Clear fuel line on diesel 1.6L getting too hot at pump

[ndorian]

I replaced the braided fuel line going from fuel filter to Injection Pump with a clear line after reading about the benefits of the clear line. I used Tygothane? I think it was, after reading, again, how great the product is. I have replaced it twice now and each time, eventually the end of the hose that is clamped to the IP starts to melt. It is brittle and deformed in that location. Wondering if anyone else has seen this. I have seen setups where the first 10cm or so of the fuel line is black and then the rest is clear. However a lot of people have clear going all the way to the pump. Is my pump/motor running too hot? Thanks

[?Waldo?]

That's pretty weird. Are you sure it is Tygothane/Versilon?

I have used the c-210-a tubing from mcmaster on many VW diesels for both the supply and return and have never once had it melt like what you show. I have used it for pump supply, return, and between the injectors.

FWIW, on the supply side, I use the 1/4" ID, 1/2" OD (5549K34). That is much thicker walled than what you show and does not even require a clamp to seal well. On the return side, because the return fittings are larger, I have used the 5/16 ID, 7/16 OD (5549k35)which has the same wall thickness as what you show because they do not offer an 1/8" wall for the 5/16" ID. No issues with melting in either case, and the return fuel is hotter than supply.

[ndorian]

Yes, I ordered it from the same company that you referenced in old posts. Mcmaster something. I will try the thicker line you speak of to see if there is a difference.

[?Waldo?]

Is the line full of diesel? It should always remain full. If it is draining back to the tank when you shut down, then I can imagine how that would allow the tubing to overheat.

[ndorian]

Well, the line develops air bubbles if the van sits for a while. The bubbles come from the tank end of line and creep forward to the pump end. I know that is a bad thing but not sure if it's what you are asking.

[?Waldo?]

Not exactly what I was concerned about. I was thinking that if the line emptied while the pump/engine were still hot, then the tubing might overheat without the fuel there as thermal mass. I don't really have any other explanation.

[ndorian]

So it looks like exactly what Waldo was describing is happening. I noticed a large air gap in the clear line near the pump. I lifted up on the line to direct fuel into the pump and got air bubbles forever. Later on the air gap had grown hugely. I don't remember this from even a few months ago, but you know. So air is coming from the pump. I also have a leak in the #1 injector that I was hoping was a hose but 3 hoses later... Could the two be related? Air from #1 injector leak being pulled through the ip back to the fuel filter/tank?

[Gnarlodious]

I used nylon tube which was hard to get onto the barbs but has been working well for about 15 years and no discoloration.
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Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit