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Miles per Gallon

Posted: Thu Jul 22, 2021 2:03 pm
by QCS
Earlier this year, I took my 1967 GPO Engineers van in for a full service with a local firm that specialise in classic vehicles. On the last previous long distance run I had done in June 2019 - a trip of about 240 miles each way, it got to the far side of London from North Wales down the A5 at about 45/50 mph and still had fuel showing on the gauge when I arrived.

After the service and fitting of electronic ignition on recommendation it was going through fuel like mad - approx 20/22 mpg on local running around! I took it back and they said that they had found an air leak in the manifold and it was sucking air in . They said they had sorted it.

Since then I've kept an accurate record of the consumption and during some local usage I get as little as 25.6 miles per gallon.

A week or so ago, I went to a vintage rally at the Evesham Vale Light Railway and tank was showing very low but just managed to get back to KIdderminster to fill up - 135 miles on about 5 gallons! So nowhere near the consumption I used to get when I went to the other side of London. I've taken it back in and they've said that I'll not get anywhere the consumption I was getting as they've cured the air leak! Running with the air leak would have been causing damage to the engine they reckon.

Any idea as to the sort of mpg I should get on local run arounds and of 45/50 mph long distance trips - the engine was converted several years ago to run on unleaded.

Re: Miles per Gallon

Posted: Fri Jul 23, 2021 4:19 am
by bbennett
My pickup had a homemade tank that was insufficiently baffled and would leak at the filler cap if topped up. It was fitted with a 1098 with I think a 1 1/2" SU. Taking the uncertainty of filling the tank to the same level into account I averaged something around 35 plus miles per US gallon of 87 octane, mostly short nonhighway trips. If you had a vacuum leak I would assume you would be running lean and down on power. Has performance improved?

Re: Miles per Gallon

Posted: Fri Jul 23, 2021 5:08 pm
by PoolGuy
In the last 18 months I've averaged 32.41mpg over 10k miles, all local stuff within 15 miles of home.