Revolution.comChevrolet Venture 2003. Pulled out thermostat, stil overheats. Coolants gets pushed out of system into reserve tank. Why. The water pump seems to work, how do you know if it does.

Sounds like a blown head gasket. That will push the water out of the engine, and get you exhaust instead.

Sounds like thermostat sticking. Be careful if the engine is running hot as you could crack a head!

Have a cylinder leakage test performed to check your head gasket. It dosn't have to overheat to have a head gasket problem. A leakage test checks if looseing combustion gases to the cooling system which would presurise the system higher than normal which causes the tank to overflow.

Does the vehicle overheat on the road? If it does and pushes big burps of coolant into the reserve tank then you could have a head gasket leak. Usually what happens with a head gasket leak is that the engine will often start and run normally but will soon start to push coolant out in a kind of foamy burp as the combustion gasses that accumulate in the engine block force their way out. You can have a small head gasket leak that allows combustion gasses to escape into the cooling system without getting coolant back into the engine and often the first symptoms of this kind of a leak is a motor that suddenly overheats, the heater quits blowing hot air and after a short while everything returns to normal for a day or so. As the leak worsens however it may keep pushing coolant out of the reserve tank with a cool or cold engine as the pressure builds to quickly for the reserve tank to handle it fully. Having said that if you have a perfectly good cooling system that is hot and take off the radiator cap it will spray blistering coolant coolant all over so never remove the cap from a warm or hot cooling system! Most additives won't stop a head gasket leak as there is just too much pressure for them to "stick" in the leak and they just get forced out of source of the leak. It's rare but you could have a water pump that's not circulating enough coolant around but usually you have different symptoms than this.

The line to the reserve tank to the radiator could be plugged up or you have a loose radiator cap or a bad seal causing the tank to hold whats in it. The coolant system is a pressurized system and if a seal is bad or a line is plugged you will experience this problem for the pressure is not there to take whats needed from the tank to deploy in the coolant system

did u bleed the air out of the cooling system? if not dop this procedure and recheck for problems.
The generic method of bleeding air from the cooling system is to use a floor jack and raise the front of the car as high as poss, then fill the coolant recovery tank full and run the engine until it just starts to overheat, high end of normal zone on gauge, then shut the engine down and run cold water over the radiator core, this will self bleed the system and the coolant will be pulled from the recovery tank, repeat as necessary, never let the recovery tank run dry or more air will be pulled into the cooling systeml , if it still overheats then you need to have the head gaskets checked with a gas analyzer for hydrocarbons present in the radiator or recovery tank

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.

When the car is completely cool,check the electric fan(s) for smooth rotation.

Clean/check/change the thermo sensor,contact and wire.

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Excavate air pocket in coolant system / check for head gasket leak

This test will kill two birds with one stone.

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MAKE SURE THE COOLANT SYSTEM and ENGINE IS COLD!

RAN THIS TEST IN A WELL VENTILATED AREA ONLY!

You will spill some coolant during this air pocket purge test.......BE KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!

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Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .

Top of the coolant reserve tank

Let it ran for 10-15 minutes.

Monitor for air pockets escaping from coolant reserve tank.

Small amount of bubbles is OK at 1-5 minute mark

After the thermostat open up (after 195 F warm up) at
5-12 minute mark or after high idle you should see less bubbles.

If you do not see any in rush of bubbles then your thermostat may be partially stuck or rusted badly inside the thermostat hosing.

Give the thermostat host few gentle taps.

If you see larger bubbles surfacing after 15 minutes then should do a hydrocarbon (HC) dye test to test for potential head gasket leak.

Let engine cold down and top off coolant reserve tank.

Start monitor for coolant lost

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A coolant flush is require every 2 years or 24,000 miles.

I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.

Make sure you get a new thermostat gasket,black RTV and fresh coolant for the job.

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Check the filter.... maybe something got sucked in...... also check that they Cyl Head Gasket is ok....

When the engine overheats, steam moves to the reserve tank to relieve pressure in the system, and can seem like it is overflowing.

Civic cooling systems always require an auxilliary fan or blower. Have this checked for serviceability. If the aux.fan is working properly, this points to other problems with your cooling system, which may include faulty hoses, water pump failure, and/or water temp. sensor failure.

Hope this helps.