Fuel vapourisation

[andrew34ruby]

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?

I'm not sure about this. Would the lighter fractions still boil at the same temperature? I'm inclined to think that the mixture will boil at a different temperature, and probably a higher temperature?

[Colin Morgan]

I'm not sure at what temperature boiling would start either.

I read that petrol has a boiling point range from about 35-70 degrees C - and somewhere else that petrol 'starts to boil at about 50 degrees C' - so the lighter fractions might start gassing off before the heavier ones, which could lead to vapour lock in the fuel lines?

(Isn't this how the different fractions are separated when crude oil is being processed at the refinery - or is there more to it? Any chemical engineers care to comment?)

[Malcolm Parker]

The only time that my RL saloon has suffered from fuel vapourisation was on a Settle to Carlisle Run on the steep climb up to Dent Station.  For some reason I was using normal Tesco unleaded at the time.  The solution to the problem was to enrichen the mixture by two flats on the SU carb.  I use the standard two blade fan and have a simple copper pipe from the scuttle tank to the carb, no heat baffle, insulation or anything, just a bit of common sense where the pipe runs.   I don't use an in line filter either, with an SU there is little chance of a blocked jet.  I think many fuel problems seem to be linked to the use of in-line filters.
My car is all black so in theory that should be the worst possible colour for absorbing the sun.   I drove down to the Centenary Rally last July in 40C heat and suffered no fuel problems, despite the under-bonnet temperature being very high due to a radiator leak.
I always run on E5 petrol.  I suspect that E10 may have a lower boiling point as it has a higher ethanol content?

[Reckless Rat]

I've never noticed any difference with whatever fuel I put in the RP. Melted lard (chip fat) seems to work just as well... however my problems with vapourisation have stopped since I swapped the 26VA to an SU H1 (and fitted a 4 blade fan). The difference though is that Bob's RN is a front tank model, gravity fed. Fuel in a rear tank should theoretically stay cooler. More annoying for Bob than the rest of you because he lives where it tends to be a bit warmer than the UK...

As an aside I knew someone with a Reliant Scimitar that suffered from constant vapourisation problems. It was finally rectified by the creation of a cooling duct to push colder air from the front of the car to the carb area to keep the temperature down, and a heat shield to shade it from the exhaust.

[Malcolm Parker]

My RL is fitted with the correct flitch plates either side of the engine.  It may seem that these could increase the temperature in the engine bay but I am wondering if they might actually improve the cooling?  As we know air flow and cooling is a complicated field and sometimes funny things happen!

[Steve Jones]

The only time I've had real vapourisation problems with my Saloon was climbing the Kirkstone Pass on two of Malcolm's Cumbria runs. Following advice from Dave Mann, I removed the flitch plate on the near side in an attempt to get more outside air past the carburettor (bronze Zenith updraught) and I had no problems when climbing hills during the heat of Morton last year or this May when it was hot during our week in and around Presteigne. Has that solved the problem? Don't know as I've not taken it up the Kirkstone Pass yet!

Steve

[bob46320]

Hi Steve. Flitch plates have never been fitted, so that is another one off the list. I am going to have a go at the 10% mix and run around with a 20 litre can of ordinary petrol (just in case).
Why did Austin move the tank from under bonnet to the rear in 1933 ?? It wasn't to reduce the production costs !
Bob

[bob46320]

Hi Dave, any idea what sort of thickness the wedges were (Ie: how much bonnet lift) - were they the sash window wedges or the household door wedges.? Worse still, were they the 2CV wheel chocks ??

[Dave Mann]

I was only a kid when they were in use, I would have thought they would have been more common in tropical countries. I'm guessing that they raised the bonnet rear edge by 12 to 1.5" it's a long time ago.

[Dave Mann]

Oops, fat fingers strike again it should read 1" to 1.5". I've looked all over Google and it failed to provide any pictures.