Don't do the silicone hose job!
 

Hi,

I am planning to do a hose job. Already bought the hose in the right sizes, searched, read, read and read more. Checked out Scuderiaciriani and Rob Robinettes site.

BUT

I was talking to an RX7 expert the other day and he says that I shouldn't. That the silicone gets damaged by oil and is no good at all. He advised I change to new rubber hoses.


Thoughts guys?......

Who is this 'expert'?

This has been discussed repeatedly - do a search.

Me, I'm going with Viton.

have anybody done hard nylon lines (like the ones used for boost gauges) coupled with viton ends?

i havent gotten up the courage to do mine yet..lol
fraid of fuckin somethin up..

i havent gotten up the courage to do mine yet..afraid of fuckin somthin up...lol

just use viton, ton of people on this forum has done this. including me

Yes, the silicone can get damaged from fuel and/or oil. However, it stands up to heat better than rubber hoses.

Ideally, the hoses should be exposed to more heat than oil or fuel. ;)

Yeah I've done my silicone hose job, and they're not exposed to that much oil or fuel, so it should be ok.

why worry about hoses??
go single turbo or non sequential.
and get rid of that nasty rats nest..

do a search on rubber hoses. there is a 5 page thread on this :)

I'd say, don't do the job at all if your car is working properly.

Don't do it if the car is running fine.

If your putting an engine in then replace the VACUUM lines ONLY with silicone.

I'm not a fan of silicone lines to the turbo actuator hoses (WG, PC and TCA). These stock hoses don't get hard very quickly and silicone line typically doesn't fit as well either. Don't use silicone hoses for the crankcase venting system either:).

That is actually an excellent idea. I had a few problems with those hoses getting oily and then popping off for the reasons you mentioned. Drove me nuts as they were the last hoses I checked.

Bogus.

The vacuum lines aren't exposed to oil in any quanitities that would be overly harmful. You obviously cannot use them for oil lines of fuel lines as the silicone is permeable to those fluids. I just cracked open my car to install a single turbo a few months ago. I replaced all my vacuum lines with silicone back in **1998** - 7 years ago. As of March the silicone was as good as new with ZERO degradation from heat or any exposure to what little oil there might ever have been in the vicinity of the vacuum lines. The 7 year old hose once wiped down of surface dust was indistinguishable from new hose I had just bought.

http://www.negative-camber.org/crispyrx7/gt35rpage3.htm
in the section: SEQUENTIAL TURBO CONTROL LINES AND CONTROL SOLENOIDS
those images are all of my 7 year old vacuum lines. Pliable and as good as new.

A datapoint.

I can also say I've been around FD's since 1996 and never have I heard of anyone in my close circle of friends most of whom have used silicone (those that have not have used viton) with issues of silicone degration due to oil problems for the vacuum lines under the UIM. I will caveat that by stating it's probably not a good idea to use them on the lines to the turbo actuators themselves (there is the potential for quite a bit of oil buildup in that area if you car is particulalry funky or leaky) even though I did and never had to replace a single line.

If you can afford or want to spend the money on viton why not but IMO the silicone is perfectly acceptable. Rubber lines are also fine, they just won't last as long as the silicone or viton.

My input,
Crispy

The pcv system has plenty of oil in it if you corner the car hard very often. I have silicone lines everywhere except on the pcv valve, the breather line between the primary inlet and the oil filler, and the TCA.

Here's the skinny.

The whole silicone deal IMHO dates from WAY back, due to 2 factors. Early silicone vacuum hose typically was relatively thin-wall, didn't fit well, and was more susceptible to damage from oil, fumes, etc. If you get *GOOD QUALITY* hose, from Hose Techniques or High Temp Silicone, your experience will mirror Crispy's - MANY years of trouble-free use. I've used good silicone lines in countless FC's I've worked on with ZERO problems.

Second, the use of Viton IMHO is from someone having problem with older, poor quality SVH lines and looking for an over-engineered solution. IMHO, Viton is a waste of money.

I agree with Jeff - you really don't need to go through and replace ALL the lines. Replace the lines that are routinely disconnected for maintenance (lines to the UIM, for example) and the lines going to/from the check valves and vacuum and pressure chambers. The tons of short rubber lines going to each solenoid will typically stay in place just fine as long as you don't mess with them. You know how everyone complains about how difficult it is to remove those old baked-on vacuum lines? Those suckers aren't going ANYWHERE.

