One Way To Back Flush A Cobra

[DavidW2009]

Here's how I back flushed a 2.3L Cobra.

Test Fixture:

1/2" Threaded (one end) PVC Schedule 40 Adapter, Lowes Item #23861 $.50

1/2" NPT X 3/4 FHT PVC Swivel, Lowes Item #194638
$2.00

1/2" X 4" PVC Pipe
$.10

Total $2.60
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Glue 1/2" X 4" PVC Pipe into Adapter. Thread adapter, using Teflon pipe thread tape, or glue, into Swivel (has female connector for a garden hose).

Insert pipe section into hose that comes from the transom, via the P/S cooler.

Connect garden hose to swivel and turn on water.

I use a 1/4 turn plastic ball valve 'Y' attached to the end of my garden hose. That way I don't have to walk 100 feet to the outside faucet. That is the yellow thing in the photo.
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I ran this back flush several times and got what I think is good flow out of the intakes. (see photo). (I'm running this off of a well with (50) PSI, about half of what city water would be.)

Question: Is it normal for a small stream of water to come out the center of the prop when back flushing? (See photo)

While back flushing, I removed the outside cover on the Cobra to see if there were any leaks around the impeller housing. Sure enough, there was a small drip, which would probably suck air during normal operation.

 

[hystat]

$4.00 at any hardware store

 

[hystat]

water coming out the prop as well as the exhaust relief is good!

good shooting on the pump housing.

 

[DavidW2009]

Thanks for the feedback.

Does that 'Y' adapter you have take the engine heat okay? That looks like one of those coolant system flush-out things for a car.

I tried a non-automotive plastic connector on my cars one time, and it did not take the heat. Had to find an auto type.

 

[hystat]

That tee is in the raw water line coming from the drive, so there's no heat there, but yes, it is a heater hose flushing tee kit for a car - comes with 3 sizes of Y and a cap.

It is great for running the boat on the trailer (it backfeeds the impeller as well as cooling the engine), and it is handy for confirming water pump performance.

I can just crack the cap open out on the lake at idle and water squirts out like mad.

 

[DavidW2009]

More info on back flushing a Cobra:

Because of the drip leak from the impeller housing discovered while back flushing, I removed the housing to reseal it. I have not run the engine since back flushing, and inside one side of the housing were about six chunks of old impeller that had been somewhere downstream of the normal flow. Probably caught on the input side of the P/S cooler.

So, with the housing off, I back flushed again and got two more chunks of impeller to come out. It now seems like a good idea to remove the impeller housing first and then back flush debris out. Then put the housing back on and back flush out the intake.

Of course, the last mechanic who installed a new impeller should have back flushed it while the housing was off, but obviously didn't.

What's strange is I always had flow to the engine. Should have real good flow now. (Only run engine on the muffs, never had it in the water. It may have had a problem show up.....)

(Okay, how do these Merc owners get the trash out of the impeller housing when back flushing? Not necessarily old impeller pieces, but any kind of trash. Seems like they would have to R & R the lower end.)