Transmission fluid level need regular top up and there is no external leak.Fluid color looks white.

To answer absolutely correctly I would need more information, but here are some distinct possibilities:
1) Transmission fluid may be low due to a very small leak, and once engine is running, the transmission pump is also running and it could take a few seconds for the transmission fluid to fill the lines and all the passages in the valve body;
2) Transmission filter could be old and partially stopped up with worn clutch face material (a normal occurrence with high vehicle mileage), and it takes a few seconds for the fluid to fill all the lines and valve body passages;
3) Transmission fluid pump may be failing; this is rare without causing other more serious symptoms and serious damage, but it is possible;
4) It is possible that it is very cold where you are and cold transmission fluid is thicker and takes longer to properly circulate throughout the transmission.
The sensors and switches in an automatic transmission are supposed to be submersed in transmission fluid at all times. If your fluid level is TOO low, serious transmission damage WILL occur. Check your fluid level by parking car on level surface with engine running at full normal operating temperature. With transmission in park, check fluid level (on almost every car made since 1990's, the transmission dispstick is identified by the red-colored handle (the yellow-colored handle is engine oil). The stick will have markings on it that indicate proper level. Transmissions should NOT leak causing low levels. If your fluid is low, you have a fluid leak somewhere. Identify it and have it fixed, or your transmission WILL die eventually.

You don't state what make, model or year the vehicle is, that being said...is the oil / fluid brown/ black like oil or is it red like transmission fluid? Some cars today have what they call sealed transmissions. Yes, they have fluid in them but there is no dipstick to check it with. The transmissions plugs that can be removed and you stick your finger in it to get the level, but you have to crawl under the car / truck to do this. Manufacturers like Kia and Toyota, and others feel that since they put in a high mileage long lasting fluid there is no need for the regular Joe to check the fluids on the car, therefore you can pay the bigger $$$ at 50k or 60K miles and let the deal tech do it for you.

If you're losing fluid then it's due to an external transmission leak, a faulty vacuum modulator, or a leaking transmission cooler. No matter which one is behind this is needs to be repaired promptly as an automatic transmission can be damaged very very quickly due to a low fluid level.

At idle and the vehicle in nuetral check your transmission fluid level. If it is low your will need to add ford only transmission fluid which will come in a variety of manufactures. Don't use the multi vehicle fluid. You will then need to see where it is leaking from. If the fluid level is good look at the color of the fluid on the stick. if it is brown that means it is burnt and probably need a transmission.

At idle and the vehicle in nuetral check your transmission fluid level. If it is low your will need to add ford only transmission fluid which will come in a variety of manufactures. Don't use the multi vehicle fluid. You will then need to see where it is leaking from. If the fluid level is good look at the color of the fluid on the stick. if it is brown that means it is burnt and probably need a transmission.

The most common transmission problem on a Nissan pickup is operating the truck with the transmission fluid low. Nissan owners needs to pull the dip-stick and see if the level is low. The fluid level must be checked when the truck engine is idling. Nissan pickup owners also need to look at the color of the fluid and see if it needs to be changed or just leveled off. The color must be transparent and not black or brownish in color. The owner must also smell the transmission fluid to see if the fluid smells burnt. If the transmission fluid smells burnt, then the transmission fluid must be changed as soon as possible. Over-filling the transmission fluid level also creates Nissan pickup transmission problems.


Read more: Nissan Pickup Transmission Problems ' eHow.com http://www.ehow.com/list_7202700_nissan-pickup-transmission-problems.html#ixzz2HntdpDoZ

To reduce wear and friction inside a transmission, the most commonly used transmission fluids are mixed with friction modifiers.

• If an automatic transmission fluid (ATF) without friction modifiers is used in a transmission designed for friction modified fluid, the service life of the transmission is not normally affected. However, firmer shifting will result and the driver might not welcome this change in shifting quality.
• Transmission durability is affected by using friction modified fluid in a transmission designed for nonmodified fluids. This incorrect use of fluid will cause slippage, primarily when the vehicle is working under a load. Any amount of slippage can cause the clutches and bands to wear prematurely. Also, because of the high heat generated by the slippage, the fluid may overheat and lose some of its lubrication and cooling qualities, which could cause the entire transmission to fail.

