Fuel vapourisation... A problem when new?!

harveyp6 wrote,...
even if it is vapourisation why must it be vapourising before it gets to the pump, rather than as it rises up to the filter?
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Physics...with lower pressure as is the situation before the pump, the boiling point of the fuel will be lower than it would be after the pump where the pressure is greater. When a liquid boils, the change of state is seen to be occuring at the surface, liquid bubbling rapidly with liquid vapour rising forth, but right through the liquid the process is occuring, bubbles are forming and rising to the surface, the change of state is taking place throughout the volume of liquid.

http://www.tutorvista.com/content/chemi ... erties.php

Ron.
 
harveyp6 said:
Two things:

Firstly why would you automatically assume that the problem is vapourisation rather than an intermittant fault in the pump,
and secondly, even if it is vapourisation why must it be vapourising before it gets to the pump, rather than as it rises up to the filter? By your logic you would fit an electric pump and then say it cured the vapourisation, when in fact all it did was bypass another fault that you never found.
Click to expand...

I concur with Harvey on this, having had almost identicle symptoms to yours except I had an electric pump under the bonnet. I tend to suspect that you have a dodgy mechanical pump, not intermittant but faulty all the time and that heat merely exacerbates the problem. My course of action would be to replace the mechanical with another known good one or secondly refurbish the existing one, then if there is still a problem look furthur afeild.

Graeme
 
ghce wrote,...
I concur with Harvey on this, having had almost identicle symptoms to yours except I had an electric pump under the bonnet. I tend to suspect that you have a dodgy mechanical pump, not intermittant but faulty all the time and that heat merely exacerbates the problem. My course of action would be to replace the mechanical with another known good one or secondly refurbish the existing one, then if there is still a problem look furthur afeild.
Click to expand...

Hello Graeme,

The given frequency of the problem and the number of cars effected would tend to suggest that Simon's fuel pump is not the specific problem. Given the operation of the pump which consists of a diaphragm and two valves, the only variable that is going to change when the temperature increases is the formation of vapour before the pump. If the pump has a fault, then it will be there regardless. If the main diaphragm has a split which compromises its abiity to draw a sufficient vacuum, thus limiting the fuel which is being delivered, then there should be fuel entering the engine. A check of the dip stick and the smell of fuel in the oil will instigate further investigation.

Ron.
 
Indeed you are possibly right, the P6 cars seem to operate "on the edge" of the reliability curve but one thing is certain the cars left the factory as functional units so something must change for them to become less reliable, in theory stock componantry will work, poorly sealing valves in the pump will reduce the ability to suck. I do not doubt that an electric pump under the tank will cure the problem but as Harvey said you will probably just be bypassing a fault rather than curing it

Graeme
 
ghce wrote,...
the cars left the factory as functional units so something must change for them to become less reliable
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Hello Graeme,

I expect that they did, or at least that was the intention.

I remember when I joined the P6 Rover Owner's Club in circa 1988, reading articles on fuel vapourisation which occured on a regular basis in the magazine at that time. I used to think...how can this be,..cold climate relatively speaking and cars are vapourising, while here in Sydney or around the country side, much higher tempertures and no problems at all. Of course that all changed in 1990 when en masse Rovers were dropping like flies with vapourisation issues. Lasting 2 years nothing corrected the problem until I installed an electronic fuel pump to run in series with the mechanical pump. Switched off until needed, it could be called into action with the flick of a switch and no more problem!!

After the two years, the fuel problem was corrected (leaded fuel at the time) and en masse Rovers all over Sydney were again working as they had been. There were many lengthy discussions with owners when I met them at the N.S.W Rover Owner's display day.

The problem has never repeated and my electronic pump remains turned off with the mechanical AC doing a fine job. So what could be the cause? The only significant variables between cars in different parts of the world are the climatic conditions and the specifications of the fuel that is provided in those locations. Fuel here and in the U.K may well have the same octane rating, but does that also mean that the flash point etc also remains the same? I would be very inclined to think not.

