What is your normal coolant temperature on the 4.0?

I'd also recommend rebleeding the system just to be sure air didn't get in.
Flushed the system and installed new cap. ECT is maintaining 210 and below. Not boiling when turned off and at idle the highest ICT was 122.
 
I have a Scan Gauge connected to my Jeep. Before replacing factory radiator with new radiator (Mopar), Thermostat (Stant Super Stat), hoses, fan clutch, and doing a coolant flush I was seeing 225 -230 on my drive home with AC on in 100 to 105 temps from Auburn to Colfax on I80 , about a 1500' elevation gain in approximately 11 miles. If I sat in traffic at all it would heat up to 220+. After replacing everything but the water pump, I now see 207 to 209* pulling the grades with AC on and can sit in traffic with same temps. The new cooling system works very well. In the winter when going to work, I can watch the thermostat cycle open/closed by the readings on the Scan Gauge because of it being mostly downhill. Normal driving on flat ground I see 200 to 204 with AC on.
 
I have a Scan Gauge connected to my Jeep. Before replacing factory radiator with new radiator (Mopar), Thermostat (Stant Super Stat), hoses, fan clutch, and doing a coolant flush I was seeing 225 -230 on my drive home with AC on in 100 to 105 temps from Auburn to Colfax on I80 , about a 1500' elevation gain in approximately 11 miles. If I sat in traffic at all it would heat up to 220+. After replacing everything but the water pump, I now see 207 to 209* pulling the grades with AC on and can sit in traffic with same temps. The new cooling system works very well. In the winter when going to work, I can watch the thermostat cycle open/closed by the readings on the Scan Gauge because of it being mostly downhill. Normal driving on flat ground I see 200 to 204 with AC on.
You aren't really going to run into trouble until upwards of 260 when the coolant starts to boil. That's about where the light goes on and says pull over. It's great that you're happy with where it's running now but it's not a big deal either way.

I think that's the important message here, leaks bad, neglect bad, fluctuations ignore.
 
I just overhauled my coolant system and took a road trip this weekend. Prior to the OH, the light would come on in traffic and run hotter (always creeping to the right) than I like on the road. This trip, outside temp was 103, 20-30 gusting head wind, at 75mph for 200 miles with A/C on, she ran between the 1 and 0 on the 210 mark, For the most part now, it runs on the dot of 210. I would say your Jeep normal.
 
I picked one up today on lunch and will be trying that this evening.
Keep an eye on things for a while after you put the new cap on. When I bought my Jeep, it had an old radiator cap that wasn't holding pressure. I replaced the cap, and within a few weeks both the heater core and radiator had developed leaks. I'm absolutely certain they weren't leaking before because we did a pressure test when the new cap went in to be sure there weren't other problems.

These were all old parts that were ready to go. They had just been hanging on at the lower pressure and couldn't take it when the cooling system was running back at normal pressure. All good after replacing those parts, though.
 
Here is something I just ran into on my buddy's TJ. We replaced his entire cooling system. Fan clutch, hoses, pump, T-stat and radiator. We got a significant improvement, but it was still about 10° higher than I thought it should be at. My friend provided a bargain brand of coolant. We flushed that out and installed a good brand of coolant and BAM! Dropped the temp to normal instantly. Lesson learned...cheapskates pay twice.
 
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I was just thinking about this question. On the tail end of my last trip the 110 degree uphill climb in and out of Vegas was grueling. The engine sat somewhere around the 220-230 mark uphill. I guess it's time to put a Mopar radiator in. It currently has an AutoZone as that was all the little town had when my original one blew up.
 
I bought one of those fancy OBDII things for my iPhone to see where I'm really at. Cruising around town with the AC on at 79F, it stays at 203 - 208. Once I stop with the AC on, it will slowly climb and peak around 222. I was able to get my intake temperature to peak at around 197 while idling with the AC off.

Haven't tried it on the highway yet, but I'd suspect it gets to around 220 ish when driving at 80 with the AC on just judging by where the gauge is and comparing to the position when the temp is 220.

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Here is something I just ran into on my buddy's TJ. We replaced his entire cooling system. Fan clutch, hoses, pump, T-stat and radiator. We got a significant improvement, but it was still about 10° higher than I thought it should be at. My friend provided a bargain brand of coolant. We flushed that out and installed a good brand of coolant and BAM! Dropped the temp to normal instantly. Lesson learned...cheapskates pay twice.
Polypropylene glycol won't do the trick in a TJ, that might be what the cheap stuff was. You need the real hazardous waste, ethelene glycol in our cooling system.
 
I was just thinking about this question. On the tail end of my last trip the 110 degree uphill climb in and out of Vegas was grueling. The engine sat somewhere around the 220-230 mark uphill. I guess it's time to put a Mopar radiator in. It currently has an AutoZone as that was all the little town had when my original one blew up.
It probably won't make much difference. Just curious, was your fan really howling when the temps were high?
 
It probably won't make much difference. Just curious, was your fan really howling when the temps were high?
Not noticably higher than normal. Everything in the cooling system is younger than 10,000 except for the radiator. It's also a 32rh so freeway speeds it revs a bit higher than newer TJs with more gears
 
You guys make me jealous with your temperature readings. Mine always sits right on 210 unless I turn the AC on or start driving fast in the heat. Then it creeps up to maybe 220. Been doing that for years and can't figure out why. Maybe I need to flush the system out again. It never sits under 210 like I wish it would, even in the winter. Woes of a 230,000 mile engine I guess.
My gauge sits right below 210 all day but Im jealous your a/c still works... mine quit at 175k and I haven't fixed it (currently has 207k) When I did my water pump and i flushed my system around 150k I noticed my system running a little cooler that. Before and then I thought back and realized previously I had put in higher than 50/50 antifreeze before the flush. If your system is slightly more antifreeze than water maybe that's your problem.Especially if it's otherwise been running great for several years.
 
Which is exactly where it should be. 100% normal and good.

I was just about to come here and ask this type of question since all my previous vehicles stayed right at the same temp consistently, so I wanted to know if slight variations were normal. Mine hangs a tiny bit to the left of 210 in most conditions, but it goes a tiny bit to the right of 210 climbing hills, in hot weather or higher speeds. Glad to know that seems normal lol.
 
I bought one of those fancy OBDII things for my iPhone to see where I'm really at. Cruising around town with the AC on at 79F, it stays at 203 - 208. Once I stop with the AC on, it will slowly climb and peak around 222. I was able to get my intake temperature to peak at around 197 while idling with the AC off.

Haven't tried it on the highway yet, but I'd suspect it gets to around 220 ish when driving at 80 with the AC on just judging by where the gauge is and comparing to the position when the temp is 220.

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I'd be interested in seeing your fancy thing that works with your iPhone.
 
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After rebuilding the 4.0 recently, I've been watching the coolant temp, oil pressure, etc. like a hawk. The guages are OK, but the Torque app on my cell hooked up to an ELM327 bluetooth ODBII adapter really tells the tale.

Coolant temp is 203 - 206 driving in traffic with the air temps in the mid 80s.
 
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Did a trail run recently in 90F+ heat and had my eye on the OBDII readout. Coolant was at 205F all day. The only time it went up a degree or two was when I got back on the highway and turned on the AC.

Does anyone else notice that the engine fan sometimes kicks up more trail dust than the tires?