Blow by system Oil breather hoses sizing | FerrariChat
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Blow by system Oil breather hoses sizing

Discussion in '308/328' started by fredbrbr, Oct 24, 2025 at 11:59 AM.

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  1. fredbrbr

    fredbrbr Rookie

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    Fred Brouwers
    #1 fredbrbr, Oct 24, 2025 at 11:59 AM
    Hi Everyone,

    I had recently noticed that one of the oil breather hoses of my 1976 308GTB's blow by system was starting to give in. The hoses on their were just green silicon heater hoses which weren't too pretty in the first place. I purchased the correct parts from Dino Parts in Germany in order to replace both. However, I just noticed that to my surprise, the DinoParts hoses seem far too large in diameter to fit on the pipe or on the valve covers... The previous random heater hoses fit very snug whereas the "correct" ones fit very loose. My question is, is it safe to fit these loose hoses on the pipe and covers and tighten them as tight as possible with their clamps?
    If not, does anyone know what type of hoses are good replacements from a DIY store, keeping it mind it gets quite hot around there and they'll be exposed to oil mist.
    I have attached the green non original hose's picture next to the "ferrari" hose to show the difference in diameter...

    Thanks,

    Fred


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  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Oct 24, 2025 at 12:24 PM
    I'd go with "wrong part" -- the hose from MCP (the official old F part supplier) looks more size-wise like your existing part:

    https://www.ferrariparts.co.uk/part/ferrari/116783

    (and the wall thickness and amount of reinforcement on the DinoParts pieces seem very excessive for that application.)
     
  3. fredbrbr

    fredbrbr Rookie

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    #3 fredbrbr, Oct 24, 2025 at 2:03 PM
    Hi Steve!
    Thanks for the quick reaction. The MCP hose looks like the dino parts one I think. Unfortunately the "wrong part" which is the green hose, is torn and can't be reused, also I can't find this brand of hoses here in europe. I'm thinking of just getting a regular 20mm thick piece of hose and cut it to length. What can be used for this application in your opinion, fuel hoses? I was thinking any hydrocarbure hose should do the job no? As it will be reasonable pressure levels and just high heat and oil mist contact.
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Oct 24, 2025 at 3:31 PM
    Can't agree with that -- look at the reinforcement in each. The MCP piece has a single layer of fibers (which is appropriate for this near-zero pressure application) while the DinoParts has about 4 layers of fibers (which also increases the wall thickness).

    Yes, needs to be compatible with hydrocarbons and have enough temperature resistance for a hot engine but only low pressures (that green heater hose was a terrible choice).
     
  5. fredbrbr

    fredbrbr Rookie

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    #5 fredbrbr, Oct 24, 2025 at 4:05 PM
    Indeed now that you point out the reinforcement layers, I do see a difference. I attached a picture of dinopart's actual webshop photo of the item and it looks closer to the MCP piece but doesn't really look like the piece I received, maybe they made a mistake, the piece was however labelled "Oil Breather Hose Valve Cover Dino 308 GTB/GTS/GTBi/GTSi" and OEM part 106335, just like on MCP...

    I agree, whoever installed those green heater hoses wasn't the smartest of the bunch, especially when I read that they're specifically not designed for hydrocarbons... would explained why it started pretty much decomposing.

    I'm thinking of replacing them with some SAE J30 R9 rated hoses with the correct diameter cut to spec, these are rated for fuel injectors and other hydrocarbons and 300°F environments, will definitely also come cheaper than the prancing horse labelled hoses...


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  6. johnk...

    johnk... F1 World Champ
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    #6 johnk..., Oct 24, 2025 at 4:14 PM
    Do a google search on cloth braded hoses. You will find many sources.
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #7 Steve Magnusson, Oct 24, 2025 at 4:25 PM
    Can agree that that Dinoparts picture looks much more appropriate, and there are plenty of steps for a mistake to happen anywhere from procurement of the bulk hose thru cutting to length and then packaging.
     
  8. moysiuan

    moysiuan F1 Rookie
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    #8 moysiuan, Oct 24, 2025 at 5:25 PM
    Last edited: Oct 24, 2025 at 5:33 PM
    That looks much to big to securely seal with a clamp. 19mm (3/4") ID is the typical size of the breather hose. Your bigger size hose is probably for the part 9 in the diagram, probably the 22mm hose ID.

    The old hose may have the flourosilicone liner, which makes it fine for a breather hose application. Regular silicone hoses are not ok for oil, even the limited amount in the breathers.

    The larger diameter cloth braided breather hose used to be available from Newco products, not sure of they still carry them - their hose was branded Continental. Italian Car Parts also has the correct sizes. http://www.italiancarparts.com/parts/308.html#hoses Or maybe here...https://teaguecustommarine.com/12-fc647-cloth-braid-push-lock-hose-sold-per-ft

    These cloth covered hoses are not so common in these larger diameters. Smooth hoses of suitable wall thickness will work as well, if you order from the various F parts suppliers they will not likely be the cloth braided style.
     
  9. tbakowsky

    tbakowsky Two Time F1 World Champ
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    #9 tbakowsky, Oct 24, 2025 at 8:31 PM
    22mm I.D for the breather pipes. You can source the braided hose on Amazon.
     
  10. ChevyDave

    ChevyDave Formula Junior

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    #10 ChevyDave, Oct 24, 2025 at 10:14 PM

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