Radiator flush and oil change interval questions

I have a '96 XJ 4.0 AW4 with 70k. I did a radiator flush and replaced the thermostat, housing, and hoses. I used a factory 195-degree thermostat. Now the average operating temp seems to be 180 - 195. Usually more towards 180, unless it's been running for a while. My temps before the flush were about 200 - 215. After idling for several minutes the temp gauge would creep up, and the auxiliary fan would kick on. Now after the flush it can idle for extended periods and the engine will stay cool, usually 195 or under. Last evening the Jeep was idling for about an hour and a half. It took 1 hour 20 minutes before the temp climbed high enough for the auxiliary fan to kick on.

What I am wondering is if I could have air trapped in the cooling system, possibly causing my temperature gauge to give me an inaccurate reading? I am worried that the Jeep may actually be getting hot while idling, just the temp gauge may not be reading correctly, so the fan wont kick on when actually needed.

Second question is how much gas would the average XJ use while idling for 1 hour?


I run Amsoil full synthetic 5W40 with an Amsoil filter. My Jeep sees about as much idle time as it does actual driving time, so this keeps me from really factoring in mileage when doing an oil change. Conservatively, how many hours should I run the oil before it would need to be changed?

Will continuous extended periods of idle cause harm or abnormal wear and tear?

Do a search on burping the system. Basically jeep in 'nose up' attitude, cap off, bottle of anti-freeze/distilled water mix, engine warm and running, thumb on throttle, keep adding till it's full then give the throttle a good rev and when the level drops in the neck dump more in and quickly close the cap. You can get air in there, especially if the thermostat does not have the little bleed hole in it's flange and is not at the 12 O'clock position in the housing. At that point the temp sensor is reading hot air trapped in the housing.

run the engine with cap off until warm and fill until full should be no problem with air, as far as oil change with what you are using you can go 10,000 miles between changes

dont worry about LOW false readings if there is air in teh system it will be hotter than the coolant, but it sounds like to me you have no problems

xjnation said:

dont worry about LOW false readings if there is air in teh system it will be hotter than the coolant, but it sounds like to me you have no problems

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Whew, that's a relief.

Can anyone help with the oil change interval? Like I said, the XJ sees just as much idle time as it does actual moving time.

Sounds to me like your XJ is cooling fine. I have only heard that it was the '90 and earlier 4.0s (with the closed cooling system) that needed to be burped.

I think I would change every 2500 miles in your case. No specific reason other than that is half of my normal 5000 mile interval.