Coolant Leak?

I have an 08 4.0 4x4 with 78k miles. My coolant level was hanging just above the low line a couple months ago, so I had my mechanic (a buddy) check it out. He couldn't find any leaks and topped off the coolant. It didn't take long for it to drop to about the same level. It has hung there until recently I noticed it was slightly below the line.
I had an appointment today with my local dealer (ugh) for my leaf spring recall, and had them look at it as well. They topped it off and did an external inspection.... you guessed it.... they didn't find anything. So now they are recommending an internal diagnostic for $350.
I drove it to work after the appointment. A couple hours later when I left, I noticed a pretty large wet spot under the front of my truck. I checked the coolant and sure enough it was down to just above the low level again. I can't see any coolant residue or any wet spots in my engine bay.
I changed my oil since my visit to my buddy and it was black like it should be. I checked my oil level the other day and it was NOT milky. I have not noticed any white smoke upon startup or while driving.
I couldn't find much by searching, mainly just 1st gen coolant problems. Do you guys have any suggestions? I hope to get this figured out without having the stealership do their diagnostics.

 

Some small leaks will go unnoticed as they dry as fast as they leak. For $350 I would buy my own tool to pressurize system and find the leak myself. The tool wont cost that much

 

Or most parts houses have those in their lender programs.

I agree with the water pump weep hole as the first check point, as well as the radiator cap, then hose attachment points, then the radiator itself.

The shops $350 is looking for a blown head gasket. Not uncommon on these from what I read but your mechanic friend can diagnose that for you for much less than $350.

 

ffs save your money

just taste the water that comes out the tailpipe,

if sweet, headgasket

if not, not headgasket

spit it out of course

 

Thanks for the info guys. Since that post I have found out that the spot in the parking lot was not from my truck after all.... which also means the dealer didn't top it off. But regardless there has been a slow leak over time.
I'll grab a mirror and check the weep hole. And do try the hobo head gasket test.

 

Could be the heater core. Usually you will smell it in the cab, but not always. Mine is leaking, but I do not smell it in the cab, and my floor is not wet. It could have picked that perfect spot to leak to where you can't see it or smell it, like mine. Worth investigating it if you can't find any problems in the more obvious areas.

 

I had a 98 Corolla that had a mysterious coolant leak. The bottle kept dropping but no coolant was leaking anywhere. I had the local Toyota dealer pressure test the system and they found nothing. Finally an old mechanic at the Chevy dealer I worked at told me to replace the radiator cap. Turned out that the cap was letting coolant slowly evaporate. Problem solved. A new cap is cheap, so you may give that a shot. Can't hurt.

 

I agree, the gas cap is a good thing to try.

If the reservoir level drops to the same point every time, then it could be a leak/crack in the reservoir itself. I"ve recently had to replace that item in my '99 Tacoma AND my '01 Corolla. That plastic Toyota uses, seems to age and crack after about 12 years or so.

 

This is why I don't use my windshield washer fluid in my 96 Tacoma- the reservoir got brittle and now has a massive hole in it. It's only like 13 bucks on rockauto, but I haven't bothered yet.

 

Spitters are quitters!

 

Sorry to revive this old thread, but thought I would give an update and provide info for anyone else that may have the same problem in the future.
I took advice from @NAAC3TACO and replaced the radiator cap (I spent a little extra for the TRD one), and my coolant level has held steady since September.

 

^^ be sure to examine the radiator cap rubber seal if you replace one. if it is swollen, or comically
oversize (the reason it may leak) oil has invaded the cooling system from somewhere

oil/atf will make rubber seals in cooling system swell and break down

happened to my 4runner, radiator cap seal was 25% increase in diameter and for
a minute wondered WTF how did this ever fit in the first place. then found atf cooler seal broke in rad...milkshake

 

A UV flashlight comes in handy trying to find a coolant leak as well. Not sure if UV works with the new type of coolant though.