Blowing Out The Carbon?

[deleted]

 

One thing Prius operates differently is that its ICE has more throttle and more WOT than one on regular car. Engine power to car weight ratio is a lot smaller (and engine isn’t run all the time) in Prius so on average ICE has more of its power used. More importantly Prius transaxle always uses the most efficient RPM (for needed power) of the engine, which normally is the one that has most throttle opening.

 

Odd, I have had different results from old gas-burning, oil-burning, and coolant-steaming automobiles:
Gas burning due to a too rich mixture: black smoke, I think more noticeable at high throttle settings (worn carburetor needles most common cause).
Oil burning resulted in a bluish smoke. For worn rings smoke noticeable on deceleration from a high throttle setting. For worn valve stem seals, smoke more noticeable on hard acceleration IIRC.
Coolant steaming (cracked head or leaking head gasket usually) was hard to see as white vapour cloud unless the outside temps were down near freezing, and even then I would usually only see it for a minute or less after start up unless the leak became very serious. Coolant vapour cloud also disappears quickly into the surrounding air whereas black or bluish smoke is more "durable", kind of like a smoke screen effect.
Hope this helps!

 

Well, we should step back a little before rushing into conclusions. I know this is an old thread but the resulting information makes it worth the asking.

Is the car daily driven, but only for a very short distance?

If so, there's a warm-up procedure called "Cold start fuel enrichment". All vehicles with an ICE do this including the Prius. Also, during this warm-up time, the ECU is in open loop state. Meaning it doesn't pay attention to any sensor that it would use to alter AFR or timing past it's base maps. What happens in short drives, say like 5 minutes or so, is the engine is not allowed to properly heat up. This actually leads to steam inside cylinders, intake manifold, and exhaust pipes after shut-down. The steam condenses and any fuel in the cylinder gets trapped by the water vapor when it condenses. This causes the carbon, and carbon loves carbon. In other words, the carbon build up will soak up any fuel it comes in contact with during engine operation only compounding the issue further. Another down side to short trips, is the monitors might not have proper time to run. IE: the monitors for engine coolant temperature sensor, AFR sensor, O2 sensor, and knock sensor(s). These monitors require a certain drive "pattern" in order for the ECU to run a diagnostics on each sensor for that sensor's "performance" (how well it's doing it's job). You could have sensor issues, but without completing monitors, you'd never see the "check engine light" come on. All this can compound into an extreme rich condition that builds up more and more carbon the more this pattern is repeated.

What can be done about this? DRIVE THE CAR!!! Take it out of town, open her up, let her breath and stretch her legs. It would also benefit to do some hard stops. Albeit for a different reason not pertaining to engine performance called deglazing. This will allow the monitors to run, will burn any moisture built up in the exhaust, the engine will warm up to where it can start burning carbon off the pistons, and the engine will be "happier".

 

Should add that direct inspection of spark plug tips and boroscope inspection of combustion chamber will confirm or disconfirm carbonization, coolant vaporization, etc.