Gas octane, blends & additives for Westies

Capt. Mike

Transfer from archives

8/7/99 (9:38 PM)

This has been hashed to death, but I fournd the following from a Bosch FI manual, so thought I'd pass on along with general comments since Bosch supplies VW's FI.

The VW is designed to run on "regular" gas. Anything more is wasted money and can cause running problems. Today, "regular" is generally 87 octane, Gov't R+M/2 method. That's about 90-91 RON.

From a Bosch FI manual (Pub #4232.21) discussing the changes in the mid-70's when even high performance cars dropped requirements to 87 octane:
They then go on to say it will cause CO levels to be high and difficult to adjust. In the catalytic converter and oxygen sensor era, this also has the effect of causing the FI system to try to compensate for the excess CO levels by leaning the engine beyond specifications. Too lean a mixture can do serious engine damage. It also strains the catalytic converter's capacity.

Old tales claim high-test gas has better additive packages. That's no longer true in any major brand. FI systems are so touchy, no manufacturer wants the reputation of fouling expensive systems. Nor do they want to be pegged as a contributor to pollution by EPA.

There are circumstances when a slightly higher octane say 'middle' or 89 is prefered. Old engines may have sufficient carbon build-up to actually raise compression. This will cause a ping under load. If your engine is pinging, try a middle octane. If it cures the problem, you will probably want to consider a head job or overhaul. Not critical short term, but it indicates the engine has seen better days, contaminated with carbon, soot and other maladies, not just higher compression.

Some head jobs and overhauls may over-machine the heads and increase compression. This is not desireable, but leaves one with the choice of new heads or higher octane. A better mechanic also comes to mind.

Certain areas of the country sell winterized fuel, or have special blends that deviate from the normal 87 octane regular. In the Rocky Mountains, it's not unusual to find 'regular' at about 83-84 octane. VW's don't like this sub-grade fuel. Some brands, like Sunoco's old 'custom blend pump' would put their economy grades below 87. The only cure for this marketing or EPA numbers game is to READ THE NUMBERS on the pump. Every pump MUST be posted with the R+M/2 method octane. Get an 87, regardless of what quality level it's called.

Octane blends. If you get a tank of sub-87 by accident, or suspect so, you can put in some high test to balance it out. I once got a tank of 'regular' near Denver that turned out to be 83 octane. It didn't run worth diddley. Every time I could squeeze in 5 gallons, I put in high-test and by the 2nd or 3rd go-around, everything was back to normal.

Winterized fuel, and gasahol are oxygenated, theoretically giving cleaner burning. Unfortunately, they also tend to reduce power and mileage, reported to be by as much as 3%. Their octane is the same, but the energy contained is not. This drop in mileage is unrelated to the octane. With most fuels containing some ethanol these day, you will have little choice but to use it. VW's should have no problems below 15% and the 10% of most blends shouldn't cause any concern. They are required by law to have a sticker (not necessarily big and prominant) on the pump.

Leaded gas: Tetraethyl lead was an additive used to increase the effective octane of gas. It is now outlawed pretty much around the world (cancer suspect in fumes & spills) and has been superceded by new technology. It had the side-effect of being a lubricant for valves & valves seats. In any newer engine ('70s on), this was alleviated by the superior technology of hardnened valves & seats. Some believe that, in OLD engines, the lubricant replacement additives in the new unleaded fuels are not adequate and a lubricant additive should be used. The jury is out. I use one in a 60+ year old flathead engine that I know is all original, but not much else. Any COMPETENT overhaul in the last 25 years should have gone to hardened valves & seats, and thus make leaded gas unnecessary. The side-effects of fouling, exhaust corrossion, increased acidity, etc., overwhelm any benefits. Ruining a cat converter ought to convince you that additives aren't the best route -- to repeat, there are no magic cures in a bottle.

ADDITIVES: Generally, not recommended for gas engines, nor by VW. Good, name brand fuel and major independents have all the additives needed for clean burning and system maintenance.

