Leaking Heat Exchanger - Merc 7.4L

[Fireman431]

2001 Mercruiser 7.4L MPI. 535 hours.

Port engine has a leak on the end cap of the heat exchanger (raw water side). It is a small dripping crack approx 1" long. Can this be removed, disassebled and safely repaired (braised, epoxied, or sealed) and returned to service?

The crack seems so minor, I would hate to imagine 600-800 dollars for a replacement heat exchanger.

Thanks for the assistance.

 

[Lyle29464]

Re: Leaking Heat Exchanger - Merc 7.4L

Most likely it can be fixed with out problem. Almost no pressure there. I would wonder what caused it. may not even need to remove it.

 

[Bt Doctur]

Re: Leaking Heat Exchanger - Merc 7.4L

6B-14 .. http://www.boatfix.com/merc/Servmanl/16/16B6R2.PDF
Might even have a cap

 

[Don S]

Re: Leaking Heat Exchanger - Merc 7.4L

Remove the heat exchanger and take it to your local radiator repair shop. They are set up for fixing that type problem.

 

[wire2]

Re: Leaking Heat Exchanger - Merc 7.4L

I see you're in FL, has the boat ever seen frost? I've seen a couple of them pop a seam if even a bit of water was left in over the winter.
The one owner insisted he had removed the plug, watched some water dribble out, then put it back. But didn't pump anti freeze through it.

 

[HT32BSX115]

Re: Leaking Heat Exchanger - Merc 7.4L

Almost no pressure there. I would wonder what caused it.

Freezing water will break cast iron easily. It would certainly crack copper.

If it's a San Juan, you could call them and they would send you a replacement cap.

You could probably even pull it and get it brazed.

 

[Fireman431]

Re: Leaking Heat Exchanger - Merc 7.4L

No frost. It gets a little cold here, but with the heat/ac set at the right temps, the interior of the boat is nice and the bilge maybe sees a lowest of 40 degrees. Besides, this happened over the summer sometime. Now, if this cracks due to Florida 100 degree summer days, then I'm listening....

I'v attached a pic to show the location of the split (excuse the size). It is the white line on the end cap of the exchanger. It extends in a 6 o'clock direction from the bottom center up towards the bolt, but never actually reaches the threaded section.

I have a feeling it cracked from pressure. I'm almost willing to bet there's an abundance of sediment in there. I'll find out when I remove it.

Thanks for the quick responses. As always, I appreciate the help.

 

[Don S]

Re: Leaking Heat Exchanger - Merc 7.4L

Get a new gasket for the end cap. If the end cap is corroded or warped, replace it too.

 

[EddiePetty]

Re: Leaking Heat Exchanger - Merc 7.4L

Ah, a crack in the 'ol endplate!!! In sunny Florida I can only imagine one of two things causing that: Fatigue from vibration/heat cycling or overtightening.
Pop it off, braze it up, flatten the endplate (or better yet, buy a new one)and install using a new gasket. Excellent time to clean the exchanger out so ya' better get two gaskets!!

 

[Lyle29464]

Re: Leaking Heat Exchanger - Merc 7.4L

I have that same cooler. It is a strange fit. the outside seals agains the cooler but the bolt does not bottom out. If you put much torque it will deform the cap. That might be what happened. I am guessing 4 or 5 lbs of torque. anyone else notice this?

 

[Fireman431]

Re: Leaking Heat Exchanger - Merc 7.4L

Ah, a crack in the 'ol endplate!!! In sunny Florida I can only imagine one of two things causing that: Fatigue from vibration/heat cycling or overtightening.
Pop it off, braze it up, flatten the endplate (or better yet, buy a new one)and install using a new gasket. Excellent time to clean the exchanger out so ya' better get two gaskets!!

This is exactly what I was thinking. I found the endplate kits online and now it's just a matter od making sure I have the right part number before ordering. Not too bad, $17 for the plate, bolt, and gasket. I can swallow that without gagging! I would rather replace the end cap than repair it, as long as I don't have to replace the whole heat exchanger.

I guess I might as well get 4 gaskets and do the other engine as well.

 

[Lyle29464]

Re: Leaking Heat Exchanger - Merc 7.4L

I guess I might as well get 4 gaskets and do the other engine as well.

I dont see where that gains you anything. In fact you could go backwords

 

[Fireman431]

Re: Leaking Heat Exchanger - Merc 7.4L

I dont see where that gains you anything. In fact you could go backwords

True. Maybe I'll just purchase the 4 and have them on hand for when/if they do head south.

When i get the old caps of the original, if the heat exchanger is full of crud then I'll probably make plans to do the other, if nothing more than to clean them out.

Or i could take it to a radiator shop and have it boiled out.

 

[Fireman431]

Re: Leaking Heat Exchanger - Merc 7.4L

UPDATE:

Removed the old endcap and gasket. Had absolutely no blockage, corrosion, or gunk in the heat exchager.

The old rubber gasket came off in one piece. There was actually nothing to clean or scrape. Put the new gasket, cap and bolt on and have zero leaks.

Time to complete the job: 2-3 minutes!

Why...WHY?!?...doesn't everything go like this? Maybe if it did, you wouldn't appreciate the ones that are easy and painless.