Ron.
 
SydneyRoverP6B said:
harveyp6 wrote,...
even if it is vapourisation why must it be vapourising before it gets to the pump, rather than as it rises up to the filter?
Click to expand...

Physics...with lower pressure as is the situation before the pump, the boiling point of the fuel will be lower than it would be after the pump where the pressure is greater. When a liquid boils, the change of state is seen to be occuring at the surface, liquid bubbling rapidly with liquid vapour rising forth, but right through the liquid the process is occuring, bubbles are forming and rising to the surface, the change of state is taking place throughout the volume of liquid.

http://www.tutorvista.com/content/chemi ... erties.php

Ron.
Click to expand...

Quite correct! The fuel downstream from the pump will be at a higher pressure and less prone to vapour lock. Is your filter before or after the pump? The added suction needed to pull through if it's before could be all it takes to induce vapourisation in the line.
 
The fuel between the pump and tank will only be at a very slightly lower pressure than between the pump and the carbs, because the fuel running through the spill return will be at that higher pressure when it re enters the line just after the tank, and as it takes the path of least resistance it will push its way back towards the pump rather than trying to force its way back up into the tank. The mechanical pumps won't pull fuel up from the tank unless there is enough in there to give it a helping hand, hence if they run out, you won't get them restarted by adding 1 gallon you need more.This in itself proves there isn't much of a lower pressure there because there's very little suck from the pump, if there was you'd get them to pull up any small amount put into the tank when run out to empty. You can also get them started without waiting for the engine to cool when they vapourise, by cooling the carbs and the line across the engine, not by cooling the pipe to the pump.

There's enough on here now for anyone who suffers with the problem to make their own minds up as the way that they want to cure it. I won't be changing what I do, and I won't be wasting any more time justifying it either.
 
Gents

Sorry to resurrect this thread but in Government speak I had my first "Fuel Vapourisation Event" today. There have been a couple of times when the engine has got a bit warm and started to almost .......missfire. Today whilst sitting in roadworks it cut out altogether. Recognising the symptoms I lifted the bonnet and let the engine cool for a bit and she started again.

Bizarrely the car has never given me problems in the year or so since I bought it. I have a theory, however......

The problem has only manifest since I cleaned the engine...........

I think that whilst the engine was covered in a thick layer of oil and crud that it might have been creating an insulating layer preventing the fuel lines getting too hot from radiated heat. Now that the engine is nice and clean there is no such insulation and the radiated engine heat can now transfer to the fuel lines causing vapourisation.........

.........in other words if your engine is dirty and you don't suffer from fuel vapourisation then don't clean it!

Thoughts?

Dave
 
Hello Dave,

Have you noticed if your engine temperature is running cooler since you cleaned your engine? What was the gauge and approx ambient temperature when it vapourised?

If the grease does offer thermal insulation properties, then would that not mean that the heat within the engine would build to a level higher than if the engine was clean? If this is the case, then the coolant temperature would be running at a higher point on an ongoing basis would it not?

What have been your observations Dave?

Ron.
 
SydneyRoverP6B said:
Hello Dave,



then the coolant temperature would be running at a higher point on an ongoing basis would it not?

What have been your observations Dave?

Ron.
Click to expand...

surely not, the thermo stat will account for the xtra load caused by the lack of radiated engine cooling, leaving the radiator to deal with with any excess temp rise, that wacking great mecahnical fan should have more than enough reserve cooling capacity. ie I doubt you would notice any changed meter deflection or engine temp change. It is interesting however that the grubby engine may make such a significant difference and I would not discount it at all put that in conjunction with the recent thread regarding ceramic coating on and in exhaust manifolds then there are a few more options in the arsenal to combat that lurking fuel vapour lock problem.
Incidently mine vapour locked the other day for the first time since I cured my electric fuel pump vapour lock inducing problem so I will be on the look out for some furthur heat reducing stratergies also.

