Back flushing my outboard

[Brian D]

Well this weekend I decided to do a little more maintenance on my Yamaha T9.9. I've noticed since I've moved the boat on Nov 15th that the cooling water flow was not what I expected.

When I start the motor I get a good flow, then it starts to trickle. However, when the motor is running at higher RPMs the flow gets stronger. I have seen the water flow from this OB and know it can be much stronger.

I have forward flushed with fresh water and Salt Away. The foam that came out of the OB was a lot. So I am guessing I had some salt buildup. But this forward flushing did not improve the water flow. Time to back flush.

I searched the internet for a back flush kit and found several examples but they were expensive. So I gave it some real thought. Build my own.

I went to Home Depot and got some parts to reduce a standard 3/4" hose to a 1/4" tube. Went to the boat to test and it worked. All the parts fit. So that back flushing begins. I just used fresh water and no Salt Away. No improvement at all. Now I am disappointed.

This weekend (Saturday) I decided to try something different. My problem is I can't keep the Sail Away solution in the motor. So I bagged it. Yep, put the motor in an industrial trash bag, lowered the motor into the water and started my back flush. The water pressure against the bag formed a seal around the cool water intake. So I inserted the solution into the motor and stopped the water flow. I watched the hose and saw no air bubbles. I had a good seal.

20 minutes later I took the motor out of the water and bag and back flushed with fresh water. The foam that came out was very encouraging. I did this four more times and the last time the water was not as foamy. I put the motor back in the back, lowered it and then went home.

Yesterday (Sunday) I got the boat ready for a mid day sail. Took the motor out of the bag and fired her up. Very little water came out. Totally disappointed. Shut her down and I think I wanted to cry but then I fired her back up again. Wow! the flow is as strong as I had expected. I monitored for a while and there was no change. Stopped the motor, when for a walk, came back and fired her up again. Same flow. Excellent.

Something to keep in mind here is not to apply too much water pressure on the back flush. I've read that one can blow out seals. So I keep the water pressure at about even with what I think it should be under normal running conditions.

If you have an outboard and do not regularly flush, you might want to consider doing so.

 

[PeteK]

Brian,

You don't mention having done anything with the pump impeller or housing liner. Has the pump been serviced recently?

Pete

 

[Fairwind]

Does the engine have a thermostat to control water temperature? Here is where most cooling system blockages begin.. Trying to back-flush an engine with a closed thermostst isn't going to get you very far...

 

[Brian D]

Pete, yes, the impeller has been replaced maybe a year ago.

Fair, that is my next task, to bypass the thermostat and flush several more times. I plan on taking the thermostat out and putting the cover back on. I have been looking for all possible avenue of cooling water flow. That one I missed. Thanks

I read that muriatic acid is something to use when flushing, but if left in or not neutralized, could cause damage. Another product that has been reported to be good was CLR. Less abrasive as the muriatic acid but as effective.

 

[BobM]

Brian,

The foaming cleaner could also have caused the pump to cavitate for a while before it could clear it. When a pump is cavitating it often helps to stop and start the pump a few times.

 

[Brian D]

Ah, so hence the fact no cooling water when I first fired it up. Great, Bob. I didn't know that. Going to have to keep that in mind the next time I do a serious flush.

 

[Fairwind]

Muriatic is just dilute hydrochloric acid, FORGET THAT !! It will attack the cast aluminum with a vengeance!! It works great on copper / brass radiators and such, and for cleaning up cement / tile work, but never on aluminum..Is your Yamaha a 2 or 4 stroke? On most modern outboards, the cooling passages are coated with epoxy at the factory and unless overheated, this coating prevents block and head rot for a long time..With the thermostat cover removed, you will get a better idea what kind of shape the cooling passages are in...

 

[sailingdog]

Try vinegar instead... won't attack aluminum very much at all..

 

[Brian D]

Fair, this is a '95, 4-stroke. I cannot vouch for the condition of the interior cooling passages. I will take off the thermostat cover this weekend and also remove the thermostat to flush again. Hopefully I can get more of the interior cooling passages.

Dog, I tried the vinegar thing last year in September. I think that is what started this whole mess. LOL I'm sure the vinegar worked but maybe it dislodged some junk and that cause the overheating. This was before I understood how to flush effectively.

 

[Fairwind]

Must be a 2-stroke... procure a new head gasket and remove the head (or try to remove the head) and then you can use a coat hanger to rod out most of the water passages and restore circulation to acceptable levels. Good Luck...

 

[Joe]

OB maintenance...

Every year I take my 9.9 2-stroke motor to the local Tohatsu mechanics on Shelter Island and have them service the motor for $75-100... oil change, impeller, etc.... Every 3 years I have them service the rest of the cooling system and rod out the passages for an additional $100 bucks.... Your flushing system sounds like it's doing the trick.... but I still think it's important to open the motor up to check it's vitals on a regular basis.