'Possible' fuel issue

[Ernest]

Hi all

I took the TR our earlier this week - hot day - following a 30 mile run I stopped for lunch parking the car in the sunshine. About an hour later, when leaving, the car would not start. So I opened the bonnet to allow more air circulation and turned off the fuel.

After waiting about 30 mins I turned the fuel back on and the car started first time and run fine for the 10 miles home.

Was the non-starting related to what has ben termed 'cavitation'? Can anyone please explain what might have happened.

Best Wishes

Ernest

[JohnC]

Might be cavitation, particularly if you have the original Lucas pump (and if it hasn't been reconditioned in 50 yrs), but it may equally (or more likely) be fuel vaporisation in the PI pipes between metering unit and intake manifold. You haven't got braided fuel hoses, by any chance, have you?

But in answer to your question, cavitation occurs in the pump when the pressure drops below the vapour pressure of the fuel. That could be caused by high temperature or by a restriction in the fuel supply to the pump, or a combination of both.

JC

[astontr6]

2 hours ago, JohnC said:

Might be cavitation, particularly if you have the original Lucas pump (and if it hasn't been reconditioned in 50 yrs), but it may equally (or more likely) be fuel vaporisation in the PI pipes between metering unit and intake manifold. You haven't got braided fuel hoses, by any chance, have you?

But in answer to your question, cavitation occurs in the pump when the pressure drops below the vapour pressure of the fuel. That could be caused by high temperature or by a restriction in the fuel supply to the pump, or a combination of both.

JC

if the coil is mounted still on the engine block this can also cause this problem of hard starting as the coil becomes very hot. My car suffered from this problem and I over came this by machining two insulation blocks made from Tufnol.

Bruce

[RobH]

17 minutes ago, astontr6 said:

this can also cause this problem of hard starting as the coil becomes very hot.

Not doubting your experience Bruce but I can't think of any mechanism which will reduce the coil performance as it gets moderately hot (< 150ºC).  

The only limitation would be the insulating varnish on the winding but to degrade that that would take more heat than the engine can provide and would be permanent.  The Curie temperature at which iron loses its magnetic properties is 770ºC so it can't be that...

[Mike C]

8 hours ago, Ernest said:

Hi all

I took the TR our earlier this week - hot day - following a 30 mile run I stopped for lunch parking the car in the sunshine. About an hour later, when leaving, the car would not start. So I opened the bonnet to allow more air circulation and turned off the fuel.

After waiting about 30 mins I turned the fuel back on and the car started first time and run fine for the 10 miles home.

Was the non-starting related to what has ben termed 'cavitation'? Can anyone please explain what might have happened.

Best Wishes

Ernest

Might be fuel vapourization. What was the ambient temperature when this fault occurred?

[astontr6]

16 hours ago, RobH said:

Not doubting your experience Bruce but I can't think of any mechanism which will reduce the coil performance as it gets moderately hot (< 150ºC).  

The only limitation would be the insulating varnish on the winding but to degrade that that would take more heat than the engine can provide and would be permanent.  The Curie temperature at which iron loses its magnetic properties is 770ºC so it can't be that...

I might have had a faulty coil but the problem went away after fitting the Tufnol insulation blocks?? What effect does hot oil have on the windings??

Bruce.

[RobH]

1 minute ago, astontr6 said:

What effect does hot oil have on the windings??

Basically nothing Bruce. The oil is electrically inert and is there to take the heat away from the windings and dissipate it through the case.

[Ernest]

Thanks all for this helpful information.  The fuel lines are not braided and the fuel pump is a fairly new (two year old) Bosch. The coil is attached to the block but by a bracket that means it is at least and inch and a half away.

I can't see an obvious solution - but if it only means that if the car fails to start following a run on a hot day then I just have to be patient and let it cool down.

In the seventies and eighties I ran a TR6 and and TR5 as daily drivers (both with the Lucas pump) and I never experienced this problem.

Thanks again

Ernest

  

[Mike C]

You've fitted a  pump fairly  recently. Make sure the pump suction is free of restrictions and low relative to the tank's fuel level.

Cavitation/ vapourization of the fuel only occurs on the suction side of the pump.