Richard, that's the first time I've heard about a problem with Valero gasoline. I run it in my truck all the time (unleaded regular) without problems at all, but my truck does not like Arco gas.

I know that Valero is in the process of switching to methanol mixed gasoline and fazing out MTBE, I wonder if that has anything to do with it.

Supposedly all gasoline is the same and only the additives are different, but that is not always true.
Basically that is correct but different refining processes product slight variations of basoline blends.
Straight run gasoline is almost always the base stock and it is blended with high octane ($$$) stocks to achieve the desired component. These high octane blend stocks are created in process units that modify the hydrocarbon molecules and are not all the same.
Types of these processes are:

reforming, where a catalyst and hydrogen are used to change the organization of the molecule (usually a platinum catalyst, very expensive) but these reformed molecules can be unstable and break down over time.

Calalytic cracking, where heat and catalyst actually break a long chain molecule like a heavy oil to smaller molecules like gasoline, (also unstable over time but not to the same extent)

or Alkylate catalytic processing where acid (either hydrofluoric or sulfuric) is used as a catalyst to mix iso-butane and naptha based molecules to make a very desirable stock.

Most refineries have very similar processes designed and licenced by either Philips, Unocal or UOP etc, but the majors have enough money to design their own versions of process units and avoid paying licencing fees.

The different processes can create a slightly different type of blend which work better in some cars and worse in others.

Here's the tricky part, just because a gasoline is sold at a mobil or sunoco or chevron or valero station does not mean it is refined by that company.
Sometimes it is, often it is not.
Gasoline is traded openly between refining companies to meet commitments so you never know who's gasoline you are getting. Sometimes a gas will not work as good, and then the next tankful from the same pump will be better. The only thing that is supposed to remain constant is the type and concentration of the additive package and the octane rating that you get from a certain brand.

So sammy, I don't know if you've mentioned it before, but what do you run in your SC?

I've never really noticed a difference between brands, but then I've never really paid attention too closely either. I usually use 76, because there is one right by my place, and they advertise no MTBE.

All this talk has me curious, and I want to try something else for my next few tanks. Probably chevron, I think.

Dan :)

I work for BP, think this is refered to as AMOCO in the US.

Within the fuels industry there is so much inter trading and swapping of fuels, you could be getting any brand of fuel from any brand of station so unless your getting somthing Like shell optimax its all much of a muchness.

When I first got the SC I was running premium, either Unocal or Shell. After a couple tanks I went down to the mid grade (89 octane), no difference.
I have chevron regular unleaded in it now (87 octane, trying to pass smog) and I still don't detect and difference but I have it leaned out a bunch so I won't know for certain until I put everything the way it should be.
BTW, MTBE is not a bad thing unless you are concerned with the alleged environmental problems.
The gasoline that used to contain MTBE in California is being replaced with gas that has as much ethanol as they can blend in. If I had a choice I would like to run gas without either additive, but I'd pick MTBE over ethanol any day.

I've tried many brands over the years and the only time I've ever noticed a difference was with ARCO gas and that was only with a turbocharged 2 liter 914. It did not like Arco premium at all.

I do tend to avoid off brand stations. One other thing I do is to always try to go to a busy station. I don't want to buy gasoline that has been sitting in an underground tank for a couple of months.

Thanks. A friend of mine is a hydrologist (I think that's right -- does the whole groundwater thing) and she studied the effects of MTBE in one of her classes. She said it wasn't so great, and I believe her, so... Basically just a 'might as well' decision.

Dan :)

You guys just like Sunoco (Sun Oil Co.) 'cause it was the primary sponsor on Penske's 917/30 :D . They don't retail on the left half of the USA; wish they did.

Have to try the Shell test. The Phillips 66 seems to be pretty good, and the LCD graphic display on the pumps have a 911 on them :p .

Well, for those who live in this area, there's a Shell station on Franconia Rd. and the owner has a gorgeous zenith blue 993 C2S. He's a great guy and will always stop to talk to the Porsche drivers that pulll up, offer to read your fault codes for free, offer his lift for DIY work, etc.

MTBE is a bad thing when it gets into the ground water. No one would argue about that.
My problem with those who are so much against it, are they saying that MTBE is bad for ground water but gasoline isn't?

I say the real problem isn't the MTBE, the real problem is that gasoline and the stuff that is added to it is leaking into the ground and that is what needs to be addressed.
Banning MTBE will not solve the problem. It will only add to the price of gasoline and reduce the available production a little.

I look at their efforts as a band aid, attack a symptom and not the diesease.
Thier intentions are probably good but they are misguided.