<!-- from fixya rte -->Engine smokes when you first start it - Kohler CH25 PA-CH730-0040 Command Gasoline Engine

Probable head gasket failure

white smoke could be head gasket leak. but white smoke will come with warm engine. If engine is first start cold. IT's only water in exhaust system

More than likely you have worn engine valve guides and or seals.

Blue smoke from the exhaust = burning engine oil.

It sounds like you have brought a lemon as if it hard to start when cold then its lacking compression which is worn engine piston rings and valve guides,and if it starts smoking when driving and if its BLUE smoke then its bad piston rings And if its BLACK smoke then its to much petrol getting into the engine which will also cause the engine to wear out quick as its washing the bores with fuel instead of oil,and that will also stop the engine from starting when hot,
SO if its BLUE smoke replace the engine
If BLACK smoke repair fuel fault.
Ron

Helllo there
Symptom: Gray or blue smoke from the exhaust. You notice gray smoke coming from the exhaust when you start your car. The smoke may or may not disappear after the car is warmed. If it is, it is less noticeable. The smoke may have a bluish tint to it. Possible causes:

1. The engine's piston rings may be worn.
   The Fix: Replace piston rings. (Generally not a DIY job)
2. The engine's valve seals may be worn.
   The Fix: Replace valve seals. (Generally not a DIY job)
3. Damaged or worn valve guides.
   The Fix: Replace valve guides. (Not a DIY job)

Symptom: Engine uses more oil than normal, and there is some smoke from the exhaust. The oil level is low between oil changes. It appears that the oil is being burned by the engine because of the smoke in the exhaust. You may or may not notice the engine doesn't have the same power as it used to.
Possible causes:

1. The PCV system is not working properly.
   The Fix: Replace PCV valve.
2. The engine may have mechanical problems.
   The Fix: Check compression to determine engine condition.
3. The engine's piston rings may be worn.
   The Fix: Replace piston rings. (Generally not a DIY job)
4. The engine's valve seals may be worn.
   The Fix: Replace valve seals. (Generally not a DIY job)

You may have an excessive rich mixture due to a sensor malfunction that is causing excessive fuel enrichment., The part that gets me is that you don't have a check engine light on. a 98 Rav4 is an OBD2 vehicle and should have thrown a code and turned on the check engine light ,if you have a bad sensor Black smoke is usually a sign of too much fuel, blue smoke is a sign of oil being burned and white smoke or steam is usually a coolant leak into the combustion portion of the engine, Verify the color of smoke and go from there. Some enrichment at start up is normal because cold engines need enrichment to start and run properly till warmed up.. Goodluck

It sounds like you may need valve seals.
The oil sits in the head after the engine is cut off and leaks around the seals into the cylinder.
When you start the engine it burns the oil and sends the smoke out of the tailpipes.
It does not hurt anything much if it is not to bad.

Ones the diesel engine gets weak its thn a hard start!, becausea diesel engine mainly fires up on good compression, i guess its time for an engine overhaul .

state what color the smoke is. White smoke is antifreeze. Gray smoke is fuel, and black smoke is oil. Also have the computer scanned so you know why the light is on.