GU SUB TANK SWITCH

Submitted: Wednesday, Aug 11, 2004 at 19:38
ThreadID: 15481 Views:1695 Replies:10 FollowUps:6
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HI GUYS
I WOULD LIKE TO KNOW WHAT WOULD HAPPEN IF I WAITED TILL THE MAIN TANK RAN OUT BEFORE CHANGING OVER TO THE SUB TANK ON MY 4.2 TD PATROL .
I HAVE CALCULATED THAT THRERE IS ABOUT 25L STILL IN THE MAIN TANK WHEN THE ORANGE EMPTY LIGHT COMES ON , CAN ANYONE CONFIRM THIS ? WANT TO SEE HOW MANY KMS I GET WHEN THE LIGHT IS ON ?
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Reply By: pjd - Wednesday, Aug 11, 2004 at 20:19

Wednesday, Aug 11, 2004 at 20:19
it would cough & stop you would then need to pump the fuel into the main tank & hope it starts
AnswerID: 72188

Follow Up By: Brian - Wednesday, Aug 11, 2004 at 20:29

Wednesday, Aug 11, 2004 at 20:29
Also would need to re prime it !

Brian
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Reply By: Bonz (Vic) - Wednesday, Aug 11, 2004 at 20:48

Wednesday, Aug 11, 2004 at 20:48
yep what they said, still, under controlled coditions it would be a worthwhile exercise I reckon
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AnswerID: 72194

Follow Up By: Member - Captain (WA) - Wednesday, Aug 11, 2004 at 22:37

Wednesday, Aug 11, 2004 at 22:37
Don't know about that Bonz! I accidentally ran my GU empty on the main tank when I first got it (didn't realise the sub tank switch turns off when car is stopped and need to push switch again to continue pumping - 80 series stays on the tank selected).

So, I waited with ignition on and pumped fuel into the main tank (could see main gauge increase) and tried to prime. After running my battery just about flat, finally got it going some 30 minutes later. But at least I now know there is 95 litres in the main tank (and 32 in sub).

Cheers

Captain
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Follow Up By: Brian - Thursday, Aug 12, 2004 at 10:55

Thursday, Aug 12, 2004 at 10:55
Captian you realy need to Hand prime the system as I believe that you can do damage to the pump if you run it dry!

Brian
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Follow Up By: Member - Captain (WA) - Thursday, Aug 12, 2004 at 20:04

Thursday, Aug 12, 2004 at 20:04
Hi Brian,

I primed the pump every time I cranked it (max 30 sec cranking) until you could not depress the button any more. In future I would remove the filter and prime continuously as I think the problem was in filling the empty fuel line from the tank to the filter. Once filled, the engine finally stayed running.

Cheers

Captain
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Follow Up By: warthog - Thursday, Aug 12, 2004 at 22:41

Thursday, Aug 12, 2004 at 22:41
I have a 4.2turbo GU and have been told to avoid running out of fuel as the rotary fuel pump relies on diesel for it's lubrication and running it out of fuel will result in premature wear. We must have come close however during a recent trip as both tanks took 126 ltrs.
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FollowupID: 332581

Reply By: duncs - Wednesday, Aug 11, 2004 at 22:30

Wednesday, Aug 11, 2004 at 22:30
I haven't done it in the GU but I did have the misfortune to run out in the GQ.

When it happened I was able to coast down the hill and pull into a service station. I filled up and turned the key not really expecting much success but it fired up and ran, a bit rough at first but it sorted itself out.

Apparently theyve self priming injectors and can cope with running out of fuel.

You don't need to prime the injectors if you change the fuel filter just pump it up with the manual pump on the filter itself.

If you wnat to try it I would turn it off as soon as it coffs and then switch the reserve on, let it drain through for a while and re-start the engine.

Let us know how yo go.

