I heard that others have used the
engine's water pump to circulate the flushing solution, so I
thought I'd try it. I use oxalic acid for the flushing solution,
because it comes in a crystalline form for easy storage and
transport, it's relatively safe, readily available, inexpensive,
and I use it for other things like removing stains on fiberglass
and cleaning teak. You need to heat the acid for best effect, and
this method provides the advantage of heating it for you as you
run the engine. The only problem I experienced was that the water
pump gasket failed during my flushout, and hot acid was spraying
out from under the pump cover. I hadn't planned on that, but a
new gasket was cut from a paper bag and everything worked out
fine. I also used the marina's pressure water to flush out loose
particles before doing the acid flush. Here's how I did it.
1. Close the seacock at the seawater coolant inlet.
2 Remove the thermostat. To remove the thermostat, remove the two nuts holding down the thermostat housing. Lift up the housing and remove the thermostat then reinstall the housing.
3. Pinch off the by-pass hose - between the water-jacket plate and the inlet to thermostat housing. I put a rag around it and clamp on a vice-grip. This will force the acid flush to clean the entire cooling system.
4. Turn off your master battery switch, then remove the alternator for easier access to the water pump hoses and fittings. Disconnect the coolant line from the output side of the engine water pump. Connect a short section of hose with a regular female hose fitting on one end to this coolant line using a barbed hose connector. Hook up your dockside pressure water hose with an inline valve on the end of it to this. The valve allows you to control the water right at the engine.
5. Disconnect the coolant line from the coolant fitting on the exhaust manifold. In its place attach a short section of hose with a regular female hose fitting on the other end, which will allow you to run water pressure alternatively from one side of the engine and then the other. For now and when doing the acid flush, this hose will return the water or mild acid solution back into the bucket. For now, put the hose end into the empty bucket and turn on the water, flushing the engine with water, until the bucket is nearly full. You'll see lots of black stuff, particles, & rust flakes. Turn off the water, dump the bucket and do it again.
6. Disconnect the pressure water hose from the engine pump side of the cooling system and connect it to the hose coming from the exhaust manifold. Put the other hose coming from the water-jacket plate into the bucket and turn on the water and repeat this process several times (step 5 and step 6) until the water is coming out relatively clear.
7. Hook back up and clamp the hose between the water pump and the water-jacket plate. Reinstall your alternator.
8. Disconnect the hose to the inlet of the water pump. Hook up your short section of hose to the water pump inlet. Put the other end into the bucket.
9. Take the other section of hose coming out of the exhaust manifold and put the free end into the bucket as before.
10. Put the acid crystals into the bucket and add about 2 gallons of water. Put the thermostat into the bucket - it comes out nice and clean.
11. You're almost ready to turn on the engine, but first hook up the pressure water to the hose that goes into your exhaust system. Since the coolant water is being recirculated through the engine and back to the bucket instead of out the exhaust, you need to get some water into the exhaust system to prevent a meltdown of anything by hot exhaust gases while the engine is running. That's why you're hooking up the pressure water to the your exhaust. The tricky thing is you don't want to run this water while the engine is not running, because water may run back into your engine, instead of going out your exhaust pipe. Same problem as cranking your engine too long without starting.
12. Now with all the hoses hooked up properly (go back and read 8, 9, and 11 if you're not sure), start the engine and immediately thereafter, turn on the pressure water. Make sure the acid solution is being circulated through your engine, that both hoses are in the bucket, etc. Run the engine until the temperature gauge reads about 180 degrees. This will allow the acid crystals to dissolve and work most effectively. Then turn off the pressure water and immediately thereafter turn off the engine.
13. Periodically over a couple of hours restart the engine and pressure water to circulate the acid. (Note: After about an hour and a half of this my pump gasket failed. I've heard from one other person who had exactly the same problem, so watch for this and be prepared to shut off your engine should it occur to you. Based on this experience, it may be a good idea to replace this gasket after you're done flushing the engine in any case, as it may have weakened it considerably.)
14. Fish the shiny clean thermostat out of the bucket and dispose of the acid. Reinstall the thermostat using a new gasket so the housing doesn't leak.
15. Reinstall and clamp the coolant hoses to the engine water pump and coolant fitting on the exhaust manifold. I recommend replacing the water pump gasket too.
16. With everything back together, open the seacock to the cooling system and start the engine to test for leaks and take her out for test.
Materials list:
1. 5 gallon bucket
2. dock water pressure & hose
3. inline on/off water valve for garden hose on the male end of the hose
4. 10' of 1/2" ID hose cut into 3 pieces
5. 1/2" barbed PVC hose connector
6. 2 female garden hose fittings for 1/2" hose
7. 1 lb. oxalic acid crystals (available in hardware stores in crystalline form)
8. hand tools
9. New thermostat gasket
10. New water pump gasket