Heat Exchanger leak 85 mercruiser 170 repair?

[juicebronco]

Boat 1985 Century with Mercruiser 170 freshwater cooling system.

I've searched but didn't come across this particular problem.

Took the boat out for the first trip of the year, and noticed water water was leaking out the back between the cap and the tube of the Heat exchanger It seemed to be lake water, as it was clear. The engine ran fine, and it never got too hot. I had ran it around a bit prior to noticing, so it had plenty of time to get warm. My initial thought with the seal must have gone bad, and I would just need to replace it. So I pulled the back cap off, gave it a quick inspection, and noticed the seam was slightly seperated between what is the tube shell and the inner section. The boat didn't seem to loose any coolant, and even with caps off both ends, the coolant isn't leaking out of the tube. I added some photos, so you can take a look and give me your opinion.

I don't know why it split there, obviously my first thought is freeze, as we experienced a February with an average temp or around like 1 degree. But I've never pulled the cap off before so I don't know how long it could have been like that. My dad can't remember if he ever has, and we've had the boat since like 88. So it could be a new split, it could be an old split, not sure. But the fact it just started leaking water there makes me think new.

I'm not an expert on these systems, but I would think if that seam was bad and leaking it would be the freshwater coolant coming out when operating.



So please take a look at the photos can give me your thoughts.

 

[Bt Doctur]

I would remove the HE, clean and solder it back up .Did the end caps appeared bowed or belled out. That's a sign of freeze damage. And YES, the HE must be drained of raw water to properly winterize it.

 

[stonyloam]

On the 470 the raw cooling water flows through the tubes in the exchanger. it comes in the forward hose inlet and flows back and forth 3 times then out the aft outlet to the exhaust elbow and out. So if you take the end caps off only raw water will come out. The antifreeze (two interior hoses) circulates around the tubes. I believe the tubes are inserted into the exchanger and soldered in place as a unit, so if you don't have antifreeze leaking out of the seam you should be OK. if you did not drain the exchanger, freezing water could have pushed the end cap out and broken the seal. When you drain in the fall (aft plug under the exchanger) poke a wire up there to make sure the hole is clear and of the water drains out. Get a couple of new gaskets (27-99960), make sure the caps are flat, and not distorted and put it back together (no need for sealant) and you should be good to go.

 

[juicebronco]

Thanks for the replies. For the record I do drain the heat exchanger, but maybe the angle of the boat was too steep, and some stayed in there?

The caps looked fine, but I didn't inspect them closely to see if there was any bowing, I'll do that.

​So I have one vote for take it off and have it soldered one for put some news gaskets on it....... I guess I'll start with new gaskets and make sure the caps are flat and go from there.

 

[stonyloam]

Yeah, if antifreeze is not leaking out now, I would not worry about it.

 

[juicebronco]

Just a follow up for future searchers.................... I made a simple press to ensure the cap was totally flat, and replaced the gasket. No leaks, and seems to be operating properly so far.