Dark brown sludge


Noticed a lump of sludge at the bottom of the coolant tank. Did some research on the forums. Some ppl say this is a coolant mixing issue. Some say its a head gasket leak. Some say its casting sand. Some describe tan colored sludge. But this is dark brown. Dont know if this is a cooler rust issue or oil in coolant issue.

I cleaned the tank and drove it about 5k to see if it comes back and so far nothing. I also noticed my coolant level shrinks by about 2 inches every year. Dont know if thats normal.
Any thoughts would be much appreciated.

 

I did a full coolant flush on my 2013 wrangler back in November 2020. When doing so I noticed that same color sludge. I happen to be working on my Jeep again and noticed the same sludge in the reservoir.

When I bought the Jeep (used) I believe the dealership had the wrong type of coolant in it because it was a totally different collar. I went with my manual and got the Mopar brand coolant and did the flush. I’m assuming the sludge is from the mixing of different coolants. I’m probably going to flush it again soon with the same Mopar coolant from last time so hopefully it’ll be “free” of whatever residual coolant was there from when I bought it.

 

The sludge was dark brown(not the tan brown) with a burnt oil smell. The rubber gaskets on the oil filter cooler were gone and mixed oil and coolant. Dealer only changed the rubber gaskets and refused to change the oil filter cooler (since this was a warranty issue, they did the absolute minimum per JEEP instructions). sludge came back within a year and i was out of warranty.

I gave up thinking Jeep actually cares. So I bought a new oil filter cooler and installed it and the sludge never came back. Took me forever (I'm not mechanically inclined) but I did a better job than dealer (thank you youtube mechanics, no thanks to JEEP).

 

To the OP.. Good for YOU DIY....Thanks for the update... SAD that the dealership sucked on this matter...