Engine/Transmission (1998.5 - 2002) Fuel filter isolator line — how to fill

[Gordon Maney]

I am installing a mechanical Isspro fuel pressure gauge. There is an isolator in the circuit to keep fuel out of the cab.

The instructions are not the best. What is the best way to fill the line between the isolator and the gauge? You fill it with antifreeze?

There is supposed to be a bleed screw on the isolator. I take that to be to bleed off the fuel side of the isolator, is that right?

 

[JLandry]

Gordon,



I'll probably get some flack for part of this, and there are probably better ways to do it, but this is the way I installed mine:

1. Install the plastic line through the firewall leaving plenty of extra length to work with under the hood and in the cab.

2. Make sure the rubber diaphragm inside the isolator is properly centered (the isolator instructions should mention this).

3. Fill the gauge side of the isolator as full as possible with a 50/50 mix of antifreeze/water using a syringe.

4. Slip the nut and compression ferrule (the sleeve) several inches up the plastic line on the isolator end under the hood.

5. Have a helper immerse the isolator end of the plastic tube into a large jar or cup of antifreeze.

6. Keep the end of the plastic line inside the cab higher than the jar of antifreeze and CAREFULLY/SLOWLY suck antifreeze up through the plastic line just like a soda straw.

7. As soon as the antifreeze reaches to within a few inches of your mouth, signal your helper to quickly insert the other end of the plastic line into the isolator and snug up the compression fitting. It's worth mentioning that these tiny compression fittings can be ruined by over tightening. Usually tightening only 1/2 to 3/4 turn after snug is all it takes to prevent leaks. Also, if you accidentally go too far and get antifreeze into your mouth, simply spit it out and rinse your mouth out with plenty of water.

8. Slip a nut and ferrule onto the plastic line inside the cab.

9. Adjust the positioning of plastic line as desired (leaving adequate slack), then trim it down to the desired length inside the cab. Basically you'll be cutting the plastic line where it's filled with antifreeze which will eliminate any air.

10. Slip the plastic line into the back of the gauge and sung up the compression fitting.

11. Start the engine (or activate the fuel pump), loosen the bleed screw on the fuel pump side of the isolator, and retighten when fuel oozes out.​

John L.

 

[Gordon Maney]

Interestingly, it does not use compression fittings. They are a push fitting with a small disc. Essentially a quick disconnect. You can connect and disconnect them quite easily.

My instructions don't mention centering the disc, thank you. Do you do that simply be reaching through the hole and pushing with a tool, or?

 

[JLandry]

My instructions don't mention centering the disc, thank you. Do you do that simply be reaching through the hole and pushing with a tool, or?

Yes... insert a blunt tool like maybe a long 1/4" drive socket extension through the gauge side of the isolator and gently push the rubber diaphragm until you feel resistance. The diaphragm will move toward the gauge side under fuel pressure, so you want it to be toward the fuel pump side when not under pressure.



I should have mentioned in my previous post that a little bit of air in the plastic line won't hurt anything. You don't have to worry about getting every last bit out.



Best regards,



John L.

 

[DIESELWRKS]

hum. my gauge isolator is diff I just filled up the gauge side with pure sylicone spray. used the can spray it fill it up close it off. in all the gauges ever done I have never used antifreeze. and have never had to try attempt to fill up the tubing going to the gauge. compression fitting on gauge ran tubing through wall fill isolator installed compression fitting on it. and put a needle valve on back side of isolator. if any thing with the push on style should be same concept but I have never used push lock style on the guages. call the maker. or look on line for them alot of time they will have install tips or how to on the web site

 

[Gordon Maney]

hum. my gauge isolator is diff I just filled up the gauge side with pure sylicone spray. used the can spray it fill it up close it off. in all the gauges ever done I have never used antifreeze. and have never had to try attempt to fill up the tubing going to the gauge. compression fitting on gauge ran tubing through wall fill isolator installed compression fitting on it. and put a needle valve on back side of isolator. if any thing with the push on style should be same concept but I have never used push lock style on the guages. call the maker. or look on line for them alot of time they will have install tips or how to on the web site

Very interesting. I realize the silicone is a liquid in the can, but also know it dries and plugs nozzles. It would not have occurred to me it would remain liquid in a line like that. A good idea.

 

[JLandry]

... put a needle valve on back side of isolator.

This is something I really need to install. My Pricol gauge works great, but the plastic line running up to it vibrates and actually creates a buzzing sound at certain rpms... annoying! These vibrations must be pressure waves emanating from the VP44.



John L.

 

[CKelley1]

the best thing to do is to put the isolator in the trash and install a snubber near the pump. if you try to use the isolator for a snubber, get a syringe from a vet and fill it with atf or diesel fuel and force the diaphragm down and fill the line to the gauge. do not use water antifreeze. when the isolator fails depending on how you have it mounted it will let bad stuff migrate toward the pump. the isolator was a very bad idea to a non existent problem

 

[Gordon Maney]

the best thing to do is to put the isolator in the trash and install a snubber near the pump. if you try to use the isolator for a snubber, get a syringe from a vet and fill it with atf or diesel fuel and force the diaphragm down and fill the line to the gauge. do not use water antifreeze. when the isolator fails depending on how you have it mounted it will let bad stuff migrate toward the pump. the isolator was a very bad idea to a non existent problem

By snubber, you are meaning a needle valve?

 

[JLandry]

the best thing to do is to put the isolator in the trash...

Without an isolator, the risk is having fuel leaking into the cab.

when the isolator fails depending on how you have it mounted it will let bad stuff migrate toward the pump.

Since the fuel is under pressure, this is a highly unlikely scenario.



John L.

 

[DIESELWRKS]

IMO the 2 isolators in the past the diaphram blew due to the high pressure of the vp. this is why I put a needle valve there to dampen this. the isolator is there for a reason. I looked but to me they sell a isolator for a reason. (keep fuel out of the cab) to each there own. but I dont know of anyone that sells a isolator with there gauge that will warranty a gauge that is destroyed by direct pressure from diesel. like I said to each there own. the 2 guages in past were destroyed when the diaphram went. now I have a needle valve also extended the isolator farther from my T fitting which is about 18" from the vp. so far 1 1/2 years trouble free.

 

[Bob Cochran]

Solution electric gauge? No need for isolator but a snubber of some kind will be necessary.

 

[JLandry]

Solution electric gauge? No need for isolator but a snubber of some kind will be necessary.

Definitely a solution, but much more expensive.



John L.

 

[Gordon Maney]

As a measuring device, I believe a mechanical gauge has a greater probability of accuracy and long life.

 

[CKelley1]

all equipment and large trucks has diesel fuel to the gauge for the last 60 years. total bs on the isolator theory. the snubber is made to keep the vibrations from destroying the gauge. get one from genosgarage.com . a glycerine filled gauge from northern for $8 and a oil pressure gauge installation kit for $10 and you have a ten times more reliable set up than that piece of junk isolator and gauge you have now