My wife 98 discovery leaks coolant from the coolant reservoir cap and then overheats. When the truck gets to normal operating temp, it starts to boil the coolant and it comes out the cap as steam and coolant. Then the temp starts to raise. If she turns the heater on the truck it sometimes help with the heating problem. Any help with this issue is greatly appreciated.

Thanks.

 

You say the coolant starts to "boil" at NORMAL operation temp? That makes me wonder if the boiling your seeing is actually combustion gases coming through the cooling system. If it is combustion gases it will over pressureize your cooling system and try to push coolant through the cap. it will also cause overheating as the cooling system now cannot disapate the heat quick enough into the coolant from the gases. Does the steam from the reservior smell like exhaust partly?

Otherwise, try a new thermostat ( probably wouldn't hurt to replace it if it's older then a year ). Make sure your coolant level is at the little ( + ) mark inside the reservior when cold with all the air out of the system. Replace that cap! Still overheating? - When it gets hot, shut the engine off and feel the radiator for cold spots. Could be plugged.

 

If you think it might be combustion gases, there is a block test kit you can buy ( or borrow from someone ) that will show if the combustion gases are in the cooling system. If it shows positive for this, you may have blown head gaskets, dropped liner or ?
Hope this helps

 

Go to NAPA they sell a block tester for 50.00.
You fill a tube with blue fluid and place it into the coolant bottle inlet run the engine if the fluid turns yellow you have a blown head gasket, cracked head or cracked block

 

hey my 2003 disco has a coolant leak and loss of power and ruff ride. what are some potential reasons for this? what should i look for?

 

Coolant leaks can occur anywhere in the cooling system. Nine out of ten times, coolant leaks are easy to find because the coolant can be seen dripping, spraying, seeping or bubbling from the leaky component. Open the hood and visually inspect the engine and cooling system for any sign of liquid leaking from the engine, radiator or hoses. The color of the coolant may be green, orange or yellow depending on the type of antifreeze in the system. The most common places where coolant may be leaking are:
Water pump -- A bad shaft seal will allow coolant to dribble out of the vent hole just under the water pump pulley shaft. If the water pump is a two-piece unit with a backing plate, the gasket between the housing and back cover may be leaking. The gasket or o-ring that seals the pump to the engine front cover on cover-mounted water pumps can also leak coolant. Look for stains, discoloration or liquid coolant on the outside of the water pump or engine.
Radiator -- Radiators can develop leaks around upper or loser hose connections as a result of vibration. The seams where the core is mated to the end tanks is another place where leaks frequently develop, especially on aluminum radiators with plastic end tanks. On copper/brass radiators, leaks typically occur where the cooling tubes in the core are connected or soldered to the core headers. The core itself is also vulnerable to stone damage. Internal corrosion caused by old coolant that has never been changed can also eat through the metal in the radiator, causing it to leak.
Most cooling systems today are designed to operate at 8 to 14 psi. If the radiator can't hold pressure, your engine will overheat and lose coolant.
INTERNAL COOLANT LEAKS
There are the worst kind of coolant leaks for two reasons. One is that they are impossible to see because they are hidden inside the engine. The other is that internal coolant leaks can be very expensive to repair.

Bad head gasket --Internal coolant leaks are most often due to a bad head gasket. The head gasket may leak coolant into a cylinder, or into the crankcase. Coolant leaks into the crankcase dilute the oil and can damage the bearings in your engine. A head gasket leaking coolant into a cylinder can foul the spark plug, and create a lot of white smoke in the exhaust. Adding sealer to the cooling system may plug the leak if it is not too bad, but eventually the head gasket will have to be replaced.
If you suspect a head gasket leak, have the cooling system pressure tested. If it fails to hold pressure, there is an internal leak. A "block tester" can also be used to diagnose a leaky head gasket. This device draws air from the cooling system into a chamber that contains a special blue colored leak detection liquid. Combustion gases will react with the liquid and cause it to change color from blue to green if the head gasket is leaking.
Head gasket failures are often the result of engine overheating (which may have occurred because of a coolant leak elsewhere in the cooling system, a bad thermostat, or an electric cooling fan not working). When the engine overheats, thermal expansion can crush and damage portions of the head gasket. This damaged areas may then start to leak combustion pressure and/or coolant.

REFILLING THE COOLING SYSTEM
When refilling the cooling system after making a repair, always use a 50/50 mixture of antifreeze and water. Never use straight water because it has no freezing protection, no corrosion protection and it boils at a lower temperature (212 degrees F.) than a mixture of antifreeze and water (which protects to 240 degrees F.).
On some late model front-wheel drive cars, refilling the cooling system can be tricky unless you "burp" the system by opening a bleeder vent or cracking a hose at a high point in the system to allow trapped air to escape. If you do not get all of the air out, the engine may overheat the first time you drive it.
The best way to refill the system is to add coolant until the radiator is within an inch of being full. Also add coolant to the coolant reservoir, filling it to the proper level. If the system has a pressurized coolant reservoir, add coolant until the level inside the reservoir is at the COLD FULL mark. Start the engine and let it idle with the radiator or coolant reservoir cap off until the thermostat opens and coolant starts to circulate through the engine. The heater should also be on so coolant will flow through the heater core. As the coolant level drops, continue to add coolant until the system takes no more. Then replace the radiator cap and drive a short distance. Shut the engine off, and after it has cooled recheck the coolant level once again. If low, add as needed.

 

The above posting is a great general rule for most things automotive. But speaking from experience, refer to earlier postings. With the Land rover V8, a "boiling over" reservoir at normal operating temps is not the engine overheated but combustion gases pressurizing the system ( which then can lead to overheating ). In the Land Rover v8 this usually is the result of a dropped liner or possibley a really, really bad head gaskets. Usually the head gasket leaks more externaly then internally unless there has been a head bolt or severly overheating issue. Liners are for the most part robust, but there has been a few that can just drop out of place. Overheating kills these engines.