Extra fuel tank won't fill

[popotla]

Landrover have just fitted to my Defender CSW the two extra fuel tanks I bought from Frontrunner, South Africa. One tank (60 litres) is "under-body", and the other (40 litres) fits under the rear fender.

My understanding is that during filling, (diesel) fuel will flow from the outlet in the fender tank, filling the under-body one. Finally, the fender tank fills, giving a total capacity of 175 litres. Later, by means of an electric pump, fuel is sent from the under-body tank to the fender tank, from where it flows - as needed and of its own accord - to the original tank.

The issue is that during fill-up, fuel is not flowing, apparently, to the under-body tank. Yesterday, on fill-up from almost empty (5 to 10 litres left in ??), I got in 121 litres, a slightly odd amount, given that the original tank is 75-litre capacity and the under fender tank 40 litres, as mentioned above.

I wondered if the problem might be due to an air lock in the piping. But wouldn't the breather tube(s) presumably fitted resolve any problem in that regard?

Please, any suggestions?

[LandyManLuke]

yup sounds like an airlock problem.

bear in mind if the breather is small it will take time for fuel to flow in to that tank. fuel can only go in and quickly as air can get out.

[western]

by under fender if you mean inside the rear wheelarch behind the rear wheel, the fuel goes through the upper tank fills the original fuel tank & then fills the upper tank, when the fuel is being used it should flow from the original tank to the lift pump/fuel filter to injection pump, the new upper tank just acts as a header tank & will just keep the original tank full until it's 40 litres are given to the original tank.

these 2 tanks have a capacity of 120 litres from dry, your original chssis mounted tank is 80 litres plus the new 40 litre fender tank equals 120litres not 175.

only Td5's have 75 litre tanks, all other pre Td5 110's have a 80 litre tank.

[popotla]

by under fender if you mean inside the rear wheelarch behind the rear wheel

Yes, that's where it is. My vehicle is a Td5, btw.

The other 60 litres included in my 175 is the under-body tank.

[pat_pending]

OK, lets see if i understand this correctly.

When you fill up from totally empty, fuel flows through the first (wing mounted) tank until the original tank is full.

Then it fills the first tank until that overflows filling the third tank until all are full.

In use the original tank empties and is topped up by the first tank acting as a header. when the fuel gauge shows empty you manually activate a pump that empties the third tank into the original.

Your problem is that you don't believe the third tank is filling as the quantity of fuel added from empty does not add up to the total capacity of all three tanks.

Am i right in my understanding?

If so, my questions are..

1. was this your first fill up with the new set up.. If so you may have to wait while the fuel makes it's way through to the third tank and then continue filling.

2. If not, and previously it had taken the full 175L, how do you know how much fuel is left in the third tank? As this will obviously affect how much you can put in.

[western]

by under fender if you mean inside the rear wheelarch behind the rear wheel

Yes, that's where it is. My vehicle is a Td5, btw.

The other 60 litres included in my 175 is the under-body tank.

Ok, think i've got your se up now, original rear mounted tank plus the side tank in rear arch plus a third under the body.

probale cause is the diameter of the feed line to the 3rd tank. if it's smaller than the fill neck then it won't be able to fill the 3rd tank as fast & could cause a airlock.

[popotla]

Hi pat_pending,

OK, lets see if i understand this correctly.

When you fill up from totally empty, fuel flows through the first (wing mounted) tank until the original tank is full.

Then it fills the first tank until that overflows filling the third tank until all are full.

In use the original tank empties and is topped up by the first tank acting as a header. when the fuel gauge shows empty you manually activate a pump that empties the third tank into the original.

Your problem is that you don't believe the third tank is filling as the quantity of fuel added from empty does not add up to the total capacity of all three tanks.

Am i right in my understanding?

Absolutely correct.

The capacities I mentioned were in fact related to the second time of filling, after the work was done, though there was a similar problem first time (just different amount in to start with and put in).

Ok, think i've got your se up now, original rear mounted tank plus the side tank in rear arch plus a third under the body.

Hi western

probale cause is the diameter of the feed line to the 3rd tank. if it's smaller than the fill neck then it won't be able to fill the 3rd tank as fast & could cause a airlock.

The inlet pipe to the third tank is quite wide (I will measure how wide), but narrower than the fill neck. Surely that's a basic design factor and would have been considered by Front Runner?

On the second, most recent filling, I gave plenty of time, I thought, for the fuel to flow to the u-b tank, but it wasn't going; the level in the header was full and steady.

[mmgemini]

Where is the Frontrunner tank. Left or right side. Normally the Frontrunner tank is on the right above the "normal" tank, therefore the Frontrunner tank fills with the main tank.

What is the pipeing like from those two tanks to the other tank. I'm going to assume the other tank is a 90 tank under the drivers seat. Am I correct ?

mike

A leopard can change its spots.

[popotla]

Hi mmgemini

The vehicle is a 110 CSW.

The header tank presents no problem. The under-body tank, 60-litre capacity, is on the right, under the passenger seat on my LHD vehicle.

The tubing from the header to the u-b is pretty wide. Presumably, Frontrunner would have made it wide enough for the u-b tank to fill with no problem.

I am no nearer to a solution.

[pat_pending]

So how do you know when the 3rd tank (under the passenger seat) is empty?

If this still contains 20 or 30 litres you'll never get the full amount in you think you should.

[popotla]

The third (under body) tank will be empty when the gauge says "E" and trying to pump from the u-b tank to the main tank doesn't alter the gauge reading.

So far, I have not been able to get any fuel into the u-b tank.