crack in external block

I have a crack in the external engine block on 3.0l 4 cylinder mercruiser. My mechanic said it is under the manifold and said he has had a lot of success with JB weld. Another mechanic said he can also do but recommends cast iron weld. The good news is both have said this is not death to the boat and feel confident both techniques will work. If its under the manifold is it going to be heat restrictive? Any other advice would be great

Also, what are the ramifications of not doing this immediately as I want to keep the boat out for the remainder of season?

Re: crack in external block

This seems to be a fairly common problem on the 3.0, my boat had the same problem when I bought it but someone had just smeared JB weld over the crack and slowed the leak. The fix I have seen most common in the forums is to drill the ends of the crack to prevent it from spreading, V out the crack with a grinder, and JB weld it. I am not a welder, but from what I have heard it is very difficult to weld cast and the problem will most likely reoccur if not welded properly.

So far mine runs fine and within normal temp ranges with the JB just smeared over the crack but I would reccomend taking the extra time to do the grinding and drilling if you are going that route. Most people I have heard of have had very good success with the JB Weld fix. Maybe someone else will pop in with experience in this.

Re: crack in external block

ABSOULOUTLEY! The only thing is that you need to look at this as a temporary fix. Although it may hold for years always check it to make sure that the JB weld is holding fine. This is how I repaired the crack in mine 3.0.

1. Sand down the surface that is in need of repair.
2. Grind a V into the crack in question.
3. Get a drill bit not to big and put some grease on the end so you will not get any metal shavings into the block and drill at both ends of the crack slowly and go through all the way into the block (SLOWLY).
4. Mix your JB and let it get a little tacky before applying.
5. Smear into the crack making sure you apply pressure into the drill holes to make sure they are filled. I let this dry then sand and repeat.
6. Let it cure and then check for leaks.

I have also found that if you remove the water hose and suck through the hose creating a vacuum you can sometimes get the JB in to crack a little more.

Re: crack in external block

Thanks guys -stomach is feeling better!