1987 SN 2001 overheating

Just helped Aaron (jax904) with his overheating problem. We went through his water system from the hull pickup to exhaust and checked everything. We found is pump impeller shredded. We located a couple of pieces of rubber, but not all, in the thermostat. Aaron replaced the impeller and ran the boat on the trailer at the ramp. The boat idled fine, pumped water, no visible leaks, all fittings tight. Tried to rev the motor. It would not rev, stuttered until he moved back to idle, idled fine, then the temp shot up.

Today he brought his boat over. Everything was tight and the impeller was correct. I noticed water dripping from the under-side of the heat ex-changer on the port side. It looks like it had been leaking for quite a while. Between cylinders 2 & 3 I can not even recognize the bolt heads, the two spark plugs have completely rusted. I was able to get the riser off and one of the water jackets passageways is completely rusted shut. I was able to get the four end bolts at cylinders 1 and 4 out.

1. Any suggestions how to get the manifold off? I think the grinder on the rusted bolt heads is the only way.

2. Is this the likely cause for the overheat or do we need to dig deeper? head gasket.....

Last week we found an automotive carb. Aaron ordered the Holley 4160 from the local shop. After we fix the fuel hoses and carb issue we will sort that side.







Thanks, Rex

I am not sure of the term? On my truck it would be an exhaust manifold. As it has water flowing through it I assume it is a heat exchanger. It is an open system. Either way the pics are of the exhaust side at the head.

Plugged up exhaust manifolds are a problem for sure, whether its the whole problem is tough to say. All water entering the engine needs to exit through them, so if they were really blocked bad, that could be the whole problem.

You said it was pumping water fine on the trailer. Where you letting the motor suck up its own water with the bucket method, or where you force feeding it with the hose?

I would think the getting up to speed problem and the overheat problem are just a coincidence. Not related.

Unless the Manifolds were so bad that they were restricting exhaust and/or allowing a lot of exhaust gas to leak out under the engine cover and choking off the engine.

We think your right, two separate issues. Any thoughts on getting the manifold off? We can only see grinding the heads of the bolts off.

You are most likely losing power because one or more of your spark plugs is so rusted that it is no longer firing. Same problem happened to me on my '96. The GT-40 heads had a cracked water jacket and leaked. Eventually one of the plugs got so rusted that it failed and the cylinder wouldn't fire. That was when I decided it was time to replace the heads.

Perfect time for GT-40 heads.

These threads cover the process. A lot of which is to try and get some Kroil in there and let it sit. Some raps with a hammer/punch also suggested.

http://www.correctcraftfan.com/forum/forum_posts.asp?TID=27162

http://www.correctcraftfan.com/forum/forum_posts.asp?TID=27162

I grabbed this quote

80SN Barnfind wrote: Jeff, I went through the same frustration on my 80SN this past summer. I ended up using a 2" cut off wheel on a die grinder to cut the heads off the socket head capscrews. With the manifold removed, a visegrip easily turned the remaining "studs" out. This cutoff size fit perfectly in the irregular shape of the manifold pockets. Noel

If you wind up needing heads, and don't want to spring for GT-40s, I've seen the standard heads go very cheap on here. Every guy that's replaced his heads with GT-40s has a set of standards somewhere being used as paper weights.