Boiled out my heat exchangers

[JRM]

I managed to boil out all three of my heat exchangers in place yesterday, and since it went so much better than I thought it might, I thought I should share the experience.

A few caveats... I'm comfortable working with hazardous materials in general and acids specifically. I'm in the HazMat Technician pool at work, and have all the gear to do it right. None of which is necessary for this job :-).

I built a home-made back flush system out of a small bilge pump, some 3/4" tubing, two 5 gallon buckets, a 2 1/2 quart epoxy mixing bowl, and a 12v socket plug.

Construction was easy. Crimp the wires together, cover with glue filled heat shrink tubing to seal. Hose clamp one tube to the pump outlet, just toss the end of the other in the bucket. One bucket for acid, one for fresh water. Little bowl for measuring flow. Plug it in the socket to run, unplug to stop.

The trick was finding the right acid. I've used muriatic acid in various projects in the past. But it has too many downsides in this application. It's nasty, smells bad, eats just about everything but glass, and no matter how careful, I always end up with holes appearing in my clothes later. So after a bit of research and thought, I settled on phosphoric acid. It's a weak acid that's metal safe, and generally considered food grade. They put it in sodas for tartness. And it's (theoretically) easily obtained.

I found some 20% by weight at a masonry store labeled as grout remover and cleaner. It's about $23 a gallon. I mixed it down to about 5% for the actual flush. The stuff had soap added, which was fine. Defender sells similar stuff for barnacle removal, and WM will get it if you ask.

I took off all the raw water hoses, and then hooked up the tubing to the inlet and outlet of my engine oil cooler. Then I ran fresh water through it, and it took 25 seconds to run a quart through, so about .5 gpm as she sat. I then moved the pump and hose into the acid bucket and let her run for an hour. Lots of big chunks started appearing about the five minute mark. After an hour I took the pump out, drained and blew out the acid, and put it back in the fresh water bucket to rinse. After treatment, it took less than 5 seconds to run a quart through. I repeated the process with the transmission oil cooler and the heat exchanger. Neither of those made such dramatic gains in efficiency, but I did double the throughout on the transmission oil cooler.

After I was done, I replaced all the engine hoses with new (how the heck do you get those things fully seated on the nipples?) and fired it up. I let it warm up and then revved it up and let it run. I had to reset my stern dock line in order to run WOT, but it didn't budge above the 180 degree mark. I couldn't exceed 2000 rpm (after changing the impeller) previously, and now I can run 3000 for an hour without blinking. Progress...

I won't know for sure until I take her down to the boatyard on Tuesday, 25-30 miles. But I think I might have just solved my nagging overheating problem. Fingers crossed. Many thanks to the forum, who's search function got a workout over this.

JRM

-- anyone have any suggestions for myself or others on things to improve? The guy in the slip next to me is going to try it when he gets his engine running again, and any thoughts are appreciated.

[DeepFrz]

Only suggestions I could make are to check your heat exchanger and mixing elbow for pieces of impeller blade. Also check and clean the anti siphon valve while you are working on the cooling system.

[Cheechako]

Hmmm.... not sure why your RPM would increase.... the engine should have reached the same rpm previously, albeit maybe overheating when it did!
I to would want to check for impellor debris and or chunks that didnt come out with the minimal bilge pump pressure...at least in a perfect world..given that it sounds like you were pretty clogged up. But great job and great info.

[JRM]

Originally Posted by Cheechako

Hmmm.... not sure why your RPM would increase.... the engine should have reached the same rpm previously, albeit maybe overheating when it did!
I to would want to check for impellor debris and or chunks that didnt come out with the minimal bilge pump pressure...at least in a perfect world..given that it sounds like you were pretty clogged up. But great job and great info.

Hmm, on rereading I can see how that was confusing. I meant RPM I could maintain without overheating. It would rev up that high before, just not without consequences. It was a long last two miles on the trip up from Ventura last year when the wind died, since we could only turn revs for about a knot and a half without the temperature climbing up.

I'm off work tomorrow, so I'm planning on doing a full oil change and fresh water system flush. If I get to it I'm going to change the belts. Then, if there's still time I'm going to take a brass brush to the seacocks and clean them up. And finish mounting the new VHF. And since I'm now into imaginary boat time, I'll add mounting the chart plotter too :-).

JRM