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Hobson fuel guage.

Technical issues not related to a DLOC car marque, eg tyres, ethanol, other car makes, etc. and legal, political and insurance
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Stan Thomas
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Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Hobson fuel guage.

Post by Stan Thomas »

Some while ago on the old forum I asked about the Hobson fuel guage, and some knowledgable chap said it could be re-piped with a semi-rigid plastic tubing - but I've mis-laid the note I made of what bore size tubing he gave.

Could he or anyone else advise please?

Simon Hyslop

Re: Hobson fuel guage.

Post by Simon Hyslop »

Hello Stan, I think that might have been me, although the knowledgeable bit doesn't quite fit. I've had a look at my own car rather than just guesstimating as I did before and 4mm semi rigid tubing like this :

https://www.beal.org.uk/hoses-tubes-fit ... m-o/d.html

is very close. Small brass olives are available in this size to make screw together joints or there are compression fittings which don't need olives.

Stan Thomas
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Posts: 795
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Hobson fuel guage.

Post by Stan Thomas »

Hi Simon,

Thanks for your reply. I've now blown out the copper pipe and tested it for leaks and it seems O.K. so I'll try things before I change to plastic pipe.

I must say these Hobson guages do have a mind of their own!

I very carefully cleaned and refilled the guage with the proper liquid just to the "empty" mark as per the instruction sheet on the 'net - but when I conneted the pipe, the fluid level sank out of sight Jentle blowing from the tank end caused the fluid to rise in the guage, but it does not settle at "zero" but below.

I can't quite grasp why it says you have to run the car for a few miles and it should hold the correct level for an hour???

Simon Hyslop

Re: Hobson fuel guage.

Post by Simon Hyslop »

Hello Stan,

The reason you have to run the car is because it is the motion of the petrol in the tank that creates the pressure that moves the air in the line that moves the fluid in the gauge. It's completely unlike the principle we're used to with the electric gauges where the level of the petrol is in itself the determinant of what the indication is. If everything is all right otherwise, i.e. no leaks, the level should thereafter remain correct. If it doesn't, there is a leak somewhere. I'm not entirely sure that the amount of fluid in a bottle from Vintage Supplies is enough to fill a completely empty gauge.

What I can say is that when they were fairly new, the gauges were completely accurate (well, it was my father who told me that from several Lanchesters he had with them) and deficiencies in them now are due to to something being wrong rather than a flaw in the design. Worth persevering!

Stan Thomas
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Wise Man
Posts: 795
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Hobson fuel guage.

Post by Stan Thomas »

I certainly will persevere Simon - thats why I took weeks to carefully repair all the burr walnut veneer before re-lacquering, and I had a speedo dial specially made!! I believe It's the detail that makes the car and gives the greatest satisfaction, not just attanding to the big bits ......................

Thanks for your advice - and I owe you a ride in a sleeve valve.

Stan

P.S.
Bring some oil!

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