Mariner 4hp - motor hot, tell-tale cold

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labougie

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Another of my little two-stroke Mariner (Mercury) single pot 4hp's odd behaviours is that after a couple of hours running at 1/2 throttle, the engine is very warm (much too warm to touch) while the tell-tale is not even warm - just ambient. Apparently there's no thermostat in this motor - does the tell-tale come out before going round the engine block? Puzzled!
 
labougie said:
Another of my little two-stroke Mariner (Mercury) single pot 4hp's odd behaviours is that after a couple of hours running at 1/2 throttle, the engine is very warm (much too warm to touch) while the tell-tale is not even warm - just ambient. Apparently there's no thermostat in this motor - does the tell-tale come out before going round the engine block? Puzzled!
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I am not familiar with the Mariner but yes I would expect the telltale to be no more than lukewarm . Its purpose is to tell you that the pump is working and delivering water to the power head. If the water channels in the power head become blocked then it will overheat regardless of a good flow from the telltale.

You should be able to touch and maintain brief finger contact with any part of the powerhead except perhaps adjacent to the spark plug. If you can't or there is steam coming from the exhaust back pressure relief port or signs of paint discolouration then its overheating due to lack of water flow through the powerhead.

If all is well you would normally expect to see some water, a few drops or maybe a mist, blown from the relief port.
 
I have one of these engines, nowadays as a spare; they are very good but quite prone to salt blockages in the head waterways, I take the head off every winter if it's been used.

A simple job but requiring a new gasket, I forget where you are but Ron Hale Marine at Southsea near Portsmouth have these gaskets etc.
 
If you are carefull removing the head you can reuse the old gasket,did mine on a Mariner 5 and then helped a friend do his.
 
Yes if you are careful and lucky you can sometimes save the gasket, if I do I make a point of a new one next year though.

As I'm not sure of the OP's experience with engines I wasn't going to recommend this.

Incidentally the Mariner 5 and Mariner 2, 2-stroke jobs I also have are rather fond of a head and salt removal at end of season too !

I run them in slightly warm oily water when the boat comes ashore, work on them over winter - it's really not much hassle - then run them again in the warm oily tub in the spring.

I also treat them to new petrol every spring, I know some here think this is too much luxury so I'd better not mention the electric blankets around these engines 24/7 for the winter and blessings by white witches before they are re-used but they do repay kindness...:)
 
I have fed coke a cola through the tell tale in a drip style set up overnight on a couple of engines, it seems to do a good job of breaking up the salt if you don't want to take it to bits. Doesn't work all the time but worth a try, I did a little mariner 2.5 last week which was dripping from he tell tale, was flowing well after
 
As that would meean you're inverting the engine - head down so any water & oil enters the combution chamber, risking hydraulic lock, conrod rodgered & even piston rings rusting & sticking surprisingly quickly, this hardly seems a sensible idea unless there's something I am missing from your description ?

Always, alwyas keep outboard heads uppermost.
 
Must admit it's a new one on me, but if it works for you then great !

I'd still have the head off in winter to clear the salt though.

One thing I meant to mention, I added a small tube about 4" long so as to make the telltale more visible from the starboard side; it's in a well ( so the overhead coke bottle would be hard to set up for taking the engine out & stowing it ), so I glance at it every so often to check the flow, and put my hand under it as a temperature guage; if there's something like weed or a poly bag around the leg the temperature soon rises, normally it's luke warm.

Just for info', I get 2.5 hours running at 90% throttle per gallon of fuel.
 
Seems to work for me defiantly I'd like to take the head off one and have a look then try it and see what it's like after.
Last one I did
 
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