have overheating issues?? Testing info - PeachParts Mercedes-Benz Forum

amosfella · #1 07-11-2010, 04:41 PM

Head gasket failure:

TYPES OF HEAD GASKET FAILURE

External Coolant Leak - Coolant leaks out along the edges of the gasket from an internal coolant passage. This is often the result of loose or broken head bolts.

Combustion Chamber to Coolant Leak - Combustion pressure forces its way past the armored skirt on the head gasket and into a coolant passage.

Combustion Chamber to Combustion Chamber Leak - Combustion pressure forces its way past the armored skirt on the head gasket and into an adjacent cylinder.

Oil Passage Leak - Oil leaks out along the edge of head gasket from an oil passage.

SYMPTOMS

External Coolant Leak - Coolant is visible leaking between the head and block.

Combustion Chamber to Coolant Leak
- White smoke in exhaust.
- Rapidly overheats.
- Emits coolant from spark plug holes during a compression check.
- CO (carbon monoxide) detectable in radiator.
- Spark plugs fouled with coolant.
- Oil contaminated with coolant.
Combustion Chamber to Combustion Chamber Leak
- Low compression in two adjacent cylinders.
- During a compression check, while one cylinder is on its compression stroke air is emitted from an adjacent cylinder and then drawn in during the intake stroke. This makes a very distinctive "whoosh-wheezing" sound.
- During a leak down check, air is emitted from an adjacent cylinder
HOW TO VERIFY THE PROBLEM
- Pressure check the cooling system and visibly inspect the block to head sealing surface for signs of coolant leakage.
- Remove all spark plugs and inspect for signs of coolant contamination.
- With all of the spark plugs removed, crank the engine with the starter for several revolutions. If a combustion chamber to coolant leak exists, coolant will be expelled from the associated cylinder.
WARNING: Keep clear of the engine compartment while performing this test. Coolant may be expelled from the spark plug holes with great force. Perform this test only with the engine cold.

- Perform a compression test of all cylinders while observing the radiator coolant level. Low compression on two adjacent cylinders or air bubbling out of the radiator during the compression check may indicate a head gasket problem.
- Inspect the oil for signs of coolant contamination.
- With light contamination, the oil will a light creamy coffee color.
- With heavy contamination the oil may appear thick and light tan in color.
- If the engine has sat for a while, the water and oil may have separated. While draining the oil, the coolant will drain out first, followed by the oil.
NOTE: Oil contaminated by coolant may also be caused by an intake manifold leak.
- Perform chemical combustion leak check. Any evidence of combustion gasses in the coolant indicates a head gasket leak.
- Perform cylinder leakage check.
Watch for bubbles in radiator (combustion chamber to coolant leak).
Listen for air in adjacent cylinder (combustion leak between cylinders).
NOTE: A cylinder leakage check utilizes regulated low pressure air to pressurize individual cylinders.

amosfella · #2 07-11-2010, 04:43 PM

STUCK THERMOSTAT
Stuck Open - The thermostat fails to fully close when the coolant temperature is below the opening point. This allows coolant flow through the radiator while the engine is cold and prolongs warm up. If the thermostat is stuck fully open, it may prevent the engine from reaching normal operating temperature.

Stuck Partially Open - Warms up slowly, runs warm or hot after warm up, especially in warm weather or under load.

Stuck Closed - The thermostat fails to open during engine warm-up. The engine warms up normally, however when the engine reaches normal operating temperature it overheats rapidly. All coolant flow to the radiator is blocked.

SYMPTOMS
Thermostat Stuck Open
- Engine temperature fails to reach, or requires an unusually long time to reach normal operating temperature.
- During cold weather the heater output temperature may not warm up.
- The upper radiator hose begins to warm up as soon as the engine is started.
NOTE: With a cold engine the upper hose should not begin to warm up until the engine has reached normal operating temperature and the thermostat has opened.

Thermostat Stuck Shut
- Engine temperature warms up normally but upon reaching normal operating temperature the engine overheats rapidly.
- If the radiator cap has been left off (for measuring coolant temperature) very hot coolant may be rapidly expelled from radiator with little or no warning.
WARNING: Never remove the radiator cap when the engine is warm. Severe personal injury may result.
- The upper radiator hose remains cool, even while the engine is overheating.
WARNING: Use a surface thermometer or infrared temperature gun to determine hose temperature. Do not attempt the feel the temperature by hand, this may result in serious personal injury.

