Different economy from each tank

[jim-bob Lurker Find all posts View Profile Close jim-bob]

I have a 2001 3ltr TD with a serious problem with economy. I get different economy out of the main tank compared to the sub tank. I have been checking economy for 6 months or more and these are the type of fgures I have been getting.

Sub tank 560 klms - 58 ltr = 9.6 klm/ltr
Main tank 470 klms - 67 ltr = 7.0 klm/ltr.

Economy is always within a couple of tenths of a kilometer of these readings.
Performance on main tank is not quite as good as the sub tank. It doesn't matter which tank I use first.
I have checked for squashed fuel lines and practactly everthing else but can not find a cause.

Could anyone offer any suggestions of what to look for?

Regards Jim-Bob.

[StormyKnight Advanced Member Find all posts View Profile Close StormyKnight]

Re: Different economy from each tank

The difference may be to do with the fuel returned from the engine. More than enough fuel is pumped up to the engine & used to cool the injection pump. The excess is returned to the fuel tanks.....

What I not sure about is which tank(s) the fuel is returned too....

[sparksy Senior Member Find all posts View Profile Close sparksy]

Re: Different economy from each tank

I agree with Stormyknight. The fuel is returned to the second tank. Used to notice it on my old 90 when the second tank was empty and running on the main, the second tank would slowly start to fill up.

Sparksy

[Leethal Advanced Member Find all posts View Profile Close Leethal]

Re: Different economy from each tank

My thoughts are that the fuel should return in a diesel to the tank drawn from.
Perhaps you have a problem/fault with the return line valves not switching when the supply lines do.

I know the petrol models return a small amount to the sub tank all the time in order to keep the in tank pump lubricated,
I doubt the diesel is the same in that aspect.

Lee

[mackerelmauler Lurker Find all posts View Profile Close mackerelmauler]

Re: Different economy from each tank

My thoughts are that the fuel should return in a diesel to the tank drawn from.
Perhaps you have a problem/fault with the return line valves not switching when the supply lines do.

I know the petrol models return a small amount to the sub tank all the time in order to keep the in tank pump lubricated,
I doubt the diesel is the same in that aspect.

Lee

Actually my Turbo-diesel returns excess fuel into the sub tank just like the petrol models.

To keep both pumps in good nick I use 1/4 Sub then 1/4 main then down to 1/2 in sub then...

Ray

[CaptAndy Lurker Find all posts View Profile Close CaptAndy]

Re: Different economy from each tank

Seems to be a common theme across all Land Cruisers.

Boss had a LC100 Petrol, real bad economy, over 30l /p100.

The second tank was empty originally, then one day after ages of winging, flicked it over to the sub tank & it was full.

[Robo76 Lurker Find all posts View Profile Close Robo76]

Re: Different economy from each tank

Hi Guys

According to my handbook and personal experience it is normal for diesel to transfer from the main tank to the sub tank. Apparently it encourages use of the sub tank and associated pump. I always fill both tanks and use the sub until empty. I then flick over to the main, by the time i get to around a quarter of a tank left in the main the sub tank is filled back up to over a quarter.

Hope this helps

[dhula Member Find all posts View Profile Close dhula]

Re: Different economy from each tank

I am quite confused now.

AFAIK the deso does not have pumps in the tanks as the lift pump (part of the FIP) drags the fuel from the tank the engine. It's also why there is the primer on the filter head.

AFAIK the return line goes to the tank that is being used

Ever since day one in my car (KZJ95) if I drive till the fuel light comes on for the main tank there is ~20 liters left in it whether i fill in the next 10 kms after switching to sub or after the sub is empty. Same with sub tank (although there is no warning light, I use when the needle is on the E line which gives ~10 litres left)