Fresh water engine flush times

[Sneaks]

A recent comment by Sark of the "Cuttysark" re: installing a fresh water wash vs salt water got me thinking since my Yamaha has a very convenient hose connection for flushing purposes.

SET SERIOUS ON:

How many gallons of fresh water constitutes an adequate flush after operating in salt water?

SET SERIOUS OFF:

For Sea Wolf Joe; how many minutes at a nominal 30 lb water pressure constitutes an adequate flush. Assume 1/2" diameter hose 6-8 ft. in length, typical Jabsco pump, ambient temperature about 68, sea level operation, fresh water PH 6.8, and a sober operator.


Don

 

[Sea Wolf]

Don-

Ha!!! If I could give you a definitive quantitative answer, I'd crown myself Captain Nemo for a Day!


Excellent question! Don't know that I've ever seen an answer, but here are some thoughts:

The longer the motor is used in salt water, the more probable there will be not just salt water in the cooling passages, but solid salt deposits on the inside of the passages should build with the time, thus requiring longer flush times. Some areas of the seas and oceans also have more or less salt in their waters, another variable.

Dissolving the salt with freshwater is the natural cure, and is very much aided by running the engine to increase the water temperature which would increase the soluibility of the deposits. But you can't do this in salt water, of course, while trying to flush with fresh water.

Still and all, the factories equip the motors with a fresh water flush port which they reccomend not be used with a running motor because of the water pump issue, which means they believe the motor can be flushed at normal ambient water temperatures. I don't have my Yamaha Owner's Manual here at home, but the time they reccomend for this could be used as a benchmark.

One might set up the flush fitting and run it for a specified time, say 2 minutes, into as bucket, then calculate how much water would pass through the system in the reccomended time period. One Answer.

Since the freshwater source is limited, however, here's another possibility:

1. Warm up the engine in salt water.

2. At least partially block off the exit routes for the cooling water to contain the flush water mixture.

3. Pump the engine full of a mixture of freshwater and "Salt Away" (I think that's the name of one product) mixed in a bucket and pumped into the engine with the Jabsco pump.

4. Let stand for 2x-3x the reccomended flush time for the product, since the water is not circulating.

5. Flush with fresh water.


There may be some problems with this system, but it at least sounds reasonable up front and conserves water. I'll bet that a test of the water passing through the engine in the test modes (engine running with muffs or on the flush fitting) will use up most of the 20 gallons in the tank or more.

Just a logical guess, not for sale, valued under $0.02, and fun for the figuring. Joe.

 

[iggy]

Sea Wolf raises the relevant questions, but the bottom line is:

"Have we flushed out the salt? Or haven't we?"

I'm not living in your area, but I might suggest a real-life experiment.

I have a conductivity detector that will easily detect fresh vs. salt water. Since all 'fresh' water also conducts somewhat, I'd need a sample of the fresh water before it enters the engine.

If you could collect samples every 30 sec, or minute (or whatever) and send them to me in small sealed containers, I could answer the real question for you. Samples only need to be about an ounce or so, so small tupperware might work. Or surplus 1/2 liter water bottles.

It would be very interesting to follow up a flush with an 'incubation period' where the motor is left (overnight?) with fresh water in it. A second flush would indicate if further deposits are removed from the surfaces of the cooling channels.

I could do this in person on one of my frequent visits Seattle if someone up there would be interested in donating the boat/motor.

(To calibrate the sensor more accurately, a pony keg of Copperhead would be just the thing! -- Disregard the 'ounce or so' comment from above; larger volumes are required for the calibration phase.)

Ed

 

[C-Hawk]

That copperhead is some good stuff---- still trying to get the recipe for a 5 gallon batch. It's a bit far for me to drive up for, and it would be fun to make my own.
hint hint :beer :beer :beer :wink:

 

[Sneaks]

One might set up the flush fitting and run it for a specified time, say 2 minutes, into as bucket, then calculate how much water would pass through the system in the reccomended time period. Joe.

Well, Joe, I just happened to find the manual for our Yamaha here and was surprised (and disappointed) to learn the manual recommends a 15 minute flush. This seems seriously conservative and I, for one, believe it's some marketeer guesstimate, and not based on anything scientific. It just doesn't pass a sanity check.

Correct me if I'm wrong, but I seriously doubt the Yamaha (or any 75-90 hp) outboard has much more than a gallon of water present in the coolant passages while running. At least that's about what runs out after I turn the flush hose off. Sheesh. The raw water passages in my Luhrs gassers took 15 years to build up significant deposits and they were never flushed. I'd be more afraid of "critter growth" than salt deposits anyway, and a fresh water flush and drain takes care of that nicely.

Time to call Yamaha methinks.


Don