VERIFYING THE PROBLEM
Remove and inspect the thermostat:
- Verify the thermostat is fully shut when removed from the vehicle, by holding the thermostat upwards towards a light, check that light is not visible between the seat and valve. If any light is visible the thermostat should be replaced.
- If the thermostat is not visibly damaged, place it in a pot of water and heat the water until it reaches the opening point. If the thermostat does not open at the required temperature it should be replaced.

amosfella · #3 07-11-2010, 04:43 PM

ELECTRIC COOLING FAN DOES NOT OPERATE

TYPES OF FAILURES
Bad Fan Control Circuits - The fan control circuits fail to energize the cooling fan when necessary. This may be the fault of either the coolant temperature switch or the cooling fan relay.

Power/Ground Circuit - A blown fuse or broken/shorted wire is preventing the fan from operating. A poor ground connection may reduce the performance of the cooling fan.

Bad Fan Motor - The fan motor fails to operate when both power and ground are applied. If this is suspected, always verify that an object has not become wedged between the fan blades and shroud, and is preventing the fan from rotating.

CAUTION: When checking the fan blades for free travel and spin, always disconnect the negative battery terminal to prevent personal injury.

SYMPTOMS
- Engine overheats at idle or low driving speeds.
- Engine does not overheat at cruising or highway speeds.
NOTE: With speeds in excess of 25 mph, sufficient air flow is forced across the radiator to cool the engine without the use of the cooling fan (under normal conditions without A/C operation).

VERIFYING THE PROBLEM
- With the engine cold, verify the radiator and expansion tank are properly filled, fill if necessary.
- Start the engine, warm up the cooling system and verify that the thermostat opens properly.
NOTE: Low coolant level or a stuck thermostat may prevent the electric cooling fan from operating properly.

- Continue to allow the engine to warm up, closely observing the cooling fan, engine temperature, and expansion tank. Check that the cooling fan energizes at the correct temperature.
CAUTION: Do not allow the engine to overheat. Turn off the engine before:
- Exceeding the normal operating temperature.
- Coolant expansion tank level exceeds the maximum.
QUICK CHECK OF COOLING FAN CIRCUIT
- Inspect:
- Cooling fan fuse.
- Cooling fan temperature switch and relay connections.
- Associated wiring.
- Verify the fan blades turn freely and smoothly.
CAUTION: When checking the fan blades for free travel and spin, always disconnect the negative battery terminal to prevent personal injury.

amosfella · #4 07-11-2010, 04:44 PM

INSUFFICIENT AIR FLOW, CAUSES
Fan Clutch Not Engaging - The fan clutch fails to engage, resulting in the fan clutch slipping on the water pump shaft.

Missing Radiator Shroud - The shroud direct air flow from the fan through the radiator. With the shroud missing air is drawn around the radiator rather than through it.

Missing Fan Blades - Results in reduce air flow and an unbalanced fan.

SYMPTOMS
- Excessive/constant electric cooling fan operation.
NOTE: The electric cooling fan is used to assist the belt driven fan during periods of high heat load.

- Engine warms up normally but gradually overheats.
- Cooling system overheats when idling or driving at low speeds, but may operate normally at cruising or highway speeds.
NOTE: With speeds in excess of 25 mph, sufficient air flow is forced across the radiator to cool the engine without the use of the cooling fan (under normal conditions).

- Cooling system overheats when under heavy engine loads.
- Very little air flow is felt flowing over the engine during hot idle.

amosfella · #5 07-11-2010, 04:46 PM

RADIATOR PROBLEMS

Plugged Radiator - Corrosion, sediment, or excess silicone sealant is blocking the flow of coolant through the radiator. Corrosion inside of the cooling tubes also insulates the coolant from the air flowing through the radiator and reduces the amount of cooling.

Leaking Radiator

Cooling Tube Damage - The cooling tubes have been physically damaged or severe corrosion has rusted through the tubes.
Water Box Seal Leak - The main seal between the water box and cooling fins is leaking. The cooling fins are crimped onto the water boxes, excessive pressure, temperature, or old age may cause these seals to leak.

CAUTION: When pressure testing a radiator, never exceed the rated pressure of the radiator cap. Exceeding this pressure may damage the water box seals.
Cracked Seams - Welded/soldered seams, usually around the inlet and outlet tubes, are cracked. These cracks are often the result of excessive force when removing radiator hoses or excessive hose clamp pressure.

