Unleaded fuel for MK IV 1 1/2 litre

I have noticed that my small engine 1 1/2 litre 1948 MK IV is sounding different with the last couple of tanks of fuel, and I know that in recent times the fuels in the UK are changing in a bid to go “green”. More additives are seemingly going in by the suppliers before it is dispensed at the fuel pump. Whilst my engine seems well set up and serviced to the normal Jaguar specifications the tappet noise appears slightly louder and I do hear more pinking. A few years ago the advice on this web-site was that owners of this era of leaded fuel cars should not unduly worry about using modern unleaded fuel, or perhaps if they did worry to add a lead replacement additive in each tank full of fuel.

Has anyone experienced this more as a recent problem with unleaded fuel? If so are there any new and better or recommended lead additives that have been tried in recent months? And if not going the additive route is there any merit (or warning) in adjusting the tappet gaps (normally 0.012"), timing, points, etc to compensate. Excess noise in my mind perhaps means potential problems - or is it simply a case that the new fuels make the engine play a different tune !!

My engine is original with no modifications or re-work, and I would prefer to keep it that way.

Petrols vary from country to country
Whilw I get the impression that ethanol is pretty universal in US , here it is an option , which most avoid. And octane ratings. Here we have normally 91 ,95 and 98. A few have 100. I usually run the mk iv on 95 and the blown car on 98. Depending on how long since last use as petrol deteriorates with time. Other wise it could be timing advance.
Or more concerning , valve seat recession could cause tappet noise.

We have 95 and 98 octane around here - and I try and use 95 in the MK IV from branded fuel stations but there is no other choice for me. Everything set up wise seems ok and petrol is the only change I can put my finger on to investigate as similar issue has been noticed on another friends classic car recently. Not noticed anything with my e-type but I use 98 in that car and obviously different age and engine!!

What is the compression ratio on that engine? I can’t imagine it being high enough to cause pinking, with modern fuels, ceteris paribus.

Ethanol is added in US automobiles to reduce smog and has been used in that capacity widely for decades.

I’ve not heard of any “recent problem with unleaded fuel”. If you have a rapid change in engine noises, it would seem prudent to inspect the valve clearances and engine compression. If your engine is original, it may simply be needing attention or getting nearer to rebuild, regardless of fuel used.

Low compression engines should be set up easily without pinking at any octane sold in a pump. I always run lowest available octane since it is least expensive. Pinking suggests timing advance merits checking.

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RACV did comparative test.
Two identical cars ne filled with ethaol added fuel one not, and drove them together, Melbourne to Sydney , the exchanged d rivers and drove them back
Then compared the cost. The ethanol was cheaper to buy per litre, but used more of it
. In dollar terms, the non ethanol car was cheaper for the round trip.

True, at the immediate pocketbook of the driver in the gas station, using ethanol both costs more and reduces the energy per gallon of fuel by enough to notice.

On the other hand, in 1965 Southern California had about 8 million people compared to 24 million today. The population of Southern California rose primarily after the invention of the automobile and so is very spread out compared to cities started when rivers or walking were important for transportation. Los Angeles metropolitan area has about 1 car for every two people.

Since 1965 the So Cal population has roughly tripled to 24 million and the smog has gone down a factor of three. In 1965 So Cal had some of the worst smog in the world. Ethanol and catalytic converters cost something but the quality of life is immensely better. California seems not to have the luxury of following the old adage “the solution to pollution is dilution”.

In my '10 Hyundai Accent:

-ethanol fuel (10%): ~32 mpg
-non-ethanol fuel ~35 mpg.

Paul’s observation of about a 10% reduction in miles per gallon when 10% ethanol fuel is used is correct.

A simple approximation to understand why is to note that ethanol and gasoline have about the same mass per gallon so 10% ethanol is by mass or volume is about the same.

Ethanol has stored energy of about 25 MJ/kg and gasoline typically about 44 MJ/kg. A 10% mix of ethanol would yield (0.1x25 + 0.9x44) = 42.1 MJ/kg, a reduction of around 5% in miles per gallon. Simple models don’t tell a full story but Paul’s real data are consistent with this.

Coupled with the fact of a great increase in passenger-miles driven, this goes to show that the much-reviled pollution controls, mandated by the government, along with the commensurate increase in research into increased fuel mileage (fuel efficiency), all have worked.

There has also been gains in industrial efficiencies, too.

However, it’ll not be enough.

Going perhaps slightly off topic to my original question, so this is what’s in the 1 1/2 litre Instruction Book for my MK IV:

It does mention the use of incorrect fuel as being an issue for pinking and poor performance. I assume lack of lead is less lubrication in the fuel and maybe therefore potentially more tappet noise? I will be inspecting inside the engine shortly.

Excess carbon using isn’t likely to be the cause, unless the head’s not been off for 70 years.

Also, pinking on the lower grade fuels of the day isn’t exactly a straight line to…today’s pump fuels.

So: what IS the compression ratio of the engine?
Has the timing been checked?

Could it run hotter (thermostat, pump…) or can the distributor move? I know it can potentially move in XK…

And of course tappet noise is different from pinking, so is it throttle/load related or not?

I am going to check the timing and tappet gaps, but need confirmation of specific set up for 1 1/2 litre (the data is different in my Instruction Book and Service Manual - like 5’ TDC for timing on one but 10’ TDC on other). I just put another Post up for this. In case there is an issue with the petrol in my tank I will drain it off and try a different brand. Unfortunately not all fuel is the same in the UK, and certainly is different from other countries I believe.

Based upon your reports, it appears to not be valve lash, and timing can slip.