Correct Grade of Petrol

[Malcolm Parker]

I run my Austins on 'super' unleaded E5.   I am running all of them on SU carburettors and find that the mixture can be two flats leaner on the 'super' grade petrol than the cheaper stuff.   So whilst the petrol is a bit more expensive, on my set-up it gives me more to the gallon which cancels things out.

Agree about the oil, it was great when you could get a gallon of 20/50 from Kwik-Save at £1.99!

[Reckless Rat]

In Macronland the difference between 95 E10 and 98 E5 is in the order of 15 cents/litre in favour of the E10, which is roughly 8,5% at current prices. (98 E5 is running at or just under 2€ and E10 around 1,83€/ litre). UK price differentials are roughly similar, but nearer 10%. Not sure you'd get that much improvement in fuel economy by just a couple of flats on the SU jet adjustment, but whatever. If it makes you happy and the cars run OK on it it's all good.

[Steve Jones]

Agree about the oil, it was great when you could get a gallon of 20/50 from Kwik-Save at £1.99!

Many years ago, returning South through Scotland with a car that had tramlined its bores, Malcolm bought pretty much all the stock of £1.99 20/50 that Kwik-Save in Kelso had so as to keep going. Seem to remember he went through an amazing number of spark plugs on that trip as well. Happy, happy days that included all the traffic on Princess Street in Edinburgh stopping until the smoke cleared when he set off.

Steve

[Ivor Hawkins]

On the subject of SUs, I’ve used them over the years, but the last three cars I’ve rebuilt, I use a low compression head and the standard jetted 26va Zenith and like the different grades of petrol, I haven’t noticed much difference in performance or economy, though I do crack on, in and Austin Seven way and keeping things simple has proved to be the way forward....well in my case anyway!

[John Mason]

I may well be wrong. If I am someone will correct me but I thought running on weak leaner mixture was a sure way to burn your valves out. I will continue on low grade supermarket stuff with a richer mixture.

John Mason.

[Chris KC]

I've long thought that 20W50 is probably a bit on the heavy side - Austin recommended straight 30 grade for touring cars and 40 for sports. The higher grade for sports cars assumes that they will be run hotter, the heavier oil thus gives the same effective viscosity at the bearing at running temperature. 
I measured my own oil temperature a while ago and it barely exceeded 65C (n.b. measured in the sump, a deep Nippy-style one) after an hour's run down country roads, so is getting nowhere near limits under 'normal' conditions. 
Thus there is no obvious justification for using a 50 grade on a touring car today, especially on a rebuilt engine with a new Phoenix crank and machined big ends. 
As others have observed, good flow is far more important, and that's where the multigrade wins hands down as 30 or 40 grade is porridge at room temperature. It may have been that consideration which held Austin back from specifying a 50 grade of course. 
One must also take into account that multigrades, especially cheap ones, tend to break down with age, so if you are not a regular oil changer (my system is "constant loss") it's erring on the safe side. But - for example - a 10W40 really ought to be more than enough.
Regrettably the only way to really know these things is to test, and there are many owners here with happy and extensive experience of 20W50, which probably dates back to the days when 10W40 and lighter grades were not around. I myself have yet to quite pluck up the courage to move away from something which I know works well enough...though in time we may have to look at other options.

[AustinWood]

we use 5/30 fully synthetic.

[Chris KC]

we use 5/30 fully synthetic.

Interesting. I recall Mr. Stepney is using 10W40, and I'm sure there must be others.

[Ivor Hawkins]

I agree with you Chris, 20/50 is probably a bit heavy, I used to use a straight 30 agricultural machinery oil for years, but of late I have been using a high zinc content “optimised detergent” (whatever that is) 20/50 and my oil consumption appears to have improved.

Next time I whip the sump off, which is a real pain as it’s a Nippy one, I’ll check out the bearings and see if there’s anything untoward, but touching wood the engine goes well.

[Chris KC]

I agree with you Chris, 20/50 is probably a bit heavy, I used to use a straight 30 agricultural machinery oil for years, but of late I have been using a high zinc content “optimised detergent” (whatever that is) 20/50 and my oil consumption appears to have improved.

Next time I whip the sump off, which is a real pain as it’s a Nippy one, I’ll check out the bearings and see if there’s anything untoward, but touching wood the engine goes well.

Not sure about "high zinc" or "optimised detergent" but I'd be very surprised if 20W50 gave you any trouble.

Yes I use a Nippy sump too, mainly because I value the extra capacity for touring, but they are a bit of a fiddle around the front end. I generally remove it before lifting the engine out and replace it in situ when the engine is back. The thing to watch out for is it can snag on the frame, giving the impression of being "seated" but actually leaving a gap all along the front edge. That's how I came to use a gallon of oil driving to Beaulieu and back last year (about 260 miles)! When the car was stationary no leak could be detected! I only figured it out when I removed the sump and found my sealant of choice had not been touched by the crankcase...