Leaking coolant, car overheating, lexus is300, 2001

he causes of white exhaust smoke can vary; however, it is common to see white exhaust smoke when first starting a car, especially on cooler days. This is generally steam caused by condensation. As the engine warms up and the condensation dissipates the white exhaust smoke (steam) is no longer seen. If excessive white exhaust smoke is present well after the engine warms up, it is necessary to have the car inspected for possible internal coolant leaks. Indicators of an internal coolant leak include billowing white exhaust smoke accompanied by a sweet odor or a low coolant reservoir level. An internal coolant leak can also contaminate the engine oil giving it a frothy, milky appearance. Even small amounts of coolant entering the combustion chamber will produce white exhaust smoke.
One of the main causes of white exhaust smoke and coolant loss is a cracked or warped cylinder head, a cracked engine block, or head gasket failure caused by overheating. A cracked head may allow coolant to leak into one or more cylinders or into the combustion chamber of the engine. Dirty coolant, a poorly maintained cooling system, a low coolant level, or a non-functioning cooling fan can cause engine overheating. In addition, engine wear can eventually cause the gaskets to lose their capacity to seal properly allowing internal coolant loss. Intake manifold gasket and head gasket failures are two of the most common sources of internal coolant loss caused by engine wear.
Never remove the radiator cap or coolant reservoir cap while the engine is hot or running as it can cause serious injury; always allow the car to cool down completely first. Checking for a low coolant level in the reservoir is the first step in determining if coolant loss is causing the white exhaust smoke. If the coolant reservoir is at the proper level but excessive white exhaust smoke is present, a cooling system pressure check is required to determine where, if any, coolant leaks are located.

Sounds like the problem WAS: out of coolant due to a leak. If there is a leak then it may not develop enough vacuum to pull coolant from the reserve reservoir. Did you open the radiator cap and look?
The problem IS: you need a new engine (or car). See a mechanic to confirm before doing this.

Sounds like you have a leaking head gasket or damage to the engine from when it overheated.
A leaking head gasket can cause compression to leak into the cooling system and pull coolant into the cylinders which is burned out the exhaust. It does not have to leak into the oil.
A shop would check for exhaust gas in the cooling system and run a compression test on the cylinders.

Yet--Hopefully

Head Gasket
Intake Gasket
Water Pump & drying off so you don't see it

P0103 Mass Airflow MAF Circuit High

YOUR TEMP GAGE WILL NOT REGISTER CORRECTLY WHEN THE COOLANT FALLS BELOW A CERTAIN LEVEL. WHEN IT IS SMOKING IT IS EXTREMELY HOT. IF YOU HAVE A COOLANT LEAK THAT BAD IT SHOULD BE NOTICEABLE EVEN WHEN IT IS NOT HOT. YOU NEED TO FIND THE SOURCE OF THE COOLANT LEAK. WATER PUMP, COOLANT HOSE, FREEZE PLUG, HEAD GASKET, RADIATOR CAP LEAK, OR RADIATOR, OR HEATER CORE. CHECK THE ABOVE AND YOU WILL FIND THE SOURCE OF THE LEAK.

First confirm that the engine IS actually overheating - steam, no heat to the interior etc. Sometimes a temperature sensor will fail and give a misleading 'overheat' reading on gauge. For that matter sometimes the gauge can fail and give the same misleading reading. Check that the cooling fan comes on when the engine temperature starts to rise above 'normal'. If not check (in order) fan fuse, fan relay, fan sensor, fan. Real overheating is caused by a lack of coolant AND/OR lack of coolant flow. Modern cooling systems are 'closed'. In other words there should be little or no loss of coolant. If the level is significantly low you have a leak....either external or internal. With the coolant topped up to the correct level and the radiator cap on, run the engine and look for visible leaks...hoses, valves, radiator etc. Internal leaks, eg. head gasket will usually be accompanied by white exhaust smoke (steam), hard starting, rough running and bubbles in the expansion tank. Sometimes, though NOT always, you will find the engine oil has a milky look and/or engine oil will be mixed in with the coolant.

Valve stem seals can cause this problem, but normally only when first started. Oil in the rocker cover seaps through the oil seals into the cylinders and is burnt up on start up.
Try a "STOP A LEAK" additive and it may reduce the oil consumption and smoke.
I found some on e-bay and it worked on my tired old escort. It even stopped the rattling tappets.

check your intake gasket for leaks