I'll offer two additive exceptions: Before each major service, where I will be changing fuel filters (15K or 30K depending on model), I add a can of valve cleaner and a can of fuel injection system cleaner to the last tank fill before the service. My thoughts are these will help break free any varnish, carbon, etc., and it will be trapped by the filter and discarded. A good FI cleaning at that interval has kept all of my vehicles going over 100K with never an injector failure. (My Porsche just turned 40 years with the original injectors.) If your system needs additives beyond these 'maintenance shots' you should address the cause or reevaluate your fuel source.
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Capt. Mike

8/24/99 (10:01 PM)

A recent email from a reader revealed there is still some confusion over octane numbers and what may be stated in manuals, particularly older manuals from the pre-EPA days.

He asked if the 87 octane regular applied to air-cooled buses. My response, and attempt to explain the octane numbers game was:

Yes, it includes ALL of the buses, air- or water-cooled. I won't pretend I've kept up with some of the more exotic VW's like the Sirocco 16v, etc. And haven't looked up the Eurovan VR-6, but all of the standard buses and beetles used 'regular' gas. That's 87 octane in the current government rating method of R+M/2 as required to be posted on all pumps.

I would estimate 87 R+M/2 equates to the old scientific 90-91 RON (Research Octane Method) octane. This may be the source of confusion as you might find the RON octane specified in an old pre-EPA days manual and in some non-North American market manuals. If your old manual called for 90 RON, you would use 87 R+M/2. 3 to 4 octane numbers is the usual difference.

Motor (knock) octane is the octane at which a test motor under a specified test load starts to knock -- pre-ignite. I don't know the exact lab specs. That's the M in R+M/2. Obviously you would not want to run an octane that allows knocking at any time, so you pick one slightly higher, but not so high it causes other ignition problems or changes the explosion point & pattern.

R+M/2 is RON octane + Motor octane divided by 2. An average of two methods. Only a government bureaucrat could come up with a new method that makes no sense to either standard.

Hope that clears things slightly. Basically it amounts to using current 87 pump octane fuel in your Westy unless it has been modified by higher compression than the factory recommended.
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Capt. Mike

3/23/00 (7:55 PM)

I've received some queries on the oxygenated fuels for winter in some areas.

EPA has designated certain areas reduce emissions by requiring an oxygenated fuel. The fuel contains substances that during the combustion process add oxygen and thus decrease CO emissions. The most common are ethenol (gasahol) and MBTE (ether).

Gasahol was generally warned against for three reasons: First, in old cars, the fuel lines may not be alcohol resistant. It attacks certain rubber blends and you could end up with a ruptured line and fire. Most new cars are already equipped with alcohol resistant lines and most replacements are safe, BUT you must check as some cheap fuel lines not designated alcohol resistant are still around.

Second, although the octane is the same, the amount of energy is less. Less power, less mileage. Ehtanol is 65% the energy of gas so a 10% blend would be 3-4% less.

Third, gasahol is hygroscopic. It will absorb and hold moisture.

MTBE is an ether compound that does much the same. It doesn't appear to attack fuel lines. It is also less energy and is able to hold moisture. Probably the lesser of the 2 evils.

CORRECTION 8/00: EPA has now decided that the product they specified may be contaminating ground water -- so expect the MTBE to be outlawed. Sound to me like the gasahol lobby has insured we'll all be using gasahol. Add to EPA's expanding oxygenated fuel areas & you can count on burning some. Be guided accordingly.

Update 9/06: The increases in oxygenated fuel requirements by EPA and politics now dictate a large majority of fuel be a gasahol blend in most locales. It is basically unavoidable. The percentage is required to be labeled on all pumps, but usually a little tiny decal where you won't normally see it. Most oygenated blends are 10% and our Westies should be able to handle up to 15% though I sure wouldn't go looking for a steady diet of it. See the "Fuel conversion . . ." topic in the ENGINE CONVERSIONS forum. [E85 is unacceptable and unuseable -- severe damage will result unless your Westy is a factory conversion.]

As far as Westies are concerned, there is little difference in the fuels, except that drop in MPG. The power losses are not that apparent.
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Capt. Mike

:cool: Fuel stabilizers:

Although not an additive from a performance point of view, some Westy owners store their vehicles for long periods of time, or use them only occassionally. If fuel in your tank sits for more than 2-3 weeks, use a stabilizer additive.

