Prado Sub tank

Submitted: Monday, Nov 11, 2002 at 01:00
ThreadID: 2346 Views:2599 Replies:3 FollowUps:2
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I have a 98 RV6 Prado and have a question on the sub tank.

Am I right in saying that..... fuel in the sub tank increases as you use fuel from the main tank? The feature is there to encourage use of the sub tank.

Therefore when testing fuel economy you need to fill and refill both tanks or fill and use only the sub tank.

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Reply By: Bernie - Monday, Nov 11, 2002 at 01:00

Monday, Nov 11, 2002 at 01:00
Hi Rusty
Yes it does increase, some thing to do with the pump & seals. I have a Deisel & use about 120L every 3to 4 weeks
not sure if filler set up is the same as petrol,
I fill sub 1st then main tank & use a torch to see fuel is visable in pipes,
(this may seem extreme but it is the only way to be sure tanks are actually full) I then run on sub 1st to approx empty then main tank untill light comes on. Then repeat same.

There is a good fuel calculater at
AnswerID: 8402

Reply By: Member - Stephen- Monday, Nov 11, 2002 at 01:00

Monday, Nov 11, 2002 at 01:00

In a word .... Yes.

I found that when doing economy measurements, I had to start and finish with both tanks full. This was because I had the habit of always using the main tank first so as to take the weight off the rear wheels before using the sub tank (a habit probably formed from my Prado-pre-suspension-upgrade days). Also my economy runs were nearly always over one or two thousand km, which were a wee tad over the range of just one tank.

AnswerID: 8403

Reply By: Mick - Monday, Nov 11, 2002 at 01:00

Monday, Nov 11, 2002 at 01:00
Rusty you don't necessarily need to refill both tanks. Start with both full and run on either and then refill to calculate amount used. If the sub is full and you use the main, no fuel will run to the sub (if it did it would overflow) Similarly if you use only the sub, no fuel comes from the main. The only time fuel flows between tanks is when using the main and space available in the sub. By the way, I've found that if I empty the sub, then switch to main, there is only a litre or two in it after nearly emptying the main.
AnswerID: 8405

Follow Up By: Rusty - Tuesday, Nov 12, 2002 at 01:00

Tuesday, Nov 12, 2002 at 01:00
Thanks for the replies!

I was wondering if this could be the reason for some of the ordinary fuel consumptiom results some are getting but ..... if it's only 1-2 litres than I guess not.

Ours is an auto and I am pleased with the 15.19 I get around town. (It is driven very carefully)

FollowupID: 4075

Follow Up By: Mick - Wednesday, Nov 13, 2002 at 01:00

Wednesday, Nov 13, 2002 at 01:00
I think that's OK around town Rusty - after all it's quite a large and heavy vehicle ... I usually use a bit more than that but have had around 15 when driving carefully. Best ever was 11.3l/100 when driven unladen Melbourne to Geelong and return with cruise set to speed limit. Usual trip I find 12.5 to 13 with normal driving.
FollowupID: 4116

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