Diesel and veg oil separating.

[Scrooge, E.]

How long, around this time of year, does it take for veg oil to separate out from diesel?
Would a month of sitting in the fuel tank (vehicle unused) result in the veg oil dropping to the bottom, near to the fuel pick up pipe?

About a month ago, I parked up on the Saturday morning with just over half a tank of diesel. As the fuel filter, injection pump and all fuel lines were full of pure diesel, I added 40 litres of veg oil in preparation for a very early Sunday morning start to Leeds, and then onto Blackpool on the Monday. I've done this on many occasions with no problems.

However, both trips were cancelled, and I didn't use the Disco until five days later, on the Thursday morning. It started first time, though as I only pottered about for about 10 minutes, it didn't get really warm up and eventually it would idle rather lumpily.
When I tried to use it in the evening, it turned over but wouldn't fire.

I've finally managed to clear the fuel lines, purge the fuel filter and injection pump of veg oil/diesel mix, and start it on pure diesel again.
However, it doesn't still idle as smoothly as it used to and at a lower idle speed, although it revs freely, albeit with a plume of white/grey smoke.
I'm guessing that:
a) the veg oil didn't have a chance to mix with the diesel properly;
b) over the course of a month the veg oil separated from the diesel and is being picked up by the fuel line;
so that it's trying to run on almost pure veg oil.

If this hypothesis is correct, I'm also guessing that a good run up the motorway to mix up the veg oil/diesel will make it run better. That would also allow me to add some more diesel to reduce the veg oil ratio.

Unless anyone has other experiences or suggestions?

[ben_uk]

i tend to pre-mix the veg oil and derv before adding them to the tank.

so i get a 20litre drum that has got 15litres of veg in it, add 5 litres of derv and then shake it like mad. seems to work well, although is more hassle than just tipping it straight in.

the best way is to twin tank it though.

[its GED]

try a bit of petrol to thin the veg so it mixes better?

[Scrooge, E.]

Will adding petrol per se force the diesel & veg oil to mix? or it the action of the liquids sloshing around the tank whilst the vehicle's moving, and also throught the amount of unused fuel being returned to the tank which causes them to mix?
I've always assumed the latter, as I've never had a problem adding veg oil to diesel, then starting off for a long run. I'm almost certain I'm having problems this time because I only used the car for 3 or 4 miles after leaving it for five days, so it's not mixed properly.

I managed to get it started Wednesday morning (as mentioned in OP)
Also managed to get it started Wednesday night - still ran rough though.
Tried to start it Thursday morning, once again it turned over but wouldn't start.
Drained the fuel filter; mostly veg oil can out. Refilled with diesel, and got it started. Still a lot of smoke whilst revving the engine.
Looks like I'll have to take it for a long run up the motorway in the early hours of Sunday morning to mix up the liquids and burn enough mixture to allow a lot more neat diesel to be added to the tank.

If I'm right, then it will be an expensive lesson learnt.

[its GED]

dont think it will force it, but it may thin the veg to the same viscosity as the dino and therefore give it a better chance of mixing...............

[Scrooge, E.]

I set up a little experiment Friday morning.

I took two milk bottles, and in to each I poured about 1/3 pint of neat diesel and allowed to settle.
I poured about the same amount of veg oil into the first bottle, and shook it up. The diesel frothed up, and lots of bubbles were held in suspension by the viscosity of the veg oil/diesel mix.
Into the second bottle I poured about the same amount of veg oil, but this time I poured it slowly down the side of the glass and allowed it to settle. There was a small amount of mixing as the veg oil passed through the diesel, but it mostly sank to the bottom.

After nine hours, the first bottle was still mixed together (some air bubbles still held in suspension), whilst the second had even more veg oil at the bottom.

Given the position of the fuel tank on a Disco (between the chassis rails), where the fuel filler connects to it (at the bottom rather than the top), and the speed I can pour veg oil into it (slowly), the action of topping up with veg oil more closely mimics the second milk bottle test. ie, all the veg oil is slowly added to the bottom, and being more dense than diesel, has little chance of mixing. And not using the vehicle for five or six days after filling made it worse....


