[Dhead]

I'm getting a little frustrated on this one. We aren't going anywhere this summer, so I've got lots of time. About 6 weeks ago I noticed a diesel leak under the coach. It was leaking on the exhaust crossover. I took some pictures and we kept getting higher up, following the leak. Last week we identified the culprit - a leak in the return line. There is a return filter on the side of the C15, above and foot back from the starter. They started with a black braided hose (about 2.5 ft) - just about getting past everything then they had some fittings that changed the braided line to end with a push-on with 5/8" green plastic hose. Reaching under that found the leak (about a drop every 10 seconds). Doesn't sound like much, until it does it for weeks...
We were already surprised by the push on fitting and we got more surprised when it was an air fitting. I doubt much that the o-rings were viton. I talked to Newell parts and know one knows anything. I definitely don't want to go back to a push on air fitting. Tomorrow I will call Service. Every Newell has a return line. so somebody should have some ideas. Its low pressure too...
I'm leaning toward a 1/2" ID barb to a 1/2" NPT male fitting. 316 SS, It is good for diesel and I can put one or two worm drive clamps. McMaster-Carr 53505K73 appears to be close.
I've had no luck finding a 5/8" compression fitting with a 1/2" NPT male end that is built for a 5/8" hard hose for diesel, or a push-on for that matter.

[Richard]

Dave,

What fitting is on the end of the braided hose? You may find it is a 37 degree JIC. It it is, you will have to transition from the JIC fitting to NPT. No problem, McMaster will have what you need.

The barb with clamps should be just fine if you have to use rubber fuel hose

Maybe this is what you are looking for. If you want to use the hard hose.

https://www.mcmaster.com/50915K332

https://www.mcmaster.com/50915K731

[Dhead]

There were 3 fittings that made the transition from the braided hose to the hard green plastic. I finally got to talk to Tracy on Friday - he confirmed that they used the push on fitting for the hard line and it was a problem on several coaches. Correct fitting was a 5/8" compression with a male 1/2" NPT. We thought we had it at Lowes, but they were made in china and beat up. Returned that, and went to ACE hardware - The one in Titusville was the biggest I've ever seen and had exactly what we needed. We had been leaning toward a barbed fitting 1/2" IO to 1/2 NPT, but we couldn't find a 5/8" band clamp. 1/2", 3/4" but no 5/8"
Got the fitting on today - Al is a wizard after all the work he has done on his beautiful 2003. No leak at all when we were done. We had to cut off about a 1/2" of the plastic line - the original install also included an angled 2-3 degree cut for the push-on that was part of the problem. not a nice 90 degree