Testing manifold

[Sangster21]

When I pulled the engine out of my new to me boat, I noticed some coolant in the bottom of the manifold where the riser bolts on. The manifold is in the closed loop cooling system, there was a block off at the riser to prevent the coolant from exiting down the exhaust. Any way I made up 3 block off plates out of plywood and sliconed them on. Tapped one for 1/4npt and hooked up an air line... gave it 10 psi and I don't hear any whooshing of leaky air. I will giv'er a bit more pressure tomorrow when the sealant has cured. I probed about with a screw driver trying to poke a hole through a passage... seems solid. It would seem to pass the test.... where the heck did that coolant come from??
Engine '76 I6 mercruiser 165hp.
Alan

 

[dan t.]

Re: Testing manifold

That gasket has been known to fail with age, specialy if it was of the "green" varity, check if the mating surfaces are flat. Just going thru the same senario, the manifold mating surface was slightly warped, I filed it flat. You should have a pressure guage on your test plate, pressure it up and let it sit for 1/2 hour and see if it bleeds off. I checked mine at 30 lb. Good luck.

 

[Sangster21]

Re: Testing manifold

Well, my testing procedure worked out fine. Unfortunately the test was more sound than the manifold. The foam erupting from the manifold says "FAIL". On the plus side, I won't be giving this old manifold the clean and paint routine.
Alan

 

[dan t.]

Re: Testing manifold

Hey, better to find it now than out on the water.

 

[achris]

Re: Testing manifold

Not a good look, but hey, you found the problem.

When you put a new manifold on, put the 'water reversing kit' on.... (Service bulletin 83-19, www.boatfix.com/merc/Bullet/83/83_19.pdf)

Chris.....

 

[Sangster21]

Re: Testing manifold

I will make sure to do the flow reversal plumbing, another member sent me the San Juan Engineering cooling diagrams. In case anyone else does this sort of pressure test. Plywood end plates are easy to make, easy to drill and tap for pipe thread.I put a small bead of silicione on the manifold before I bolted the plates on. I put a ring of silicone on the fitting before I threaded it it. A tiny bit of air leaks right thru the wood fibres! A pressure test with gauge would leak down for sure. I laid the manifold on its back, propped it levelish and filled with water. No bubbles no troubles. In my case, bubbles and a new manifold!
Alan