Stabil® is probably the best known brand, but pricey in full car tank quantities. I use Penray's Fuel Prep 1000, designed for the trucking industry. (Available at any Cummins dealership/shop) It's much more concentrated so comes in at just a few cents a gallon. I've used it in all my antique cars, generators and small engines for years with excellent results. For gas engines, they recommend you double the quantity used in diesel. 3.1 oz. treats a typical 12-gallon fill-up. Last I bought was <$3 per pint -- enough for 125 gallons of diesel or 62.5 gallons of gas.

Even that has it's limits -- maybe a year at tops. So running the tank through, or changing fuel, is still a smart move.
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Capt. Mike

Transferred from another post to consolidate topics.

Add Lubro-Molly Jectron #LM2007 to gas tank?

filmcan, Member, 10-26-2000 01:00 AM

Capt Mike, what do you think of Jectron (you add it into the gas tank). My mechanic (who was a VW dealer mechanic in L.A. during the 70s) said that when VW started recommending it, their injector failure rate went down by 20% nationwide. I'm usualy not a fan of additives, but if VW really reccomended it then maybe it's okay.
First, I'd question whether that is an official VW AG from Germany recommendation, or something the dealer, or district service rep is pushing. (Or the parts dept. trying to pad their numbers?) I'd have to see the offical VW service bulletin before buying in. Now that he's not with VW, is he maybe repeating something he heard? From their salesman?

Many years ago, VW did market a fuel tank additive under the Autobahn line. (I don't question it may have been supplied by LM since LM is a big German OE supplier.) In their publications #W42 652 700 0, "Fuel Quality". and #901.552.118.21. "Gasoline and Engine Performance", they suggest their Autobahn additive IF you are having driveability problems. These were printed during the period deposit control additives were not universal. They named a half-dozen brands of gas that did have them. "If the brand of fuel you are using does not contain these additives, talk to your VW . . .."

Canadians, whose fuel is blended with different additives, were advised to consult with their fuel suppliers over deposit controls. Today, though they have different packages, I'm sure they're of equal effectiveness.

[Side item FYI: Coleman still does not recommend Canadian gas in their dual-fuel stoves & lanterns as Canadian fuel additives are different and not compatible with their liquid-to-gas flash generators. I continue to use Canadian fuel in mine, but do a long run of Coleman Fuel when I get home and clean up the equipment. Plus carry a spare generator -- a generator is cheaper than a couple weeks of Canadian Coleman Fuel prices!]

My recommendation on additives above is thus unchanged. Don't get me wrong; they don't usually hurt anything -- except the alcohol/methanol 'driers' (can attack hoses & seals) or the polyglycol 'lubricators' (burn a water-based product?), but they rarely add anything or do anywhere close to what is claimed.

I would guess your mechanic's quoted data is, at best, a hypothesis without any serious research behind it. First of all, since most major brands of gas have now included such good additive packages in their products, how much this alleged reduction in failures is attributed to the better fuels now available? Also, a dealer typically services newer cars -- the rate of dealer shop use for cars beyond warranty plummets and most cars in the 10+ age bracket rarely see the inside of a dealership. So is he comparing it to newer cars that have more reliable injection systems? To be valid, the test would have to be done on identical type, age & mileage vehicles, an equal amount with & without, and in sufficient numbers & mileage for valid statistical analysis. We're talking a hundreds of vehicles and thousands of miles each. Controlled conditions, same fuel souces, equal starting mileage. Not too darn likely!

My post above suggests a good cleaner might help 'keep' a system clean, as in a tankful before every fuel filter change. But that's more of a system & line maintenance than any injector failure preventative.

There are cleaner systems available. Lubro-Moly & Penray both have reasonably priced home systems that use a pre-measured cartridge substitute for the vehicle's fuel system to clean & purge everything. Commercial shops usually have large elaborate machines. These are to clean an already dirty system. They are not gas tank additives.

My personal experience, having owned FI vehicles for 40 years now, is I have NEVER had an injector failure. Does my little maintenance shot help? Who knows? But unless you're buying your fuel in Mason jars from a guy named Bubba, I think it's pretty safe to say you're already getting those additives in that liquid gold they sell at the corner pump. They sure charge like it!
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Susan M. Hall

New member
I just got back from a trip to the Grand Tetons--was up very high in the Rockies and bought some gas that was 20% ethanol---about an hour later my engine just quit. Waited a while and it started, ran for 15 minutes, then quit. Verdict was vapor lock from the additives--put some octane booster in it and added some Texaco regular and didn't have a problem after that.


