The warning signs in your car’s fluids

You probably know that maintaining your engine oil and automatic-transmission fluid at the proper level is critical to getting the best performance and the longest life from your car. But you might not realize that the color and consistency of those fluids can also alert you to troubles that might not otherwise be apparent. By knowing what to look for you can avoid major problems that could leave you stranded.

First, some basics

• Check your car's fluids at least once a month, referring to the owner's manual. Normally, it should take only a few minutes.
• Make sure the car is on a level surface and the shifter is in park. If the car has a manual transmission, apply the parking brake.
• If the engine is warmed up, be careful not to burn yourself on a hot part. Wear gloves if necessary.
• If you need to add oil or fluid, use the type specified in the car owner's manual.
• Change the fluids according to the manual's maintenance schedule.

Red flags

As you check the level of oil or transmission fluid, look closely at its condition. If you see any of the following signs, you should have the car checked out by a mechanic soon.

Engine oil

Fresh oil is translucent, and it's normal for it to become dark brown or black over time. If there are any thick globules on the dipstick, however, the engine could be developing sludge. That could block oil passages and keep the engine from being properly lubricated, which can cause excessive wear or damage.

A light, milky appearance in the oil indicates that water or coolant might be leaking into it through a defective gasket or a crack in the engine. If so, the oil level might also be too high. Have the car towed to a repair shop.

Make sure that the oil is cool enough to touch and then slide your fingers along the dipstick. If the oil is gritty or dirty, it and the oil filter should be changed immediately. Bits of metal in the oil are a sign of internal damage; have the engine checked out right away.

If the level is consistently low, there's either a leak or the engine is burning oil. An external leak will be apparent by drops on the ground under the car. An internal leak could show up as oil in the coolant. And bluish smoke from the tailpipe signals burning oil. Check the oil as often as necessary to keep it at the correct level until you're able to get the problem fixed.

Automatic-transmission fluid

When it's in good condition, the fluid is translucent. However, if it's dark or black, the internal clutches could be slipping, a sign that a transmission overhaul might be in your future. That problem can also give the fluid a burnt odor.

If water or coolant is leaking into the transmission, the fluid will appear light pink. Not only does the leak need to be fixed, but because coolant can affect internal seals, the transmission might need to be rebuilt as well.

If the transmission has overheated, the fluid can become oxidized. Such fluid has a tacky, varnished texture or is foamy (indicated by bubbles on the dipstick). Foamy fluid inhibits lubrication, which can lead to excessive wear or damage. Overfilling the transmission with fluid can also cause foaming.

As with the oil dipstick, bits of metal on the transmission dipstick are a sign of internal damage requiring immediate attention.