Losing Prime

The place to discuss problems and routine maintenance questions and tips. This is for topics that are specifically diesel-related.
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Joined: Thu Jun 11, 2015 11:34 am
Location: Southern California
Isuzu vehicle(s): 1983 diesel short bed

Re: Losing Prime

Postby Dongshoreman » Sun Jun 10, 2018 9:15 pm

Sadly I think my last post was a bit premature. After replacing the bleed screw o-ring and a successful test after 24 hrs, I got into my P'up a couple days later and I had lost prime again. I decided to change the fuel filter since it was due anyway, and what I found was kind of interesting. Threaded onto the bottom of the plastic sensor assembly that screws on to the filter is a brass hose barb that holds the fuel hose going to the hand pump. I decided to take it off and when I put my wrench on it I found it surprisingly loose. I probably could have taken it off by hand. Upon inspection I found that the barb was missing an o-ring. See the photo below, I put an arrow where I think the second o-ring should go. Please anyone feel free to weigh in on this if I am mistaken.
hose barb with arrow.jpg

Another reason why I am pretty sure that this hose barb needs two o-rings is because the lip of the edge of the threads is fluted and looks like it is designed to accept an o-ring. Picture below:
sensor assembly.jpg

I ended up replacing both o-rings on the hose barb and it seemed to make a nice seal once I installed it. Here's a photo of the hose barb with both o-rings and their sizes:

hose barb two orings.jpg

After installing two new o-rings on the hose barb I realized that the plastic bleeder screw is similar. I inspected the bleed screw and found basically the same setup: A gap on the top of the bleeder screw that fits an o-ring, and the same fluted lip on the threads on the hand pump. I installed a second o-ring on the bleeder screw as well. Here is a picture of the bleed screw with both o-rings and their sizes:
Plastic bleed screw.jpg

I ran out of time today to finish the job, but I will try to prime the system and start up tomorrow, and then test again after letting it sit for a day or so. I will try to post another update later on this week with a verdict on whether or not this fixed the problem.

1983 Diesel Shortbed

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Re: Losing Prime

Postby puttputtinpup » Mon Jun 11, 2018 4:53 am

This is very good information! Thanks Jake. Ill save tjis in my. Personal archives for quick reference in the future.

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