Engine oil is getting in engine coolant and the resultant mixture is escaping though the radiator overflow container. The oil level on the dipstick drops significantly after a short drive. The GM dealer said it was the radiator, but after replacing the rad, the coolant-oil mixture is still escaping, and the oil level is down. There is no coolant evident in the oil - just oil in the coolant.

There can be numerous reasons for coolant loss.

External Coolant loss
1. Coolant escaping from the radiator cap. Replace the cap.

2. There is an external leak in the system which could be from a hole or crack in the radiator(especially the plastic sections) or a hole in a radiator hose or there is a loose hose connection.

3. The water pump gasket has deteriorated and coolant is escaping from around the water pump fitting.

4. There is a crack in the coolant overflow reservoir and coolant is leaking out.

Internal Coolant Loss
1. Coolant is escaping into the engine's cylinders in which event you will see white smoke coming out of the exhaust and you will also have combustion gasses leaking into the coolant passages which will cause bubbles and overheating of the coolant. This problem will be due to a failed cylinder head gasket, a crack in the cylinder head or both.

2. Coolant is escaping into the engine lubrication system and in that event you will see evidence of coolant in the engine oil. Pull the oil dipstick and check the condition of the oil. If it looks a bit like chocolate milk and not just normal oil colouring you have coolant in there. Also check the radiator cap when the engine is cold. There may also be evidence of oil in the radiator coolant that is stuck to the radiator cap and around the neck of the radiator.
This problem will also be due to a failed cylinder head gasket or a crack in the cylinder head or both.

Whatever the cause in your case don't hesitate to have it checked out by a competent professional If you lose coolant and you allow the level to run significantly lower than normal the engine will overheat and you will cause very expensive engine damage.

Sounds like one of the following problems:

Coolant problem.
Don't rely only on water in the radiator / expansion tank. You must have a mixture of water and coolant in the radiator. The coolant prevents the water from boiling.

The cooling system is pressurised and this means that water will boil much lower than 100 degrees Celsius.

Adding coolant reduces the water's ability to boil at the lower temperature.

Coolant is sometimes sold as Summer Coolant or Coolant and Antifreeze.

Thermostat problem
The thermostat is a mechanical valve that opens at a certain temperature. This allows the hot water in the engine to circulate to the radiator where it is cooled down and then returned to the engine.

If the thermostat is faulty, this valve does not open and the temperature will increase and cause damage to the engine.

Thermostatic Switch problem
The thermostatic switch is an electrical device that detects the high temperature of the coolant and activates the fan to draw cold air through the radiator.

When you are driving, cold air is normally forced across the radiator as the car moves along. If the car stops for long periods in heavy traffic or the car is parked but the engine is left to run, the cold air is not being forced through the radiator.

When the coolant reaches a certain temperature, the thermostatic switch activates the fan which draws air through the radiator to reduce the temperature of the coolant. This happens if you are stopped in traffic or even if you are driving along - it's about the temperature of the coolant and not whether you are stopped.

The switch may stop working and it needs to be replaced by a mechanic.

Circulation problem.
The water pump is driven by a drive belt which runs when the engine is working. If the engine has been used a lot and it has not had regular maintenance, the water pump can become worn.

1: The seal where the water pump axle goes into the pump housing can leak and coolant will be lost increasing temperature. The pump needs to be replaced and the coolant system refilled.

2: The impeller in the water pump forces the water around the cooling system. If this has worn out, the water pump needs to be replaced. I have seen a worn impeller. It was badly corroded because the correct mix of water and coolant had not been used.

Low Oil Level
Most people forget that oil also helps to reduce the temperature of the engine.

Oil reaches many part of the engine where the hardest work is done, like the bearings. The oil is then circulated around the engine where the coolant wicks away the heat in adjacent chambers. The coolant and the oil never actually meet,

The oil level should always be between the MIN and MAX marks on the dipstick.

Too little oil means the engine will wear out faster and it will not cool as efficiently.

Too much oil means an increase in oil pressure which could result in the gaskets being breached.

Oil levels should always be checked with the car or vehicle stationary on a flat surface. Grab tissues. Remove the dipstick and wipe it with the tissue. Replace the dipstick and wait for a few seconds. Remove the dipstick a second time and check the level

If the oil level is too low, make sure you get the correct oil for your vehicle. Some use oil, some use part synthetic oil and some use fully synthetic oil. Oils are graded for different types of engine. The grading is usually shown as 10W/40 or 15W/10 depending on your engine.

As a guide only, you really need to add a little at a time and check it, it takes almost a pint of oil (500ml) to raise the oil level from the MIN mark on the dipstick to the MAX mark.

Conclusion
An overheating engine is a big problem as it can lead to very expensive repairs. It is better to spend a little money and keep it working nicely than to save money and end up paying a lot of mechanic bills or buying another car.

Problems can include:
A blown head gasket - oil mixes with the water and coolant to create an emulsion that will make the car overheat faster.

