Sub tank fuel gauge

[Pradonamedbruce Lurker Find all posts View Profile Close Pradonamedbruce]

Hi all,
hope this question is in the right place!

90 series 1998 Prado petrol manual.

ive never owned a car with a sub tank before, when I got this one the guy wasn’t sure if the fuel was switching over or not. Had my mechanic look at it he said it seems ok. I put fuel in both tanks.

my main tank was sitting on 1/2 full, my sub tank was sitting on 3/4 full. When I switched to sub tank I was driving fine for about 5 mins then noticed the gauges seemed to have swapped? The sub tank gauge was now on 1/2 and the main tank was on 3/4.
is that normal?

[mal58 Junior Member Find all posts View Profile Close mal58]

In the 90 series, I recall that the fuel return line from the engine goes back into the Main tank, irrespective of whether the fuel is being drawn from the Main or the Sub tank.

So it is possible that some fuel from the sub tank ends up in the main tank. However, for 5 minutes of driving its only going to be a miniscule amount (Milli-litres, not litres).

I recall that it does take some time for the fuel levels to settle after filling and they do vary depending on whether the car is parked on level surfaces or a slope.

I suggest that you just need to keep an eye on the guages over a few fills to see how they behave for your car.

[RedAdventureWagon Member Find all posts View Profile Close RedAdventureWagon]

The sub gauge is a bit inaccurate however on mine it consistently draws from the selected tank with very little if any variation on the other gauge. As

mal58

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mal58 says the sub return goes into the main but it's unnoticeable in terms of main gauge movement whilst using the sub.

My sub gauge is a little unreliable and sometimes goes to zero but just tapping it lightly restores normal operation - haven't looked into this problem but it doesn't affect anything.

If you are definately getting a gross flow into the main tank maybe the fuel pressure regulator (on the back of the fuel rail) is letting more by than it should? But again just monitor I think and use the odometer to gauge range if you're going far.