I have a 2007 TL with 160,000mi on it. I think it might have a small coolant leak, but it's hard for me to tell. I keep finding a little bit of dried coolant around the cap of the reservoir. It isn't spilled coolant; I clean up the engine bay if I make a mess. The crusty coolant keeps reappearing despite wiping it clean on multiple occasions and the coolant level in the tank has been slowly lowering since I filled it around 6 months ago. There aren't any visible cracks in the cap and the temp gauge has never shown any signs of overheating. Car runs fine with very occasional hissing from what I assume is coolant contacting hot engine parts.
The TL coolant tank looks much different than other cars I've had in the past (mostly GM cars), but coolant is not supposed to be able to leak out of the reservoir cap, right? What problems could this leak cause?

 

Could some coolant be getting past the hose? I don't see a clamp on the tank side.

 

Yup put a clamp/zip-tie around the reservoir end of that tube.

If you still see dried coolant after that, replace the tube

 

Thanks for the suggestion, I never considered the hose. I have zip ties, so I'll put one on and fill up the coolant tank to MAX so I can track the level.
I have another question: the L-shaped piece of plastic connecting the radiator hose to the reservoir cap, is that supposed to be able to move at all? I noticed it has a little bit of play up and down.

 

That's the coolant overflow tank, make sure it's filled up half-way and that there are no cracks. Both my 04 and 07TL have had that small part crack and do what is happening to you.

it's about $4 from the dealer for a new one. Also it looks like the rad cap is not fully turned closed.

 

Yes, the L-shaped connector is supposed to swivel within the cap, that way you can tighten the cap down while the hose remains pointing in the correct direction.

 

It's been several says after putting on the zip-tie and it's still leaking, so it's probably the cap.
The radiator cap is on all the way - it's been like that as long as i can remember and doesn't tighten any further. I even asked my mechanic to try and tighten it at one point in case I was too much of a wimp or something haha.

 

Even though it's been a while, I'll follow-up. The leak was caused by the O-ring: the O-ring was missing from the underside of the cap. Dunno where it went, I had no idea an O-ring was even supposed to be there. Here's a diagram of the reservoir cap:
The O-ring is #4

 

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I only just now realized why I have a very slow coolant leak. The reservoir cap is supposed to screw on. Mine broke off cleanly at the seam. Too cleanly. I assumed it was supposed to just lay there. So thanks.