I recently purchased a new discovery 2004 woth 100k miles on it. When i had got it i did a full inspection for leaks and checked the coolant level before and after test drive. Today, My coolant level was low so I added some more only to find it still lowered a bit shortly after. I can't seem to find any leaks, however when I got under the car to change the oil I noticed this:

One of the bolts holding the transmission to the engine was loose. I tightened it, but I don't like how clean that looks. I also noticed the transfer case was leaking, and I will need to address that also, not sure if it's a gasket or what. Anyways, did I get a car with a blown head gasket or should I try to see if it's leaking elsewhere?

 

Looks normal for a D2 to me, check your throttle body heater plate for leaks, check all hose clamps, check carpet on passenger side to see if it’s damp (heater core leaking), and remove top fan shroud and inspect radiator for any leaks (near the upper phillips head screws, or the nipple).

Transfer Case wise they all seep. You could try switching to 85/140w vs 80/90w to see if that slows it down.

 

Did you notice if the coolant level started to rise once you unscrewed the expansion tank cap off? Even after a day the cooling system should have some pressure and release the cap will allow the coolant to flow back up into the tank. Also, for good measure make sure the cap is still good (if you hear hissing while the engine is warm, your cap is scrap). Cheap fix. I also have a leaky Tcase which is on the list of never ending items to address lol

 

I checked it at night and it depressurized rose back in, to about where I had it filled. Is it normal for it to take hours to do that?

 

I believe that is normal. To give you an example - I haven't driven or started my truck since Sunday but yesterday I opened the hood and saw that my coolant had dropped pretty low. Unscrewed the cap and before I could grab the coolant jug, the level came back up to where I filled up before the weekend.

It threw me off a few times as well and what I've come to realize is that some of the coolant will stay in the radiator/engine/hoses even after it depressurizes. when I first purchased my truck from Copart, I was chasing an overheating issue for sometime and when I finally figured out how to bleed the system correctly, I started marking where I filled the coolant. Useful if you think there is a leak.

Now when I go to fill it I always fill to the rim where the lower half and upper half of the expansion tank meet.

 

I wouldn't fill to the seam. That's a good way to wear out the seam and spring a leak. That's a weak point of the reservoir.

 

There is a cold fill level mark just below the seam that's visible on cleaner reservoirs.
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Exactly!

 

I should've clarified what I meant but yes, I agree as to not filling "to" the seam but just below it. With the new expansion tank it has been much easier to see where that fill level is.

 

I’ve always filled my D2’s to just above the fill line aka the seam and I have never blown out a reservoir. The pressure is the same regardless if it’s air or coolant.