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Testing exhaust manifolds for leaks...

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  • Testing exhaust manifolds for leaks...

    That's one trick I've never heard of - pretty slick! Thanks for sharing it, Bubba. Sounds like it would be a bit easier than the way I've seen it done.

    My shop pressure tests the old-fashoned way- by blocking off the ends and attaching a hose with a special fitting. The fitting has ports for a pressure gauge and schrader valve. They put (I think) 20 PSI air pressure into it and check for leaks with soapy water and a brush. They do this (of course) after rodding out the risers and manifolds to clear any scale or rust, and then blowing out all the passageways.

    One thing to consider with using acetone- any rubber hoses it touches should not be re-installed on the boat.
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    I see a lot of folks asking for a simple way of testing their exhaust manifolds for leaks so I thought I would share a method I have been using for several years that is both easy and almost fool proof.

    Supplies needed.

    A short (12") length of water hose that fits the water inlet on the manifold. (You may need two lengths. See drawing)

    1 gallon of Acetone

    Hose clamps to secure the hose on the manifold.

    See the attached image below (ok, its crude but you get the idea) of a typical marine exhaust manifold. Depending on your manifold you may or may not have the optional water connection but they all have a single connection for the water inlet.

    If you have a second water port you must either attach a second hose (as shown) or cap off the port. (Either works fine.)

    Connect the water hose to the inlet on the manifold and arrange it so it is higher than the very top of the manifold discharge (the part going to the riser).

    Now with the manifold level, pour acetone into the hose until the manifold is full and the acetone is right at the top of the manifold. (Don't over fill.)

    Thats all there is to it. Let it sit for 20-30 minutes and look for any signs of leakage and for a drop in the level of the acetone. There should not be ANY signs of dampness (leaking) in the exhaust gas side of the manifold nor any leaking to the exterior of the manifold. If there is its time to buy a new manifold.

    But what about pressure to test it you ask? There in is the simplist part of all this, you do not need to apply any pressure to the liquid (acetone) side of the manifold for this to work. Say WHAT? No pressure? But, but, but...

    The reason is that acetone is VERY thin and has almost no surface tension compared to water. Water is 4 times as viscous (thick) as acetone and has a MUCH higher surface tension. (Surface tension is why you can fill a glass higher than its rim or why bugs can walk on water.)

    To give you an example, if you had a small opening (crack) that acetone will barely pass through, you would need roughly 20 PSI of pressure to force water through it. In other words the acetone will "leak" well before water ever would. Even if the water is under pressure from the water pump.

    If there is no signs of leaking, pour the acetone out (keep it) and flush the manifold with water and your ready to put it back on the engine.

    Hope some of you folks find this usefull.

    Locking and putting in the Adults Only sticky at the top of the forum.
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    Last edited by Fun Times; April 16th, 2014, 05:24 PM.
    Don S.

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