Running Prado diesel tank dry query

Submitted: Tuesday, Feb 12, 2008 at 21:49
ThreadID: 54521 Views:4225 Replies:8 FollowUps:7
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Hi,

If at speed I run one tank dry on a 2002 Toyota Prado 3l diesel and I change tanks, will the engine 'suck' sufficient fuel through and keep going without having to stop and bleed the system? Thanks.
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Reply By: fisho64 - Tuesday, Feb 12, 2008 at 21:56

Tuesday, Feb 12, 2008 at 21:56
It may do, but it is a silly idea to do it deliberately.
Besides the sucking of long accumulated dregs from the tank, the fuel also lubricates the injector pump.
You wouldnt drain your sump then drive til the oil lite comes on-would you??
AnswerID: 287153

Follow Up By: helping - Tuesday, Feb 12, 2008 at 22:29

Tuesday, Feb 12, 2008 at 22:29
Thanks for your quick reply fisho64. Re. fuel contaminants, 99.9% would sink and would be eventually ingested into the engine / filter. When a tank is nearly empty, the concentration of contaminants increase but will get ingested eventually regardless or how full the tank is. I suppose you couldn't have low-point fuel drains as you do on all aircraft. Pity. I have been keeping a log of Km. covered when the low level light comes on and I change tank at that point. I then note the fuel uploaded and work out an available amount of fuel after the light comes on. This method gives different results each time. It's a pity there's not an accurate 'fuel used' counter available for cars etc. as are found on aircraft. Typically, they are accurate to one tenth of one percent. A cork on the end of a piece of wire and a light would seem to be at the bottom end of technology. Thanks again, H.
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FollowupID: 552343

Follow Up By: Wizard1 - Wednesday, Feb 13, 2008 at 11:49

Wednesday, Feb 13, 2008 at 11:49
I too have a 2002 Prado TD. On average you have around 20 litres, give or take a few mils, of fuel left. If you know your average fuel consumption rates, eg 11L/100 km highway (use the worst rate not the best), then it would be fair to assume you could safely travel a further 100 km or so and still have enough fuel in the tank that you have not run dry and sucked in the crap.

The sub tank is a different matter as it has no low level light/indicator. But from my data I have around 10L left when the needle is at empty.

Without a trip computer it is as simple as recording the KM when the light came on for the main tank, then switch to the sub-tank. Then measure how much fuel to put in, simple. Do this a few times to get the average distace and remaining fuel. Then do the same for the sub-tank, but choose a mark eg. 1/4 full or empty.
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FollowupID: 552399

Reply By: The Explorer - Tuesday, Feb 12, 2008 at 22:06

Tuesday, Feb 12, 2008 at 22:06
Hello, I have done it many times (on a work 80 series) and no problem - but dont forget you're on empty and try an overtake a road train. Cant comment on potential for increased wear to fuel pump. Can only assume it would reduce the life of some parts but by how much, who knows.

Cheers
Greg
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AnswerID: 287155

Reply By: GerryP - Tuesday, Feb 12, 2008 at 22:15

Tuesday, Feb 12, 2008 at 22:15
Tried it once with a 105 series, 1HZ diesel. Did not work at all. Ended up having to prime all the way from the tank. Got there eventually, but a real bitch. I just wanted to know how many k's I had left after the red low fuel light came on with the after market LR tank. Just in case anyone is interested, I got another 100 k's out of it.
Cheers
Gerry
AnswerID: 287159

Reply By: spinifex - Tuesday, Feb 12, 2008 at 22:25

Tuesday, Feb 12, 2008 at 22:25
The fuel isn’t sucked by the engine as there is an electric delivery pump inside each tank. Most modern diesels are self priming due to this concept. I think the Prado is unique in the fact that either tank delivers straight to the engine (Not transferred from sub to main tank as in other cars)

From my experience if you are monitoring the fuel situation and switch over at the first hint of loss of power you will have no problems.

As for sucking up the sludge, the intake of the pump is in a fixed position at the bottom of the tank so you will get any sediment that settle out regardless of the tank being full or empty. (Most have a gauze intake strainer)

Other may have more exact info relating to the Prado.

