What does it mean when I have brown sludge in my anti freeze reservoir in my 2001 grandam?

SOURCE: Brown sludge in water reservoir

i would guess that it's your head gasket, are you getting any creamy residue on the bottom of your oil cap too, may be worth having a compression test done on your engine first

SOURCE: 2001 grand cherokee anti freeze

First, DO NOT DRIVE YOUR VEHICLE OR RUN THE ENGINE AS LONG AS YOU HAVE THIS CONDITION!!! (exception:can be run 1-2 minutes... for short intervals while testing only). If you run/drive, you can cause severe damage to engine bearings.
1. If residue in radiator appears as semi-thick (like milk shake) light coffee colour, It indicates engine oil in cooling system. Major cause is a blown head gasket or cracked cylinder head. This condition usually is accompanied by an overly high oil level on dipstick and wet residue on inside of oil fill cap that is similar to what was found in radiator.
Testing includes pressure test of cooling system. Other symptoms are white smoke from exhaust pipe or coolant on one or more spark plugs (depending on severity or location of failure).
2. If residue is reddish in colour, it indicates a failure of transmission cooler coil within radiator. There is no safe test for this other than identification of contaminant and radiator replacement, including complete trans flush. This condition is far less common than head gasket problems.
3. There are two other coolant entry points to consider depending upon which engine you have: Coolant on any V8 or V6 engine can enter crankcase through intake manifold seals. Some engines use an intermediate housing between the water pump and engine which have passageways for coolant. Gasket failure can allow coolant entry into the engine at this point. (This is also rare but can happen if any bracket bolt that passes through the water pump and intermediate housing has been left loose during or after an alternator, or other accessory repair)
4. If no leak is found, if you just bought vehicle, find out if headgasket has just been changed It is possible that either residue from previous failure was not flushed from system, some type of block sealer was put into cooling system or if gasket was changed, perhaps condition was not corrected and still exists.(ie: gasket replaced but head was cracked or warped and not replaced).
In any case, this should not be ignored or dismissed!!!
Good luck!!!

SOURCE: Sludge in oil and losing anti freeze

Sounds like a blown head gasket, possibly cracked head if the engine was driven while this problem existed and got hot.

SOURCE: 1990 BMW 735i: oil in the coolant reservoir

If your car is an automatic there would be lines from the transmission to the rad to cool the transmision fluid. Over time the lines inside the rad have been known to corrode and start leaking. This would put oil in your coolant. You would be looking for small steel lines going in and out that would trace back to the transmission. Hope this helps.

SOURCE: My son's car overheated. Went to get some anti

The overheating is caused by the sludge. It is very easy to correct this problem. Remove the radiator cap and open the drain valve at the bottom of radiator. If possible, remove the reservoir and flush out with water. Make sure to get all sludge out of reservoir, then reinstall. Once the radiator stops draining, insert water hose (without nozzle) and turn water on. Keep the drain valve open. Run water through radiator until it runs clear. Once it runs clear, start the engine and let it run while keeping the water running through radiator. Allow engine to run until the thermostat opens up. Continue running water through radiator with engine running until the water from drain runs clear. Once you have done that, turn off the engine. Close the drain valve and refill radiator with proper mixture of coolant and water. Once radiator is filled, start engine and let circulate through engine. Coolant level will drop as the coolant starts circulating. Shut off engine and top off radiator. Fill the reservoir with the required amount of coolant. Testing the coolant at least once a year will help prevent this from happening again. Coolant should be replace a minimum of five years, less if coolant bottle specifies.