Can somebody please explain how the isolator works.

 

Fuel on one side, membrane in the middle, antifreeze on the other side.

Fuel pressure pushes the membrane, which pushes the antifreeze, which registers on the guage.

I think that's how.


phox

 

All an isolator is is a rubber diaphragm that isolates the fuel from the gauge. When pressure acts upon the diaphragm it's flexing creates pressure on the downstream side. Some use a liquid such as antifreeze on the downstream side others just air. Gauge isolators are mainly used to keep gauges from clogging with solids, exposure to corrosive materials, and to keep flammable materials out of sensitive areas.
Diesel fuel doesn't really fit any of those descriptions, is barely flammable and an isolator really isn't needed.
I know some gauge manufacturers claim an isolator is required by law on fuel pressure gauges and always include them. I've never seen the law but assume it's either very general or only applies to gasoline.

 

So if I use the isolator that the guage came with, I can just fill the tube that runs from the isolator to the guage with antifreeze, or is it better to leave it empty? Sorry for all of the questions, the guages didnt come with very detailed instructions.

 

Mine came prefilled with a little red cap on the end of the line. The directions said to cut off what you needed and to not worry about the air bubbles in the line. I installed it exactly per instructions and no problems at all for me.

DB