I have a 2001 Cherokee 4.0 with about 188k on it. Just changed the oil today and noticed this orange/brown, gritty sludge built up under my radiator cap. All the coolant seems to be leaked out from both the radiator and the coolant reserve. I Thought I had fixed this problem about 8 months ago with a coolant and radiator flush but I guess not. Any experience or ideas on what the root problem is and how to fix it? Thanks!

 

It's Rust from a neglected cooling system. You may have to flush the entire several more time to start clearing it up also make sure that you use a 50/50 water to antifreeze mix

 

when is the last time you replaced you radiator cap? If its been a while i would start there after flush.

 

I'd be concerned about this. You should start with a comprehensive search for a coolant leak. Get under the engine with a good light and a warm engine and see if you can find one.

If you can't find a leak, it's very possible that you have a cracked cylinder head. The head from the factory on the 00-01 has a casting defect between cylinders 3-4.

You're either leaking coolant or burning it. Your job is to find out which.

Commit this sentence to your memory. The #1 symptom of a cracked 0331 head is "unexplained coolant loss".

 

This can be many things. What does the peanut-buttery substance feel like? Oily, greasy? Gritty like rust? It looks like oil mixed in with coolant to me, and if so, you very likely have head gasket failure, or a cracked cylinder head.

If you're using something other than OEM-spec G-05 coolant, this could account for the rusty vomitage. I've seen this sort of thing when Death-Cool, er, Dex-Cool was used.

First things first, as already mentioned: find the source of the leak. If not exernal, it's time to do a compression check to see if the head gasket or a cracked head is to blame, and move on it. Don't just flush/fill and ignore this one.

 

On this one the sludge in the radiator is goofy gives you more things to check. though on these the trans fluid runs through the radiator and if on of those lines breaks loose it will do this same thing. Id say compression test if all is well hell check your trans fluid is it way over full is brown too you may just need a new radiator and flush the trans fluid.

 

Coolant in an automatic transmission is quick death.

 

when coolant gets low or if there is a leak air will get introduced into the system and rust will form....especially with the "any make,any model" OAT or HOAT (G-05) coolants. These long life coolants are great ONLY if you maintain your system. Once these organic coolants form this brown mud they turn into a highly corrosive liquid that will eat radiators,hoses,water pumps,head gaskets, thermostat housing. Flush,flush, and flush.

 

Thanks everyone, some good tips. The radiator supposedly had just been replaced and was brand new when I bought the jeep in 2010. There was definitely no sludge in it though. I have never replaced the cap, but if it's a bad seal it sounds like it could be letting air in and be a factor in the problem. When I flushed it last summer i had them do a pressure test and they couldn't find any leaks, which I was a little skeptical of because I had the same problem then that I do now, just with a lot less sludge. I kept my eye on it for a couple months after the flush and it seemed to have fixed it. Surprise, surprise I also have a solid oil leak and it looks like it's been that way for the last 80,000 miles or so. I've been told buy a mechanic were I work that I need to replace the radiator, flush the system and flush the transmission be because he thought coolant was getting into the trans (such as has been suggested here) but that was his guess without looking at it or seeing this picture. I've also been told its because oil is leaking into the coolant system, but that will be more expensive to fix so I will probably start with the radiator and then see if I have to address any gaskets and such. Thanks again!

 

When you rub the rust ops i mean sludge between your fingers is it gritty. if so its rust. if its slick its oil! I would look into radiator hoses with built in wire coil support. i had this happen once coils rusted out creating rust foam in radiator check hoses for coils inside. its an easy start.

 

I think you need to start by figuring out where your coolant is going. You need to determine the root cause of this.

As I mentioned in an earlier post, it's either leaking or burning it. You mention that your radiator and coolant reservoir were almost empty; you have a major issue here.

Sure the sludge is a concern, but that could be related to a cracked cylinder head.

Don't ignore this very real possibility. It is not that uncommon with the 2000-2001. If you can't find a leak, then either perform a cylinder leakdown test or pull the valve cover and look for a crack between cylinders 3-4 with a pressurized cooling system.

Search for lots of light reading on the 0331 cylinder head. Knowledge is power here.

 

Was that pic taken after the rad was drained or was it taken after only removing the rad cap?

 

Since you suspect it's leaking, disconnect your trans cooler lines, put a cooling pressure tester on there and pump it up.
If you see coolant seeping from the trans cooler fittings on the radiator, that's a big problem. Get the trans fluid changed ASAP, then do it several times again with 50 or so miles between.
If the trans cooler holds but you still lose pressure, I'd start checking the head.

 

It has been a while but I wanted to provide an update on what I have done an found so far for anyone who is having the same problem and reads this later on.

The sludge was definitely rust and not oil or tranny fluid mixing with the coolant. As I found out in this process, the engine block is cast iron and therefore, prone to the possibility of Rust. So I had the radiator replaced and did the thermostat at the same time. I also had radiator lines and cooling system flushed . This helped for a little while and definitely helped with the sludge. However, still was experiencing a loss of coolant. So I had a pressure test done and it was leaking from the water pump. Replaced this myself with the help of a buddy (neither one of us has almost any mechanical experience, tools or expertise, so it's definitely something you can do yourself. Although, being first timers it took us jut shy of 7 hours from start to finish with a full system flush, so be prepared to spend a Saturday doing it) and discovered what I believe to be a main source of the problem. The blades of the fan inside the pump were shredded off completely. So much so that I picked a piece of the pump out from inside the engine block. I also noticed that the fan appeared to have been scraping into the inside of the engine block as there was and indentation in the metal that had been warn/scraped down. This spot lined perfect up with the original water pump blades. New water pump and thermostat now with a flushed out engine block, so we will see if it's fixed. Loud/squeaky serpentine belt when I turn on the AC though... Maybe to to tight or loose?

 

I'd suggest on a weekly basis, when the motor is cold, remove the rad cap and inspect not only for coolant level, but also color. The crud in that 1st pic didn't happen overnight.....far from it.

At the 1st sign of coolant changing color/getting cloudy, remove the bottom rad hose from the water pump and drain coolant into a pan/bucket (for disposal). Re-attach the bottom hose and re-fill with fresh 50/50 coolant......takes 15-20 mins and $15-$20 to do this. No flush needed, but again, just drain and refill at the 1st sign of coolant changing color. Doing it this way will keep coolant looking green/clean and most important, providing 100% protection. Read/do my sig.