OK I did a search and found that this seems to be common in 4.0's. I had what I thought was a hole in my lower radiator hose today so I bought a new one and drained the coolant to change it and the old coolant that came out was solid brown. It looked it over and it didn't appear like their was any oil in the coolant it just seemed like a rusty sludge. I put my finger into the water neck of the radiator and scooped out a bunch of just brown sludge as well. I found out later that it was my water pump that was leaking and not the hose so I have a new water pump, serpentine belt, and radiator hoses. So here is where I am now. I have the new lower hose on and the system is full of water which is slowly leaking out right now over night. What steps should I take next? Should I go ahead and flush it several times with the old water pump on it or should I go ahead and install all of the new parts and then fill it with water several times and flush it? Also should I do a reverse flushing using the heater hose? Just looking for opinions for I do anything next.

 

rust in the system from sitting or oil in the system

 

No one have any advice?

 

flush it with the old water pump onn tell brown stops coming out then put the new water pump on

 

x 2. Use only DISTILLED water when you do the final filling with antifreeze (if you mix it yourself, or you could use a premixed 50/50 solution).

 

Same thing happened to my buddy's Jeep and here's what we did to fix it.

- separately clean out the old water pump, hoses, heater core hoses, thermostat, and the radiator until all you're getting is clean water from each of those.
- put all that stuff back on (seal the thermostat with the old gasket and blue rtv, saving the new gasket for the new thermostat) and do a regular flush. If you're still getting crud, flush it until you get clean water. you'll most likely get a leak from the thermostat but as long as it's not a big one you'll be okay.
- Once you're getting nothing but water, THEN put on the new stuff and fill it with either a 50/50 mix on your own (distilled water only) or a premixed antifreeze (Prestone or Peak).

make sure you replace your thermostat, gasket and use some blue rtv on it when you're doing all this. The crud probably got onto the old one and it'll go bad fast if it hasn't already. Another thing to consider is a new radiator. You'll never get ALL the junk out of it unless you really want to spend a full day doing a flush. It'd be a good opportunity to get a larger one to help keep everything cooler. It's not necessary, but just food for thought.

 

That is pretty much what I had planned to do but I am glad to hear that you have done it and had good success. Where did all of this brown sludge come from in the first place? Is it just part of the water jacket rusting into the coolant or something? I don't plan on going with a new radiator right now but I probably will get around to that in the summer sometime. This truck spent some time up north so just about everything in the engine compartment has rust on it. The power steering and transmission cooling lines are kind of worrying me a little so I plan to totally replace those when the weather gets a little bit warmer as well. Heck even the fuel rail is really rusty.

 

it looks like just rust which means is sat for a long time without running but if you flush it and it turns back into brown sludge you need to replace the head gasket its letting the oil leak into the coolant. smell the old coolant does it smell like oil or gas in it

 

if it looks like this you need a new headgasket

 

I have been working on vehicles for years and seen many blown head gaskets and never once did the coolant look like this. It was always much thicker and more noticeably oily. I checked my oil and it shows no signs of coolant in it either. After reading here on this forum there are tons of posts where others have had this same problem and it wasn't the head gasket so I am hoping that is the case. This seems to be a very common problem with 4.0's.

 

mine was brown flushed it nothing since

 

Thing is antifreeze is also anti-corrosion but some people don't realise this and stick plain water in the header tank just because its summer.

 

I flushed the system out 5 times today until the water was completely clear. I replaced the thermostat, water pump, hoses and serpentine belt and now everything is running good. I could not believe the amount of rust/brown sludge that was in the system. I talked to a guy at the local 4x4 shop and he said that every Jeep with a 4.0 he has ever owned was that way after 100k.

 

I've got 200,000 + on my '96, and it was never like that, or even close.

 

Well knock on wood, glad the xj I just bought didn't have none of that