Fuel Line size. (1 Viewer)

[Aussiemike]

Hi Guys,
I am adding another fuel filter to my vx 80 4.2 T.
The fuel we get here in Kenya is not good and need extra filtration.
Question is.
Can I reduce the hose size from the 12mm hose going into the original filter?
Bought a Kleenoil filter for my diesel line and fittings are smaller.
In other words how important is the original 12mm size?
Cheers
Mike

 

[Malleus]

If you reduce the fitting size you reduce the flow volume and increase the fuel line pressure. How much depends on how much you reduce the diameter by. With a diesel, you could get by with 10-mm, but I wouldn't try anything smaller. You'd starve a gasoline engine this way.

If the filter fittings themselves is the only change, meaning that the flow volume on either side of the filter won't change form OEM, you'll likely damage the filter from the pressure change (pressure increase into the filter and pressure decrease out), but it may take awhile. Again, it all depends greatly on the magnitude of the change.

What you really have to be concerned with is the inside diameter of the fittings, that's where the fuel is. It doesn't really care about the external threads. You may find that the ID difference is very small, in that case it should not be a problem.

If you want to find out how much the pressure change will be, use the formula Pressure= Force / Area. Calculate the OEM pressure (or just install a pressure gage) then substitute the area of the new fittings and compare the pressures. If you don't know the OEM pressure, substitute any number you like for force, the relationship is linear. Just use the same force number in both calculations. The disadvantage to doing this is you'll only know what the pressure relationship is, not the ultimate new pressure, which is what the filter element cares about.

 

[Aussiemike]

Thanks Malleus. Much appreciated for the detailed answer.

 

[IanB]

I'd either change the fittings on the new filter housing if possible, or find another that maintains the fuel line diameter. I'd want to avoid any bottlenecks in fuel delivery if it was my truck.