Does the coolant reservoir to overflow tank need to be full for 1996 jeep grand cherokee 6cyl 4.0l gas vin s laredo if it is empty will it cause radiator to over heat.

Hi. The PCM is located in the engine compartment, right rear corner, on firewall and behind the engine coolant overflow reservoir.

Pull the dip stick for the oil , its probably over full ! The reason is that you have a bad head gasket ! So water / coolant are mixed with the oil !

It has to be the float, may need recalabrated

Hi Tiffany,

The engine coolant does not "circulate" through the reservoir in your Jeep. This system works on the fact that things expand when they are hot and contract when they are cold. When the radiator is full, the coolant expands when the engine gets hot and the overflow runs down the small hose to the reservoir. When you shut the engine off, the coolant contracts and a vacuum is created inside the radiator causing fluid to be drawn out of the reservoir and into the radiator. When you start your engine and it gets hot, the cycle begins again.

If the radiator is empty, this sytem cannot work. There will not be enough vacuum generated in the radiator to draw the fluid from the reservoir (too much empty space and not enough coolant contracting as it cools).

You need to find out WHY the radiator is low. If it is low, there is a reason for it. Either something is leaking EXTERNALLY like a hose or water pump, or something is leaking INTERNALLY like a blown head gasket or a cracked cylinder head. Proper diagnosis is recommended.

The hose is an over flow drain. If you've seen no signs of leaks then most likely your radiator cap is bad. The cap helps to pressurize the cooling system, if it is bad it allows to much coolant out to the over flow tank and the extra is dumped while your driving. When you turn off your engine the fluid is drawn back into the radiator and your coolant mysteriously disappears.

the fuel tank capacity if it is a 6cyl. 4.0l then it should be about 20 gallons

Both the 4.0L and 4.7L engines use 195� thermostats for all model years from 1999-2004. When replacing a thermostat it is very important to install one with the same temperature rating (the only exception might be with certain performance modifications or chips that recommend or require a different temperature thermostat).

4.0L engine - Draining the cooling system WARNING: DO NOT REMOVE THE CYLINDER BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR DRAINCOCK WITH SYSTEM HOT AND UNDER PRESSURE. SERIOUS BURNS FROM COOLANT CAN OCCUR.

1. DO NOT remove radiator cap first. With engine cold, locate radiator draincock on the right lower side of radiator facing to rear of vehicle.
2. Attach one end of a hose to the draincock. Put the other end into a clean container. Open draincock and drain coolant from radiator. This will empty the coolant reserve/overflow tank. The coolant does not have to be removed from the tank unless the system is being refilled with a fresh mixture. When tank is empty, remove radiator cap and continue draining cooling system. To drain the engine block of coolant, remove the cylinder block drain plug, located on the side of cylinder block below the exhaust manifold.

4.0L engine - refilling the cooling system Coolant recommendations and cautions: The recommended mixture is 50/50 ethylene-glycol and low mineral content water. Never use pure antifreeze. Only Mopar Antifreeze Coolant, 5 Year/100,000 Mile Formula (glycol base coolant with corrosion inhibitors called HOAT) is recommended. This coolant offers the best engine cooling without corrosion when mixed with 50% distilled water. Antifreeze mixture must always be at least 44%, all climates year round. Maximum protection (-90d) is provided with a 68% mixture protection. If the percentage is lower than 44 percent, engine parts may be eroded by cavitation, and cooling system components may be severely damaged by corrosion. CAUTION: Mopar Antifreeze/Coolant, 5 Year/100,000 Mile Formula (MS-9769) may not be mixed with any other type of antifreeze. Mixing of coolants other than specified (non-HOAT or other HOAT), may result in engine damage that may not be covered under the new vehicle warranty, and decreased corrosion protection.

CAUTION: Do not use coolant additives that are claimed to improve engine cooling. 4.0L coolant capacity: 1999-2000: 13.0 qts. (including 2.3 qts. for resevoir) 2001-2004: 15.0 qts. (including 1 qt. for resevoir)

1. Tighten the radiator draincock and the cylinder block drain plug(s) (if removed).
2. Fill system using a 50/50 mixture of ethyleneglycol antifreeze and low mineral content water. Fill radiator to top and install radiator cap. Add sufficient coolant to the reserve/overflow tank to raise level to FULL mark.
3. With heater control unit in the HEAT position, operate engine with radiator cap in place.
4. After engine has reached normal operating temperature, shut engine off and allow it to cool. When engine is cooling down, coolant will be drawn into the radiator from the reserve/overflow tank.
5. Add coolant to reserve/overflow tank as necessary. Only add coolant to the reserve/overflow tank when the engine is cold. Coolant level in a warm engine will be higher due to thermal expansion. To purge the cooling system of all air, this heat up/cool down cycle (adding coolant to cold engine) must be performed three times. Add necessary coolant to raise tank level to the FULL mark after each cool down period.

For more details, you can refer to the Jeep WJ Service Manual Section-07-Cooling-System-Ewj7

Hope helped.

Fuel level sending units are known to go bad on these.

the alternater may need exciting try reving it pretty hard to excite it

the sending unit is more then likely a mess, take it back to where you bought it and demand they fix the problem