Twin Tanks

[jeff s Avid PP Poster! Find all posts View Profile Close jeff s]

Hi All.

Just have a question with the twin tank setup.
Explaining this I will call from empty to 90L the lower tank and from 90L to 180L the top tank.

1: If the tanks are full (180L), does the car take fuel from the top tank till its empty and then from the lower tank untill they are both empty?
Or
2: Does it take fuel from both tanks simultaniously and use both intank sensors to combine the signal to the fuel gauge.

I know the 90L light illuminates whilst between E and F untill turning off and starting at 1/2 gauge when more than 90L in the tanks up to F (180L).


If (1) is correct there must be two intank fuel pumps,?
If (2) is correct there might only be one pump. But im sure there is a hose joining both tanks ( which goes over the rear axle, I think)
Or if neither are correct,,, how the hell does it work?
If (1) is correct, and the car is only driven with about 1/4 to 1/2 in the lower tank for years on end, would that mean the top tank would dry out or go bad?

I have had the car since new and still dont know.
It don't think it matters but I have allways wanted to know and first asked this question at the dealer. You can add the dealers blank expresion here.......

Thanks.

Jeff.

[John Member Find all posts View Profile Close John]

Gidday Jeff,

Somebody kindly sent me a picture of the fuel system some time ago, but I can't find it ops:

You don't have to worry about fuel going bad. The engine is always fed from the main (90L) tank. While ever there is fuel in the sub tank it is continuously transferred to "top up" the main tank via a jet pump (also called an Ejector Pump). The jet pump has no moving parts and uses the venturi effect (by a small stream of "high pressure" fuel from the fuel pump) to draw the fuel from the sub tank. Once the sub's empty there will be a small amount of fuel circulating around the bottom of the sub because the jet pump will still have the "high pressure" fuel running through it.

We have several of these pumps in the aircraft I fly, exactly for that purpose. We have a number of fuel tanks in the wings. They all transfer the fuel from the wingtips all the way to the main tanks located near the fuselage. They also serve the purpose of ensuring that a constant supply of fuel is always available when manoeuvring (G-forces). They do that by having several pumps and pickups in each tank. Because there are no moving parts they don't wear out.

I can't answer how the fuel gauge works, though.

[jeff s Avid PP Poster! Find all posts View Profile Close jeff s]

Thanks John.

Thats interesting stuff.
I must accept the lack of response to a similar lack of knowledge of the workings of the tanks by everyone else.
I would never have guessed the Jet Pump (venturi)..


Jeff.

[John Member Find all posts View Profile Close John]

Hi Jeff,

I made inquiries into why Toyota changed the system from the 90 series. The answer was "reliability problems" with the electromechanical tank-changing system. Personally, I'd never heard of it! My sister had a 90 series petrol and apart from having to remember to change tanks she didn't have a problem with hers. :roll:

My own opinion is that a relatively simpler system such as what we have on our 120's is also cheaper, (and more reliable?) considering there are no moving parts

[steveo Junior Member Find all posts View Profile Close steveo]

Twin Tanks

The manual only shows one pump in the main tank. send me you email address and I'll send you tha pdf.