SYMPTOMS

Plugged Radiator
- Engine gradually overheats under all conditions, regardless of driving speed.
- Coolant may show signs of heavy rust contamination, and there may have recently been problems with leaking freeze plugs.
Radiator Leaks
- Coolant visibly leaking from or around the radiator.
NOTE: The coolant leak may be very slight at first, and may require pressurization to become evident.

- Cold coolant expansion tank levels drops after every trip.
HOW TO VERIFY

Plugged Radiator
- Inspect the condition of the radiator coolant and if possible view the coolant passages through the radiator cap. If the radiator is plugged:
- The coolant may be heavily contaminated with rust.
- The coolant passages may be visibly blocked with corrosion, scale, or silicone sealant.
- Verify the operation of thermostat and cooling fan.
- Verify coolant hoses are not restricted or pinched.
- Check the difference in temperature between the upper hose and lower hose. If the radiator is plugged:
- The upper hose will become extremely hot while the lower hose will also become hot.
NOTE: There may still be a temperature difference (10- 20°) between the upper and lower radiator hoses because of the air flow across the radiator.

WARNING: Use a surface thermometer or infrared temperature gun to determine hose temperature. Do not attempt the feel the temperature by hand, this may result in serious personal injury.

- The upper hose may appear pressurized/hard while the lower hose may de-pressurized/soft (or in extreme cases may be sucked inwards)
NOTE: Plugged radiators may be flushed or rodded-out. Rodding-out a radiator involves removing water boxes and running a rod through the internal coolant passages to remove any built up corrosion or scale.

Radiator Leaks
- With the engine cold, verify the cooling system is filled with coolant and fill if necessary. Inspect the radiator for leaks.
- Using a pressure tester, pressurize the cooling system and inspect for leaks.
NOTE: If leaks are detected at or near the radiator hose connections, inspect the flanges closely for cracks.

If a coolant leak is found in the radiator, the radiator should be remove and repaired or replaced.

amosfella · #6 07-11-2010, 04:48 PM

Heater core problems
Leaking Heater Core - Leaks generally develop in one of two places:
Heater Hose Flanges - The tubing flanges to which the heater hoses are connected are soldered onto the heater core. When removing the hoses from the heater core excessive pressure may crack the solder joint, resulting in a leak.
Coolant tubes - Corrosion or an over pressure condition ruptures the tubing. CAUTION: When replacing heater hoses, always twist the hose loose prior to pulling the hose off. If the hose will not slide off easily it should be cut off. Plugged Heater Core - The coolant passages in the heater core are relatively small and may become easily blocked with corrosion, sediment, or silicone sealant.
SYMPTOMS

Leaking Heater Core
- Coolant is observed leaking from the vehicle near the back of the engine on the right hand side.
- The windshield is fogged up when the defroster is turned on.
- There is a distinctively sweet smell of coolant coming from the heater vents within the vehicle.
Plugged Heater Core - Heater will not produce warm air.

HOW TO VERIFY
Leaking Heater Core
- Pressurize the cooling system.
- Safely lift and support the vehicle. Examine the heater core drain tube for signs of coolant leakage.
NOTE: This is a small black tube coming out of the bottom of the fire wall in the engine compartment. This tube is designed to drain condensation from the A/C system and prevent leaking coolant from spilling onto the carpeting.

CAUTION: Do not confuse normal condensation leakage for coolant leakage.

- Examine the carpeting in front of the passengers seat for signs of coolant.
If coolant is found in either of the two places the heater core should be removed and inspected.

Plugged Heater Core

With The Engine Warm:
- Turn the heater on "HOT" and turn the fan on "HIGH" speed.
- Verify that there is a temperature difference between the two heater hoses. The inlet hose should be warmer than the outlet hose.
WARNING: Use a surface thermometer or infrared temperature gun to determine hose temperature. Do not attempt the feel the temperature by hand, this may result in serious personal injury.

With The Engine Cold:
- Verify the cooling system is full of coolant
- If a heater control valve is located in the coolant hoses, remove and test the valve prior to replacing the heater core.
- Test the heater core for restrictions:
- Remove the heater hoses from the heater core.
- Using regulated air pressure (less than 6 psi), blow air through the inlet to the heater core.
- If air does not pass freely, the core is plugged.

WARNING: Wear safety glasses and stand away from the heater core when performing this test. Coolant and sediment may be expelled with great force from the heater core outlet.

amosfella · #7 07-11-2010, 04:51 PM

DRIVE BELT PROBLEMS

Loose Belts - Belts which are tensioned too loosely will slip on the pulleys when a load is placed on them (Fan clutch engages, engine speed increases).

