outboard cooling - diagnostic help needed

[snowleopard]

I got my Mariner 3.3 running after it had sat for a couple of months in a locker. All seemed to be well and it runs happily at idle or at speed until I checked the water flow.

No water comes out of the pee hole so I poked it out then put a syringe on it and pushed water through. The water comes out of a couple of holes close to the pump so obviously there are no obstructions. When the engine is running I can feel air/gas coming out of the pee pipe and also see it bubbling out of the holes in the leg. My first thought is that there must be a leak into the water jacket from either the cylinder or the crankcase but if that was the case I would expect it to run badly or not at all.

Any ideas?

 

[VicS]

Replaced the pump impeller?

Also check the water tube between the pump and engine for obstructions.

Not sure if it applies to these or not but corrosion can block the passages where the water tube reaches the power head. (It probably does if this is a rebadged Tohatsu) so while the bottom is adrift to replace the pump impeller connect a hose to the water tube and make sure you get a good water flow from the tell-tale and coming back down the leg from the power head

 

[snowleopard]

There's no blockage. It's the source of the bubbles that's worrying me.

 

[VicS]

There's no blockage. It's the source of the bubbles that's worrying me.

Its the lack of water from the telltale that would bother me!

The bubbles and the gas you can feel blowing from the telltale may be exhaust gas, blowing back though engine cooling system exiting via the telltale and also blowing back through the pump, past a knackered impeller and exiting via the water intake.

While renewing the pump impeller it is wise to check there is no obstruction by flushing water through the whole system but if you are certain of that don't bother

 

[snowleopard]

Update:

I've now dismantled the leg (not easy, sheared a couple of bolts that had corroded into the aluminium). The impeller is in a fair state so I'll replace it but the culprit turns out to be a blockage as I can't pump anything up the feed pipe from the pump.

Water up the pee tube comes out of the exhaust OK so the blockage must be at or close to the point where the feed tube enters the block. That explains why gas from the exhaust is coming out of the pee tube.

I'm very nervous about trying to strip the head of the motor in case I get more sheared bolts. As a first try I want to try squirting something up the pipe to clear the blockage. Any ideas what might tackle the blockage without damaging the castings? Vinegar?

 

[VicS]

I've now dismantled the leg (not easy, sheared a couple of bolts that had corroded into the aluminium). The impeller is in a fair state so I'll replace it but the culprit turns out to be a blockage as I can't pump anything up the feed pipe from the pump.

Water up the pee tube comes out of the exhaust OK so the blockage must be at or close to the point where the feed tube enters the block. That explains why gas from the exhaust is coming out of the pee tube.

I'm very nervous about trying to strip the head of the motor in case I get more sheared bolts. As a first try I want to try squirting something up the pipe to clear the blockage. Any ideas what might tackle the blockage without damaging the castings? Vinegar?

Vinegar is probably not strong enough.
A sulphamic acid based descaler such as Fernox DS3 might be better.
Rydlyme perhaps even better still but at this point I start to get nervous about the aluminium
BUT
The trouble is that if its blocked you cannot get a chemical cleaning solution in to where it is needed.

I am afraid the answer really is to separate the power head from the leg and dig out the blockage.
Somewhere among Lakesailor's pictures you'll find a picture or one of these, or similar, illustrating the problem

 

[Lakesailor]

Yes. You need to separate the power head from the leg. I bust a couple of bolts but they are easy to drill out and retap.
Splitting the power head from the leg can need a bit of force as the drive shaft can get corroded into the flange. It's just a push fir, but can become very tight. There are one or two spots around the joint where levering is possible. Otherwise if you resort to a hammer use a hardwood drift to reduce the chance of cracking anything.
It may just pull off of course.

The channels arrowed get bunged up. The two arrows on the right indicate where the water goes to and from the head. They are a bit narrow I thought so opened them up a drill size.

You are going to need a new powerhead/leg gasket. About £8 I think.

I also took the head off which was less troublesome as the bolts are relatively massive. Don't overtighten them on re-assembly.

 

[VicS]

Don't overtighten them on re-assembly.

The cylinder head bolts are only tightened to 85 lb in (lb in not lb ft), or 9.6 N m in new money

 

[snowleopard]

Any tips for releasing stainless studs in aluminium? heat? hammer? WD40?

 

[Lakesailor]

I've usually found them quite good. Have you tried tightening them a touch before undoing? Counter-intuitive, but often enough to free them.

 

[ex-Gladys]

Years ago I bought a 36" breaker bar to undo a 36mm clutch hub nut on a motor bike. One of the best investments I ever made, whenever anything feels tight I pick up aforementioned, because rather than wellying a short drive, you can exercise much more control, keep the socket firmly centred on the nut/bolt whilst applying sufficient torque to undo.

Gentle heat will also help, ally expands much quicker than stainless, also a crisp tap on a bolt with a hammer can help... All those years of Jap bike mechanics finally of use!