I've managed to syphon out about 2 gallons - could hardly taste any diesel: when I get it started again, I'll run it around some country lanes - that'll get the liquids sloshing about, then up the motorway and burn off another couple more gallons so I can add some more diesel. That should mix it thoroughly.

[parrotveasey81]

[Scrooge, E.]

I put a new filter on it earlier this week.
It started fine on Wednesday on fresh diesel, then after a minute or two it ran lumpy.
After leaving it running for 5-10 minutes, I could switch off, switch on, switch off etc as many times as I wanted. However, leaving it for a few hours thus allowing the engine to cool down and it would go back to turning over but not firing.
Draining the filter suggests almost pure veg oil is being picked up from the tank.
Hence next time I start it, I'm going to go for a drive to slosh the tank about, and to burn some fuel off so I can add fresh diesel to reduce the veg oil ratio.

I've had higher ratio of veg oil in the middle of summer on long runs and not had a problem.
As I mentioned in OP, when I've arranged to go on a long journey, I've run the tank down, put diesel in then driven home to top up with veg oil. Since it would have almost pure diesel in the pipes, filter and injection pump, it's never been a problem to start again. Only this time the two long runs were cancelled, and the next time I started it I didn't go far enough to mix up the liquids. Hence it drawing a higher veg oil ratio than normal.

Battery is on charge to ensure a high engine turn over rate.

Update on the experiment: mixed up bottle still mixed up, no visible seperation (and almost no air bubbles); non mixed up bottle slightly more veg oil seperated out and sunk to the bottom.

[its GED]

now add some petrol to the separated bottle and see what happens

[parrotveasey81]

if i was you i would just check the glow plugs just incase as even if one has gone down it will be hard to start with veg oil mix

[Scrooge, E.]

[its GED]

i can access my fuel tank through the passenger compartment, same for you?

[Scrooge, E.]

It's a 1996 Disco. Land Rover thoughtfully built it with a rusty boot floor in case Mother Nature decided to have rest for 15 years....

I started it this morning: as per the past few weeks, it idled roughly, and at about 250rpm less than normal.
There was a small amount of smoke constantly emitted from the exhaust. Revving the engine caused it to run slightly smoother, but with quite a lot of smoke from the exhaust.

I left it idling for 20 mins whilst I changed a tail/brake light, during which time the idle didn't improve. Stank of veg oil though...

Light fixed, I took it for a run around the village, moving off the drive and from junctions at engine speeds just above idle so as not to cause too much nuisance, whilst braking hard at junctions. I could still see smoke when the engine was revved, and it still wouldn't idle smoothly.
After a mile or so of twisty roads, I drove down a straight piece of lane in the countryside....
Nothing behind me for quarter of a mile, nothing in front for the same.
So I pushed the accelerator through the bulkhead and looked in my rear view mirror.....
LOTS of dense smoke - I could hardly see the spare tyre

Got to the next junction, and it was idling perfectly. Pulled out from the junction, no smoke.

Took it for a 60 mile drive, no problems whatsoever.

Parked up on the drive, no smoke at idle, or whilst revving the engine.

I decided not to top up with a couple of gallons of diesel - if my hypothesis was correct (pure veg oil at bottom of tank causing problems starting), I shouldn't have a problem starting now it's thoroughly mixed up.
I've arranged a lift into work tonight just in case, but I'm going to try to start it when I leave for work. If it starts ok, and then again in the morning after the temperature has dropped, I'll be almost certain that was the problem, and know what to do next time.


BTW, re the experiment: the petrol/veg oil/diesel mixture has not mixed any more, and the veg oil/diesel mix has a tiny bit more veg oil at the bottom of the bottle.

[terence]

she will start, just keep cranking.

take it for a good slosh down the road to mix it up

always add diesel to veg in the tank.

although i rarely notice them not mixing unless its really cold.

new glowplugs as suggested is a very good idea.

[Scrooge, E.]

After the run this afternoon, it started first time tonight. A little smoke for the first 20 seconds or so.

I don't know if there was any residual heat still in the engine after 6 hours - it was a lovely hot day in my part of Leicestershireland.

The big test will be tomorrow morning, after it's had to cool down completely.....