The formulation of an ATF must also be concerned with the viscosity of the fluid. Although the fluids are not selected according to viscosity numbers, proper flow characteristics of the fluid are important in the operation of a transmission.

• If the viscosity is too low, the chances of internal and external leaks increase, parts can prematurely wear due to a lack of adequate lubrication, system pressure will be reduced, and overall control of the hydraulics will be less effective.
• If the viscosity is too high, internal friction will increase resulting in a greater chance of building up sludge, hydraulic operation will be sluggish, and the transmission will require more engine power for operation.

To check the fluid, the vehicle should be level and running and the transmission should be at operating temperature. Check the condition of the fluid.

• The normal color of ATF is pink or red.
• If the fluid has a dark brownish or blackish color and/or a burned odor, the fluid has been overheated.
• A milky color indicates that engine coolant has been leaking into the transmission's cooler in the radiator.

If there is any question about the condition of the fluid, drain out a sample for closer inspection.
NOTE The correct fluid specifications and checking procedures are stamped on the dipstick.

• Some fluids have a burnt smell when they are in good condition, so be sure this is not the normal condition.
  • Burned fluid is usually caused by failed friction parts in the clutch packs or bands. Friction material might be evident on the dipstick. The transmission will probably require rebuilding soon.
• Sometimes it is easier to tell if the fluid is contaminated by feeling it, rather than by seeing it. Place a few drops of fluid between two fingers and rub them together. If the fluid feels dirty or gritty, it is contaminated with burned frictional material.

After checking the ATF level and color, wipe the dipstick on absorbent white paper and look at the stain left by the fluid. Dark particles are normally band and/or clutch material, while silvery metal particles are normally caused by the wearing of the transmission's metal parts.
If the dipstick cannot be wiped clean, it is probably covered with varnish, which results from fluid oxidation. Varnish will cause the spool valves to stick, causing improper shifting speeds. Varnish or other heavy deposits indicate the need to change the transmission's fluid and filter.

CAUTION
Abusive driving can overheat a transmission and cause fluid oxidization and breakdown. Stay within the recommended towing load for the vehicle. Avoid excessive rocking back and forth when stuck in snow or mud.
Low fluid levels can cause a variety of problems. Air can be drawn into the oil pump's inlet circuit and mix with the fluid. This will result in aerated fluid that causes slow pressure buildup and low pressures that will cause slippage between shifts.
Excessively high fluid levels can also cause aeration. As the planetary gears rotate in high fluid levels, air can be forced into the fluid. Aerated fluid can foam, overheat, and oxidize. All of these problems can interfere with normal valve, clutch, and servo operation. Foaming may be evident by fluid leakage from the transmission's vent.
If the transmission fluid was low or there was no fluid, raise the vehicle and carefully inspect the transmission for signs of leakage. Leaks are often caused by defective gaskets or seals. Common sources of leaks are:

• The oil pan seal,
• Rear cover and final drive cover (on transaxles),
• Extension housing,
• Speedometer drive gear assembly, and
• Electrical switches mounted into the housing.

The housing itself may have a porosity problem, allowing fluid to seep through the metal. Case porosity may be repaired using an epoxy-type sealer.

02/'03 L200/L300's don't have transmission dipsticks most likely reflecting Saturn's confidence of a leak-free transmission, leaving only a red fill cap on the transmission. The actual method for checking transmission level is a very abnormal method; parking on a level surface, removing the transmission oil level bolt/cap from the transmission, observing whether or not fluid flows out. Excess fluid will flow out automatically establishing the proper level and amount of transmission fluid. Less would mean topping off by pouring some into the top access fill hole and observing if fluid flows out the leveled drain hole until fluid flows out. This would indicate proper levels and replacing the top and access plug is all that's necessary. Messy as compared to the old method. The access bolt will be sized differently from the other bolts holding the transmission sump on. I would assume your '01 L200 is the same. Use regular Dexron ATF red transmission fluid.

Is your car a standard transmission or automatic? Could be transmission fluid. Does it look or feel like oil?

with the engine running :)