View Full Version : Cracked Exhaust Manifolds

01-05-2009, 01:29 PM
Here is my problem. After I took out my MC pro 190. after summer, I drained the block and took out the impeller. I bought the boat in September and it has a new ford 351 engine fitted (not new manifolds). Anyway With only 10 hours of use on her I am not going to change any oils til after next season so I got a wide enough bucket and long enough hose back to the oil cooler and my idea is to run her once a month with only antifreeze circulating through her, I tried it out first with water and no problem, I then drained the block and pulled the impeller, waited a couple month til it got a bit colder then was going to run the antifreeze. I ran her with water first and noticed both manifolds are cracked and leaking water. Yes we did have a cold snap in between and i should have done the antifreeze before that. The cracks in the manifold are about an inch long and very faint, The block thankfully is OK. I would have thought a drain plug would have been on the manifolds too, not so, anyway Can they be welded or would i be better to just replace them. I feel a bit of a fool for letting this happen and any advice is appreciated thanks

01-05-2009, 01:38 PM
Each manifold should have a screw in plug on the rear, so water can be drained from them.

01-05-2009, 01:53 PM
Also, you should still change the oil, even with only 10 hours on it, if you plan to let it go unused for an extended period of time.

01-05-2009, 02:00 PM
I am gonna check to see the screw plugs again. The mechanic at the dealership said I wouldnt need to change oil at them hours as its a new engine and just run in. That is not my problem Though, I would like advice on welding the manifolds, good or bad idea ? Or spend a bit more and get them replaced.

01-05-2009, 02:15 PM
I would get them replaced. But that is just me!!!!!

mark g
01-05-2009, 02:31 PM
Abe i would think it better to replace them with new, after saying that i had a small crack in one of my manifolds a couple o years ago had a local mechanic braze the crack and its still going strong, if you can find a good mechanic that knows his stuff regarding welding etc you might be fine.
Just on a side note the crack i had was only a couple inches long cant remember but think it only cost me 20 at the time.

the screw in plugs should be under the exhaust hoses at the back of the manifold tried to find a pic but no luck

good luck

01-05-2009, 02:32 PM
If the cracks are an inch long (I thought you guys use metric), grind the metal out along the cracks, wipe them with solvent, use a heat lamp, heat gun or blow dryer to warm the iron and use Marine Tex, JB Weld or some kind of epoxy that is made for extreme conditions. Cast iron isn't that easy to weld without causing stress, which usually relieves itself in the worst way, at the worst time.

Dan K
01-05-2009, 02:33 PM
Manifolds are generally high carbon castings that are either difficult or impossible to properly weld. At least that is what I was told when i took mine to a welder. bought new, check skidim.com they should have them.

01-05-2009, 03:32 PM
Thanks Guys, I,m in two minds here but after reading some of these replies I will get them replaced. Have been shopping around here in the UK and surprisingly not that expensive. I,m just glad nothing else is frost damaged. And my antifreeze is at the ready. Thanks again guys for all the advice. Roll on next Summer.

01-05-2009, 03:36 PM
Manifolds are generally high carbon castings that are either difficult or impossible to properly weld. At least that is what I was told when i took mine to a welder. bought new, check skidim.com they should have them.

Cheers Dan, Have checked skidim. Yes they are cheap I have shopped with them before. The problem is the shipping, Import and other charges to the UK. Plus the Pound is not as strong against the Dollar right now. Thanks anyway

Bruce Carr
01-05-2009, 03:41 PM
I have had good results in brazing (as opposed to welding) cast iron manifolds, both auto and marine. Let them air cool after you weld them and there should not be a problem with residual stresses. That being said, if the manifolds are pretty old and rusted thin, it may be just as cost effective to get new ones for the long run.

By the way, be sure and find the drain plugs at the aft end of the manifolds before it freezes again. The plugs are about 1 inch in diameter (3/4" NPT thread). Replace the original steel plugs with brass plumbing plugs if you still have the originals. Good luck.

01-05-2009, 04:11 PM
Abe, not that big a deal. Spend the money and replace them. It isn't worth the hassle or worry. They go bad over time and if they weren't new, well no big deal. Pay the money and get some piece of mine. They are are pretty easy to replace yourself.

01-05-2009, 04:37 PM
Abe, I do not see the need to run it every month, especially if it costs you the money to replace the exhaust manifolds even once. Many of us in the states leave ours sit for 3-5 months in the winter, but with antifreeze in the block and fresh oil in it. plus fogging oil in the cylinders. Look at the winterizing info on this site if needed. Again, I think many will agree you do not need to run it every month. Keep battery charged, teak oiled (for you Harold!), and it should be ready when it warms up.