Mariner 9.9hp cooling problem

[hectik]

Hoping somebody might be able to help i have a Mariner 682C 9.9hp that is constantly stopping pumping water, ie stops spurting water out of the waterpump indicator hole.
this has happened 5 out of the last 7 times. The water pump has been replaced 4 times now. The engine starts and idles great but once under power it only lasts a few minutes before the stream is reduced and then stops all together.

The strange thing is when this happens i can leave the boat for a few months, then restart it in a tank and it runs fine, pumping water perfectly without the water pump being changed, i have encounted this atleast 4times since the problem reared its head. Had the idea that it may be the thermostat but even that doesnt make sense.
Any ideas?

 

[joed]

Re: Mariner 9.9hp cooling problem

Stops comletely or slows to a trickle? Mine sort of does that when the thermostat opens and closes.

 

[hectik]

Re: Mariner 9.9hp cooling problem

it just stops completly, bit of a ticking noise and sizzling sound when i cut the engine when the water stops. Im paranoid about it so i watch the outlet like a hawk checking every 30 seconds or so. If you had a car that broke down every second trip you wouldnt trust it and junk the thing, but the engine runs very sweet and starts like a dream but the cooling issue is really becoming a major prob.

The last time out the water stopped pumping and i havent run it since then, but based on previous experience if i start it in the tank it will pump water again.
Some of the threads ive see about the mariner cooling problems are mostly about some mariners not discharging water untill the thermostat opens up but this seems to be the opposite, strong stream when started and idling, and when first underway. If there is a blockage then i wouldnt be able to run it until i cleared the blockage, but it will stop and then i can restart, even months later and the water will be dicharged again.

Just i wild guess, but is there the possibility of some sort of air lock in the cooling system, ie bubble forming somewhere in the cooling passages preventing water pumping past it?

thanks for you help.

 

[joed]

Re: Mariner 9.9hp cooling problem

It almost sounds like the thermostat is working backwards. Is that even possible?

 

[hectik]

Re: Mariner 9.9hp cooling problem

i think ive finally figured this problem out, talking to a very experienced outboard tech with about 30 year experience and a great background in the older model Mariners.
it sounds like it may be a leak in the exhaust port which doesnt affect the water flow at idle, however under power the pressure from the exhaust port leak is overpowering the water flow, cutting off the tell tale spray.

it sounds logical however doesnt really explain where the diverted water is going.

ive taken the thermostat, housing and cylinder head off to clean out the water passages. im taking a wild guess here, im hoping that if i replace the gasket on the exhaust manifold, this would stop the problem, but i have my doubts.
Any one have experience with exhaust leaks?
any ideas would be much appreciated

 

[sschefer]

Re: Mariner 9.9hp cooling problem

I just had a quick look at the parts manual for a 91 9.9 two stroke. Assuming yours is simiar, your mechanic is probably right.

Figuring out where the water is going has been an on going mystery for years. Just check all the gasketed parts for flat and put it back together with new gaskets and you should be o.k.

That thing about checking for flat,,,,, yeah,,, it's really important.

 

[hectik]

Re: Mariner 9.9hp cooling problem

Thanks sschefer,
ive flattened all the mating surfaces with 800 grit on a machined steel plate,
going to cut the thermostat gasket from some blank gasket material i have on hand, dealers talking $20 for the thermo gasket and another $80 for the cylinder head gasket here in Australia, still to price the exhaust manifold gasket but the asking price of older Mariner replacement parts is rediculus.

Going to check with parts dealer the prices on the same gaskets using the yamaha part numbers for for the identical powerhead that is fitted to the 81 Japanese Mariners and see if im getting screwed by the Mercury guys.

The only other prob ive got is in my haste to resolve this cooling issue i did the dumb thing by trying to remove the cylinder head without removing the powerhead from the rest cowling etc, and snapped the heads off two of the mounting bolts on the lower cylinder area, all of the bolts from this section were much more difficult to remove due to the corrossion and gunk build up
that forms in the lower water passages.

ive gotten the cylinderhead off but i cannot remove the broken studs that areprotruding about an inch out of the block, Treated them for a few days with WD40 but no luck, can i heat the area with a small flame from a pencil torch to expand the block around the bolt to loosen it slightly, just not sure if the heat on the block with transfer into the bolt also and cause it to expand too, any ideas?

 

[sschefer]

Re: Mariner 9.9hp cooling problem

Thanks sschefer,
ive flattened all the mating surfaces with 800 grit on a machined steel plate,
going to cut the thermostat gasket from some blank gasket material i have on hand, dealers talking $20 for the thermo gasket and another $80 for the cylinder head gasket here in Australia, still to price the exhaust manifold gasket but the asking price of older Mariner replacement parts is rediculus.

Going to check with parts dealer the prices on the same gaskets using the yamaha part numbers for for the identical powerhead that is fitted to the 81 Japanese Mariners and see if im getting screwed by the Mercury guys.

The only other prob ive got is in my haste to resolve this cooling issue i did the dumb thing by trying to remove the cylinder head without removing the powerhead from the rest cowling etc, and snapped the heads off two of the mounting bolts on the lower cylinder area, all of the bolts from this section were much more difficult to remove due to the corrossion and gunk build up
that forms in the lower water passages.

ive gotten the cylinderhead off but i cannot remove the broken studs that areprotruding about an inch out of the block, Treated them for a few days with WD40 but no luck, can i heat the area with a small flame from a pencil torch to expand the block around the bolt to loosen it slightly, just not sure if the heat on the block with transfer into the bolt also and cause it to expand too, any ideas?

Yes, heating is the easy way. If you've got MAP gas down under you'll get the job done much quicker. You don't have to over do it but Aluminum does dissapate heat quickly so it can take a while to get them to start moving.

I heat the bolt not the block when I can and then use a pair of vise grip plyers and they usually come out. When they don't I take them in and have them drilled out and repaired (not cheap).

As to your pricing prob with gaskets. Yes, Merc list prices are way out of whack for consumers because Merc wants to give the edge to the guys that have spent thousands of dollars on tools and training to become Merc Certified Mechanics. I personnaly like that they do it because I've been on the other side of the counter and know how hard it is to make a brick and mortar retail buck.

You can get better pricing right here on iBoats using Sierra replacement parts or if you want original Merc parts you can go to boats.net and get the best pricing I've found yet.

You can also try eBay but I just recently did a cost comparison and only on rare ocassions was i able to beat the boats.net pricing for new parts.

You also might want to PM Faztbullet, he has some great prices also.

 

[Faztbullet]

Re: Mariner 9.9hp cooling problem

This is a common problem in the earlier 6-9hp mariners, most of the time it is the S/S exhaust plate is bad or the water tube. The tube is so thin and what happens is its gets a hairline split in it, When engine is cold crack is closed and as exhaust temp rises in exhaust housing it heats up and opens reducing water flow. If engine gets to hot it will vapor lock internally from steam and not allow water into power head.

 

[hectik]

Re: Mariner 9.9hp cooling problem

Faztbullet you are a genius,
That is the best description of the problem/resolution ive heard over the past two years, ive only recently been advised that it could be an exhaust leak issue, but offered no solution to resolve.

thanks for the advice, much clearer than any manual.
i'll let you know how i go.

Ohh and thanks again Sschefer