Can you diagnose a car based on the fluids that show up on the garage floor?

Dear Car Talk

Dear Car Talk | Mar 01, 1993

Dear Tom and Ray:

Could you give a general diagnosis of a problem by the color, amount, thickness, or odor of the fluids you find on your garage floor? For instance, a small amount of greenish liquid I see under my car might mean what? You'll be helping so many of us by giving us some knowledge before we go to the mechanic. Thank you!

TOM: Good question, Pat. Fluids found under the car often DO give you clues about what's wrong. And as you might guess, their locations are also big hints.

RAY: For instance, the slimy, greenish fluid you see under the front of your car is probably coolant. Coolant is usually green or greenish-yellow or on a few cars, even red). It has a slightly sweet smell. If you find coolant under the car, you probably want to have your mechanic do a pressure test to determine where it's leaking from.

TOM: If you see a thicker, dark brown or black spot under the car, that's more likely to be motor oil. Although it's a golden color when it goes in, by the time it comes out, it's usually been darkened by engine sludge. It feels slippery on your fingers, and usually drips out "spots" rather than "puddles."

RAY: It often takes a trained eye to find the source of an oil leak, since there's so much oil splattered all over the engine anyway. But a good mechanic should be able to figure it out.

TOM: If you see something even thicker than motor oil, it could be gear oil. Gear oil has a consistency almost like molases, and has a rather disgusting sulphury smell, sort of like the inside of my brother's gym bag.

RAY: A puddle that's pink or pinkish-brown could be either power steering fluid or transmission fluid. If you're losing power steering fluid, you could easily damage your power steering pump, so that's worth checking out right away.

TOM: Transmission fluid is pink when its new, and gets browner as it gets older. So if you see something that matches that description, start saving your money or looking for specials on bananas.

RAY: During the summer months, it's not unusual to find puddles of water under your car. They're probably from the air conditioner, and that's perfectly normal. It's just the water or "humidity" that your air conditioner has removed from the passenger compartment.

TOM: Oh, and there's one more thing we forgot to mention. My brother once starting seeing yellow puddles on his garage floor. But he solved that problem by letting the dog out a little earlier in the morning.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One