Adding paraffin to petrol.

[BRIAN MARSHALL]

Hi, I drove for several miles behind an open top 1920s Bentley 3 litre (maybe 4.25 litre) today, and there was that unmistakeable smell of paraffin (kerosene), like an old Fordson tractor, strongly suggesting that some had been added to the petrol. I know that this is illegal as no duty has been paid on it,but wonder WHY ? Does this improve the way the engine runs ? Does it in some way counteract the dreaded ethanol in the petrol ? Can a vintage car owner give us the answers ?
Brian

[Deleted User]

Last year I left about a gallon of petrol in my tank over winter and was unable to start the bike with this in it when Spring at last came again. I drained the petrol out of tank and carb and replaced with 2 gallons of fresh petrol and the bike started easily. I could not comfortably leave that gallon of ‘stale’ petrol in the can so poured it into the bike with the fresh stuff and set off on test ride to see how it ran after the winter lay-up.
Perhaps the sight of the sun or the daffodils had an effect on me, but I was convinced the bike was running better than ever with none of the usual popping on the overrun or snatching when at very low RPM. When I stopped for a while with the engine running, I detected a faint whiff of burning paraffin. I stopped a few more times on the run and detected the same odour every time. I have also noticed this odour when using a mixture of old and fresh petrol in my lawnmower!

I assume that the octane rating of the petrol that 1920’s Bentley (and our Scotts) was intended to run on, was lower than the stuff we have available today, so I suppose the owner could have blended a lower rating with the paraffin. As I am led to believe the modern octane petrol burns at a faster rate and requires, in older engines at least, less ignition advance to get maximum expansion at the optimum position of the piston. Retarding the ignition timing results in flatter engine characteristics and takes some of the pleasure away, so a lower octane petrol would allow the original ignition timing settings to be used.

Or was that Bentley running on a ‘stale’ petrol mixture as I was ? Interesting.
John

[BRIAN MARSHALL]

Hmm…. The higher the octane rating, the SLOWER it combusts. They used to add tetraethyl lead to petrol to increase the octane rating, slow down the ‘bang’ and therefore reduce ‘knocking’, ‘pinking’, or detonation, enabling higher compression ratios to be used, and thus more power. Years ago Lofty Avis wrote about running his Scott on paraffin when there was fuel rationing. He had to start up on petrol, then ease over to paraffin when the engine was thoroughly warmed up, just like the old farm tractors. He said that there seemed to be more torque and tractability, (no pun intended !), at lower revs, but less top end power.
Brian

[David J Waring]

Your observations are very interesting, although I suspect that you both have a better sense of smell than I, Brian & John!
From my experience of pre war & vintage cars, I am sure that the Bentley would run on petrol with some paraffin added, but with such cars in the “price upon application” class, I would doubt that the owner would risk it, and think that stale petrol is the more likely answer.
Lesser 4 stroke low compression engines (e.g. side valves) would run on such a mixture, and possibly run on paraffin alone on a hot summer’s day, if warmed up on petrol first. However, there would be unburnt fractions, which would settle on the pistons, pass the rings and dilute the sump oil, unlike a 2 stroke*, which stands a chance of ejecting the fractions to exhaust.

*This is based on personal expeience, when as a 15 year old, I ran an old air cooled 2 stroke around the garden on hot household paraffin (Aladdin Pink), by starting up on petrol, then switching to an auxiliary tank, from which the paraffin ran in a copper pipe wedged in the engine cooling fins to deliver it hot to the carburettor. The engine ran reasonably well on this preheated fuel, although unburnt fractions of the paraffin emerged as a black liquid from the exhaust. Examination of the crankcase showed some build up of the black liquid, but the two stroke appeared capable of dispersing most of it, so continued to run and receive some lubrication. The only thing to remember with the paraffin was to switch back to petrol before stopping for any length of time, as restarts on paraffin were only feasible if still hot. (Full story in Yowl Dec 2011)

[Deleted User]

Back in the last century, I was an impoverished apprentice at the huge BT-H plant at Rugby and after crashing my Bantam one time too many, my dad sold it and presented me with a 1938 Morris Ten Four. At £2 15 shillings a week from which I had to pay most for the hostel, I decided to run the Morris on 50% cheapest petrol at 4 shillings and twopence per gallon and 50% Paraffin. It went just fine. Now my memory is not perfect, but I seem to recollect that the “POOL” petrol of infamous memory we had just after the conflict with those who were our enemies but are now our friends, was about 75 octane, In 1929, however I am sure that the octane rating of the fuel was no higher than 75 and perhaps lower. A percentage of paraffin should return burning speed to be a bit nearer to the design conditions. As we are using fuel with a different burn speed, I rebuild engines to take this into account.
Anecdote. If you are a bit crazy like me and decide to use a Scott for racing, it is necessary to use all the tricks to get competitive power. About four years back, I finished the season with the engine going fine. Next year, new premium pump fuel as usual, I got detonation and rough running. Pull the engine down and recheck everything, put it together, just the same. The only variant was the fuel to which, I discovered, more ethanol had been added. I went on the internet and compared anti Knock additives that had been tested on a Ricardo Knock test machine. The top performer was an Australian product called NF. I then went to a local garage who specializes in expensive Classic cars. He sells the old leaded four star fuel and told me that he would only run one of his classic cars on the modern muck in an absolute emergency. So with a highly tuned engine and not wishing to use methanol, I take one gallon of four star leaded to which I add 220cc of Castrol R 40 and 15cc of NF anti knock and it all works just fine. Of course I am using petroil which I prefer and have a three way dripper which gives a small drip feed to each main and a small feed to a brush oiler that runs above the bottom run of the primary chain and extends its life considerably.
Kind Regards Roger

[Deleted User]

a friend of mine an old farmer used to run his old rover on paraffin start and stopped it on petrol ,he only stopped it once on paraffin took him all day to sort it out.thats the way the old t,v.o tractors worked

[BRIAN MARSHALL]

What was the difference between TVO (Tractor Vaporising Oil) and paraffin (Kerosene) ?
Brian

[Deleted User]

im not sure Brian but the farmers called it paraffin

[Deleted User]

Tractor vaporising oil (or TVO) is a fuel for internal combustion engines, produced from paraffin (kerosene). In the United Kingdom and Australia, .

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