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i've looked around on the net, and i want to replace my hoses with silicone ones. but i don't know what size they take. i've also searched the forums, does anyone now the size of them? thanks much
pOeace
 

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I did all my small bore hose in silicon and tried some different sizes out. I found the best size is 4mm internal diameter with 2mm extenal wall width.
HTH
 

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If one replaces, say, a 3mm internal diameter hose with a smaller or even larger one, how will this affect running of the engine?
I tried out 3mm silicon first but found it actually smaller than the 3mm rubber hose :! The 4mm silicon worked out the same internal diameter as 3mm rubber. Don't think there would be a problem with slightly different hose (I did a few hundred miles with differing hoses and no ill effect) but probably best to keep it all the same.
 

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saab savior has a really good silicone line set that replaces everything in the engine bay that is rubber line.
Includes enough line to do the vacumm lines, windshield washer lines, and cruse control lines.
I bought the kit and it works great.
You can buy it at www.saabsavior.com
 

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The Universal Starter Kit from hosetechniques.com worked great on my 1987 900 Turbo. Just size the hose according to the nipples it is going onto. It'll stretch if it needs to.
 

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Nasty bump here, but in my lengthy absence from these boards, someone asked me about my experience with silicone vacuum lines and I figure the post may have broader interest.

Here was my reply:

Doh, I was away for a while, but I'm back now.

I haven't gotten around to figuring out the exact lengths. The more I think about it, the less good of an idea I think it would be to try to match it exactly. There are lots of variances between different years and options, and even if they are identical otherwise, it is fun and easy to juggle your Ts and come up with a completly different routing for your lines. As far as I can tell, most of the vacuum ports are about the same, so you shouldn't get into trouble if you, ahem, improvise. To play it safe, replace one line at a time.

The Universal Starter Kit from Hose Techniques should set you up wonderfully, with plenty to spare.

The second picture on my website gives a really awful overview of the lines I did. You can almost, but not quite, get a rough idea of what I replaced.

http://www.silversaab.net/

Basically, I did every vacuum line under the hood, except for the two going to the inside of the cab (one for cruise control and one for the gauge).

That doesn't include the windsheld washer lines for some reason (apparently I was feeling lazy when I did this), but I've got loads of hose left over and easily could do them, I think. Didn't check the diameter, but the silicone can easily stretch or compress (with a zip tie) to fit if it isn't too far off.

I also did my throttle cable which technically isn't a hose.

Oh, and when they say not to use it for lines that carry oil and gas, they really mean it. I did my PCV line (the one with the check valve) and it got ugly in a hurry. I think it was mostly just cosmetic, but you are better off sticking with rubber hose there either way.
 

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I think the smaller vacum hoses have a i/d of 3.2 mm so I think you could use 3 or 4 mm silicon hose. I have just bought the 3 mm stuff for a snug fit.
Cheers,
Deano.
 

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Resurrecting an old thread...

Had my Saab Tech inform me that the 4mm silicone vacuum hose I used to replace old ones was not sitting snugly and thus whistling due to air leaks. He recommends replacing with a size down (3mm). I see in this thread many have used the 4mm even though the OEM for Saab is 3.2mm ID (also posted in this thread). Question for those who put 4mm hoses in,... Any performace issue? Leaks? Whistling?
 

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I have 4mm fuel hoses instead of vacuum hoses. Had them on old 8v and on my daily driver... No problems and they last (may be cheaper than silicone). I can’t imagine fitting smaller id fuel hose on those nipples, silicone should be more elastic...
 

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On a non-turbo you don't have to worry as much will poor fitting hoses... there is no pressure in the intake system to blow them off. On turbos, a snug fit is critical. 3.5mm is the correct size.
 

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Want to be clear here... In this thread both 3.2mm and 3.5mm IDs as the OEM has been posted. Where can we verify the correct OEM vacuum hose ID?
 

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3.2mm is specified for the NG900/9-3. There is no such specification for c900 (AFAIK). 3.5mm is the correct size for c900. I don't think you can even buy 3.2mm hose in the US with any reliability; 3.5mm will work for both. I buy 100' a year on average. :)
 

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Thank you! I am asking all of this as I replaced some lines about two years ago with 4mm ID silicone hose and some are no longer tight on the nipples so I have some leaks. I am know wondering if I may experience the same with the 3.5mm ID hose. Considering buying 3.0mm ID hose to ensure a maximum tight fit. Your thoughts/experience on using 3.0mm ID?
 

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3mm silicone will fit, but good engagement will typically lead to stretching and sometimes splitting. I've used it in a pinch, but it wouldn't be my recommendation. Also, be sure you're not using silicone on the valve cover breather - most silicone won't put up with petrochemical vapors... it will discolor then fail. Only on (mostly) pure air.

This 3.5mm hose has been here for 10 years and is still in perfect shape.

2010:



2020:



It's specifically this:


which is apparently out of stock right now. :)
 

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+1 to avoid 3mm... I have had (earlier mentioned) 4mm fuel hoses cracked where they fit nipples. Fuel hoses are thicker but I would not go with thiner (more strechible?) 3mm silicone hoses anyway. 3,2mm fuel hoses are available but I think they would be hard to fit and prone to cracks on nipples. I am not in any way asociated with fuel hose manufacturers or reselers 😁
 
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