Hope this helps
Spinifex
AnswerID: 287161

Follow Up By: Member - Phil G (SA) - Tuesday, Feb 12, 2008 at 23:07

Tuesday, Feb 12, 2008 at 23:07
Spinifex,
Theres no pump in the tanks of the Prado diesels. - Fuel is sucked by the rotary injector pump on the motor.
You're right about the gauze strainer - the Prado uses a nylon gauze bag which sits within the baffles to collect fuel.
And yes, there is no transfer pump - there are a pair of solenoids (supply and return) so fuel is returned to the same tank it came from.
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FollowupID: 552351

Follow Up By: fisho64 - Wednesday, Feb 13, 2008 at 10:33

Wednesday, Feb 13, 2008 at 10:33
"the intake of the pump is in a fixed position at the bottom of the tank so you will get any sediment that settle out regardless of the tank being full or empty"

think you will find it isnt right at the bottom, but raised up a little to give a similar effect to a water seperator. Hence (as mentioned before) the lower you go the greater the concentration of crud and water.
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FollowupID: 552387

Follow Up By: spinifex - Wednesday, Feb 13, 2008 at 15:55

Wednesday, Feb 13, 2008 at 15:55
I stand corrected on the Prado detail. My opinion was based on a generic knowledge of modern diesel engines

Sorry it didn’t help
Regards
Spinifex
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FollowupID: 552439

Reply By: Member - Phil G (SA) - Tuesday, Feb 12, 2008 at 23:15

Tuesday, Feb 12, 2008 at 23:15
Your Prado had a rotary injector pump that sucks the fuel from whichever tank is selected, and sucks it through the fuel filter. Theres a fuel return line, so excess fuel is returned to the tank it came from.

When you run a tank dry, small amounts of air get through, but are separated off at the pump and disappear down the return line back to the tank. But bigger amounts of air make their way through the injector pump abd up to the injectors.

When you run short on fuel, your Prado will lose a bit of power. If you flick the tanks straight away and take your foot off, the air will get eliminated and all will be well again. If you wait until it stutters, it will probably cut out - rather dangerous on the highway, and damages your pump.

To do this repeatedly will shorten the life of a very expensive injector pump. The pump relies on the diesel fuel for its lubrication, so its easy to do some damage.
AnswerID: 287172

Follow Up By: Member - Phil G (SA) - Tuesday, Feb 12, 2008 at 23:18

Tuesday, Feb 12, 2008 at 23:18
Just to add, that if it cuts out, then stop, lift the bonnet, and pump the rubber plunger repeatedly on the top of the fuel filter to bleed the air through. Then try to restart it. If you just repeated crank it, it will eventually start, but your pump will suffer.
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FollowupID: 552352

Reply By: traveller2 - Wednesday, Feb 13, 2008 at 15:30

Wednesday, Feb 13, 2008 at 15:30
Should never be done, the fuel lubricates and cools the injection pump, many 1hz powered cruiser owners have found out that it is a very expensive exercise when the injection pump starts to play up through excessive wear. First sign of probs is hard starting when warm.
Would you run the engine with no oil pressure? your injection pump doesn't like it either
AnswerID: 287275

Reply By: Member - Derek L (QLD) - Wednesday, Feb 13, 2008 at 23:40

Wednesday, Feb 13, 2008 at 23:40
Good to read everyones replies but you run a high risk of picking up some junk in the bottom of tank if you let it run empty before you switch tanks you could get a block in ya filter or worst still blocked injector or 2. So just switch tanks when ya warning light comes on. I wouldnt like to be pulling apart an injector out there.

Derek L
AnswerID: 287376

Follow Up By: traveller2 - Friday, Feb 15, 2008 at 09:30

Friday, Feb 15, 2008 at 09:30
Forget about pulling an injector apart, in most late model diesels they are not serviceable and a full replacement set can mean topping up the mortgage, just from a bit of dirty fuel.
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FollowupID: 552852

Reply By: helping - Friday, Feb 15, 2008 at 22:37

Friday, Feb 15, 2008 at 22:37
Thank you to everybody for a selection of very informative replies.
AnswerID: 287703

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