Mercruiser IO sneaky leak

"I have an 87 Cobia with a Mer

"I have an 87 Cobia with a Mercruiser I/O on it. 4-5 years ago I could run all day then pull the plug on the ramp and barely get a drop of water out of the boat. Now there is always water in it and I have to run the bilge often.

Last summer discoverd a leak in the drive shaft bellows right after the coupler went out. I had the shifter boot replaced at the same time. I thought having them repaired would stop the leak as well but it didn't.

I've tried to look for where the water is coming in repeatedly, but can see nothing. I've inspected the hull and everyplace that a screw or bolt goes through the hull at or below the water line, all appear to be okay.

One more thing that might be the key. It seems that a couple of times when I have had the boat beached with the lower unit down to help keep the boat from getting pushed to far up on shore. The boat has filled up very rapidly with water, almost to the deck in less than an hour. That is why I suspect it has something to do with the stern drive. The question is what?

I hope someone can help this thing is making me crazy!

Wingman"

"Take a look at the Transom mo

"Take a look at the Transom mount. I have seen
The Housing eaten away because their was a bad connection to the zincs, Next to the bellows
You will have to remove the drive and bellows
to see it, But first try haveing someone in the boat and with a garden hose spray with a heavy
streem of water and watch for water come in the bildge, cover each section good before moving on."

The transom mount seal may hav

The transom mount seal may have a leak(loose). Put the boat up in the front and fill it with water and see where it runs out.

Both are good ideas. I'll

Both are good ideas. I'll try them out.

Wingman

"I went through something like

"I went through something like this earlier this summer. Turned out to be a rotted transom (ouch!). There were no obvious signs on the outside of the boat that the transom was rotted, but in the water it leaked. After removing the engine and stern drive it was obvious the wood was soft and letting water in. It's in the shop right now having a new transom installed. (Expensive, but for an older (1988) boat it is in good shape and I just couldn't bring myself to strip it and crush the hull.)

Anyway, I hope your problem is much cheaper to solve than mine! "

"I don't think I have the

"I don't think I have the same problem, at least I hope I don't. The transom will get a close inspection now.

Was the water coming through cracks in the gel coat?"

"No cracks in the exterior gel

"No cracks in the exterior gelcoat, in fact it looks nearly perfect from the outside. The water was getting in past the sterndrive mount (where the sterndrive contacts the exterior transom) as the transom flexed. With no stress on the transom it was more or less watertight, but apply a load and it leaked."

"Well Bamboo, turns out you we

"Well Bamboo, turns out you were right my transom is shot. What a belly drop that was! after bouncing the lower unit up and down by hand and seeing the transom flex. I drilled a couple of test holes from the inside of the boat. After drilling through the fiber glass all I hit was saw dust.

How much is your repair job costing you?

Wingman"

"I'm sorry to hear that is

"I'm sorry to hear that is your problem as it is an expensive fix.

I looked into several options such as the pourable Seacast transom repair, stuff you squirt in to make the rotted wood hard again, and a wood transom replacement. I went to a few local shops (Cocoa Beach, Florida) and got a range of quotes.

My boat is a 19' Thompson bowrider with a 4.3L Merc. It's a good looking boat, and actually built pretty well so I couldn't bring myself to toss it. The range of quotes I got ranged from 2000 to 4000 (for the seacast pourable repair). I ended up going with a reputable local boat shop that is going to replace the transom with marine plywood for about 2500. BTW - There is no need to cut the outer skin of the boat to replace the transom. It can all be done from the inside so your exterior isn't affected.

If you are experienced with glass and resin work, you could probably do it yourself...but I don't have that type of time or skills.

Hope this helps you some. If you have any more questions I'd be glad to answer what I can.

Good Luck!"