Thursday, Dec 14, 2006 at 11:23
Even though this subject has been covered here many times before, it appears that there are still a number of GU owners who do not understand how their sub-tank system works!!
Here it is again>>>
The wagon sub-tank capacity is (approx.) 40 litres, and was advertised as such when the GU range was introduced.. This was revised after it was realised that come fill-up time, ppl were only getting (approx.) 30 litres into the tank.. The revised _useable_ capacities are/were - Diesel 30 lt, Petrol 36 lt.. Still the same (40lt) tank!.. I believe the 2000 & later models were revised yet again to 32lt for diesel.. again, the tank remains unchanged..
The reason for this is simple...
Nissan in their wisdom have the system set up so that each & every time the engine is started, the transfer pump runs for a few seconds, therefore transferring a small amt of fuel.. (each & every time the engine is started, remember)..
Presumably, this is to keep the pump primed & lubricated..
Therefore to accommodate this, (in their wisdom) nissan have set it so that _approximately_ 10 litres of diesel remains in the (40lt) tank when the transfer pump switches off..
(petrol models obviously leave a bit less in there, hence the larger "useable" capacity)..
It follows thereforefore, that the (diesel)fill capacity will be _approximately_ 30 litres...
Are you with me so far???
OK, so if for example one is to (ahem) "drain the tank dry" as per the pump switch cut-off, and then not fill the tank immediately thereafter, but do a week or so of round town stop-start driving during which time the engine is frequently stopped/started, that remaining 10 litres (approx.) is now being depleted.. (a small amt each & every time the engine is started, remember...
Now, when the time comes to fill 'er up..
Lo and Behold!!! the (ahem) "30 litre tank" now holds more than 30 litres!!!
Shock, Horror, Bugga!!! .. Ive been robbed!!!.....
No, ya haven't really, if ya understand how yer fuel system works ;-)))
Catch ya later...
Ed. C
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Follow Up By: Member - andrew B (Kununurra) - Thursday, Dec 14, 2006 at 11:47
Thursday, Dec 14, 2006 at 11:47
Gday Ed
Almost on the money - although I believe that once the sub tank has been drained of the 30 litres (32 usually in my case!), the float switch or whatever that turns the transfer pump off also stops the few second tansfer at startup - the same way it does when both tanks are full - the transfer pump won't start unles there is about 10 litres or so used up from the main tank. (you can check this either by the soud of the pump or get someone else to turn the ignition on as you look down the main tank filler and watch the fuel dribbble in.
I also hot wired the transfer pump one day and got about 3 litres before it ran dry, it then took 35 litres to fill. There was possibly 5 litres remaining below the outlet, giving the 40 litre tank.
That is the only time I have ever got over 32 litres in the sub tank, its usually about 31.5, but sometimes 32, possibly the last bit of transfer happened when the car was not level.
I, as many above, find it to be a good indication of a pump's accuracy, and as yet have not found a problem, but I'd enquire as above (politely), and if not taken seriously I would not return to that servo......hope it doesn't happen up here, as we only have 2 !
Cheers Andrew
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Follow Up By: Member - Ed. C. (QLD) - Thursday, Dec 14, 2006 at 12:53
Thursday, Dec 14, 2006 at 12:53
G'day Andrew,
Yeah you could be right, though that is how it was explained to me..
I'm aware that the pump won't switch on if the main tank is much more than about ½ full, though I'm not sure of the exact amt here..
Most times, when filling at my local Woolies/Caltex outlet, I seldom (if ever) manage to get even the 30lt into the tank, even when filling right up to the filler spout.. More often than not, the meter will go to about 28.5 -29 litres before I simply can't get any more in there.. However in the scenario I described above, I will indeed get more than the prescribed 30 litres into the tank (same pump), though I must say that I've never managed to get any more than about 32 or 33 litres, so yes there must be a point at which that start-up transfer is disabled..
I have a friend with a GU111 who regularly gets +35 litres into his "32 litre tank"..
It would appear that there are subtle differences from vehicle to vehicle..
It should be remembered I believe, that these figures can only ever be _approximate_ at best, and ppl should not be at all surprised or dismayed to find that their "30 litre tank" will occasionally take more than the prescribed 30 litres (or 32 as the case may be)..
You hit the nail on the head I think, when you mention the likelihood of the last bit of the transfer taking place when the car is not level.. possible (and probable) variations right there..
Catch ya later..
Ed. C
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"He who lie underneath automobile with tool in hand,
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