Question about 1990 BMW 5 Series
Visable contamination of coolent system brown substance in cooling waters.
No contamination of oil is visable when I check the oil level.
The brown sludge is what coolant looks like when it breaks down, this stuff usually accumulates in the coolant recovery tank, have a good professional flush done where the block is pressure flushed and wash out the recovery tank with hot water and detergent.
Posted on Dec 04, 2008
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Posted on Jan 02, 2017
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It appears that you have a minor leak at where a hose attaches to an engine or radiator pipe. When the engine is hot any leak will evaporate quickly and therefore not be seen. As the coolant heats up it will expand into the overflow tank but once the engine is stopped the extra heat build up will force the coolant out the leaking joint. As the engine cools, the leak prevents the coolant from being sucked back from the overflow tank.
The heater hoses and those pesky little bypass hoses in the cooling system tend to go hard and split if they are over 10 years old. Check all hoses and clamps for a good tight fit and replace any hoses that have gone hard or have become soft and stretched. Those spring type hose clamps tend to be less effective in clamping as the hoses age. Worm drive ones are the best to use.
If unsure take vehicle to a cooling system specialist and have them do a pressure test and more thorough diagnosis.
If problem persists, then it could indicate a problem with the head gasket (Usually caused by allowing engine to become excessively overheated when cooling system has run dry) allowing very hot high pressure combustion gases into the engine water jacket, which super heats the coolant in the engine block, which then boils off, and is released via the cap or any leaks. If the head gasket is really bad it will leak water into the cylinders and into the oil in the sump. This is indicated by an emulsion of water and oil mix on the dipstick. You will also see white smoke (water vapour) from the exhaust.
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There is a TSB for this problem. Here it is.
Bulletin No.: 04-06-02-007
Date: August 11, 2004
Low Engine Coolant Level Indicator Always On (Diagnose Low Coolant Level System Operation/Check Sensor for Oil Contamination)
2000-2002 Buick Century, Regal
2000-2001 Chevrolet Lumina
2000-2002 Chevrolet Impala, Monte Carlo
2000-2002 Pontiac Grand Prix
2000-2002 Oldsmobile Intrigue
Some customers may comment that the low engine coolant level
indicator is always illuminated.
The cause of this condition may be due to engine oil
contaminating the coolant. Possible sources of oil contamination are internal
engine leaks, improper service procedures, or the addition of some types of
anti-leak additives to the cooling system. Once in the coolant, the oil leaves
deposits on the level sensor creating an insulating film. This film results in
a false activation of the coolant level indicator.
Diagnose low coolant level system operation and check the sensor
for oil contamination using the procedure listed below.
Important: No coolant supplements should be used in GM cooling
systems, other than what is approved and recommended by GM. The use of
"aftermarket" over-the-counter sealing and cooling supplements may
affect the operation of the low coolant level sensor. Discoloration of the
coolant recovery bottle is normal and does not necessarily indicate that
coolant contamination is present. Flush cooling system only when instructed by
Verify that the coolant is at proper level in the radiator and
the coolant recovery bottle. If the coolant is low, add proper amount of 50/50
water and DEX-COOL(R) mixture. If the low coolant light operates properly,
diagnose the cooling system for loss of coolant as outlined in SI. DO NOT
proceed further with this bulletin.
2. Remove the low coolant level sensor. Refer to Coolant Level Module Replacement in the Engine Cooling sub-section.
3. With the key on, the engine off and the coolant level sensor disconnected from the vehicle wiring harness, observe the low coolant light:
^ Light is on - Chassis wiring or instrument cluster concern.
Follow the appropriate diagnostic information in SI.
^ Light is out - Proceed to Step 4.
4. With the key off, connect the coolant level sensor into the vehicle's wiring harness. Connect a ground wire (1) to the battery negative terminal. Using a sharp probe (3) attached to the ground wire, ground the coolant sensor probe (2) as shown in the illustration. Make sure a good contact is made. With the key on and the engine off, observe the low coolant light for at least 15 seconds.
^ Light is on - Replace the low coolant sensor and re-check
^ Light is out - Proceed to Step 5.
5. Using a small wire brush or emery cloth, polish the low coolant level sensor probe to remove any film or oxidation. The probe should be a bright brass color when finished. Use Brake Parts Cleaner to flush removed deposits from the low coolant sensor probe. Re-install the low coolant sensor into the vehicle and proceed to Step 6.
6. Flush the cooling system and install new DEX-COOL(R) mixture as outlined in the SI. Check the vehicle's warranty history to determine if any engine gasket had recently been changed. If there has not been a recent gasket replacement, locate and repair the source of the engine oil contamination.
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