New member
It was originally suggested to me that I fill up with the expensive stuff because the van was sitting for about a year. Perhaps this is true only for older buses. Now that I know better, my question is, what type of problem would result from "more difficult to ignite?" I noticed today that there was an unusual amount of gas needed to start off in first, thought it was just me, but it was exceptionally difficult. I was wondering if that is just the type of problem you would have. Everything else is working beautifully, but, since my VW mechanics are on a date tonight, :confused: I thought I would ask.
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Capt. Mike

The single tank of higher octane won't harm or cause unusual running problems. Gas deteriorates rapidly after about 3 months and by the end of a year can be full of moisture and have lost considerable volatility.

Thus the one exception to additives is to use a stabilizer if the fuel is to sit for more than a few weeks. Stabil® is the most common brand but overpriced; there are numeous others -- see the Penray topic in SUPPLIERS.

If draining and refilling with fresh isn't an option, just run this tank to half -- keep refiling with standard 87 regular until you've diluted out the residual. In this case you are restoring volitility and removing/filtering out contaminates, not changing octane.
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New member
We did fuel testing on a Formula V engine. Absolutely no changes to the engine, only fuel. Regular gas, Premium gas, 94 Octane, Aviation fuel, Aviation fuel with toluene, Aviation fuel/premium fuel/toluene, Regular gas with octane booster, Premium gas with octane booster. Most horsepower was with Regular gasoline!!!! The higher the octane the slower the flame (less knocking). With a higher octane you can advance the ignition timing, therefore making more horsepower. But, for the road, why pay oil companies more for less horsepower?? We did the dyno tests when I owned Bow Wow Performance, on a Stuska Dyno.

Capt. Mike

Transferred to consolidate same topic.

Pete Boucher Junior Member posted November 04, 2004 07:10 AM

We just got back from a trip to France and Italy in our '83 air cooled 2.0 westy. In Italy they no longer sell normal 97 octane 'Super' petrol (only Unleaded 95 and 98 octane). I live in Spain and it looks as though more and more service stations are taking the old 'Super' off their product range "due to market forces beyond their control".

We ran on Unleaded while we were in Italy (didn't have much choice) and it didn't seem to do any harm. I've heard it's possible to convert old engines to run on Unleaded. I've also heard that because of its aluminium heads and steel valve liners the westy engine doesn't need a lead (or lead substitute now) additive in it's fuel.

Has anyone else had this problem here in Europe? Do I need an Unleaded fuel conversion?

Thanks for your help!


Capt. Mike

Answered above: your Westy does not need "super" high-octane fuels; in fact it's a waste of money and makes the engine run worse. It also does not need leaded; no VW has needed leaded since unleaded became standard in the '70s. In fact, if you have a catalytic converter, leaded will ruin it and have an adverse effect on engine running as it fouls the O² sensor.

The only question you face is, "What octane method does your area use?" The US & Canada have come up with a bureacratic average of 2 methods that makes no sense to either, as discussed above. You may find Europe still uses RON method which will give you a number higher than the US method by about 4 octanes. Don't use higher octane than your manual calls for!
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New member
I was told and have used this method in my vw for years with no adverse effects. 8oz of mineral spirits per tank. Comments? I have also used this in many of my BMW air cooled motorcycles, 186K on one so far. After all I believe STP is 98% mineral spirits anyway.

Capt. Mike

Waste of perfectly good mineral spirits. Did you read the comments on additives in the opening post? Does NOTHING to help engine; since it does not burn as clean as gas, may actually harm things. Changes effective octane rating.

Wikepedia, the on-line encyclopedia has a nice definition of octane measurement:

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 (regular) in Europe.

The octane rating may also be a "trade name", with the actual figure being higher than the nominal rating.

That pretty much confirms that the old & European octane rates equate down about 4-5 for the new US/Canadian government method.
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New member
Originally posted by Capt. Mike:
In the Rocky Mountains, it's not unusual to find 'regular' at about 83-84 octane. VW's don't like this sub-grade fuel. Some brands, like Sunoco's old 'custom blend pump' would put their economy grades below 87.

I understand that at altitude 84-85 octane is equal to 87 octane at sea level, due to lower oxygen in the air.

