Joined: Mar 2018 Posts: 682 Threads: 33
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Location: Lot region FRANCE
It's summer and getting hot again. Even with all my insulation of fuel pipe (horizontal expansion loop), exhaust pipe wrapping, 4 blade fan etc we suffered vapour lock groaning up a long hill in second after completing about 80 miles of our outing.
It was the end of the day, about 36 C . Stopping and feeling the 1932 RN's bulkhead fuel tank I would hazard a guess that it was in excess of 55 C. as today on another run out the tank seemed relatively cool at 48 C (temperature sensors re-installed)
Looking on the Bravenet site, there is a recommendation of adding 10% kerosene / heating fuel. Apart from legal issues, anyone here tried it ?
Bob
Joined: Aug 2017 Posts: 982 Threads: 97
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Location: Cheshire
Have tried 10% kerosene in petrol in a 1926 Vauxhall - it gave it a slightly higher top speed in tests - would expect it to be fine in a Seven. I believe that the adding 10% is allowed in the UK, but it wasn't really worth it from the power point of view. As to helping vapour lock - not sure about that - would be interested to hear if it does make a difference. Not that I have a vapourisation problem in Cheshire - as yet.
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Back in the scorcher of 1976 my 34 box suffered really badly from vapour lock, I found a quick fix to get going was simply to pour some cold water on the petrol pump and carb, it was so bad on the way to the Beaulieu Rally I had the bonnet off and on the back seat best regards Rob.
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Location: Deepest Frogland 30960
Car type: 1933 RP Standard Saloon
Strange though that yu are still suffering despite all the mods. It must be really frustrating. I had to run with the bonnet half open (carb side) on long hills in the RP until I fitted the 4 blade fan. I would have though that would have sufficed but obviously not. Have you tried running with the bonnet open, Bob?
Joined: Mar 2018 Posts: 682 Threads: 33
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Location: Lot region FRANCE
Hi Bruce. I guess we keep going until the problem arrives - normally half way up a hill where you can't stop! I have made a "bonnet prop" which I can install within minutes once stopped.
My temperature measurements indicate that the carb temp is within a degree or two of the fuel tank temp. However when the tank is "super hot", a stop of 10 mins or so and then bonnet off is sufficient to drop the carb temp by a couple of degrees and away we go again.
What I would like to find out is what did Austin do when they sold to India etc. Are todays problems down to fuel or equipment?
Our latest "attack" was on a hot day and long run with some good hill climbing in 2nd. Difficult to replicate after implementing some changes. I have an idea of "Teeing" off a bottle of fuel mix - 10% heating fuel and when the "attack" comes, switch over. We will see!
Joined: Aug 2017 Posts: 2,930 Threads: 160
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Location: Sherwood Forest
Car type: 1938 Talbot Ten Airline
Many years ago I tried running my Seven on a mix of paraffin and petrol - totally unscientific but I would guess around 10% paraffin - and there appeared to be no difference in running or performance. I have no idea whether it ran any cooler - we didn't seem to have such hot weather back then and certainly not the traffic hold-ups. The blend probably still had a higher octane rating than pre-War fuel.
Joined: Aug 2017 Posts: 982 Threads: 97
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Location: Cheshire
Looking up the boiling point of petrol, it gives a range of 35 to 70 degrees C as petrol is composed of various hydrocarbons - some boiling at a lower temperature than others. So, if a fuel tank reaches about 50 degrees C, the lighter fractions in the fuel will be ready about to boil, if the aren't already. As the temperature in the carb is similar - just a couple of degrees higher - it seems that not much heat is being added in the fuel lines? However, once vapour has formed and flow stops, then further heating of the stationary fuel will occur e.g. by radiation from the hot manifold. A baffle could help reduce this, but if the tank is so warm, there isn't much margin before problems occur again?
Adding 10% kerosene would mean that 10% of the fuel has quite a high boiling point, the remaining 90% will still contain the light fractions that will boil in the range 35 to 50 degrees C. Therefore, adding 10% kerosene might not help much in avoiding vapour lock occurring?
Running with the bonnet raised or off presumably helps keep the fuel in the tank much cooler on a long run? 50 degrees seems very warm - I also wonder what range of operating temperatures Austin considered, given they were happy to export to places like India. Other than a four-blade fan, were there any other modifications?
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17-07-2023, 10:12 PM
(This post was last modified: 17-07-2023, 10:13 PM by Peter Naulls.)
My brother's Chummy suffered terribly on the Eurotour 6 years ago, but only in traffic. It would run all day at any temperature and up any gradient but couldn't cope with idling, so we resorted to pushing it!
We talked about making a water-soaked wadding jacket for the carb - utilising the cooling effect of evapouration, in the manner of one of those old cooling-boxes we used before fridges were commonplace. Once home the motivation to find a solution seemed to disappear however.
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Removing the bonnet will mean that the petrol tank will be heated by the sun, you could try fitting rubber wedges under the rear edge of the bonnet to lift the rear edge up to increase the air flow. About 70 years ago you would see these wedges used to improve engine cooling.
