2002 Jeep Liberty 3.7l Overheats sludge in coolant resivoir

It will be a cold day in hell before I take this thing to a shop (and i’m broke broke broke). Professional help would be greatly appreciated.

It has 197k and change.
It’s not throwing any codes whatsoever.

I can drive it all day and it wont overheat as long as I keep it under 2000 rpm.
If I take it over 2000 rpm, it slowly heats up, but I can cool it down by slowing down. I can do like 50 mph max without it threatening to overheat. I’ve never let it get above 3/4 without pulling over and letting it cool off (I know how heads like to warp and crack).

Rubbery sludge in coolant resivoir (almost positive it’s oil) but absouluely NO coolant in the oil, there never has been. I do all the oil changes myself and check it quite often. I’ve been keeping the resivoir full but it loses coolant daily (no leaks on ground anywhere, ever. I’ve already removed the resivoir and cleaned it out severeal times, but since it has more than one chamber it’s almost impossible to fully clean without replacing. The hose that runs from the top chamber to the bottom blows off from time to time (I finally put hose clamps on it). I’ve flushed the cooling system several times but still the sludge comes back. I’ve removed and cleaned the thermostat (still good) and housing (had very little sludge). I flushed out the heater core but the heat is still weak.

Makes a loud whistling noise at idle, the noise literally stops everytime I give it gas. (this is where I was thinking Intake Manifold Gasket, maybe vacuum leak) You gotta love these plastic manfolds. BUT it’s idling low (650 rpm once fully warmed up) not bogging or sputtering whatsoever. Fans are working completely fine. It loses oil but again, no leaks on the ground whatsoever. I thought at first it was burning it (high milage, worn piston rings) until I noticed the coolant resivoir was gunked (wasn’t very long and I know I didn’t mix different kinds. I check everything (more than regularly) and it loses quite a bit of oil.

Before everyone says head gasket, it isn’t losing much power (if any at all), no white exhaust, and as mentioned before there’s no coolant in the oil.
Whatever it is, I can repair it myself but before I tear this thing a new one replacing gaskets and seals I’d like to be completely sure.

If you’ve had the same thing happen to you and/or you are positive what the problem is, your help would be amazing I will fly to your house and shake your hand because if it’s a head gasket this things going to the bottom of the river.


Immediately, my first thought was head gasket. It’s possible, although unlikely, it’s something else. You’d need to perform some pressure checks (compression, leak-down, listening for leaks in the cooling system and crankcase, chemical sniffer tests for figure out what’s mixing and where) and see what’s going on. Not having coolant mixed with the oil is interesting, but not conclusive. Not losing power isn’t conclusive, either. The HG (as you probably know) separates all of those system between the block and heads.

Not having all systems (oil, coolant, compression) mixing together isn’t uncommon. However, with the pressure build, it sounds like the water jacket is mixing with the compression gasses. Blow-by into the jacket will build that pressure, and pollute your coolant - leading to your “sludging” problem, excess pressure and your overflow line being blown off.

There are several people swapping the 2004 motor into the 2002 chassis. I can’t say how difficult that might be, or even if it’s worth it. Personally, I’m not a Jeep Liberty fan, so I’d just find another ride - but that’s me. I’m also not exactly a fan of the platform which apparently was designed by Fiat. I’m also not quite “broke, broke, broke”.

I’m sure you’ll get more opinions shortly.

Best of luck.

+1 to head gasket.
They can fail in several different ways and degrees of severity.