Except for the occasional trip to the flat land, my '89 Westy has been running on 84-85 octane for the last 18 years and over 170,000 miles. So far no problems and still running strong. I am curious to your "bad" tank of gas when filling in denver. Sure, my van has more power at sea level than at 9,000 feet, but that goes for most cars, especially underpowered barn on wheels like the Vanagon.

Anyone know if this is true? Is 85 octane at altitude is equal to 87 octane at sea level? In the end, I shall keep running her at 85.

Capt. Mike

The rationale behind the lower octane at higher altitudes is a typical combustion engine draws in less air per cycle due to the reduced density of the atmosphere. This directly translates to reduced absolute compression in the cylinder, therefore deterring knock. However, the older VW FI systems (Type II & Vanagon) do not have anti-knock sensors. (They showed up with the Eurovans.) Thus they do not adjust timing to compensate for knock.

Bear in mind that the reason for the 84 octane gas in the mountains is NOT for performance or to save you money -- it is soley for pollution reduction. Thus in theory, and in many cases, it works fine. However, VW states (at least in my owner's manual) in bold print, Do NOT use any fuel lower than 87 octane. It does not differentiate for higher altitudes. It does suggest that if you have knock, use of a higher octane may eliminate the ping without harm to the engine.

Ask yourself, if the ECU is adjusting mixture for altitude, and its adjustments are based on 87 octane fuel, how does the resultant mixture come out for 84 octane?

The purpose of octane is to reduce engine knock (which can be fatal to the engine). If you are sure you have no knock, ever, then the theory has caught up with reality. However, even the experts (CU & others) warn that taking the 84 octane fuel below those altitudes can be harmful. Since the engine in these Westies is in the rear, hearing engine ping is even more difficult. If knock can be serously harmful, even as short-term in a single tankful, I think it better to err on the side of caution. Don't get me wrong -- if the 84 is working for you, by all means go for it. I don't like pouring unnecessary money into my gas tank, either.

I would hope that residents in those sub-octane areas have done some serious comparison and testing. I found a couple testing formats on the Internet. Lacking that, and for the traveler passing through, I will stay conservative and suggest staying at 87 octane per VW requirements.
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New member
Do not use Arco (or Valero) gas!

There is a well-reviewed Westfalia mechanic (his lot had many VW camper vans, porsches, and other VW's waiting to be repaired) who showed me documentary evidence that using Arco gas made it difficult to pass smog tests, lowered gas mileage, and lowered compression in cars brought in for repair. If the damage was not too severe, it could be reversed by changing to other brands (such as Exxon, Mobil, Chevron). He also showed me that Arco had burned out valve seats (he had dozens of them he had replaced hanging from a large ring). Upon analysis, Arco was shown to contain such elements as Chromium, Nickel, Sulphur, Potassium, Phosphorous, Calcium, etc. It should contain NONE of these.

If anyone has run on Arco for years and gotten good results I will reconsider.

[Moderator Note: Please substantiate these allegations with copies of scientific reports or references -- most additives are now controlled by EPA thus the charge is not plausible. I have been unable to locate any credible scientific reports, just blogs, peititons & forums and since you have blocked your email, cannot ask off-site questions (like who is this "well-reviewed mechanic" and where can I find his publications and reviews.) -- Westy Tech]

The mechanic showed me a bunch of burned out valve seat rings. He claimed they were from Arco users. He showed me sheaves of work orders where the mileage was poor, compression was poor; he substituted non Arco gas and mileage improved etc. Also he showed me his chemical analysis of the gas. He had records of meeting with Arco staff and their indifference to his claims. I cannot imagine why he would be singling out Arco unless he had good cause.

I have reported my concerns to the EPA.

That's as far as I want to take it. I know it doesn't rise to level of fully and scientifically reliable. It is anecdotal, but strong. You make your own decisions as to what gas you will use. I will go with another brand.
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New member
Arco user

Greetings from Portland,
Read your message today re: Arco gas. I have been buying gas at my local Arco station here in Portland for since 1997. I use it in my 96 Jetta, 84 Vanagon and my 82 Westfalia. Never had any problems. I have never heard a discouraging word until now. I assumed all major stations are tested, quantity and quality. On the other hand my wife prefers 76 stations for her Suzuki. Have a great summer, be safe on the road, Dan