Outboard overheating problem.

[Metalface]

Hello, I'm new to this forum.

I have a 4hp Yamaha outboard, i've had it about 4 years and it has always worked fine, but the last time I used it, it overheated whenever I tried to speed up, it ticks over fine and will run slow but other than that it overheats. The coolant water coming out of the back turned to steam, I'm guessing that its overheating anyway.

I've never used it in salt water but as it came to me second hand it probably has been in salt water at some point in its life.

Has anybody got any ideas, I'm guessing it could be the impellor, but what exactly I have no idea.

Thanks in advance to anyone that could shed any light on the problem.

Mark.

[Locozodiac]

To start look for any water obstructions on tail, remove, torq cylinder head to specs. Check water indicator to see if impeller is working. I would go for a complete water passages maintenance, specially if the engine was used on salt water and you don't know anything about it. Take cylinder head appart, remove water incrustations, clean well all water passages with thinner, decarbonize piston and head, change head gasket, torq to specs, change impeller, check impeller housing for cracks, leaks, change if needed, put new spark plug. Test if it's ok.

Happy Boating

[Ian Sharlot]

Originally Posted by Locozodiac

To start look for any water obstructions on tail, remove, torq cylinder head to specs. Check water indicator to see if impeller is working. I would go for a complete water passages maintenance, specially if the engine was used on salt water and you don't know anything about it. Take cylinder head appart, remove water incrustations, clean well all water passages with thinner, decarbonize piston and head, change head gasket, torq to specs, change impeller, check impeller housing for cracks, leaks, change if needed, put new spark plug. Test if it's ok.

Happy Boating

That all sounds a bit over kill to me...... I think at this point, check that the tell tail is not blocked to start with, and the next port of call is the impellor, as you say. It's a gear box off job, not major as long it's not siezed on.

[m chappelow]

it will probley need a new impeller so think i would have a look at the impeller and water pump housing first ,then whilst its off make shure that the pump passages and pipes are not blocked up with sand mud or silt ,i once had an engine in for repair and the pump was fully blocked with fine needles from a larch tree that was above the water barrell the person had been flushing his engine in .

[Locozodiac]

Originally Posted by Ian Sharlot

That all sounds a bit over kill to me...... I think at this point, check that the tell tail is not blocked to start with, and the next port of call is the impellor, as you say. It's a gear box off job, not major as long it's not siezed on.

Metalface has stated "The coolant water coming out of the back turned to steam" so will asume no blockage on tail tale, maybe impellor had it's waterloo and engine has completely overheated, 4 years is a good time for mayor water passages interior cleaning, impeller & cylinder head change, it's not a complete engine overhaul, just time maintenance. Will have same engine working perfectly as before. Had this same problem years back, and it was due to mayor salt obstructions in all water passages over the years, even though the engine was fresh water flushed for 5 minutes after each use.

[spartacus]

I'd opt for new impeller (water pump kit) and check the thermostat housing. Could be the housing is totally salted up? In which case - clean out, flush and refit new thermostat.

If this doesn't work, then I'd think about cylinder head, etc.

To clean tell-tale channel - use nylon strimmer wire - perfect for the job.

[Locozodiac]

Originally Posted by spartacus

I'd opt for new impeller (water pump kit) and check the thermostat housing. Could be the housing is totally salted up? In which case - clean out, flush and refit new thermostat.

Might be wrong as don't know this 4 HP Yamaha model, but don't think has a thermostat, many brands small portables 5 HP or less, simply don't use them.

[spartacus]

Might be wrong as don't know this 4 HP Yamaha model, but don't think has a thermostat

You're right Loco if the outboard is a 2-stroke. If it's a 4-stroke (F4) model then it will be part number 66M-12411-01.

[Locozodiac]

Originally Posted by spartacus

You're right Loco if the outboard is a 2-stroke. If it's a 4-stroke (F4) model then it will be part number 66M-12411-01.

Yes, both answers are right, Metalface has not specified if it's a 2 or 4 strokes engine on his post, so both are valid each one on their current model.

[markb]

had the same problem on a mariner 4hp which i believe is the same as the yam,changed the impeller problem solved hope this helps