Water is coming out through the top of water reservoir tank. over heats obviously once it doesnt have water. We thought it could be the thermostat and changed it. Just bought it 157,000 according to previous owners, it was in perfect condition. Help there arent any mechanics who service landrovers in my area. Unless I drive 4 hours away which is impossible.

 

Deep breath, you'll get through this. Land Rovers are notorious for high temperature problems, for a variety of reasons. Don't drive it if it's overheating, the aluminum engine will not forgive you. The temp gauge in your dashboard is almost useless, anything above 9:00 is too hot.
The cap on the reservoir tank helps to keep the system pressurized. If you look at the underside, there is a plastic disk which is spring loaded and should move a little if you press on it. This could be your problem, and the good news is that it's an easy fix. The part isn't hard to find, your local auto parts store might even be able to order one.

 

98 1998 Land Rover Discovery Expansion Tank Cap - Cooling System - ALLMAKES 4X4 - PartsGeek

 

OK.

1. Is it a 99 D1 with underhood fuse box between battery and coolant jug, or a 99 D2 with fuse box beside coolant jug? As a crossover year, you will find parts easier to obtain if you add or subtract a year depending on model. The tail lights are higher on the D2 as well.

2. If a D1, the radiator will have a top mounted plug on the battery side. Usually made of plastic so it crumbles if you touch it.

3. The heat gauge in both trucks would be awarded the "worst POS design" by most owners. It stays in a "normal" range even when the engine is overheating. See pix below, note coolant temp and gauge position. The D2 is engineered to point at 50% from about 130 - 240F.

4. So if you are going by factory gauge, it won't be a fair fight. A scanner or OBDII code reader will show you exact temps. The Ultra Gauge at $70 is very popular.

5. Coolant loss can be for a variety of places:

A. Coolant cap is weak and won't hold pressure while driving, vents fluid on the road. A paper towel zip tied around the vent hose can confirm.

B. Leaks around any hose clamp.

C. Leaks out of odd gaskets, including head gasket, valley pan gasket, front cover gasket, water pump gasket, thermostat, and throttle body heater gasket.

D. Head gaskets can leak outside to air, inside to oil (makes it look like milkshake and higher than normal on the dip stick in bad cases), inside to combustion chambers (steam cleans plugs, makes white smoke out exhaust, makes gurgle noises under dash as bubbles flow thru the heater core).

E. External leaks can be found by renting/borrowing a coolant pressure test set from a parts store, it pugs into the coolant jug (be sure you have correct adapter), you pump up to 15 PSI (no more) and wait 30 minutes for leaks to show themselves, engine off.

F. Exhaust gas in coolant can be confirmed by a chemical test (about $50, does 15 tests), it smells the coolant and changes color. Exhaust gas is usually head gaskets and sometimes cracked block.

G. It is very common for new Disco owners to think they are OK because gauge has not swung to end of scale.

F. If you changed the thermostat, on a D1 it would go in this hole, the spring end fits inside the block. A 180F model is available, which is what I run because I don't live in the frozen North. A D2 has an external thermostat inside a big plastic chamber, you can also get a 180 model for those.

G. Your radiator can be clogged. Test with truck warmed up, engine off. Fins on radiator top to bottom should be within 10F. Lower horizontal rows clog first, so they read cooler. A D1 rad can be cleaned and rodded out by a shop, and D2 radiator is replace only.