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Hello all!

I've recently replaced my water pump, and I was wondering what is normal operating temperature range on 4.0L Jeeps? I have celsius temp gauge, and most of the time it's one line below half ( it's around 85 degrees celsius~=185F. I have 195F tstat in Jeep. When I'm on 7-10% incline, temp would rise near half mark- 100C (210F). 
Jeep has 32rh automatic with 33 inch tires. Before I installed those tires temp would always stay near that 185 mark - one line below half mark. Water pump, tstat, radiator - all new. Air burped out of cooling system.
Only thing that comes to my mind is strain from bigger tires and fact that now engine runs on lower rpms than before, which makes water pump and fan turn slower.

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zidodcigalah...185-degrees F would be the minimum to run; the EFI/MPI system needs a full warm-up to come off its enrichment cycle.  The Mopar MPI conversion kit recommends use of the OEM 195-degree F thermostact that you are running.

Given the added load of the 33" tires without an axle ratio change, warming to 210-degrees F would be likely on these grades.  You could suspect other things like the engine speed decrease (your thought) or a fan clutch issue, but the 185 degree F operating temp under most circumstances is very acceptable/desirable.  Your Jeep likely suffers from the 33" tires and stock gearing.

When I set up the '99 XJ 4.0L with a long-arm lift and 33" tires, I changed the original ring-and-pinion gears to 4.10 ratio from 3.55 OEM.  The 3.55 OEM gears were actually "tall" to start with, and if I had it to do again, 4.56 would have been smart.  I added weight with the ARB front bumper, Warn rear bumper/tire carrier, bigger tires and spare tire, etc.  Gearing is now the equivalent of "stock", in fact I did not need to change the speedometer pinion, the speedometer is right on with the original speedo driven gear.

And yes, my engine will creep from 195-F to around 205-F when under load at higher ambient temperatures.  The OE electric fan helps considerably, but your Wrangler does not have one like the XJ.  You do have a nicely sized mechanical fan and shroud, though, and if the fan clutch works properly (check it), you should be okay.  If you can stand the noise, a heavy duty aftermarket fan clutch will often keep temps lower when the engine is under load or temps run high outside.

210-degrees F makes us wary but will not hurt your iron block-and-head Jeep 4.0L engine.  Also check the ohms reading at the CTS, these sensors can be off and give a false gauge reading.  If you have a surface infrared tester, try that at the thermostat housing to see whether the housing temp closely matches the CTS signal and gauge reading.

Moses

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Thank you Moses. Right now I have opposite problem. I've put in new brand new thermostat today, 195F rated. Everything is in place as it should be and now water temp won't rise above first quarter mark (that is about 70C deg). I think it's not stuck open because water is cold inside radiator until temp rise to that mark.

I know there is CTS in tstat housing, and another sending unit in the back of the engine - but I'm not sure if they are to blame because i used to get higher readings with old thermostat in it. Old tstat is stock, seems like it was never replaced before.

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I tested resistance from CTS and temp sending unit  -

CTS: 1008 ohm steady (guess when tstat is steadily opened, it goes lower and then higher until it finally reaches 1008 ohms)
TSU: 272-275 ohm depends where second probe is grounded

From some resistance tables I've found on the internet, 1008 is somewhere between 80 and 90 C (175 and 194 F). Would this be normal even if tstat is rated at 195F?
For TSU I have only found some tables but they don't say that its for temperature sending unit. 270 ohm would be around 87-88 C. 
All the time temp gauge shows around 70-75 C, it reads lower.

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zidodcigalah...The thermostat is a mechanical device and independent of the CTS or any electronic/electrical functions.  CTS ohms should be consistent with the actual coolant temperature.  That is why I suggested measuring the thermostat housing temperature—close to the coolant temp sensor.  Compare the real coolant temperature to the CTS and gauge reading;  see whether the sensor and gauge are accurate for the coolant temperature.

An infrared "no contact" surface temperature test is very helpful here.  I use a NAPA infrared thermometer that cost about $80 a decade ago.  There are inexpensive non-contact infrared thermometers available from Harbor Freight and elsewhere.  These surface tests can confirm local overheating and help you trace the flow of coolant as the thermostat opens.  Thermometers like this can be inaccurate on rubber surfaces, so check heat at metal points when possible.  

If the gauge is accurate and if your Jeep's cooling system is full and "burped", with no sign of low coolant (overflow reservoir filled to the correct line and radiator full when cold), the low temperature reading is likely a thermostat issue.  This could be:  1) a defective or upside down thermostat, 2) a stuck open thermostat, 3) a thermostat that is cocked or for some reason allows coolant to bypass when below opening temperature, or 4) a lack of circulating coolant at the thermostat area/housing.

Also, I'm sure you're aware that the water pump for an XJ Cherokee and the Wrangler are different, they rotate in opposite directions.  When you installed the new pump, was the impeller facing in the correct direction?  This could affect coolant circulation.  At the least, confirm from the part number that you have a Wrangler 4.0L pump and not the reverse rotation pump for an XJ Cherokee.

Moses

 

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I'm aware that thermostat is completely mechanical device. I tested resistance on CTS and temperature sending unit (that little one at the back of the engine) for another reason - if they both read similar temperature - then probably its thermostat problem because its not that likely that they both failed at the same time. From ohm readings I got, they both read around 87-88 degrees celsius so I guess its inaccurate temp gauge that is giving me problems.

Anyway, I will try with another new thermostat and check if there are improvements. If not then I guess its inaccurate temp gauge or bad temperature sending unit.

As for the water pump, I checked impeller orientation. They are both in same direction, even the water pump I have removed had stamped "R" mark on impeller and housing. Part number shows that this water pump fits both XJ but with 2.5 engine and YJ from 1991 to 1995 with 2.5 or 4.0.  

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Gauge is inaccurate, but I'm not sure yet if it is something wrong with a gauge or with sending unit. I can't see how gauge can fail. Yet, temp sending unit Ohm readings are just as they should be.

Seems that my old stock thermostat (that probably came with a vehicle from factory) was bad and was opening late or not opening completely, and since gauge shows smaller readings than real, that confused me because even though engine was running a bit hot gauge needle was just where it should be. 

New thermostat I bought from Crown was opening a bit soon, so engine wouldn't reach recommended operating temp (195f).

I took Motorcraft fail-safe 195F thermostat, and even though I still have inaccurate gauge readings, engine warms up to operating temp. I know this because I hooked PCM to Snap On MT2500 and CTS reads 90-91 degrees Celsius (equals to 195F), while gauge reads about 176F. I will try first with new sending unit, and if that doesn't help, then the gauge is to blame.
 

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Good diagnostics!  I've seen errors with aftermarket senders.  My XJ Cherokee 4.0L runs right at thermostat temperature (195-F) yet reads 5-degrees higher with an offshore aftermarket sender from AutoZone.  I've changed thermostats, no change.  The OEM sender read right at 195-F.  (The original sender had a minor seepage leak, or I would still have it in place.)  I should have stayed with an OEM or Mopar sender.

Let us know if another sender is the fix...

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