Mariner 8hp outboard water flow help

Brambles

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Please help.
I have a Mariner 8hp 1998 saildrive, model 8MLSM.
Recently serviced with new impellor.
When running, the flow of water from the engine is intermittant. From full flow, the stream tails off to nothing, then after a few seconds comes back boiling hot and steaming, runs fine for a few seconds then tails off again. This is a constant thing, the cycle lasts about 15 seconds and happens the whole time the engine is running. Does this engine have a thermostat, and could it be this? Or is this perfectly normal. Any other suggestions greatfully received, otherwise back to the repair shop for another few weeks!!!
Many thanks
 

VicS

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Hi and welcome to the forums.

I'm not familiar with the Mariner as I run a Evinrude, the cooling system of which I know only too well!

The behaviour you describe is definitely not normal. I would expect the stream from the "pee hole" to be continuous and never boiling hot or steaming.
I would expect the engine to have a thermostat so that might be worth checking but I suspect blocked water passages will be causing the problem.

I have This web site noted as a source of downloadable manuals for Mercury and Mariner outboards which may be useful if you are inclined to tackle any problems yourself but if you have had it serviced by a dealer I would be inclined to take it back to them as they clearly have not properly tested it before returning it to you.

The iBoats forums are an excellent source of help and advice on outboards and by coincidence there is an absolutely identical question on the Mercury/Mariner board at the moment!!!! I will be surprised if you do not get some good advice there
 

Lakesailor

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[ QUOTE ]
a common problem but as long as it comes on after a while it should be ok.

[/ QUOTE ] Certainly not if the water is steaming and hot. My Yamaha's pee stream was never more than barely warm. a little tohatsu I have and my brother-in-law's Johnson both has hot water coming from the pee hole and have both been cured by a good clean-out of the waterways, and new impellers (and a new water tube grommet in the case of the Johnson)
If you can't put your hand in the pee stream comfortably there is a problem.
 

landlockedpirate

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Don't panic, my dads 8hp mercury of the same vintage does exactly the same.

First time I used it I had kittens cos I thought it was broke, so I went straight to local dealer. He told me that the engine has a thermostat and this bahaviour is normal. Big relief on my part (and a bit of worry, turns out dad had not even noticed the issue !)

Your engine is the same but with different badge, so no problem.
 

Greenwichman

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Had a Mariner 8 in my last boat.

Cooling stream varies with temperature, controlled by a thermostat. That said, there should not be steam ..... either the thermostat is buggered or there could be salt deposits blocking the exit hole for the stream.

Suggest trying to use a piece of seizing wire to poke about up the hole and clear it. I found this action necessary every 4 months or so.

Hope this helps.
 

srp

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My Yamaha started to produce steam - the thermostat was completely bunged up with salt. Poked out all the waterways, chucked the thermostat as far as I could and didn't replace it, end of problem.
 

Clyde_Wanderer

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Yes, the mariner has a thermostat, if you remove the plate on the side of the cylinder on the throttle control arm side ( left )
infact you will see the shape of the thermostat housing on the outside of this plate, just remove the plate and as someone else says chuck the thermo as far as you can, and check that all is not clogged up inside the plate while you have it off.
 

m1taylor

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Ditto with my Yam 4hp 4 stroke. I looked at the parts diagram, and sure enough the older models, of which this is one, had a thermostat. From my understanding of thermostats, it should be closed on cold start in order to raise the engine temp to operating temperature as quickly as possible. Then the thermostat will open and let go of the water - hence it starts with a hot flow and after several minutes. Thereafter it constantly opens and closes to maintain an even temperature +/- a set number of degrees. That is certainly the way my 2000 model of the yamaha 4hp 4 stroke works. i had it checked using a digital temp sensor on the block (on the thermostat housing) and it held an even 57 degrees + or minus 2 degrees. It seems to me that the safest way to know whether an engine is cooling is to use a temp sensor. I just wish there was one you could fit to an outboard - anyone done this? Tell tales are not great for telling you what you need to know. I have a mariner 2.5 which I cleaned the passageways out in a total strip down. It streamed water out of the tell tale, but then stopped to a dribble one day - but the engine stayed an even temp because water was still flowing, outletting through the exhaust. The problem was the tell tale, not the cooling.
 

m1taylor

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Just a thought on the 'steam' - on some outboards the tell tale flow goes through exhaust coming from relief holes on the leg - can give the appearence of 'steam'.
 
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