Best way to pressure test an exhaust manifold?

[cjray03]

Hi. I have a 1970 Fiberform 16' with the 120 HP in it. I had some issues recently after it ran hot. Like it wouldn't shift into reverse. Got it all fixed up with a new shift cable. Anyways, like I said it ran hot. Now I noticed water in the oil. Also, I had it in the shop for the reverse issue (which they did NOT fix) and they told me my exhaust manifold was cracked. The guy put some JB weld on there, but I am sure it didn't work. I pulled the manifold and in doing so noticed the gasket between the riser and manifold was toast. I am about 97% sure this is where the water was getting into the block. At any rate, I re JB welded the manifold, it seems to have held up well. I need to pressure test it to be sure it has no other cracks and that it is holding. What is the best way to do that? A hose to the inlet side I see, but how to block off the outlet? Should I put the riser on then block it off? Thanks in advance for the information. Sorry for the winded post, just wanted to get as much details as possible out there.

 

[ScottinAZ]

Honestly, the best way to test the manifold is with it off. Then block one side and fill with acetone. There really is no good way to block the riser end, as it’s intended to be open for the water to exit the exhaust. If you had a blown riser to manifold gasket, I would agree that’s a likely intrusion site.

 

[Lou C]

If it’s cracked in one spot that’s all I need to know it’s scrap iron. If you want to keep that engine running replace it.
I know it’s money but if you’re in a freshwater region where exhaust systems last nearly forever….this might make you feel better…my salt water boat is on exhaust system # 3 in the 21 years I’ve owned it and is going to get # 4, in a couple years! Here every 5-7 years you replace. You can fill with acetone just be careful it’s very flammable. They are not under much pressure not like a closed system with a pressure cap.

 

[stresspoint]

100% as Lou C posted , replace the thing , that patch job may get you by , but its pot luck when its going to fail and most likely write your motor off.

 

[cjray03]

Thanks for the info. I found one that I think fits, Brand new it's $360 or so. Comes with all the needed gaskets too. I guess it's worth it for the peace of mind.

 

[Lou C]

It definitely is…on my old engine it came with the OMC one piece V6 manifolds. The set it came with I had no idea of the # of hrs so I replaced those after I had it a couple of years in 2004. Next replacement was in 2011 again with those OEM manifolds. By the time the next replacement was due in 2017 those were long since NLA. So what I did was convert it to the later style (2 piece) used by OMC & later Volvo. I got the manifolds & elbows from Barr marine & the rest of the parts I got from Volvo Penta. Expensive but fit like factory & no leaks. $1300 or so for the whole conversion. However next time I have to do it I only have to do the manifolds & elbows so the cost is a lot lower like $800.
So as a data point in salt water over 21 years I have paid a lot in exhaust replacements to avoid a trashed motor….
2 OEM REPLACEMENTS about $900 each
1 aftermarket/Volvo conversion $1300
So in total that’s $3100 in exhaust maintenance and I did all the labor myself….so Pat yourself on the back you’re getting away CHEAP!
Salt water boating is great; we never have low water levels or floods (unless a hurricane comes up the coast) BUT between manifolds & bottom paint & maintaining trailers it gets expensive!

 

[KJM]

Yeah, as above. I wouldn't trust a good motor on jb weld holding. I almost ruined an engine thru using a leaking manifold. Those manifolds are expensive, mine was over $1000 cad. One of the reasons I converted the boat to OB!