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I've been researching fuel hose replacement for a '97 993, Looking at available factory replacement hoses, they are using 6255-Cohline-3124 8mm hose, which is a rubber armored Polyamide hose. The hose is available from Bel-Metric (RHPOLY8x14), as are the collars and some conical end fittings. I have found several links to AN hose kits, refurbishing services or shops that will crimp new PTFE hose on existing fittings. What I have not found is any information about the expected service life of a Polyamide (Nylon) fuel hose. Which brings me to my question. Rubber hoses have a service life of no more than twenty years (assuming proper composition for fluid type). PTFE is advertised as for the life of the car. So what about factory specification Cohline 3124 Polyamide hose?
The cost of materials is minimal, and if the engine or lines where already removed I would plate the fuel rails and install new hose. However, the effort to R&R the lines/hoses on an otherwise in service car is not minimal. The car has 69,000 miles on it, and not burning oil. It is possible the engine will not be out again until 100,000 miles, for a top end. Will the fuel hoses last long?
Lots of info in the 928 forum around fuel lines, as most of those cars where made before the introduction of Polyamide lined hoses, and there has been fires. What is the experience of 993 brain trust? Are these cars experiencing fuel hose failures, aside from physical damage related to service work?
You're on the money to bring up the issue of fuel lines Alan. In my experience we're already past the life of factory fuel lines and without question every 993 engine build at Ninemeister is now having the fuel lines re-manufactured as part of the job.
With the fuel lines off the engine there are two simple tests you can carry out to judge whether the line is safe to use:
1. The first test is to attempt to grab the end fittings with your hands and attempt to rotate the ends within the crimps. If they rotate there is insufficient crimp force and they should be replaced.
2. The second is to bend the rubber lines, testing them for rigidity and inspecting the length of the pipe for surface cracks. Any evidence of excessive stiffness or cracking and they are toast. Worst case, you bend them and they break in half, like the ones below.
Our solution is to re-manufacture the lines by removing the fittings, re-plate to the original yellow zinc passivate finish then machine crimp on a replacement, double braided synthetic rubber hose that is E5/E10 and race fuel compatible.
This 993 turbo pipe failed the bend and crack inspection test As did the one from the other side We have the original end fittings re-plated Replacement hose are machine crimped Restored set for a 964 engine New hose is exterior braided
I’ve been considering both a direct factory Cohline Poly hose replacement, as well as current PTFE Kevlar hose. If I go the PTFE route, as your service appears to be based on, I have no doubt it with be the first and last time for this car.
I spent significant time this past year, refreshing this car. This is one of the last items to address before some serious road trip commence. My hoses look fine, are not cracked and playable where they can been inspected. This is why I asked about what has been seen, and those hoses look terrible. I do wonder if turbo heat added to the failure.
A direct replacement with the Cohline 3124 hose is attractive because it can be done with the long lines in the car. If the engine was out, I’d plumb with the braided line, end to end.
Thank you for your reply, insight and beautiful work. I’d be right over, if you where in Southern California.
How easy or difficult is this to do with the engine in place or can't it be done?
The 993 only has two lines in the engine bay, one from the filter to the rail and the other from one rail to the other. You naturally have to remove the fuel rails to do the job which means lifting the intake with the engine in-situ. No big deal as you can lower the engine on a jack whilst doing the job.
I’ve been considering both a direct factory Cohline Poly hose replacement, as well as current PTFE Kevlar hose. If I go the PTFE route, as your service appears to be based on, I have no doubt it with be the first and last time for this car.
I spent significant time this past year, refreshing this car. This is one of the last items to address before some serious road trip commence. My hoses look fine, are not cracked and playable where they can been inspected. This is why I asked about what has been seen, and those hoses look terrible. I do wonder if turbo heat added to the failure.
A direct replacement with the Cohline 3124 hose is attractive because it can be done with the long lines in the car. If the engine was out, I’d plumb with the braided line, end to end.
Thank you for your reply, insight and beautiful work. I’d be right over, if you where in Southern California.
Alan
Cheers Alan.
This issue first came about during the build of the black 9m11ST for a Florida client built on a 964 he sourced that had a 12 month plus build. After the car went together we ran the new 3.8 engine up for the first time and noticed a feint whiff of fuel. No apparent leaks, but after leaving the car overnight and inspecting again in the morning EVERY single fuel line joint was leaking. Our conclusion was that the fuel had soaked into the rubber and swelled it into the crimp, but once dry the rubber shrank back and all the fittings failed a subsequent twist test. At that point, all lines came off the car and engine and were re-manufactured as above.
Costs are interesting. A new rail and feed pipe for the 993 engine is priced at £980 (£817+VAT) new from Porsche , whereas the 9m pipe re-manufacture is £275 (£225+VAT). There are more pipes on the 964 engine and similar pricing applies, cost of new Porsche exceeds £1000, 9m re-man is £510 £425+VAT. On major builds we also replace the rubber sections in the under body feed & return sections.
Our replacement hose is reinforced synthetic rubber, Aeroquip for the 9.0mm on the 993 and Goodridge for the 5/16" 8mm 964. Both hoses are rated for permanent exposure to bio and high octane race fuels.
