I have a 2000 Jimmy. It appears to have black gunk in the engine coolant area (oil?). I am not sure what to do. Advise please.

Hi Dave You can google castrol for advise on recommended oils and coolant for your vehicle. I have always used 15/40 engine oil and green coolant from Holden. Hope this is of some help.
Good luck.

Dexcool, if you'r adding fluid- the pink stuff. If you're draining all out, recommend using the green stuf, normal coolant. Dexcool has been known to rust the radiator out over time.

blown head gasket --cracked head --or damaged engine block blue smoke is oil being burnt and the milky gunk is coolant/water mixing in with the oil

Coolant could be leaking above that point then trailing down. Check all the hoses and the overflow tank. Or try to follow the trail of coolant up from that point.
If your engine is running hot/overheating you could have bigger issues, check your oil and make sure it isn't creamy colored.
Also, it is a chysler, they are a HUGE pain, make sure you are using DEX cool (orange coolant) if you mixed the green in your car you will want to flush out the system and refill it (when you refill you can use either color but never mix the two, the two colors mixed will get gummy and cause your thermostat to stick, possibly gum up your pump and cause your car to overheat which can wreck your engine)

oil in the radiator is from a failed transmission oil cooler that is in the radiator tank. You will also have water in the transmission oil as when you shut off the engine the coolant pressure may enter the oil lines through the crack in the cooler.

Have the cooling system flushed and replace thermostat. For oil leak try some oil stop leak from auto store, they work on small leaks( will take a couple of days to work).

The reason you engine over heats is the engine cooling fan(s) are not coming on. They run by a coolant sensor and a fan relay.
You may also want to make sure you have the proper amount of coolant in your system.

Is your Jimmy a push button 4x4, or do you have to pull a lever to shift to 4x4 ?
Please let me know so I can help guide you through either of these repairs.
We aslo have the parts you need :
www.aescompaniesllc.com
click on the contact.

The passenger right side of the car doesn't have any flanges for cooling system, if that's correct then your radiator has a leak or puncture.

The driver side of vehicle has both the in and out flanges for the radiator. Very common to see leak at the drain valve leaking (not closed tightly). In the same area would be bottom flange of radiator which the composite flange is degrading and causing the leak.

The middle part of the bottom engine compartment is where your oil/coolant cooler assembly just above the oil filter. A loose oil filter could be the cause 95% of the time and 5% would be a bad o-ring from the oil cooler to the oil filter flange.

Flush the coolant system and replace with new antifreeze.

2 types of engine coolant one is green other is pink wrong one is used it changes color to black! witch one did you use? your vehicle may be faced with this I found 5 cars like this with this problem= wrong coolant installed!