Car is leaking yellow fluid - what is it?

I noticed this morning that in the snow underneath my car, there were some drops of yellow fluid..some of the drops were brownish. It looked like it was from the rear half of the car, though I'm not sure of that. The spots are about half way between the left and right sides of the car.

It was very noticeable when I was first took the car out for a drive (20 minutes of city driving), but then I couldn't find any other yellow spots when I tried a little later to figure out where exactly it was.

The car is a 2000 Mazda Protege LX with automatic transmission and just over 100,000 km on the odometer. I had the 96,000 km service on it a couple of months ago (and that included a new timing belt).

The fluid in the coolant reservoir is green and it's at the "full" level, so I'm assuming that wasn't what was leaking.

What else could it be?

Neighbour's cat? Just kidding

Could be brake fluid. Check your level.
The colour can range between yellow and brown as in this pic
http://www.dixonmotors.co.uk/images/...brakefluid.jpg

The only other thing that passes through the location you describe is gas.

Funny timing..the brake line blew on my 626 two weeks ago..

Someone walked by and had to go?

I already ruled out the possibility that it was bodily fluids -- no footprints nearby, and the yellow spots were in different places where I had left my car this morning (driveway, and on the street when I was shoveling the driveway).

The brake fluid is a pale yellow, but the spots in the snow seemed pretty bright....kind of like the fluorescence of coolant. And the brake fluid reservoir is also full.

If I can't "reproduce" the problem to find what section of the car the leak is coming from, should I just keep monitoring the fluid levels and check to see if any of them are dropping noticably?

Rusty water? couldjust be some melted snow that was on some rusty part, just an idea that came to mind when brown was mentioned

Originally Posted by sumfunny

Rusty water? couldjust be some melted snow that was on some rusty part, just an idea that came to mind when brown was mentioned

Could be.

Would rusty water be bright yellow, though?

Found here http://www.grubbsauto.com/technotes/spots.html

Black or dark brown - Usually found under the engine, these spots are likely to be engine oil. It's not unusual for an engine to leak small amounts of oil over a period of time. However, if you see puddles larger than a tablespoon, you should bring your vehicle to a service center for diagnosis and repair.

Bright green, bright yellow or pink - These puddles are probably formed by radiator coolant or antifreeze leaking from the cooling system. If you notice even a moderate amount of fluid, have the radiator level checked immediately.

Red or pink - If you find these spots under the center of a rear-wheel drive car, a good bet is that this fluid is from the automatic transmission. A small amount is nothing to worry about, but you should consult a service technician if more than a little is found. If your car has front-wheel drive, red or pink fluid that is found toward the front of the car may or may not have come from the automatic transmission. A small amount of the fluid should be checked by a qualified technician to verify its origin.

HA! This thread just gave me a very good idea of how to take revenge on a guy...

Just poor some diff coloured liquids under his car. He'll spend $$$$$ just trying to figure out what it is.

Originally Posted by actng

HA! This thread just gave me a very good idea of how to take revenge on a guy...

Just poor some diff coloured liquids under his car. He'll spend $$$$$ just trying to figure out what it is.

That's hilarious!

Have you ever used Rain-X de-icing washer fluid?

It's the only liquid that's bright yellow I can think of.

Originally Posted by Kenneth

Have you ever used Rain-X de-icing washer fluid?

It's the only liquid that's bright yellow I can think of.

Nope. Just regular blue windshield washer fluid.

CLimb under and have a look.

Could be rostproofing if you've ever had your car sprayed.

Could be oil or lube from a joint.

Smell is a good indicator, tranny fluid smells acrid, sort of like vodka or something...power steering fluid smells almost acidic, fi thats a smell. ..brake fluid is watery and smells very little...oil will still be oily, and smell like oil, lol.

Old school trick is to park over a piece of cardboard box overnight so that you can inspect the fluid the next day.

Honestly you shouldnt have to take your car in (not saying you do) to find out what is leaking you should do some more homework on cars in general....talk about a waste of money for an inspection....to fix it, probably, but to inspect...climb under there and see where its coming from yourself.

Do a process of elimination, check all fluid levels, etc.

I'd say its motor oil, personally, but from that area....hmm....maybe differential fluid but I'm not sure if FWD cars HAVE rear Diffs.

Sometimes oil will leak down along the muffle/exhaust though....which could explain its position.

Check your tranny fluid, although the colour sounds off, some tranny fluid is orange which could LOOK yellow-ish in the snow, or mixing with grease/dust/dirt on its way out the bottom of the car.

Gas is generally easy to tell, because it smells so strong.

In that region of an FWD car I'd guess stray oil, brake fluid or fuel because your oil and fuel lines run to the back of the car, but thats about it.

Originally Posted by actng

HA! This thread just gave me a very good idea of how to take revenge on a guy...

Just poor some diff coloured liquids under his car. He'll spend $$$$$ just trying to figure out what it is.

great idea, lol,
but i guess it may be the antifreeze or brake fluid- really rare on mazda though, or maybe radiator oil-coolant

OH PS:


A LOT of under-car leaks will only occur under pressure IE when the car is driven.

That would explain why it 'goers away' so to speak, after its been sitting.

It will leak under the pressure of driving, and then drip down for a while after you park (obviously)....as you have said.

run the car in the driveway a while to see if that exposes the uncooperative mechanism, might be easier.