause engine damage. The higher the octane rating the more resistant the fuel is to heat

Answer 3

87 should be fine for that engine. The octane would not affect the way the engine does or doesn't start after short trips. I'd check with your mechanic, it may need some minor work for the starting problem.

Answer 4

It may shave off a few years, but it is a cumulative effect. At 195K miles, I do not think it is going to help to change now.

The red section on the temperature gauge is the area where you are doing permanent damage to the car. The only way it should ever get that hot is if your radiator and coolant systems malfunction.

It sounds like your starter motor or carborator (assuming you do not have fuel injectors) is heat sensitive, which would inhibit startup.

Answer 5

you're confusing two different methods of measuring octane. In the US, pumps use the R+M/2 method, so use regular, or 87 octane.