Duncs
AnswerID: 72213

Reply By: Member - Roachie (SA) - Wednesday, Aug 11, 2004 at 22:41

Wednesday, Aug 11, 2004 at 22:41
Mark,
Three things to say......
1) PLEASE DON"T SHOUT....(it is considered rude to use upper case ol' mate)
2) Although I've got a 145litre replacement tank, it still uses the original sender unit in the tank. I have driven around 100klm with the orange light on and it took around 135 litres to fill the main tank.
3) Recently I had a bad experience out in the bush. I'd been camped with the Patrol facing up hill on the side of the track all night. Next morning we decided to go for a short drive up the track. I started her up and idled for about 5 minutes (as i always do) and Gerk (who was with me in his truck) and I started off up this fairly steep (low range) hill. My main tank gauge was showing between quarter and half (closer to quarter though). My sub tank was still full. As I started to climb I lost nearly all power. I pulled up and used the hand throttle to hold the revs at about 1100. Any harder on the loud pedal and she'd cough and almost stall......take my foot off the pedal and she'd die in the bum. So with the 1100 showing and hand brake on (gotta love transmission hand brakes), I got out and chocked the wheels and lifted the bonnet. Note that wife and kids abandoned ship and left me to my own devices. I've got a Lucas/CAV filter system with glass bottom bowl and 1st thing I noticed was small air bubbles coming up from the bottom bolt through the diesel in the glass bowl. I soon twigged that she was sucking air. Jumped back in and hit the aux tank switch. About 2 minutes later she was purring again; nice as you like!!!!
Hope this helps.....
Cya
AnswerID: 72220

Reply By: V8Diesel - Wednesday, Aug 11, 2004 at 23:37

Wednesday, Aug 11, 2004 at 23:37
Mark, a bit off the subject but one thing to remember on the GU when you are doing lots of city driving is that the aux tank pumps into the main tank for a while every time you start up. Sounds silly but that 'full' tank can rapidly become a half tank quite quickly without you doing anything. Could be a trap if you're ever depending on it.
AnswerID: 72228

Reply By: Well 55 - Thursday, Aug 12, 2004 at 07:14

Thursday, Aug 12, 2004 at 07:14
I have done a further 105k after the empty light came on and when filled up still had 5lt left in the tank. That was between Archer River and Weipa so it was flat running most of the way.

The wife was not impressed.
AnswerID: 72238

Reply By: Member - Michael- Thursday, Aug 12, 2004 at 09:49

Thursday, Aug 12, 2004 at 09:49
Hi Mark

I'm curious myself, would like to know how far my GU 3LTD would travel. The only problem I can see is that if there is any crap in the bottom of the tank, you are going to suck it through the fuel lines into the filter.
Cheers
Mike
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AnswerID: 72256

Follow Up By: Alex - Thursday, Aug 12, 2004 at 19:09

Thursday, Aug 12, 2004 at 19:09
fuel is always drawn from the bottom of the tank , so any junk in the bottom of tank will go through and hopefully be caught by filter
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FollowupID: 332554

Reply By: crowie - Thursday, Aug 12, 2004 at 10:04

Thursday, Aug 12, 2004 at 10:04
Mark

Your probably right. I have a ZD30 with same tanks and there is about 25 litres left in the main tank when the warning light comes on "permanently". I have tested it several times on the highway so I would know when I was off road what I had left. You can work out the theoretical average distance you can travel from your normal fuel consumption, no need to run it to empty to find out. Leave yourself a margin of error to be on the safe side. For me about 150/200km depending on conditions.

Regards
AnswerID: 72260

Reply By: basecamp15 - Thursday, Aug 12, 2004 at 20:24

Thursday, Aug 12, 2004 at 20:24
I ran my main tank down to see if my low fuel light was actually working, it wasn't and I ran out.
It was a simple matter to leave the car on 'on' while having the sub tank pumping. During this time I was hand priming using the pump on the fuel filter and when she was primed, started her up no worries.
Being a 4.2 turbo I had to idel it for a bit to get enough from the sub tank into the main tank before taking off again.
And you will pump a fair bit each time you start the engine too. It's possible to actually have only half your subtank left before actually draining it yourself if you do a lot of stop start driving.
Cheers, Mark.
AnswerID: 72365

Reply By: Pluto - Friday, Aug 13, 2004 at 09:14

Friday, Aug 13, 2004 at 09:14
Mark,

My guesstimate on the reserve capacity is similar to yours, or a little less. I have run my 2.8GU for about 150km with the warning light on before refuelling. I believe I had less then five litres left when I refuelled.

As for leaving the sub tank transfer until the last moment, I don't think there is any reason to do this. You run the risk of damaging the fuel pump and (as Captain pointed out) waste a lot of time getting started again. My regular practise is to transfer the sub tank once the main tank is showing room to take the transfer. Afterall, the fuel in the subtank is not available for use untill it is transfered. This also maximises the flushing of the sub tank and avoids the slightest chance of stale fuel.

Pluto
AnswerID: 72430

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