Is it safe to backflush an outboard?

[CWKboat]

(Apologies for incorrectly posting this in non-outboard repair forum earlier)

I have a '87 XR@ 150 HP with a suspected blockage in a cooling port as I have high water pressure. Is it safe to attach a garden hose and fitting to t-stat housing (with t-stat removed) and effectively backflush the cooling system with higher pressure?

I just wanted to make 100% sure there's no chance of getting water in the cylinders. Otherwise, I guess I try the normal route through the water pump tube.

Thanks for any thoughts!

 

[82rude]

I say ok to do.If you got water in the cylinders from doing it that way you got bigger issues than blockage. The t stat is part of the cooling route.

 

[Chris1956]

Have you checked the poppit valve? If that sticks or is clogged, you can have high pressure.

 

[CWKboat]

I replaced it last year, and most recently checked and there was no debris and it didn't seem to be binding as I could move insert/remove the poppit easily in the rubber housing. I may just replace it again as I know it's inexpensive.

 

[Sea Rider]

Do same, but a Karcher washing machine is hooked at lowest pressure on removed thermost port and flushed for some minutes, works fantastic well. Don't expect to have a immaculate clean interior as when engine was new. The only issue is that if head gasket is very old, dried, hardened, have not been re torqued from new will probably have tiny water droplest pass onto combustion chamber which should be cleared when engine is turned on again.

Happy Boating

 

[jbcurt00]

(Apologies for incorrectly posting this in non-outboard repair forum earlier)!

CWK,
In the future, just PM any Mod and ask them to move a topic from where you started it, to where you'd like it moved.

Often a simple

Oops, wrong forum, please move

post will be enough that a Mod will see it and move it for you. No need to start a duplicate topic.

I merged the 2 topics and left them here in the Merc forum

 

[jimmbo]

If you are worried about water getting in the cylinder, take the plugs out, spray some oil in, crank the engine spread to it around. After you are done your flushing, crank the engine again, any large amount of water will exit thru the spark plug holes. Put plugs back in, attach a water supply to the engine, start it up and run till warm, that would get rid of any remaining water.

 

[CWKboat]

CWK,
In the future, just PM any Mod and ask them to move a topic from where you started it, to where you'd like it moved.

Often a simple post will be enough that a Mod will see it and move it for you. No need to start a duplicate topic.

I merged the 2 topics and left them here in the Merc forum

Thanks, and will do. Thanks for merging the topics.

 

[CWKboat]

Thanks to everyone for the suggestions, I will go ahead and give it a shot.

 

[Sea Rider]

If large amount of water is found inside combustion chamber when high pressure washing, you have already a faulty head gasket problem...

Happy Boating

 

[CWKboat]

I took the thermostats out and spliced into the hose going between the 2 thermostat housings with the garden hose fitting (and plugged the other spliced end). I flushed it off and on for 10-15 minutes while alternately plugging the tell tale and copper water tube with my thumb.

Definitely no obstructions from the tell tale or the water tube. Didn't seem to have comparably as much flow from the exhaust -- even when I blocked both the tell tale and copper tube for 4-5 seconds. No debris seemed to come out with the water -- all clear.

I then took the poppet cover off and removed the spring and then reinstalled the housing. I could then see water dumping out of the block and the pressure was noticeably less when I plugged the tell tale and copper tube.

It seems like I had a lot of pressure in the block with the poppet/spring installed normally and the spring loaded poppet assembly definitely did not seem to be opening when I plugged the water tube and tell tale.

I have ordered the poppet parts from iboats including the carrier, and also will replace the complete water pump assembly including the base since I have the lower unit off. It has a SEI lower unit, so I've ordered all of the parts from them. I'll report back in a few days once I've had a chance to get everything back together.

Thanks for all the help and kind replies.