Belts Tensioned Too Tightly - Excessive drive belt tension will place pressure on the water pump seals and bearings. This may result in a premature failure of the water pump.

Incorrect Belt Routing - Drive belts may be incorrectly routed in a way that reduces the total contact area between the belt and pulley. This allows the water pump or fan pulley to slip although the belt may have been tightened to the correct tension.
Belts Aligned Incorrectly - The drive belt does not line up straight between the drive pulley and operating pulley. This may result in premature belt failure or belt squeal.
Incorrect Belt Type - The drive belt should fit properly, the width of the belt should match the width of the pulleys.

SYMPTOMS
Loose/Incorrectly Routed Belts
- Vehicle overheats under low speed (less than 25 mph) or high load conditions:
- High temperatures.
- A/C operation.
- Climbing long steep hills.
- Belt squeal (resulting from the belt slipping on the pulley).
Belt Tensioned Too Tightly
- Repetitive water pump failure.
- Repetitive drive belt failure.
Incorrect Belt Type / Belt Alignment
- Belt chirping.
- Premature belt wear (edges frayed).
HOW TO VERIFY
With the engine "OFF" and the ignition key removed
- Check drive belt tension. See: Engine\Drive Belt
NOTE: As a general rule you should not be able to turn the pulleys by hand, if the pulley rotates and the belt slips, the belt is too loose.

- Check drive belt condition. The belts should not be frayed or glazed.
NOTE: Glazed belts have a shiny/glassy appearance along the friction surface, resulting from belt slippage on the pulley. Once a belt is glazed it may tend to slip even with the correct belt tension applied. Glazed belts should be replaced.

- Check the pulley alignment. Pulleys which are out of alignment may be the result of:
- Improper parts installed.
- Worn bearings or bent brackets.
- Improper arrangement of washers or shims.
NOTE: If a component has recently been replaced, verify the installation is correct

amosfella · #8 07-11-2010, 04:52 PM

Leaking Water Pump - As a water pump ages, the seal and bearings begin to wear allowing for leakage around the shaft. Improperly installed gaskets may also be a source for leakage.

Eroded/Separated Impeller - Severe corrosion may cause one or more blades to become separated from the impeller. In extreme cases the entire impeller may become separated from the water pump shaft.

SYMPTOMS
Leaking Water Pump
- Coolant leaking from the shaft or from the inspection hole.
- A growling noise coming from the worn water pump bearings.
Eroded/Separated Impeller
- Engine overheats with no visible causes:
- Coolant is full, with no leaks.
- Cooling fan operates properly.
- Water pump belt is intact.
- Thermostat may operate properly (depending on the extent of damage to the impeller).
HOW TO VERIFY
Leaking Water Pump
- Pressurize the cooling system and inspect the shaft and inspection hole for coolant seepage.
- Start the engine and allow the cooling system to warm up to normal operating temperature. Stop the engine and reinspect the water pump for leakage.
NOTE: If the seals are just beginning to wear out the water pump may only leak while the engine is running and shaft is turning.
- With the engine stopped and the ignition key removed, check the water pump pulley for wobble. If any lateral movement is detected the pump should be replaced.
NOTE: Verify the pulley is securely fastened to the shaft prior to replacing.

Eroded/Separated Impeller
- Check and fill radiator if necessary.
- Verify no coolant hoses are kinked or obstructed.
- Verify the thermostat and cooling fan operation.
WARNING: Do not allow the engine to overheat.

NOTE: A plugged radiator and an eroded/separated water pump impeller will exhibit many of the same symptoms. If the radiator is plugged there may still be flow across the heater core while if the water pump impeller is eroded or separated neither the radiator or the heater core will have flow.

- With the engine running and warmed up to normal operating temperature, check for coolant flow through the radiator and heater core:
Heater Core:
- Turn the heater on (with temperature control to "HOT") and turn the fan to "HIGH" speed.
- If flow exists the inlet hose should be 15-20°warmer than the outlet hose.
- If no flow exists both hoses will be the same temperature.
Radiator
- With the cooling fan on and the thermostat open, compare the temperatures of the upper and lower radiator hoses.
- If flow exists the upper hose should be 15-20°warmer than the lower hose.
- If no flow exists both hoses will be the same temperature.
WARNING: Use a surface thermometer or infrared temperature gun to determine hose temperature. Do not attempt the feel the temperature by hand, this may result in serious personal injury.

amosfella · #9 07-11-2010, 04:53 PM

Diagnostic info came from alldata diy's diagmostic manual.