White smoke from 4 stroke outboard

[Colin24]

My small sailboat has a Honda 8 hp four stroke outboard; it’s about 4 years old.
The other day, after motoring for about 3 hours down the Orwell I called in at Harwich, but when I left I noticed white smoke coming from the exhaust.
I have never noticed any smoke before.
There is no discernable change in performance or engine note.
What is the most likely cause and how worried should I be.

Answers that a mechanical numpty can understand please.

Colin

 

[allangray3]

White smoke from 4 Strokes is often a sign that water is getting into the combustion chamber. Usually from a damaged Head Gasket, or to a lesser extent from the fuel. Checking the tank is easy. Headgasket needs compression test.

 

[Colin24]

Hmmm… I’m pretty confident the fuel is not contaminated. Would there be any visual signs that the head gasket may be the problem, just by looking ?
There is not a lot of smoke. Is this something that means not using the engine at all until it’s been sorted or is this the sort of thing that I could live with for a short time and keep my eye on it ?
I was hoping to go for a sail tomorrow.

 

[Sixpence]

If the head gasket has gone the only real signs you'll get will be from the exhaust , unless you check the oil regularly . If it's got milky deposits or froth of any kind and doesn't look or feel right , sail yes , motor ? , suptoyou

 

[duncanmack]

You may find that a tribe of very small red indians ( sorry, native americans) have taken up residence in your outboard and are trying to communicate with you by means of smoke signals.
On the other hand ..........

 

[fishermantwo]

[ QUOTE ]
I was hoping to go for a sail tomorrow.

[/ QUOTE ]

I think you should go sailing. My guess would be fuel type/brand. Only use quality fuel and not the lowest grade ULP.

Blown headgasket will sometimes allow water into the sump oil, sounds like thats not the case here. Headgaskets can also fail and allow cooling water into the combustion chamber. In this case you will get steam, particularly at start up. With a car engine with a pressurised cooling system and the engine is shut down, water can be forced into the compression chamber by the unequal pressure. If you pull the sparkplug with the engine cold and peer down the hole, you will see some drops of water. Small amounts will soon burn off at start up. Really bad leak will stop the motor turning over.

 

[Lakesailor]

The motor may continue working, that is revolving and producing thrust, but the longer you use it the more likelihood of damaging moving parts through oil contamination. Head gaskets don't heal themselves. Damaged ones only get worse.

 

[VicS]

I'm not saying that it is not the head gasket BUT IMHO the more likely cause is a reduction in cooling water flow. Perhaps not enough to cause any other symptoms of overheating but leading to steam coming from the exhaust.

It may be because it needs a new water pump impeller or it may be because the water passages are restricted. It may have been simply because the water intake was blocked by something. You should consider these possibilities before removing the head.

Carry on using it for now but check the oil regularly for signs of water ingress. If that is found the it does rather confirm the head gasket theory Then get it fixed without delay. Otherwise try to monitor it for signs of over heating. Stop using it if it gets worse.

Don't forget to report back when the problem is positively identified.

 

[Talbot]

Yes that would be my suggestion. flush the engine through with furnox or something similar and see if the water flow increases before doing major surgery.

 

[Lakesailor]

Good point, but is it overheating? Is the pee stream getting warmer than usual. If it is overheating it could lead to a headgasket failure. Doing nothing is not a good option.

 

[VicS]

Fernox is a brand name. They do a wide range of products for central heating systems etc.. The acid based descaler is DS-3, but there are other sluge removers etc Which product will rather depend on the cause of the problem. Just discovered that our local Homebase stocks DS3. If they do any branch is bound to!

 

[VicS]

[ QUOTE ]
see if the water flow increases before doing major surgery

[/ QUOTE ]

I have just read your post again. The trouble is most of the cooling water leaves via the leg with the main exhuast gas flow so it is not easy to tell if the overall flow is good, poor, improved or not. The flow from the "pee" hole is not necessarily a reliable guide although obviously if it is considerably below normal and is itself not blocked then something is wrong.

 

[the_wanderer]

I must agree with VicS. I have owned a Honda B 75 for twenty five years. The alloy they use is a bit iffy and prone to corrosion, blocking the water passages. I dismantle my manifold every year and clean out the accumulated gunge.

The thermostat also may be broken. Take it out and heat it in an pan of water to see if it opens.

Good luck.

Regards.

Alan.

 

[VicS]

IMHO it is worth testing a thermostat accurately. I recently posted details of the procedure HERE

 

[brianrunyard]

Is the "white smoke" steam?
Could reduced cooling water flow be causing overheating, when did you last check the impellor?

 

[VicS]

[ QUOTE ]
Is the "white smoke" steam?

[/ QUOTE ] I think you will find that has been the assumption throughout the thread