Bio temperature, viscosity and lubrication.

[Julian]

I had a problem on my previous Disco where the engine felt like it was missing, especially noticeable under load.  The problem was cured by fitting a secondhand IP.

The same problem has manifested it's self on my current Disco.  The first thing I did was to change the IP for a spare I had, but that failed to cure the problem.  Since that time I have ... changed the filter, cleaned out the sedimenter, changed all the injectors for secondhand items, fitted a new head, valves and associated components, new push rods, 4 new rockers, one new lash cap, carefully set the tappets, checked the crank shaft pulley damper is OK and checked there's good pressure being produced by the lift pump.

Driving it recently, I've noticed that the problem gets worse the hotter the fuel/engine gets.  I've made this heated filter to combat HMPEs ... http://www.vegetableoildiesel.co.uk/forum/viewthread.php?tid=27774, so I can see the temperature of the fuel in the filter.  Electrically it heats to between 25°C and 30°C.  Running off the cooling system it rarely gets hotter than 40°C in operation, but after a hot engine has been switched off temperatures in the filter can rise to 65°C, presumably by thermal syphon from a hot engine.

From kind answers on the VOD and trawling the internet the temperatures to which I'm heating the fuel shouldn't be the cause of the problem, but I'm coming to the conclusion that the problem lies with the IP despite changing it.

I'm wondering if the change in fuel temperature from an ambient to running temperature would alter the viscosity of the fuel sufficiently to exasperate ware/damage in the IP, making the problem more noticeable.

Any diesel experts able to confirm?

[nigelb]

I doubt very much that the lubricity of bio or veg alters with the changes of temperature you describe Julian. I don't doubt for a moment that the viscosity changes with temperature elevations but its lubricity should remain the same.

Nige

[Julian]

I'll see if I can find them again, but I had a paper from a Lithuanian University open which gave details of the changes, then IE crashed and I lost them.  I Know I'm only talking of a few degrees difference, but with tolerances in an IP being very small, I'm wondering if it might make a noticeable difference.

[Julian]

There we go it was downloaded from the link on this page ... http://www.tandfonline.com/doi/abs/10.1080/16483840.2002.10414034

[K.H]

If its noticeable would bypassing the heater for a while make it go away or is it a progressive problem?

[K.H]

Could it be related to the cetane value of your fuel? what is your main feedstock higher or lower than pump diesel?

[Julian]

If its noticeable would bypassing the heater for a while make it go away or is it a progressive problem?

I have the coolant heating on a valve and obviously I can switch the electrics off, but that only prolongs the heat up period.  Eventually the IP will reach running temperature and the problem is as bad as ever.

The heater issue is a bit misleading, I don't think it's that hat's causing the problem, but by switching it on and off it seems to be pointing to fuel/IP temperature that makes the problem evident.

[K.H]

Can you increase the lubrication of your bio as a test?
With the cetane it was the fact that pinking in old cars always got worse the hotter the car got and that was down to octane

[Julian]

Could it be related to the cetane value of your fuel? what is your main feedstock higher or lower than pump diesel?

No Idea of cetane values, but I don't think that the issue.  If it were power would be down across all 4 cylinders.  It seems to be just one cylinder not firing fully.

[K.H]

Could it be related to the cetane value of your fuel? what is your main feedstock higher or lower than pump diesel?

No Idea of cetane values, but I don't think that the issue.  If it were power would be down across all 4 cylinders.  It seems to be just one cylinder not firing fully.

Just one cylinder? that rules out both my ideas,i will go away now

[Julian]

Can you increase the lubrication of your bio as a test?

I guess adding 2 stroke oil might increase the lubrication, but I'm guessing the damage has been done and something is worn in the IP (in fact both IPs I've tried) which is exasperated when slightly hotter fuel is used ... hence banging on about viscosity.  But as Nige points out the viscosity change will be very small.

Wonder if it could be heat increasing a warn part beyond tolerance?

[Julian]

Could it be related to the cetane value of your fuel? what is your main feedstock higher or lower than pump diesel?

No Idea of cetane values, but I don't think that the issue.  If it were power would be down across all 4 cylinders.  It seems to be just one cylinder not firing fully.

Just one cylinder? that rules out both my ideas,i will go away now

Oh on, don't go away!  It's quite a novelty to corespond without being slagged off!

[Head Womble]

Have you managed to determine which cylinder is misfiring ?
Have you done a compression test across all cylinders ?

From what I understand the timing advance is dependant on the pressure in the return side of the pump,
so as the fuel changes viscosity so will the return pressure,
now if you've got one injector that's not set at the right pressure this could be magnified by the timing advance,
this is purely me thinking out loud so don't read too much into it.

[Julian]

Have you managed to determine which cylinder is misfiring ? ... No

Have you done a compression test across all cylinders ? ... No, not on this car.  Had it done on the last Disco and although there were differences between cylinders, it was nothing untoward for a 140K mile engine.  The test cost 50 quid last time and as the problem was the pump, this time I just changed the pump straight away.

From what I understand the timing advance is dependant on the pressure in the return side of the pump,
so as the fuel changes viscosity so will the return pressure,
now if you've got one injector that's not set at the right pressure this could be magnified by the timing advance,
this is purely me thinking out loud so don't read too much into it. ... I've changed all the injectors and still no difference.

[Tony]

That's interesting Julian.  I almost have the opposite problem.

First pump, used to start and run smoothly on first crank.  Over time it developed a strange pinking noise when off-load at about 50mph (hot engine).  This eventually became a permanent feature at all RPMs, except when the engine was heavily loaded or on overrun - then it went quiet.  This pump also started to give noisy starts, it was clatter badly at idle until the engine was warm.  A very metallic clatter that indicated injection was too far advanced.  This was alleviated slightly by reducing the cold start advance.

It would always clatter worst in winter (cold starting and when pinking hot).

Anyway, when that pump eventually failed and I swapped it out, I was delighted that my new pump started the engine from cold perfectly again.  Turn the key, and instant, smooth start, perfect idle and no pinking when hot.

This changed over time with bio usage, now I get the clatter from cold (that doesn't seem to be alleviated by retarding the cold-start) but in every case when it gets hot it purrs along like a kitten.

I've been scratching my head about this behaviour for some time, as there aren't many rubber seals in the system that could stick in place and change the timing behaviour.  The only seals on the hydraulic advance piston are on the end caps.  And I took my old pump apart and there was no accumulation of soap in the advance mechanism.  I tried changing the overflow restriction solenoid as the one I took off my old pump was pretty gunked up, but this made no difference to the new pump (and the one I took off was pretty clean).

What I have noticed is that if I put an electric fuel pump on the pump inlet feed (forcing fuel into the lift side of the pump) that cold clatter is greatly reduced from startup.  But I didn't run it like this for long as one of my temporary fuel system joints to add the pump was spraying bio out (dubious pipe size adapter used).

I don't know if this info is of any help to you as your problem seems to be the opposite way around.  But it may be related to pump timing or give you some ideas.

I remember Dickjotec refitted a pump on his Delica and experienced some rattling that was fixed by adjusting the pump timing.  I can't remember if this was with hot or cold running - it might be worth asking him for his experience though.