I should also mention that we have the correct Cohline oil line & spherical metric fittings in stock which allows us to make custom or repair most 911, 964 & 993 oil lines to factory standards..
Last edited by NineMeister; 11-12-2021 at 08:20 AM.
Cheers Alan.
This issue first came about during the build of the black 9m11ST for a Florida client built on a 964 he sourced that had a 12 month plus build. After the car went together we ran the new 3.8 engine up for the first time and noticed a feint whiff of fuel. No apparent leaks, but after leaving the car overnight and inspecting again in the morning EVERY single fuel line joint was leaking. Our conclusion was that the fuel had soaked into the rubber and swelled it into the crimp, but once dry the rubber shrank back and all the fittings failed a subsequent twist test. At that point, all lines came off the car and engine and were re-manufactured as above.
Costs are interesting. A new rail and feed pipe for the 993 engine is priced at £980 (£817+VAT) new from Porsche , whereas the 9m pipe re-manufacture is £275 (£225+VAT). There are more pipes on the 964 engine and similar pricing applies, cost of new Porsche exceeds £1000, 9m re-man is £510 £425+VAT. On major builds we also replace the rubber sections in the under body feed & return sections.
Our replacement hose is reinforced synthetic rubber, Aeroquip for the 9.0mm on the 993 and Goodridge for the 5/16" 8mm 964. Both hoses are rated for permanent exposure to bio and high octane race fuels.
That's a great option and a very fair price Colin. I went with new factory lines and rails because I didn't know of other options. Over $1100 UsD and 6 wks from Germany. I replaced them solely for piece of mind while I was doing a rebuild last winter....didn't feel like getting in there again anytime soon. 😁
Cheers Alan.
This issue first came about during the build of the black 9m11ST for a Florida client built on a 964 he sourced that had a 12 month plus build. After the car went together we ran the new 3.8 engine up for the first time and noticed a feint whiff of fuel. No apparent leaks, but after leaving the car overnight and inspecting again in the morning EVERY single fuel line joint was leaking. Our conclusion was that the fuel had soaked into the rubber and swelled it into the crimp, but once dry the rubber shrank back and all the fittings failed a subsequent twist test. At that point, all lines came off the car and engine and were re-manufactured as above.
Costs are interesting. A new rail and feed pipe for the 993 engine is priced at £980 (£817+VAT) new from Porsche , whereas the 9m pipe re-manufacture is £275 (£225+VAT). There are more pipes on the 964 engine and similar pricing applies, cost of new Porsche exceeds £1000, 9m re-man is £510 £425+VAT. On major builds we also replace the rubber sections in the under body feed & return sections.
Our replacement hose is reinforced synthetic rubber, Aeroquip for the 9.0mm on the 993 and Goodridge for the 5/16" 8mm 964. Both hoses are rated for permanent exposure to bio and high octane race fuels.
Do you sell these hoses for the 993? I would gladly purchase since my engine is currently out.
I replaced mine also. I’ve experienced a fuel line failure resulting in engine fire before (VW fastback many decades ago) and have no intention of repeating. Thanks for raising awareness here!
It seems to me that having the hose crack or break during the bend test would be the best case scenario. Worse case would be the test weakens the hose but with no external cracks visible. Once I have the engine out all rubber hoses get replaced regardless whether they pass a test. They are 25 years old.
In fact I have two engine rebuilds planned for the next 12-16 months. I already have the 993 engine rebuild scheduled for this January even though the car runs perfectly. Fuel hose replacement is one main reason. Not the only reason but it’s important. It’s not like they transport air or water. I also have a few oil leaks to do and possibly a top end rebuild depending on some tests.
My 911SC engine will be rebuilt later in the year. Those original fuel hoses are 42 years old. I’ve been waiting 37 years for it to indicate it needs a rebuild, but after 217k miles, leak down figures are still 10-15% so I’m going to proceed anyway.
One question, I assume the fuel rails are metal. Do they need replacement and if so why?
Last edited by autobonrun; 11-12-2021 at 12:59 PM.
When I pull the lines, I intend to reuse all the metal fuel rails and ends. I will have them re-plated and put new hose on.
On the 993 stock hoses have a polyamide (Nylon) core covered by a rubber armor layer. The metal ends have a sharp barb on them, different than what is used for traditional rubber hoses. The Poly core is pushed on with direct, non-rotating force, and the collar is not crimped.
My research indicates failures in the Poly tube will be either a loose end fitting (rotation), or a catastrophic rupture. Most observed failures seem to be a result of twisting during service. Which is why I am wondering about the life of the hose/tube if undisrupted.
There are enough service items, I think I’ll just pull the intake manifold and do them all. That way I can get the wires on the SAI pump, fuels hoses, replate various brackets, change the lifters, valve cover gaskets, wires and all the seals. Then I can drive with peace of mind until it’s time for a top end. Sounds like a couple sold weekends over holiday break. The pleasures of VarioRam. I like to think of it as a 10 lbs turkey in a 5 lbs bag…
I’ll post back if I find anything surprising. Mostly it’s just preventative maintenance and peace of mind.
11-11-2021, 06:50 PM
Service Life of 993 Fuel Hose