A warped cylinder head - the overheating cause the cylinder head to warp and reduces the life of the engine.

Metal fragments in the engine as the metal expands beyond the engineering tolerances.

Looks like you have a leaking head gasket or cracked head. You can buy a head gasket leak detector kit that will let you know if there is CO2 gas escaping through the radiator. I think that it is this gas leak that makes it look like your radiator is boiling.

COOLANT-ADDING ADDITIONAL
Do not remove radiator cap to add coolant to system. When adding coolant to maintain correct level, do so at coolant reserve/overflow tank. Use a 50/50 mixture of ethylene glycol antifreeze containing Alugard 340-2 y and low mineral content water.
Remove radiator cap only for testing or when refilling system after service. Removing cap unnecessarily can cause loss of coolant and allow air to enter system, which produces corrosion.

COOLANT LEVEL CHECK
The cooling system is closed and designed to maintain coolant level to top of radiator.
WARNING: DO NOT OPEN RADIATOR DRAINCOCK WITH ENGINE RUNNING OR WHILE ENGINE IS HOT AND COOLING SYSTEM IS UNDER PRESSURE.
Remove radiator cap. The coolant level should be to top of radiator. If not, and if coolant level in coolant recovery bottle is at ADD mark, check for:

• An air leak in coolant reserve/overflow tank or its hose
• An air leak in radiator filler neck
• Leak in pressure cap seal to radiator filler neck

TRANSMISSION and OIL LEVEL CHECK TUBES


I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Add it to the clear plastic overflow tank. --- Underhood Check

Engine oil--Check the engine oil level.

Coolant--Check the radiator coolant level in the reservoir.

Battery-- Visually check battery cables and connections.

Automatic transmission--Check the fluid level.

Master cylinder--Check the fluid level.

Power Steering--Check the fluid level.

Windshield washer--Check the fluid level.

Belts & hoses--Visually check all belts and hoses for wear. NOTE: In addition to the items listed above there are cases with some manufacturer's where odd components such as manual transmission/transaxles and front differentials many be equipped with a dipstick found underhood for fluid level check. If you are unsure of a dipstick on your vehicle, check with the owners manual.

Oil in the coolant caused by blown head gasket or cracked head. This will also cause overheating. :o(

bad low coolant switch or still low on coolant.

Engine Cooling The cooling system components are the:

• engine coolant temperature sensor (ECT sensor) (12A648)
• radiator (8005)
• degas bottle (8A080)
• radiator draincock (8115)
• water pump (8501)
• water temperature indicator sender unit (10884)
• water thermostat (8575)
• dual speed fan motor assembly

The water pump circulates the coolant.
The water thermostat:

• controls the engine coolant temperature.
• allows quicker engine warm-up.

The degas bottle:

• provides a location for fill.
• contains coolant expansion and system pressurization.
• provides air separation during operation.
• replenishes the engine coolant to the system.

The fan motor (8C607):

• operates only when the ignition switch is in the RUN position.
• will not operate with the switch in the OFF position.

The engine coolant flows:

• from the lower radiator hose (8286) to the water pump.
• from the water pump to the engine block and the cylinder heads.

A closed water thermostat returns the engine coolant to the water pump; an open water thermostat allows the engine coolant to flow to the radiator.
Engine coolant provides freeze protection, boil protection, cooling efficiency and corrosion protection to the engine and cooling components. In order to obtain these protections, the engine coolant must be maintained at the correct concentration and fluid level in the degas bottle.
When adding engine coolant, use a 50/50 mixture of clean, drinkable water and engine coolant.
To maintain the integrity of the coolant and the cooling system:

When checking for a blown head gasket, one of the most common tell-tale signs is a milky-gray ring around your oil cap. When coolant enters the engine oil through a crack in the head or through a blown gasket, it evaportats and leaves a milky ring around the oil cap. Another easy way to tell is to check your oil dipstick. Change your oil and pull out the dipstick. Make sure that you take note of how far up the dipstick the oil is. Top off your cooling system and fill your cooling resevoir to the top. Screw radiator cap back on and start engine. Run engine for about 20-30 mins. or until it reaches normal operating temperature. Allow engine to cool (engine must cool completely to get accurate oil reading!!). Check oil dipstick again. If the oil has a watery appearence and has risen noticibly up the dipstick, the you probably have a blown head gasket or a warped head. Also look for a dripping, sweet-smelling liquid coming out of your tailpipe. Any of the above symptoms could be the result of a blown head gasket. The easiest way to tell is with a compression meter. This replaces the spark plug and lets you know what compression each cylander is running at. If your compression is abnormally low, then you have a blown head gasket or a warped head. (note: consult repair manual for appropriate compression of each cylander.)

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.

check the hoses, check the radiator, check the fan, fuse and relays, check the thermostat. check to make sure the head gasket is good, by check for oil and water mixture on the dipstick, same will appears brown