Outboard overheating problem.

Metalface · 20 December 2008, 21:52

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 · 21 December 2008, 00:11

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 · 21 December 2008, 16:34

Quote:

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 · 21 December 2008, 18:21

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 · 22 December 2008, 05:41

Quote:

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 · 25 December 2008, 12:11

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 · 27 December 2008, 05:15

Quote:

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 · 27 December 2008, 14:12

Quote:

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 · 27 December 2008, 17:07

Quote:

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 · 27 December 2008, 19:26

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

Locozodiac · 29 December 2008, 23:48

Quote:

Originally Posted by 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

If you already have experiemented a engine overheat, would be advisable to torq head cylinder to factory specs as the head gasket will be a bit lose due to heat. Engine will work better.

Metalface · 12 January 2009, 22:03

Sorry its took me so long to reply, I lost my internet.

Anyway, its a 2 Stroke. Thanks for all the replys, when I get a minute I'll pull it apart and have a look.

noel · 30 August 2009, 18:39

I am also new to this, so please bare with me
I have a Yamaha 2 stroke 4HP and the water dose not flow out in a smooth pace.
I have change the impeller and still no difference.
Can you tell me where the thermostat is.

Thanks, neol

m chappelow · 30 August 2009, 20:34

i cannot comment on your particular make but not all of the smaller outboards have a proper tell tale water stream squirting out or with yours it could be just blocked up where it comes out ,with some it just goes out with the exhaust relife ports as a fine mist ,and most small engines dont have a thermostat,

Metalface · 09 May 2010, 23:21

Well its been about 18 months since I posted this topic and I've finally got round to looking at it tonight.

I took the water pump to bits and the impeller looks fine and clean. I tried the engine in some water mainly because its been a while since it was run and I couldn't get it to overheat, it most need to be underload/in gear before it gets hot enough for the tell tail to turn to steam.

So whats next? Take the head off?

Chris · 10 May 2010, 20:48

Quote:

Originally Posted by Metalface

Well its been about 18 months since I posted this topic and I've finally got round to looking at it tonight.

I took the water pump to bits and the impeller looks fine and clean. I tried the engine in some water mainly because its been a while since it was run and I couldn't get it to overheat, it most need to be underload/in gear before it gets hot enough for the tell tail to turn to steam.

So whats next? Take the head off?

No, change the impellor. It might look fine does not mean it will work though. 4 years is a long time for an impellor change eitherway.

If it then overheats I would move on to water passage cleanup etc.

Metalface · 10 May 2010, 22:26

Thanks mate, I'll give that a try then.