All of the coolant leaked out of my '94 Range Rover. After I refilled it, I noticed it all drained out (in about 5 minutes) where the engine meets the transmission directly underneath (housing area) the vehicle. Is there a freeze plug by the transmission? Help!?

 

Have a friend pour in water as you lay ontop of the engine and look for the leak, it is coming from the top and running down.
No freeze plugs on the back of the engine but it very well could be a head gasket at the back of the engine.

 

Intake gasket just as likely, best to pressure test with uv tracer dye in system to make certain it's not a leak from intake and head gasket (s). Did it ever get overheated???

 

I spoke to a mechanic. He said it's probably a head gasket. I'm working on it again this week. I just purchased it, so i don't know if it over heated. How hard is it to replace a head gasket or in intake gasket?

 

DIY headgaskets is a start Fri after work and finish it up on Sun. before the Simpsons.
Assuming you have all the parts and tools needed.
For a shop, drop it off Mon morning and pick it up Wed morning.
~$1500 at a indie shop, under $500 DIY.

 

I am a tech by trade and own a few Land Rovers. Yes, they have head gasket issues, shoulda had an extra set in the glovebox at delivery new!! They leak from every conceivable place and a few places you'd never guess. That being true, it's important to use a tracer dye to be certain where all the coolant leaks are. I've run across plenty of models with EXACTLY the same leak area and it was an intake gasket that failed. At 90k with good maintenance history, it's not at all surprising to replace head gaskets.
Its like everything else, if you have the right tools, the knowledge and time, it's not a big deal. I would push for quality and complete work over speed. Since the top end will be off, check very closely at the condition of the lifters-cam lobes-rocker arms (detailed inspection) also the heads should always go to the machine shop for a complete inspect and resurface. They will usually clean up the valve seats and put in new valve guide seals as needed. If the motor is a sludge collector, you will know as soon as valley is exposed and then I'd take itm further and drop pan to clean all components as much as possible. I run everything through a sonic cleaner as you can't get things any cleaner. It's the little details that separate a decent job from a pro job that you will appreciate. The engine overhaul manual is online as a PDF file and is Land Rover written. Read it a few times, really...
Return lifters, heads, pushrods to the same place they came, use composite gaskets, NEW head bolts as they are "stretch to yield" borrow a good torque wrench and be very cognizant of proper torque specs in the order they are given. Always run a tap down each hole to remove any imperfections that will throw off your torque readings. Be liberal with cam lube on the lifters and lobes (assuming the cam and all lifters are good) otherwise your project will get real big fast as youll be pulling the front block goodies as well to pull the cam. The only deviation that comes to mind is to ignore the LR assertion that gaskets go on dry! Only head gaskets, everything else will benefit from a gasket dressing. My rebuilds don't leak, land rovers do.... Enough said on that
Remember, this is a vintage 60's V8 pushrods motor, even the 04' Disco has the same basic block design. Thus, as with any pushrods motor, you should add cam lube with the oil at each oil change. That's because oil no longer has zinc for cam/lifter lubrication. The government took it out a few years back for clean air etc.
As a result, pushrods motors are prone to earlier cam/lifter wear. Most noticeably in motors with high lift and long duration like built hot rod motors, but to a lesser degree, all stock motors are vulnerable long term. Keep the oil changed and if you are using etheyne glycol coolant (green) then it's gotta be flushed every two years. There is no exception if you are intending to maximize system integrity. (that goes for all brake fluid as well-it's hygroscopic so attracts water) in simple terms it'll cause corrosion in brake components. Have a budget and plan to be down a vehicle if the unexpected is discovered. Mostly, if you move through the project thinking in aviation repair terms, you will do well. Aviation equates to check, double check and then check again. A failure on them is usually catastrophicm, difficult to "pull over" if something goes pear shaped on a test drive
PS. If you have a filthy engine internally and do the pan, remember to make certain the pickup screen is clean and also if you use non chlorinated brake clean you can wash out the valley with the lifters out and get 90% of the muck removed. Before you start teardown, do some common sense checks: what's the oil pressure hot at idle and at 2500 rpm using a gauge and same with engine at a cold start up. Do all the vehicle gauges and warning lights work? How about belts, hoses, tune up components and water pump from the underside?? What might you need to order in advance. Last thing... You can't be too clean, I treat every vehicle like it's in a semi sterile environment. Keep opened engine covered with plastic when not being worked on and clean clean clean everything well. It only takes a very little amount of contamination to ruin a motor in short order.
Have Fun.....