Cooling system maintenance: what's next?

My '00 4.0 XJ started running a bit on the hot side this summer with highway temps right around 210 and idle temps about 220. So, I started with the easy stuff and recently flushed the system, installed a new 195 degree t-stat and refilled. The old coolant that I drained out was pretty nasty. While that did help, it's still not running as cool as I would like. Highway temps are registering about 198 on the gauge (which I'm happy with), but as soon as I get stuck in traffic, the temps goes back up to around 220. It will drop back down once I get moving, but it comes down very, very slowly.

I also made an attempt at cleaning the radiator by powerwashing from the engine-side, but I didn't get any significant amout of crap out, so I don't think there are any blockages in between it and the AC condenser.

To the best of my knowledge the radiator, fan clutch, hoses and water pump are all original and now have 150K on them.

This weekend, I am going to clean/degrease the engine. I have had a leaking valve cover for quite a while now and it's pretty dirty. I can't help but think the oil and grime on the engine woud insulate it somewhat from airflow.

So, I'm wondering what you guys think my next step should be? I've read about the ZJ fan clutch upgrade, but don't want to blindly throw "upgrade" parts at it without knowing the true source of the elevated temps.

Thanks.

The cooling system is just that, a system, which depends on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others and your cooling system will overheat.

Focus on the fan clutch and water pump. Preventative maintenance is always a good idea.

-Use a flushing/cleaning solution and then drain and fill the radiator with a fresh 50/50 coolant and water mix.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside.
-Replace the thermostat with a STANT brand 195*.
-Replace the radiator cap if your Jeep has one. An old worn out cap will allow boil overs as the coolant flashes to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. Looking OK and working OK is not the same thing.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.


Read more about cooling systems here - http://www.offroaders.com/tech/engine-overheating.htm

Thanks for all of the info. From what you stated below, and what is mentioned at the link, I think the engine degreasing and fan clutch will be my next steps, followed by the water pump, hoses and radiator if necessary.

I forgot to mention that I did replace the radiator cap when I did the initial service and the electric fan is working as it should. Hoses seem to be in good shape, but I will replace them if I need to do the water pump or radiator.

Thanks again!

Toss the fan clutch. Never seen one last 150,000 miles. While you are at it, get the best one, it is well worth the extra 5-$10. I got the Hayden / Emperial brand at Advanced Auto and love it.

Running hotter at idle is typical sign of fan clutch going bad.

You're not overheating yet. The efan shouldn't even turn on until 223 degrees.

winterbeater said:

You're not overheating yet. The efan shouldn't even turn on until 223 degrees.

Click to expand...

unless the AC is on... mine would kick on just above 210... when I had AC.

The efan is an automatic on when the AC switch is turned on, with the AC is off the efan is then controlled by the temp switch.

RTFM said:

The efan is an automatic on when the AC switch is turned on, with the AC is off the efan is then controlled by the temp switch.

Click to expand...

On 91-01 there is no temperature switch as such, rather a relay powered the computer. The computer turns the fan on all the time with AC on (if clutch is powered, the efan gets power), and when the computer senses about 220 F at the thermostat housing it turns the efan on via the same efan relay.

Ecomike said:

On 91-01 there is no temperature switch as such, rather a relay powered the computer. The computer turns the fan on all the time with AC on (if clutch is powered, the efan gets power), and when the computer senses about 220 F at the thermostat housing it turns the efan on via the same efan relay.

Click to expand...

Not on the later models. My '00 and I am not sure which other years but assume at least the '01 also, are activated through the computer (via relay) based on temperature sensor reading and refrigerant pressure reading. 223F or 300PSI.

#1 cause of "temp creep" at hot idle is the FAN CLUTCH.

150k on yours, get it out of there.

Ecomike said:

On 91-01 there is no temperature switch as such, rather a relay powered the computer. The computer turns the fan on all the time with AC on (if clutch is powered, the efan gets power), and when the computer senses about 220 F at the thermostat housing it turns the efan on via the same efan relay.

Click to expand...

OOOps Should have mentioned EARLY models.... as mine is an '89 I tend not to think of later years.....