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Old 12-18-2004, 09:49 AM
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Don Moyer Don Moyer is offline
 
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Thumbs up Procedure for acid flushing and pressure flushing

Here is the procedure for acid flushing and pressure flushing as taken from our FAQ and service and overhaul manual. You'll find our flushing kit very helpful in performing this essential maintenance task.

ACID FLUSHING: The following acid flush is most effective when used as a preventative maintenance measure every 3 to 5 years:

CAUTION: Be sure to wear proper protective clothing (including eye protection). Always add acid to water when mixing, and if possible, hang a bucket over the exhaust outlet to catch acid solution when discharging from boat.

1) Mix 1/3 gallon of household muriatic acid (30% concentration) into a 5 gallon bucket of water.

2) Draw the entire 5 gallons of acid solution into the engine through an inlet "T" fitting between the raw water through-hull and the inlet to the raw water cooling pump (the same "T" as used for winterizing the engine). For best results, thermostat should be removed and the by-pass hose temporarily clamped off. All the acid solution will then be pumped through the block by running the engine. Stop the engine as soon as the bucket is empty.

NOTE: Some of the acid solution will find its way into the exhaust system, which might loosen up any crud that may have built up within the water lift muffler and connecting plumbing.

3) Start the engine after letting the acid sit in the water jackets for about 15 minutes and run it long enough to thoroughly flush out the acid.

4) If it has been possible to retrieve the acid solution from the back of the exhaust system, add approximately 1/2 pound of household baking soda to five gallons of acid solution prior to discarding.

PRESSURE FLUSHING (PRELIMINARY STEPS):

1) Remove starter and alternator.

2) Remove the three 1/8" pipe-threaded water jacket drain plugs. Two of these plugs are in the block (one is located at the forward end of the block beside the starter, and the other is located beside the distributor base). The third plug is in the lower rear corner of the manifold.

NOTE: If the cooling system has not been serviced in many years, the plugs may have to be drilled out. If, after drilling out the plugs, the threads cannot be cleaned up with a 1/8" pipe tap, the drain hole(s) can be drilled out to 7/16" and threaded using a 1/4" pipe tap. Pipe taps and replacement 1/4" brass pipe plugs are available at most hardware stores.

3) Probe into each drain with a coat-hanger-sized wire to insure that it is open. If the drain on the manifold is clogged, it will be virtually impossible to open it without removing the freeze-out plug nearest the drain and probing the drain from inside the cooling jacket. While the drain in the manifold is not used to inject pressure water, as in the case of the drains in the block, it is still preferable to open the drain if at all possible.

FLUSHING THE BLOCK:

1) Install a 1/8" pipe-threaded 6" long brass nipple in one of the drain holes in the block and a 1/8" hex-headed brass pipe plug in the other block drain.

2) On early model engines, use a 1/8" brass 45 degree street-el (provided in kit) to facilitate reaching the drain hole behind the distributor.

NOTE 2: On late model engines, the 6" nipple can be left installed in the aft block drain after the flushing operation is complete to facilitate draining the block for winterizing or other servicing (use a 1/8" brass cap to close the end of the nipple). On early model engines, there is insufficient space for the nipple after the alternator is reinstalled; however, the 45 degree elbow can be left in place with a 1/8" hex-headed pipe plug installed to make subsequent draining somewhat easier.

NOTE 3: Early model engines have a cast iron crossover tube between the head and manifold which makes it difficult to flush the block and head separately from the manifold. In some cases, this cast crossover tube has been replaced with a rubber hose and 90 degree fittings. If this is the case on your engine, you may be able to install a discharge hose on the fitting on the head to be run overboard. You can then proceed with the following steps as in the case of a late model engine.

Steps 3 through 7 apply only to late model engines.

3) Remove the thermostat housing, both fittings, and the thermostat.

4) Install a 3/8" brass street-el in the outlet of the thermostat housing (the side marked "MAN"), and a 3/8" pipe plug in the inlet (the side marked "WP").

5) Reinstall the thermostat housing, but leave the thermostat out until after flushing is complete.

7) Install bushings on the end of the 6" nipple in the aft block drain as necessary so as to be able to install a swivel type garden hose fitting. It's also very convenient to install a small ball valve before the garden hose fitting so that you can stop/start the pressure from the hose for more aggressive flushing.

8) Flush the block until the effluent from the discharge hose is clear.

9) Move the 6" nipple to the other block drain, and flush that end of the block until the effluent of the discharge hose is clear.

FLUSHING THE MANIFOLD:

1) Remove the 1/2" fitting at the rear discharge of the manifold. Inspect and clean the 1/2" pipe thread opening as necessary.

2) Connect a garden hose to the rear outlet of the manifold for overboard discharge. A 1/2" male pipe thread by 3/4" male garden hose fitting is ideal for this purpose.

3) Install a second garden hose fitting to the front (inlet) of the manifold. Connect a garden hose to this fitting, and flush the manifold with as much water pressure as possible. As in the case of the block, it's a good idea to install a ball valve between the garden hose fitting and the manifold to enable you to stop/start the pressure from the hose.

4) When flushing is complete, remove garden hoses and all flushing fittings. Reinstall the thermostat, and reassemble the rest of the cooling system.

Best regards,

Don
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