Fuel vaporisation problem TD21

For all TD 21, TE 21, TF 21 and TC108G cars
John bullock
Posts: 2
Joined: Fri Jul 06, 2018 12:15 pm
Name: John bullock

Fuel vaporisation problem TD21

Postby John bullock » Tue Jul 10, 2018 10:49 pm

When having a fully overhauled engine and ancillaries fitted to my TD21, I decided to have the previously re-routed fuel lines returned to factory spec and the electric fuel pump removed.

My delight with a now very cool running engine, excellent oil pressure and a significant improvement in performance turned to disappointment the moment that the spring turned to summer due to a severe fuel vaporisation problem that to be honest, removed all the pleasure in taking the car out.

I did not want to re-route the fuel lines, reinstall an electric fuel pump, or attempt any of the other suggestions like wooden clothes pegs or bags of ice. In desperation I tried a product from the USA ( but available here in the UK ) by the name of “Cool Tube” - this is a corrugated nylon tube covered in a reflective metallised material, with very high temperature resistance, both direct contact and reflective.

I was very dubious, but this has transformed the performance of the car which has been happily running in the recent 25 deg. plus heat, longest run being 1 1/2 hrs non stop without a whiff of fuel or stutter of the engine.

The inside diam of the tube is 1/2 inch which fits nicely over the TD fuel lines. Because the tube is slit down one side and very flexible it slides easily over the fuel lines without having to disassemble them. Just four Pieces need to be cut to cover the fuel line from the mechanical pump to the carbs. Cost circa £60 - two 3ft packs. There are other similar products available, all with similar heat resistance but this one seemed the neatest and easiest to fit in my view.

Fitting time just 15 minutes, (and less time to remove and re-fit if you wanted to show the car) and together with some nice stainless steel ties to finish to job off, it does nor look too obtrusive in the engine bay!

Posts: 40
Joined: Wed May 23, 2012 6:55 pm
Name: Charles Van Ingen

Re: Fuel vaporisation problem TD21

Postby vaningen » Sat Jul 14, 2018 7:33 pm

I wonder how long your engine will run normally when stuck in traffic with the temperature at 25C. It strikes me that the fundamental problem with these cars nowadays is that modern petrol vapourises at 50C whereas years ago it was 80C. I find that the temperature of the float chambers after a run is 50C; so fine when going along but tricky in a traffic jam.

The only problem that I remember in the hot summer of 1976 was hesitation in the first 3/4 mile after stopping at a motorway services until cool petrol was drawn through.

So my TD21 has an RT fitted electric fuel pump at the tank which simplifies starting but they reckon that the original fuel line routeing is ok; however, the Roland Simmonds view was that routeing the fuel line to come up to the carbs was advantageous as it allowed bubbles to disperse.

Posts: 340
Joined: Mon May 21, 2012 10:14 am
Name: Richard Wallach
Location: Melbourne, Australia

Re: Fuel vaporisation problem TD21

Postby RichardWallach » Sat Jul 14, 2018 11:53 pm

Two most interesting posts. Thankyou John for sharing your solution. It would be worth letting members know where you purchased the flex shield. Here in Melbourne 25C is a mild day. A summer temperature of 35 degrees or more is quite common. I have no problem with my TA21 overheating or having fuel starvation issues. In the end it comes down to the body design. The TA being very old fashioned has a bigger under bonnet air cavity which allows for the expelling of hot air.


John bullock
Posts: 2
Joined: Fri Jul 06, 2018 12:15 pm
Name: John bullock

Re: Fuel vaporisation problem TD21

Postby John bullock » Sun Jul 15, 2018 2:36 pm

Particular thanks to Richard for reminding me of Melbourne summer temperatures! My wife and I made five consecutive Australian high summer visits to Melbourne to visit family until 2016 when they returned home. Something else!

The TD has been out in heavy traffic with temperatures approaching 30 deg (month long heatwave over here), and so far no problem to report, and good not to have that vapour smell in the cabin. Also re-starting first turn when parked up for a while when hot.

For anyone interested, the Cool Tube product is made by Design Engineering of the USA. They make a whole range of such products aimed at the performance/hot rod market, so not really Alvis territory!

I purchased my tubing from Demon-Tweeks.com who are big suppliers to the boy racer market here in the UK, but will also accept orders from senior citizens like me.

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