Blew out end cap on lehman 120 heat exchanger

Good afternoon.

I have a 26 foot Downeast style boat with a lehman 120. It is cold here in the northeast and we had a few days of temps below 15 degrees. (2-3 inches of ice developed around the boat)

I have the boat in water on a dock with two block heaters and a thermostat on raw water strainer set at 70 degrees. (Keeps engine box around 65 degrees using the engine itself as a heating element.

It has worked like a charm all season. Engine starts right up all the time. This morning, went to fire her up. Engine was about 59 degrees via laser temp. (All areas on block). Went to crank her over and it cranked as usual for the first two cranks, then slowed for the third. (I stopped cranking at this point figuring I’d give the batteries a minute to catch up, but unusual for me)

This repeated itself until the engine started and then I heard a pop and exhaust and water came out the side of the heat exchanger. No biggie. Engine ran fine.

I turned ingine off, tapped the side plate back on the heat exchanger, put a hose clamp around it for reinforcement pulled out pencil zinc as a vent and cranked it up again, ran for about 4-5 minutes, ran fine and shut down. (There always exhaust coming out pencil zinc aperture)

I am assuming that the exhaust snorkel in the back had frozen up and caused back pressure and the weakest point was the side plate.

Now, I’m concerned, but figure it’s a 700$ mistake. (Cost of new exchanger).

Any thoughts? I’m sitting on her now scratching my head, lol. No internet surfing is finding me an answer.

I`m scratching my head a bit too. I`m struggling to understand which of the three heat exchanges have a side plate that can be held on with a clamp and any that have exhaust coming through. Do you mean the exhaust manifold?

No, lol. It’s the heat exchanger. (It has the two side plates with rubber gaskets). It’s the old sendure type. (Big copper tube with little copper tubes running through it. ). I’m oretty convinced that the back pressure of exhaust worked its way back to heat exchanger through the raw water exhaust elbow. (This is where the raw water is dumped into exhaust at the elbow.)

I tapped the plate back on (it tore the little frame off the main 4 inch tube). I out the hose clamp over the whole exchanger to create more friction to hold it since the welds are gone. It’s holding, but hissing, lol

This is a link to image.

Sorry, can’t load image.

You are confusing people calling them side plates. Everyone calls them end plates.

If indeed the exhaust was frozen shut be alert to water entering exhaust manifold and into engine

Take HX to a radiator shop, they may be able to re-attach the end caps.

Did your power go out? Always a risk when depending on heaters to prevent freezing.

Thanks for the replies. I sort of got disgusted and left the boat and was driving home to order new HXer when I saw the post about the water in cylinder worry. Drove back and pulled HXer and fired her up to make sure she had no water in cylinders.

As far as fix or replace the HXer, I’ll figure it out. I have a few truck radiator places I could take it, but was planning on replacing it in the spring before this happened. I have 8 years on it and was told they should be replaced every 8 years. (And every 2-3 years for the oil and trans HXers)

As far as the power shut off, no. I shot it with the laser thermometer before starting and the block and raw water system were warm. It’s 15 feet to the back of the boat and the exhaust has a “snorkel” on it. (It is an elbow on the transom that routes exhaust into the water. This supposedly reduces noise)

The snorkel was iced up. (Or the exhaust pipe running back, or both). Lesson learned.

Thanks for the feedback everyone