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Martin Cutler
Posted on Thursday, 19 April, 2001 - 11:06:   Edit PostDelete PostView Post/Check IP

Hi guys and girls,

Have done a few hundred miles now on straight unleaded petrol instead of the Lead Replacement crap they are selling, and the car seems to be running fine. Idle is now much smoother, and plugs aren't sooted up. Will keep you posted as to valve clearances.

Marty in Sydney
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Bill Vatter
Posted on Thursday, 19 April, 2001 - 11:50:   Edit PostDelete PostView Post/Check IP

In the US, unleaded is all we have been able to get for quite awhile. Regular unleaded is generally 87 Octane (R+M)/2 and sometimes at higher elevations 86 octane. The early post war 6 runs very well on this gasoline without any special additives. The principal drawbacks to the unleaded gas are two:

1. Higher octanes are achieved by addition of light weight hydrocarbons that are more volitle. Thus, all unleaded gasoline and especially the higher octane fuels are more likely to boil in the lines under the bonnet and in the carburettors, and the high test does not stay fresh very long. Therefore, if your car does not ping on regular, use regular, and don't buy the high test stuff. Vapor lock is not usually a problem in an early post war car because the fuel pump in in a cool spot, but boiling fuel will certainly make your car run poorly at best.

2. All unleaded fuels are less stable than the old leaded gas, and they will form varnish deposits if left to stand for several months. This is because one of the unleaded gasoline components is a cracking product of natural gasoil, a gummy substance that is virtually worthless in its natural state, and the cracking products have a tendency to recombine back into gasoil over time. This resultant varnish-creator can cause valves to stick, and when that happens the engine usually needs to come apart. If you do not use your car enough to require fuel every two months or less, you are a candidate for varnish problems.

About a year or two ago, an acquaintance of mine tried to run out some stale gas in his P-II, and wound up with stuck valves. Don't do that. Use your gas up within two months of purchase, and there should be no problems. If you store your car over the winter, drain the gas when you put your car to bed, and use this gas in another car before it goes bad. If you forget and wind up with a tank full of stale gas, drain it out and give it away to your enemy.
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Martin Cutler
Posted on Friday, 20 April, 2001 - 10:35:   Edit PostDelete PostView Post/Check IP

Hi Bill,

Thanks for that info. I have a tank full of unleaded sitting in my Austin 7 that will definitely be stale now! I also use my 1925 Dodge very infrequently, so looks like I should fill it up when I go out on a rally and try and leave it as empty as possible on my return.

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Jim Bettison
Posted on Saturday, 05 May, 2001 - 11:27:   Edit PostDelete PostView Post/Check IP

Further to the UL/LRP discussion: Yesterday I met an old friend in the fuel trade. I asked about the use of UL in older motors, just to get a view, and he volunteered a comment - strictly unattributable - that the shelf life (I guess really the tank life) of UL as sold in Australia is six weeks. Fits with what Marty said; I didn't have the wit to ask about LRP, Next time.

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Alan Padgett
Posted on Sunday, 24 June, 2001 - 08:03:   Edit PostDelete PostView Post/Check IP

I have been very interested in this subject since we have had to use unleaded in the UK. We have a new unelected government in Brussels called the EU . This makes all our laws now ! Try that for lack of freedom, in the US.

The unleaded fuel in the UK is 95Ron not suitable for high compression engines which we are told to reduce the advance and which I think if done much will have other bad effects. We have Super unleaded which has about 98 Ron but is quite expensive.And limited in availability. ( The UK have the most expensive gasoline in the world with about 80% tax on it )We have the awful LRP which is potassium based and does nothing except cause more polution, not least because it is so unecomonic.

The cars that need lead for their valve seat protection are only of use with a leaded fuel and we do have a clause in our gasoline supply that limits a small sale of .5% of total to be low-leaded. This is very hard to find but is a small concession.

We now have the regular unleaded having a low sulphur content. Please does anyone know what the side effect of this might be ? we know it is again more uneconomical and a greater polutant as a result. I can't wait for an electric car ! Hee Hee. Alan Padgett
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Alan Padgett
Posted on Sunday, 24 June, 2001 - 17:04:   Edit PostDelete PostView Post/Check IP

Bill Vatter, I wonder if you could be kind enough to give us more on this serious matter of the gasoline going 'off' in a short time from purchase of it.

