Clouds of White Smoke

[john cowie]

Our BMC1.5 appears to be running well when under normal cruising conditions - chugs away quite happily without much exhaust smoke.

However, when increasing revs suddenly to avoid a boat coming round the bend in the opposite direction everything disappeared in a huge cloud of white smoke. The engine did what was required of it and stopped the boat, but it took some time for the air to clear sufficiently for us to assess how close we had come to collision!

It's also noticeable that, under load (pushing against a strong current, for instance) there is considerably more exhaust smoke.

Any thoughts? It would be nice to be able to solve this one.

 

Cheers - John 

[GUMPY]

If my memory is still working:

 

Black smoke = over fuelled 

Grey/blue smoke = burning oil 

White smoke/steam  = water leak 

[Tony Brooks]

White fumes = vaporised unburned fuel.

 

As you are not complaining about coolant loss or overheating, I would tend to rule out steam at this time.

 

If the injectors are not atomising properly then globs of unburned fuel may be expelled into the exhaust, but I would expect a greyish tinge to the exhaust because poor atomisation is likely to cause CO and then carbon formation during combustion.

 

It might be a loss of compression on one cylinder, but as you do not complain about a misfire, that can be ruled out at this time.

 

If you have not had the injectors tested for   a good number of years (say 10 plus) that might be a good first step, especially as it is not too difficult to get them out yourself, but please loosen the injector pipes on the pump, as well as undoing the big nuts on the injectors. Otherwise, you may well bend the pipes as you pull them clear of the injectors so they go back under tension - that can lead to pipe failure.

 

If you are over-propped, it will overload the engine (technical term) and cause black smoke when the revs can no longer rise, but you keep opening the throttle to try to get more speed. When pushing current, try backing off the throttle a little. if the smoke gets better or clears, there is every chance that your prop is too large (assuming it is not bent or fouled). However, if you only operate in the o smoke rev range, no damage will be done.

 

 

[Mike Coombes]

35 minutes ago, Tony Brooks said:

White fumes = vaporised unburned fuel.

 

As you are not complaining about coolant loss or overheating, I would tend to rule out steam at this time.

 

If the injectors are not atomising properly then globs of unburned fuel may be expelled into the exhaust, but I would expect a greyish tinge to the exhaust because poor atomisation is likely to cause CO and then carbon formation during combustion.

 

It might be a loss of compression on one cylinder, but as you do not complain about a misfire, that can be ruled out at this time.

 

If you have not had the injectors tested for   a good number of years (say 10 plus) that might be a good first step, especially as it is not too difficult to get them out yourself, but please loosen the injector pipes on the pump, as well as undoing the big nuts on the injectors. Otherwise, you may well bend the pipes as you pull them clear of the injectors so they go back under tension - that can lead to pipe failure.

 

If you are over-propped, it will overload the engine (technical term) and cause black smoke when the revs can no longer rise, but you keep opening the throttle to try to get more speed. When pushing current, try backing off the throttle a little. if the smoke gets better or clears, there is every chance that your prop is too large (assuming it is not bent or fouled). However, if you only operate in the o smoke rev range, no damage will be done.

 

 

I agree Tony.

 

I loaned my NZ based yacht to a friend who somehow got water in the combustion chambers.

 

After fixing the engine mechanicals it smoked with white smoke on start up.

 

Leaking injector nozzles was the cause, the saltwater ingress had ruined them. New nozzles fixed it, it ran really well afterwards.

 

Getting the injectors pressure tested is a cheap option.

[StephenA]

20 hours ago, john cowie said:

Our BMC1.5 appears to be running well when under normal cruising conditions - chugs away quite happily without much exhaust smoke.

However, when increasing revs suddenly to avoid a boat coming round the bend in the opposite direction everything disappeared in a huge cloud of white smoke. The engine did what was required of it and stopped the boat, but it took some time for the air to clear sufficiently for us to assess how close we had come to collision!

It's also noticeable that, under load (pushing against a strong current, for instance) there is considerably more exhaust smoke.

Any thoughts? It would be nice to be able to solve this one.

 

Cheers - John 

 

Did the white smoke smell?  

 

When pushing against the current what colour is the smoke, and does it smell?

