Detailed steps on how to service your Heat Exchangers. It's all pretty straight forward stuff and you should be able to service them in a day.
The following are the steps and general process:
1. Shut the thru-hull that supplies sea water to the engines.
2. You need to drain the coolent from the fresh water side of the exchanger/engine. There will usually be a drain plug on the lower end of the exchanger, probably the aft end. Remove the filler cap, then unscrew the drain plug and drain the fluid into a bucket. If you can get a bucket into position, use a funnel and a piece of hose to channel the fluid into a bucket. Failing that, you can let the fluid run into the bilge, but then you have a bit of a clean up problem on your hands. Remember to turn off the bilge pump at the switch panel before draining into the bilge; use a manual hand pump to pump the fluid into a bucket and clean the residual with a sponge. The bucket, if it works, serves one other purpose, it indicates the volume of fluid needed to recharge the system afterward.
3. Drain the sea water side. On my engine I have a drain plug on the oil cooler for the gear box which is lower than the heat exchanger and all in the same system. Look for it as you may also have a drain plug somewhere else. Again unscrew the lowest drain plug in the system and drain the sea water into a bucket, or the bilge.
4. After draining both sides of the system, you can remove your end caps and look inside. Check for bits of impellers that may have broken off and calcium build up. Having gone this far, I would recommend going the extra mile as follows.
5. Now remove all the hoses in any order appropriate, unbolt the exchangers from the engines and take them out to the dock.
6. Take a fresh water hose and with the end caps removed, flush the exchangers with fresh water.
7. Inspect for calcium build up inside the pipes, if necessary take a metal rod similar in diameter to the inside of the tubes and pass it through to push out any calcium and debris that may be blocking the tubes. Then flush again with fresh water.
8. Once you are happy that the exchanger is clean and you can see clearly through all of the tubes, you can reassemble in reverse order. Even if they don't look worn, it's work replacing the end cap gaskets as a precaution.
9. Replace the drain plugs and open the thru-hull. The salt water side of the engine will self bleed.
10. Fill the engine with coolent. I recommend buying a pre-mix coolent, but if you use undiluted coolent, dilute it ONLY with distilled water - - tap water will be band for both your engines and the exchangers. You will have a bleed valve somewhere on the engine, quite possibly on top of the housing for the thermostat, but look all over the engine for something at the highest point of the fresh water circuit. Open the bleed valve and fill the system until this valve begins to weep fluid, then shut it off and continue to fill the header tank until full, then replace the filler cap. If you have an expansion tank, you can now fill that to the desired fill line.
11. Recheck that all of your hoses are connected and tight with no signs of leaks. Double check that your engine intake thru-hull is open. Now start the engine (in neutral) and let it run for a couple of minutes (2-3 min). Shut the engine off and check the coolant level - - top off if necessary. Repeat this process 5-6 times until you are happy that the engine has taken all the coolent it wants. Then run the engine for at least 20 minutes, monitoring the fluid level and also checking for leaks at temperature.
12. When you are happy there are no leaks and the fluid level at temperature is stable, shut down the engines. Job Done!
Here's another tip for you. If you find your exchangers to be particularly clogged up when you inspect them, it would be advisable to take them to a mechanic for an acid bath. While there, he can perform a pressure test just to make sure there are no leaks between the fresh and salt water sides. But this depends a little on how old your engines are and how long it has been since a full service check was performed.
In the end it is a pretty straight forward job.
Captain Ian Fagg