White Smoke and Power Loss from Outboard

earlofzetland · 03 May 2014, 06:20

I have a 1998 Honda BF8A. When running it at full throttle the other day i suddenly experience a loss of power and when i turned around white smoke was coming from the exhaust holes. The engine seems to be pumping plenty of water and runs fine at lower speeds. Spark plugs and fuel filter have recently been changed. Any help would be much appreciated. Thanks EofZ

neil.mccrirrick · 03 May 2014, 06:51

If this was a car I'd say the head gasket has gone. Someone will be along soon to correct or confirm

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spartacus · 03 May 2014, 07:04

Could be that white smoke was steam. When was the impeller last changed? Id inspect that first to check there isn't a broken blade. I'd also check the thermostat. Remove it and test it in boiling water to see it opens. You may need a new gasket to reinstall.

Take the cowl off the outboard and check the head gasket for any corrosion or signs of gases when it's running on muffs. Finally, change the fuel, the loss of power could be water in the tank.

earlofzetland · 03 May 2014, 07:23

New impellor was put in last year and it has hardly been run

EofZ

spartacus · 03 May 2014, 08:28

Quote:

Originally Posted by earlofzetland

New impellor was put in last year and it has hardly been run

EofZ

Impellers are good for every other year, so assuming that's fine, then check the other things I indicated. While you're at it, check the oil level and that the oil isn't contaminated.

RIB-Teccie · 03 May 2014, 10:01

Cooling system check and then head gasket, outside chance of a bottom crank seal.

If you have had water entering the combustion chamber, it can seize the engine, so some oil down the bores would be advisable until you have time to fix. WD 40 down the air intakes to protect the crank, do this with engine running.

earlofzetland · 04 May 2014, 20:06

Cheers for the advise so far guys. To help my understanding of the possible cause could someone explain why a dodgy thermostat would cause a loss of power?

A1an · 04 May 2014, 20:16

Dodgy thermostat could cause an engine to overheat, if it overheats too much it can cause the head gasket to fail or the engine to tighten up.

Both symptoms can cause loss of power.

earlofzetland · 04 May 2014, 20:46

Thanks. Wouldn't a steady stream of cool water from the telltale indicate the thermostat is working ok?

A1an · 04 May 2014, 20:55

No, its not a given. Tell tales can come off before going around cooling jacket.

earlofzetland · 05 May 2014, 18:07

Checked the head gasket while running for leaking gases but seems fine. No sign of water in the fuel but a lot of dirt. This may account for the loss of power at full throttle but would it also cause the white smoke/steam from the exhausts?

captnjack · 05 May 2014, 18:28

The head gasket also keeps the cooling water from getting into the cylinder bores. This failure wouldn't be seen on the outside as a leak but would produce lots of white smoke.

You have to remove the head to see for sure.

Seaflyer02 · 05 May 2014, 18:35

Sounds like head gasket. If used in salt water take plugs out after you have run it and see if there is a build up of crystallised salt around the electrode.

I had similar with a 50hp years ago.

Good luck

earlofzetland · 05 May 2014, 19:46

No signs of salt on the plugs or water in the engine oil.

captnjack · 05 May 2014, 20:25

If the oil looks normal the head gasket's probably ok. I'd look at overheating more thoroughly, check thermostat in hot water with a thermometer. Then check that there's no crud in the cooling passages.