another overheating thread..

Okay guys im lost on this one.. 99 4.0l sport ax15 4x4 200300 miles stock ride height and gearing

I have replaced the following. Upper and lower hoses. Water pump. Thermostat super stant. Radiator cap (Stant). Radiator. Heater hoses. Thermostat housing. And a oem single core radiator.

I have flushed... Flushed again.. Flushed maybe three more times.. Oh and then i flushed it some more..

My problem is when on the highway my temp gauge creeps up slowly and will usually go beyond the first notch after the middle. This drives me insane. I put on average 75 to 100 miles on the rig every other day.. Im not burning coolant and my oil looks good. This has been going on for a while now. Should i really be worried about it creeping up to that line?
Also what should i be looking for? Any input helps.

Have you replaced the temperature sender?

Coolant temp sensor? And check with an IR thermometer to confirm that your temperature is actually what your gauge is showing. I went through the same scenario four years ago until I checked with the IR unit and found that the temperature actually wasn't creeping up past the 210* marker on the highway. Different for my 93 with the separate gauge sender but the same principle applies.

I verified it with an ir the readings are correct

what about the fan clutch?

In the city im fine. Its when im on the highway. Fan clutch works as it should. The thing is i don't want to upgrade to a dual core radiator when for 195000 miles a single core did its job.

My best guess would be a partially blocked exhaust, or exhaust leak blowing on the block (mine was leaking at the donut flange), and my daughters was a cracked exhaust header.

Is the transmission overheating, or slipping?

I have never seen a single core OEM radiator? Which radiator did you buy?

Is the belt tight?

50/50 coolant?

Ambient temperature? Is the high way drive up hill, mountains?

Check the O2 sensor signal with a high impedance volt meter, see if it is running lean? Check the fuel pressure too!

Plugs, wires, cap and rotor good? (timing....lean issue)

Have you tried OBD-II set up for live operating data with a laptop?

OHHH, and is the E-fan working when it should????

Ecomike said:

My best guess would be a partially blocked exhaust, or exhaust leak blowing on the block (mine was leaking at the donut flange), and my daughters was a cracked exhaust header.

Is the transmission overheating, or slipping?

I have never seen a single core OEM radiator? Which radiator did you buy?

Is the belt tight?

50/50 coolant?

Ambient temperature? Is the high way drive up hill, mountains?

Check the O2 sensor signal with a high impedance volt meter, see if it is running lean? Check the fuel pressure too!

Plugs, wires, cap and rotor good? (timing....lean issue)

Have you tried OBD-II set up for live operating data with a laptop?

OHHH, and is the E-fan working when it should????

Click to expand...

The exhaust bit is a good call. Im fixing on getting a new catback and a new cat. 200k on it i feel is enough for replacement

Its a manual tranny but its working fine hehe.

I used to work at a shop over the summer and was curious about it running lean and causing this but i had it hooked up to a snap on solus pro and all the senors were in spec and running normal. I average 21-22 on the highway at 75 ish so thats all pretty normal here.

I have an exhaust leak in my muffler but my header and exhaust flange all are nice and snug, with no leaks..

Its a spectra radiator purchased at autozone http://www.autozone.com/autozone/pa...dak?counter=0&itemIdentifier=517553_266534_0_

My efan and everything kicks on as it should I live in miami so my ac is always cranking this time of year hehe.

Ive ran preston coolant flush, 50/50 white vinegar for a week flushed this sucker with a garden hose so many times.

The radiator is a year old. Im fixing on getting a csf 2 row to see if this will fix my problem.

as for the cap rotor plugs n wires i havent dont those since i got the xj in 08 about 50k miles ago but the wires and plugs all look good to me

Scanners are great, but they do not see wire resistance between a sensor and the ECU, like 10 to 20 ohms. I still prefer to go directly to the O2 sensor with an old style high impedance analog meter to check what the O2 sensor is saying AT the sensor. Having a Renix jeep has trained me to not trust signals at the end of the data trails, LOL. A bad harness ground connection of just 10-20 ohms can play havoc with the what the ECU thinks is going on (especially with TPS, MAP and O2 sensor data. CTS and IAT are much less sensitive), and thus the scanner data can also be just as biased as the ECU data. If there is a wire or connector loss bias in the O2 sensor circuit it will show up as a lean or rich O2 sensor reading at the sensor (I forget which it is on the HO engines).

Has it been emissions tested recently? Any sign of lean conditions at all, like high NOx?

Sounds like a new Cat, PreCat may help, but also sounds a like a little better radiator, 2 row might be much more forgiving!!!! Especially in hot humid areas running the AC on the highway.

NO emmisions here in florida but I am going to take your advice. Im sure im due for a cat, and the xj is from ohio so my exhaust bangs around under the car a couple of the hangers a busted so Im gonna get a gibson catback and magnaflow cat. Also I think im going to just order a 2 row radiator. I dont want heat to be the end of this thing.. Its barely broken in.

Ill test it with an analog multimeter and see what i get.

Is the catback a pre cat? If so, I learned something new recently on the Pre-cat on my daughters Saturn. Turns out the precat helps pre heat the O2 sensor, instead of using a third 12 volt wire and internal electric heater in the O2 sensor on the 2001 Saturn. I am wondering if Jeep did that in the later models?

I think the ones with the California emissions package. I just have a normal manifold and one cat, one upstream one downstream O2.

Ecomike said:

My best guess would be a partially blocked exhaust, or exhaust leak blowing on the block (mine was leaking at the donut flange), and my daughters was a cracked exhaust header.

Click to expand...

Thanks so much for this post....my 2000 XJ has been overheating in heavy traffic and I have noticed a gradual loss in power over the last few months. As far as parts changed: Thermostat, water pump, CTS, radiator, hoses, cooling system flush. So on a whim today, I had the catalytic converter checked and it was beginning to go bad. HUGE difference in the exhaust note after changing...I have not driven it enough to evaluate power or cooling difference.