It is hardly practical to keep draining the tank if the fuel is in for only 2 or 3 months. In fact few people have the means of so doing with out a great deal of hazard to life with the risk of fire very evident. Modern cars do not have easy means of filling from a funnel and so on.

I am very surprised this situation has arisen. I am old enough to have experienced some 60 years messing with gasoline. My father had cars pre-war and certainly it has always been the case that gasoline would get left in tanks for some time unused.

Perhaps we should ask the fuel companies for their advice. Although I have no doubts Bill has got an accurate picture, it is just so silly to have fuel so poor it will not stand without deterioration.

Alan Padgett
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Martin Cutler
Posted on Monday, 25 June, 2001 - 11:29:   Edit PostDelete PostView Post/Check IP

Hi Alan,

Not to get too political, but we have the oil companies to blame for the current Catalytic converter/LRP/pollution issues. The current method of utilising a catalytic converter is a scientific dead end. Lean burn technology would have been a wiser thing.......
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Bill Vatter
Posted on Tuesday, 26 June, 2001 - 11:54:   Edit PostDelete PostView Post/Check IP


I may have exagerated a bit to be safe when I said "a couple of months," but US unleaded fuel is much less stable than the old leaded fuel. The general consensus among US hobbyists is that cars not run over the winter should have the tank drained to prevent varnish problems in the springtime. We also have products called fuel stabilizer or similar term available in the auto parts stores. As I recall it is not very expensive, perhaps $3-$4 for enough to treat 20 gallons. The manufacturers of these products claim that if you add it to your tank the stability of the fuel is greatly increased, and they market it for use in cars that are operated infrequently. I use this product in my pleasure boat that stands idle from late September until June. (Dump some in at the end of the season.) I have had no problem with this engine, and I do not drain the tank.

During the driving season, It seems easy enough to buy no more fuel at one time than you will use in two or three months. I drive my Rolls-Royce regularly for pleasure and for the health of the car. Not using your car is bad for it for many reasons.

We have had unleaded fuel for a long time, and there has been much study of this potential problem among antique car enthusiasts, but not so much recently as it has all pretty much been said already. Several articles have appeared in the RROC publication Flying Lady. I think everyone now agrees that the early post-war six does not need leadded fuel, nor does it nead a lead substitute. The problems with accelerated valve seat wear pertain to cars with performance camshaft profiles operated at high RPM. These two conditions combined cause the valves to go closed against their seats with considerable impact, resulting in accelerated wear if hardened valve seats are not used. Tetraethyl lead somehow causes a cushion for the valve slamming closed. Rolls-Royce cars have neither performance camshafts (quite the opposite with the early cars) nor are they operated at high RPM. Some people add an upper-cylinder lubricant to their fuel, and I have heard it said that this will help prevent valve seat damage in cars susceptible to this problem. Marvel Mystery Oil is the most popular of these products.

Now I thik the V-8 Clouds are a different situation, but I never payed much attention since I don't have one of those.

Good grief all of this fussing about petrol. I fill up all the time with regular unleaded and don't think twice about it. My car runs fine. Lets go driving.
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Martin Cutler (
Posted on Friday, 24 May, 2002 - 11:40:   Edit PostDelete PostView Post/Check IP

Hi Guys and Girls,

Have now done 10,000 miles in the Mk VI since putting it back on the road. I am still running straight unleaded, and just checked tappets, they where all within 1-2 thou, so no real problems there. The lead memory on the exhaust seats seems to be holding them up OK. After running the car fairly hot during Vivian's little "parade", I have fitted a 16 inch thermo fan, and as heat buildup is the greatest enemy to the motor, I hope this will ensure a much longer life.

Of interest is that the car was designed to run on 74 octane "pool" petrol after the war, with 93 octane premuim petrol not being available till 1953. It is noted in the Bentley Owners Club book that using higher grade petrol will not give an improved performance, use of a fuel of lower octane number may result in damage.

I think I will keep running straight unleaded 92 octane for the time being.