Common advise on this forum is to replace the vacuum hoses with silicone. Well, I started down that path and quickly fell out of love with silicone hose. After shearing one hose at the nipple with moderate force and shearing another trying to remove it, I figured that Silicone hose was not a long lived, high integrity option in the real world. It is prone to tearing and to my knowledge no OEM has adopted Silicone Hose and I very much doubt that is due to cost.

I bought some eBay FKM hose (FKM is the ASTM term for DuPont’s Viton materials). On opening the shipment it stunk like Chinese rubber (I don't know why but it is distinctive) and continued to stink next day. I wasn't confident just what I had so it went in the bin. It was still outgassing on garbage collection day!

Undeterred, I bought some 75 Duro Viton tube from a local supplier of technical tubing. At least it didn’t stink!

All went well for a couple of months then secondary turbo boost started to die. It took more than a little effort to find the cause, but hidden from view, the Viton tube feeding manifold pressure to Charge Control Actuator and Charge Control Relief solenoid valves had split at the manifold nipple.



It seems that Viton, while not as fragile as silicon, is also prone to tearing, especially in response to scuffing of the surface. A check across all the other hoses did reveal one other hose, while still sound, showing signs of progressive tear propagation at the nipple expansion point where it had been scuffed by the hose pliers.

The fact that some hoses have to connect different diameter nipples does not help. Both my failures were at the expanded end. The failure came from stretching a 3mm hose over a 5mm nipple.

So, the question is, what is the best material for the vacuum and pressure hoses in 2025?

Should we go back to nitrile which is tough and has good tear resistance? Maybe big brand stuff like Dayco Emissions Control/Fuel Vapour & Vacuum Hose. NBR/PVC, -34 to 125°C, Petrol/Ethanol vapour resistant or Gates EPDM Vacuum Hose -40 to 125 °C.

Either of these should go for many trouble-free years at the rate FDs get used these days. My 85,000 km, 26-year-old stock vacuum hoses were in surprisingly good condition. The ones over the turbos were starting to harden a little but all could have been reused. I only changed out the hoses because it seemed like a good thing to do while I had the UIM off.

 

The term "you get what you pay for" stands true here.

High quality rubber like what the factory uses works well but will always harden over time, I would consider it a replacement if you didn't want to go silicone again, mine lasted almost 30 years which is pretty good for rubber. The Go-To for replacement in our cars I would still consider to be high quality silicone. Sounds like you may have gotten low quality or a bad batch of silicone or even bought some with too thin of wall if you had trouble with multiple hoses. I have silicone hose that has been on the wife's S14 for about 20 years running to the wastegate so its near heat all the time and its still very soft and works well. Just note that depending on what silicone hose you get, it may not be suitable for fuel/oil which isn't always needed (like in the rats nest.)

 

Silicone hose is supreme. Seems like you bought not good hose both times. Same here, I have silicone hose that has been on my car since 2017 and has been installed and removed many times with no failure. In addition the hose we have been using since we opened is very good, seals without zip ties and stretches over larger nipples without tearing. It also has incredible tear resistance if pulling it. It's black but will start to turn white the harder you pull on it.

We have easily ran through well over 1000ft of hose in various sizes with absolutely 0 failures as youve experienced. Silicone is supreme, buy name brand hose and try your testing again. seems like you're either handling it wrong or buying hose that is not appropriate for this application.

 

I used Viton for all of the small hoses in 2005 when I did the hose replacement job. All are still intact and functioning. I don't remember for sure where I bought them, but it was likely from "Hi-Temp Silicone." I did use several sizes to assure they fit properly and were not over-stressed.

https://www.rx7club.com/3rd-generati...4/#post3975239

 

i've never had issues with silicone hose splitting, you must be getting some cheap chinese stuff. and yes, even name brands wind up with cheap chinese crap. the world is getting stuffed with people trying to save pennies with lesser quality materials, because china makes everything and can't seem to keep their sticky fingers clean of watering down base materials to save a buck.

 

Yep, GOOD QUALITY silicone hose is the way to go. I have worked with cheap stuff and it will do just like you have said - split, kink, turn to mush when exposed to oil, etc.

Most of the silicone vacuum lines on my car are from 2004 with probably 80,000 miles on them. They are like new.

3.5mm and 6mm is most of the hose on the car. 4mm is too loose. Hose should be THICK WALL too.

Viton hose is fine but it's very inflexible and kind of a pain to work with.

Dale

 

silicone hoses weren't commonly manufactured when these cars were new 30 years ago, as well manufacturers don't like to waste money on R+D of new product testing, that is the simple reason why they stuck with rubber lines for decades. the simple fact is car makers only build cars to last for 10 years/100k miles and that is all, rubber fit the bill for that and was cheap. saving $1 per vehicle may seem absurd, but when you sell millions of cars a year it adds up.

car makers have always had the ability to make stout reliable cars, but that costs money, money they likely would never see a return on.

would all of us here rather have had silicone hoses from the factory for an extra $50 on the price of the car? that's an astounding YES! but some pencil pusher decided against it, if it ever even made it to their desk in the first place. cars now don't even utilize vacuum lines for most anything, maybe an odd one here or there so engineering has made them obsolete.

foresight is a luxury, we don't even use rubber for fuel lines or metal for fuel tanks anymore because harsh fuels make them problematic by nature. plastic fuel tanks and fuel tubes would be wonderful, for all those barn finds that have rotten fuel systems and no parts available for them these days. imagine siphoning out 20 year old gas and putting in fresh without all that BS, what a nice thing it would be to have, i have an FC with rust holes in the tank due to old fuel and finding a good one within a days drive is like searching for that needle in a haystack.