Fuel cooling pipe

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shep
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Fuel cooling pipe

#1 Post by shep » Fri Apr 07, 2017 7:49 pm

Hi all, I'm sure this has been on here before but my PI is cutting out in the hot weather and I think its fuel vaporisation around the pump. I have a bosch pump fitted and I was wondering if the lucas curly fuel cooling pipe would fit. Has anyone done this?
Cheers Paul.

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Jonathan Lewis
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Re: Fuel cooling pipe

#2 Post by Jonathan Lewis » Sat Apr 08, 2017 9:24 am

From memory, the Bosch pump units are of smaller diameter than the motor body on the Lucas pump, so a cooling coil intended for Lucas PI may not readily fit.

Secondly, the construction of the Bosch pump is such that the motor (what you're trying to cool on the Lucas pump with the cooling coil) is effectively fuel-cooled to begin with. In either case, the fuel cooling feature only tends to work best with a relatively full tank of cool fuel; as the temperature of the fuel load rises (remember that it receives warmed fuel returned from both the pump and the MU on the engine), then it obviously becomes progressively less efficient at taking excess heat away from the pump.

Something to bear in mind is that the Bosch pump is designed to work at rather greater fuel flow rates than the Lucas unit, so any restriction in terms of pipework/filtration on the supply side could be causing cavitation problems which might be more apparent in warm weather.

Can you hear the pump running after the car cuts out? If not, are you sure that it is a fuel problem, or might it be ignition-related (see past threads on distributor arms and other components suffering intermittent failures when warm) or perhaps a problem with the electrical feed to the pump? (the inertia switches fitted to Mk2 cars can sometimes be troublesome).

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Re: Fuel cooling pipe

#3 Post by Alec » Sat Apr 08, 2017 11:11 am

Hello Shep,

I would take Jonathan's last suggestion first. It is fundemental that the pump gets full voltage at the pump. My P.I. has a relay in the boot (and the battery, but that's not a requirement) with large section cables. This gives a sound basis to work from should you still experience problems.
A cooling coil is made very simply by using copper brake line. It shouldn't matter if the tank is full or not as it uses the refrigeration principle of releasing the pressure of a liquid causeing it to cool, that is why it is connected into the pressure relief valve discharge to the petrol tank. How good a refrigerant petrol is I wouldn't have a clue though.

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Jonathan Lewis
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Re: Fuel cooling pipe

#4 Post by Jonathan Lewis » Sun Apr 09, 2017 12:53 pm

Alec wrote:It shouldn't matter if the tank is full or not as it uses the refrigeration principle of releasing the pressure of a liquid causeing it to cool, that is why it is connected into the pressure relief valve discharge to the petrol tank.
Fair point, Alec, but the heat that the returned fuel is taking out of the pump via the cooling coil still ends up back in the tank, heating the fuel load and potentially contributing to cavitation problems as soon as that warmed fuel reaches a pressure drop point (e.g. across a filter) or something warmer still (e.g. the pump), and that heating effect will presumably be quicker with a part-full tank than a mostly-full one? Not saying that cooling coils don't have a use, but that they do have limitations.
Alec wrote:It is fundemental that the pump gets full voltage at the pump. My P.I. has a relay in the boot ... with large section cables. This gives a sound basis to work from should you still experience problems.
Absolutely. If anything, perhaps even more important with a Bosch pump than a Lucas one...

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Re: Fuel cooling pipe

#5 Post by Alec » Sun Apr 09, 2017 4:20 pm

Hello Jonathon,

the issue of the cooling coil is something that probably has not had a lot of research. As I said I have no idea how good a refirigerant petrol is. In a refrigeration circuit it is hot pressurised liquid that once it passes through the expansion valve is then cold (gas) and remains so for it's time in the evaporator so is cold not hot. I'm fairly sure the petrol remains liquid so perhaps there is not that much refrigeration going on?

I did for a while run a cooling coil but have not used one for years and have not experienced any pump issues without it (this is still with the Lucas pump).

Alec
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Re: Fuel cooling pipe

#6 Post by Jonathan Lewis » Sun Apr 09, 2017 5:57 pm

Hi Alec,

I seem to remember from experience with a length of transparent plastic pipe in the return line from the PRV that the fuel stream going through was liquid rather then spray, but interspersed with a lot of bubbles; presumably pockets of vapour resultant from the pressure drop effect as the surplus fuel exits the PRV? What refrigeration (as opposed to simple heat transfer) effect there might be, I have no idea.

But - I think that we are in danger of straying into the realms of thread drift here... :wink:

Jonathan

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Re: Fuel cooling pipe

#7 Post by shep » Mon Apr 10, 2017 6:09 pm

Cheers for the replies, I think I will check all the wiring first then before going down the cooling route! Thinking about it, it may well be an ignition fault cos it does stutter now and then so I will check and renew anything that needs it. Really do appreciate your help, you've given me other options to try, thankyou!

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Re: Fuel cooling pipe

#8 Post by Jonathan Lewis » Mon Apr 10, 2017 8:11 pm

You're welcome :)

As far as I'm aware, Bosch pumps don't have a reputation for overheating, hence my wondering if it is an electrical problem with ignition or the supply to the pump. Your problem could be due to fuel vapour-locking but, if so, I suspect that the issue is more likely to be with a clogged filter or some other restriction in the fuel feed than through pump overheating.

Good luck - let us know how you get on!

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Re: Fuel cooling pipe

#9 Post by shep » Tue Apr 11, 2017 7:54 pm

I will do thankyou. Hopefully something easy!

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Re: Fuel cooling pipe

#10 Post by Mike Stevens » Fri Apr 14, 2017 8:57 am

I've had 2 PIs, both with (different!) Bosch pumps and have never experienced pump overheat problems. The current PI has a high current feed direct from the battery (via a fuse in the engine compartment!) to relays which use the original supply wires for their coils for both the PI pump and HRW, (and one for a boot mounted radio, but that is a different story!).

I would investigate any possible ignition problems before necessarily blaming the PI system. However, fitting a relay is definitely a good idea!

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