Is It Necessary To Use Premium?

Going with the manfacturer's interval is usually a good bet.

But, the difference in appearance of the valve train in an engine that has had the oil changed at a 3,000 mile interval vs. 5,000 is amazing. Enough that I've switched to a 3,000 interval.

But, my '83 Camry with 5,000 mile (or worse) oil changes now has 250K miles. Lots of varnish on the valve train, but it doesn't seem to be hurting anything.

If its a 6 cyl then manufacture says premium required.

The purpose of higher octane is to suppress "knocking," the pinging sound you hear when the gasoline vapor ignites prematurely when compressed in the cylinder. So try a tankful of regular and see if it knmocks. If it does, go back to premium at the next fill-up. Otherwise, you've won!

Uncle Ben

You should stay with Premium for 3 reasons:

1. Reduced octane gas will cause the engine to knock
2. Reduced octane gas will cause the engine to retard timing, hurting performance.
3. You'll get less mpg with lower octane gas.

Think beyond the pump price number.

My V6 Tacoma "recommends" premium. It gets enough extra mileage on premium that the per mile cost is cheaper. It runs OK on regular, but I do the math every time I fill up.

What a shock! The manual was meaningful!

No, otherwise the ECU sensed the knocking (via the knock sensor, imagine that) and retarded timing to *stop* further knocking and engine damage...reducing effective engine power output in the process.

Now, does that still sound like a win?

Yup, which I've confirmed on my own car.

Yousuf Khan

I'm no automotive engineer, but I can't see how retarding timing would stop the knocking, since the knock is caused by compression, not a spark. As for engine damage, I am equally skeptical, although I accept a slight loss of engine power.

Igniting the charge even furhter before TDC does not allow it the opportunity to ignite from compression.

Carl

It's a simple fact that it does. You can argue why, but advanced timing will cause spark knock. Just talk to anyone who's worked on cars before all the electronic controls, back when timing was controlled purely by engine RPM and vacuum. Peak performance was obtained by advancing the base timing as far as possible without knocking. If you advance too far, serious knocking occurred.

Toyota used to have a small knob on the distributor called an octane selector. It let you fine tune the timing ... you retard it if the engine knocks. Or you can advance it for better performance on premimum fuel.

^^^^^^^^^^

This gave me a good laugh. I was just skimming through this thread and was wondering why the playground name calling. Went back and re-read to see what was going on. On understanding it still brings back high school shop days and timing lights and twisting the distributor to advance the timing.

He he. Back in my drag racing days I connected a manual choke cable to a distributor on my 47 Pontiac. Great fun.

wrenden

It was known as "twist'er till she knocks and back off 5" (degrees that is). Worked wonders back in those days!

Use what the manufacturer recommends. If regular is called for you are wasting your money useing premium.

Again what does the manufacturer call for. Usually turbo vehicles require more frequent oil changes.

Can we agree that knocking is caused by too early an ignition?

So advancing the timing would make the knock even worse.

Retarding the timing would do nothing, since the mixture would already have ignited from the compression.

So I don't see how any adjustment to timing would eliminate knocking due to low octane. (If it would, think of the money we could save.)

Uncle Ben

snipped-for-privacy@yahoo.com wrote in news: snipped-for-privacy@n67g2000cwd.googlegroups.com:

Generally if it asks for premium you should use it. The ECU can compensate for other fuel types but the engine performance will suffer and likely any savings made at the pump will be eaten up by the poorer gas mileage.