I know Pettit is a fan of using Goodyear rubber vacuum line - that's their deal. I think, again, that it's a case of using poor quality line way back in the day. Also, Pettit tends to go for the simple and "working" solution - SVH is something of a "flashy" mod when you use colored lines. Considering they come from a solid race background, they're more interested in something solid that works, not something colorful and flashy.

I'm also firmly of the opinion that a lot of the vacuum line woes that many FD owners have had were caused my Mazda dealers doing the fuel recall. You have to tear stuff WAY down to do that recall, and I think many of the mechanics didn't get the line routing correct, re-used the stock lines that were vulcanized and popped back off very easily, etc.

Long and short of it - SVH is a really good idea. If you're going for pure reliability, keep a stock of it around to replace old, tired Mazda line when you remove a component from the car. If you have the engine out of the car and you're waiting on parts, might as well do a full job if you feel up to the task. But, if someone came up to me with vacuum line probs, I'd simply replace the lines that needed replacement, replace the check valves, and go from there.

Dale

Wow, great solution.:rolleyes:

Anyways, if you are super worried about oil, there are inline filters that you can put in the pressure/vaccum sides to prevent excessive oil from going into the lines.

IMHO the inline filters just add another point of failure. I've seen a number of the filters that come with some boost controllers split in half and fail.

The better idea instead of trying to make things oil-proof is to re-do the PCV system. Vent the crankcase to a catch can and don't let all that oil get sucked through the intake and into everything.

Dale

Well Dale, you've made me feel a little better about buying that HOSE TECHNIQUES kit, and a very nice set of viton check-valves ;) just to have on hand. Even though my hoses and check-valves were all changed in 2001 by the previous owner (about 25k ago), they were changed out for OEM rubber hoses and valves. :scratch:

It's simple. Stock rubber or any other normal rubber degrades with heat, oil, or fuel fumes. Silicone is better in heat, but still degrades with oil and fuel fumes. Viton is very resistant to all 3. Keep in mind there is cheap silicone, and good silicone. Good silicone is an outstanding material for this application.

Naturally, the cost goes up with Viton. I have it, and it's probably overkill. But a guy here (HighTempSilicone) did a run of Viton tubing specific for this car and I couldn't pass up the opportunity. I didn't expect that fuel and oil will degrade my hoses, but it's a little extra insurance. Viton is the Ferrari version, IMO, but I don't think you're going to see any real difference with Silicone. They are both much better than stock rubber.

So this 'expert' either didn't communicate the real tradeoffs well, or didn't really understand the differences.

Dave

I call BS on what your mechanic said. I replaced all of my hoses with hosetechniques's yellow silicone kit in 1999. Last month I put a new motor in and every hose I replaced back in 1999 still looked brand new.

IMO, the stock rubber hoses are really good. They are pre-bent to the right angles and cut to the right lengths to ensure they they won't kink. Also, the package with check valves is a really good value.

This is true, but there is always a chance that the turbos will leak some oil. FWIW, I would be more worried about the solenoids being exposed to oil than the hoses.

True. I think that few people have seen what silicone hoses look like after 10 yrs and 100K + miles.

I like the hoses down by the turbo actuators to be the pre-bent rubber style. I hardly ever have to replace those.

Silicone hose has it's own failure modes. Silicone is prone to tearing easily, get one nick in it from cutting it and you might have a creeping cut that will make it fit the nipple loosely and leak. Silicone hose also breaks down with heat and age. I have used silicone hose under the intake manifold with good results, it is not the end all be all hose though. If you do use silicone make sure to use the thick hose, the thin walled stuff is garbage and much worse than the original hoses.

I haven't tinkered with Viton hose.

If you haven't already, go here: http://www.geocities.com/sdrx7_club/technical.html
and click on "Report" under Item 7.

Your choice...

The viton from HiTempSilicone is an excellent replacement material. The hose exerts a terrific 'grip', and does not need to be glued or clamped. Plus, the black hose looks like the original equipment hoses. A couple of dollars more, but well worth it. Now that it's done, it's too bad my car runs like crap now, though- I'll post that on a new thread.