Graeme
 
SydneyRoverP6B said:
Hello Dave,

Have you noticed if your engine temperature is running cooler since you cleaned your engine? What was the gauge and approx ambient temperature when it vapourised?

If the grease does offer thermal insulation properties, then would that not mean that the heat within the engine would build to a level higher than if the engine was clean? If this is the case, then the coolant temperature would be running at a higher point on an ongoing basis would it not?

What have been your observations Dave?

Ron.
Click to expand...

Hi Ron

There's been no noticeable difference in running temp since I cleaned the engine. Since I had my rad recored (before I cleaned the engine) the temp gauge sits covering the 8 most of the time. Ambient temp was probably in the region of 15 degrees C. I was stopped at roadworks in quite a long queue of traffic which was moving very slowly. The electric fan kicked in as the gauge travelled over the 5 and the temp sat there steady for the whole time. After about 10 mins of this there was a noticeble change in the engine idle from the usual smooth running to becoming almost like a missfire. Realising what was happening I put the heater on full to try to draw some heat away but a few minutes later the engine died altogether. Temp gauge was still sitting steady over the 5. After letting things cool down for about 10 mins the engine started again and I was able to get going. I made it far enough forward in the roadworks to get through the lights shortly after so had no further problems.

ghce said:
that wacking great mecahnical fan should have more than enough reserve cooling capacity.
Click to expand...

Graeme, I took the mechanical fan off when I fitted the electric. I'm going to have a look at ways to wrap the fuel pipe in heat resistant material to see if that helps. Failing that the mechanical fan will go back on to see if that makes any difference.

Dave
 
When i was wrestling with my fuel vapour problems I often thought that the best cure short of a reroute of the fuel lines (as has been recently posted here) would be to vent the engine bay either passivly or by forced fan. I dont beleive that it is the engine heat that causes the problem so much as the removal of the built up heat in the cavity around the engine that effects the fuel system.

Graeme
 
ghce said:
I dont beleive that it is the engine heat that causes the problem so much as the removal of the built up heat in the cavity around the engine that effects the fuel system.
Click to expand...

You could well be right there. There's a lot of heat generated by the exhaust manifolds that radiates around that area too. I've asked a few people that I know in the extreme performance car business for advice on what can be done to protect the fuel lines from radiated heat, but how about fitting a couple of fans somewhere in the engine bay to draw cool air in from outside. Not sure where to fit them but there must be something out there. Or even just something to keep the air moving around the cavities to prevent the build up of heat......

......or maybe I'll just re-route the fuel lines..... :? Most of the posts about re-routing the fuel lines have been in conjunction with fitting an electric pump. I wonder if I could re-route out to the wheel arch and back in to the mechanical pump. Hmmmmmmm :)

Dave
 
I think that piece of rerouting is exactly what gareth did...

Does your fuel line along the bottom of the engine have the heat resistant covering on? Mine has it but i've seen a couple without it...

Rich
 
rockdemon said:
Does your fuel line along the bottom of the engine have the heat resistant covering on? Mine has it but i've seen a couple without it...
Click to expand...

No it has no covering on it......but it will do soon. Do you have a picture of the covering on yours?

Dave
 
Hi all

Got my "cool tube" fitted this weekend and it seems to have helped. Let the engine get nice and hot with no vapour lock when stationary or when pulling away :D

I've covered the fuel pipe from the pump....
CIMG3873.jpg


along the side of the engine block.......
CIMG3875.jpg


and up over the back of the engine to where it joins with the flexible pipe under the air cleaner box.......
CIMG3874.jpg


Time will tell I guess, but hopefully it's £25 well spent.

Dave
 
Very similar to the stuff I used on my MK 2 Escort racer, that was to stop the speedo cable melting though :LOL:
It worked :wink:
 
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