Introduction:
Fluid Replacement Intervals:

Fluid	Normal Life	Extreme 1
Engine Oil	7,000 mi.	3,000
Transmission Auto	20-60,000	12,000
Differential (Rear-end)	30-60,000	12,000 2
Transfer Case (4WD)	30,000
Engine coolant	75,000 or 5 yrs.

Note: Many people recommend changing engine oil every 3,000 mi. or 4 months even if they are driving under extreme conditions. 1. Extreme Driving:

• frequent short (< 5 mi.) trips
• Dusty conditions
• Trailer towing
• off-road driving
• 50% of your driving at high speeds is during hot (> 90 deg) weather

Fluid Levels:
Overfilling Oil:
See also engine diagram

What are the effects of overfilling oil?
Summary:

• Damage from overfilling does not occur until the level of oil reaches the bottom of the spinning crankshaft webs, which would beat the oil into a foam. The air in the crankcase would become an oil mist, which would be blown out the crankcase vent system, and the oil would become aerated, which would not pump well. Even so, there would be no damage in moderate driving as enough oil would continue to be pumped and the excess would eventually be blown out over the engine. Most likely the driver would soon notice the smell and smoke of oil on the exhaust system, and raise the hood to find an oily mess.
  Source: Subaru Forester Owners Forum
• If this "blowby" exceeds the ability of the PCV valve to draw in the vapors, the excess blowby will flow through the breather hose to the air cleaner housing where it then re-enters the combustion chamber, where it is burnt - damaging or destroying the catalytic converter, or O2 sensors. You will see smoke coming out of the exhaust when this happens.
• In one case below (car talk forum) it resulted in a thrown rod.
• Excess oil can contribute to higher pressures and excessive vapors in the crankcase and could cause leaks as the extra oil is forced past seals and/or gaskets.
• Vehicles are designed with sumps that can take an accidental overfill of a quart or quart and a half without harm, as such mistakes happen frequently.

At the Tundra forum (www.tundrasolutions.com/forums/engine-and-drivetrain/) they said:
"If the oil level is extremely high and reaches the crank it can make the oil foam resulting in a LOSS of lubrication and make your engine labor harder with the extra oil.
A quart of oil only raises the level in the crankcase about 1/4.
An extra quart and one half won't cause a problem."

One person said "Excess oil can contribute to higher pressures and excessive vapors in the crankcase and could cause leaks as the extra oil is forced past seals and/or gaskets.", but most think that foaming is the only problem.

Most modern engines run with a slight VACUUM in the crankcase, which is maintained by the crankcase breather valve and PCV Valve (I am not sure but I think our Tundras us a Variable-FLow PCV Valve). However, the crankcase CAN become "PRESSURIZED" (at least in theory) due to a clogged PCV valve (which I am sure you know that the VAPOR from HOT engine OIL and also from exhaust gases escape past the piston rings via the PCV valve. If this "blowby" exceeds the ability of the PCV valve to draw in the vapors, the excess blowby will flow through the breather hose to the air cleaner housing where it then re-enters the combustion chamber (Not trying to give you a PCV Valve101 lesson.
Having said all that, THE THEORY IS THAT THE INCREASED OIL CAN LEAD TO INCREASED "BLOWBY" WHICH IN TURN CAN LEAD TO A CLOGGED PCV VALVE AND/OR BREATHER VALVE. A plugged PCV valve can make your truck run richer, BUT a clogged breather hose could possibly cause the engine to consume oil because of the INCREASE in the crankcase vacuum.

A Lexis owner reported his dealer added new oil without draining the old. Afterwards, everything seemed fine, but I noticed that it was putting out lots of blue smoke, especially under hard acceleration. I checked the engine but couldn't find anything wrong. I took the car back and told them about it. They didn't seem real concerned. They checked the engine out thoroughly and reported that everything was fine. I guess it was, becase I drove it another 15,000 miles and had no problems. So I suppose a measly half quart overfill won't make any difference.

Rod Knox said:
The engines that I have seen drastically over filled were smoking profusely from the tail pipe and running badly, often stalling at idle. None had a catastrophic failure. But then, none were 3.9L Mopar V6s. If a piston and a crankshaft throw are in the crankcase they would raise the level quite a bit. Was the engine running normally without smoking for 175 miles and then suddenly with no warning POPPED? The dip stick will have a residue on the length that extends out of the tube. Hydraulic lifters usually get quite noisy and cause a dramatic power loss long before a rod gets thrown due to oil foaming. The dark color and burned smell is puzzling. The worst overfill that I have cleaned up after had 10 quarts drained when it made it to the shop on its own power with the dipstick blown up out of its tube and oil sprayed up on the hood. It was a 4 cylinder Isuzu pickup.

What are bad effect of overfilling engine oil in an engine? - Yahoo! Answers:
Far worse, however, is that the surplus oil will be blown into the air intake manifold, from there it gets into the cylinders (together with the air), where it is burnt - damaging or destroying the catalytic converter, or O2 sensors,which is really expensive! Ideally, the oil level in your engine should be somewhere between the "min" and "max" marks on the oil stick for everyday use. See Question re oil flow engine vs tank - Pelican Parts Technical BBS

See:
Antifreeze page
Oil recommendations