 

Don't think I've ever seen a BMC 1.5 run totally smoke free

Edited August 26, 2025 by StephenA

[IanD]

20 hours ago, john cowie said:

Our BMC1.5 appears to be running well when under normal cruising conditions - chugs away quite happily without much exhaust smoke.

However, when increasing revs suddenly to avoid a boat coming round the bend in the opposite direction everything disappeared in a huge cloud of white smoke. The engine did what was required of it and stopped the boat, but it took some time for the air to clear sufficiently for us to assess how close we had come to collision!

It's also noticeable that, under load (pushing against a strong current, for instance) there is considerably more exhaust smoke.

Any thoughts? It would be nice to be able to solve this one.

 

Cheers - John 

 

White smoke = Habemus Papam 🙂 

[john cowie]

Further to Tony Brooks' comment:   White fumes = vaporised unburned fuel.

We had the engine thoroughly reconditioned a year ago which included injectors etc and after settling in it's been running very nicely. 

I am wondering whether the white smoke could be caused by the engine not getting up to temperature. We have a cooling water temp gauge with the sensor next to the thermostat but the gauge rarely moves above 50 degC. What temperature  should it be running at?

Presumably, if combustion temp was  too low and the quantity of fuel suddenly increased, it might not burn effectively and just produce white smoke? 

Thanks for your interest

John

[Mike Coombes]

42 minutes ago, john cowie said:

Further to Tony Brooks' comment:   White fumes = vaporised unburned fuel.

We had the engine thoroughly reconditioned a year ago which included injectors etc and after settling in it's been running very nicely. 

I am wondering whether the white smoke could be caused by the engine not getting up to temperature. We have a cooling water temp gauge with the sensor next to the thermostat but the gauge rarely moves above 50 degC. What temperature  should it be running at?

Presumably, if combustion temp was  too low and the quantity of fuel suddenly increased, it might not burn effectively and just produce white smoke? 

Thanks for your interest

John

 

As I suggested in my earlier post, remove the injectors and have them tested. If they leak before they should open you will get white smoke, if the spray pattern is poor you will get bad mixing and white smoke. I was allowed to see mine under test, it was clear they were 'dribbling' well before the opening pressure.

 

From recent direct experience.

[NB Saturn]

14 hours ago, Mike Coombes said:

 

As I suggested in my earlier post, remove the injectors and have them tested. If they leak before they should open you will get white smoke, if the spray pattern is poor you will get bad mixing and white smoke. I was allowed to see mine under test, it was clear they were 'dribbling' well before the opening pressure.

 

From recent direct experience.

 

And don’t necessarily trust the reconditioned to get them right, I had a faulty factory-exchange injector supplied some years ago, which took me some time to diagnose because I stupidly believed the exchange unit couldn’t be faulty.

[Mike Coombes]

23 minutes ago, NB Saturn said:

 

And don’t necessarily trust the reconditioned to get them right, I had a faulty factory-exchange injector supplied some years ago, which took me some time to diagnose because I stupidly believed the exchange unit couldn’t be faulty.

 

As a Motor Trade professional with over 63 years experience, yours is clearly a very unusual situation.

 

However, not unknown.

 

I was once 2nd I/C of the largest Lucas Service branch in the UK, at Park Royal, in West London. Over 70 employees.

 

We had the same issue with 3 service exchange units, two starter motors - expensive truck ones - and a CAV Injector pump. Again, very expensive.

 

It was due to theft of the properly reconditioned units by a storeman. He replaced the units in their part numbered boxes with ones he had carefully 'dollied up' to look good.

 

However, injectors that have been overhauled can be tested -and should be-post overhaul, by high pressure testing. Very quick job, a few minutes only. 

 

Just like having them tested in case they are defective.

 

Getting back to your premise, when I was the Mechanic Trainer for Kawasaki Motors UK Ltd. their most excellent Workshop Manuals ALWAYS suggested that if a suspected electrical unit was suspected of being defective but tested OK, exchange it for a known GOOD unit, not a new one.

 

Electronics and testing 45 years ago were not what they are today, it was good advice.

[Kingdom Isambard Brunel]

There is no reason that a new unit must be OK, it could be faulty.  Ford Transit oil pumps in the early '70, stuck pressure release valves exploding oil filters, new ones did exactly the same!