Perhaps - one would have to test. Without any significant source of air over the primary radiator not much heat will be lost. The OP describes falling temperatures when moving and rising temperatures when stopped - classic symptoms of a dead fan clutch.

210 is in the middle of the gauge because it's in the middle of the actual operating range. There are a lot more temperatures in section 7 of my FSM than 160 and 218. For instance the electric fan turns off at 209. This is a pretty good indication of where normal operating temperature should be.

However, there is an actual section describing testing the fan clutch, note specifically steps 6 and 7 (page 7-18 to 7-19 of 1999 XJ FSM):

VISCOUS FAN DRIVE

TESTING

If the fan assembly free-wheels without drag (the fan blades will revolve more than five turns when spun by hand), replace the fan drive. This spin test must be performed when the engine is cool. For the following test, the cooling system must be in good condition. It also will ensure against excessively high coolant temperature.

WARNING: BE SURE THAT THERE IS ADEQUATE FAN BLADE CLEARANCE BEFORE DRILLING.

(1) Drill a 3.18-mm (1/8-in) diameter hole in the top center of the fan shroud.

(2) Obtain a dial thermometer with an 8 inch stem (or equivalent). It should have a range of -18°-to-105°C (0°-to-220° F). Insert thermometer through the hole in the shroud. Be sure that there is adequate clearance from the fan blades.

(3) Connect a tachometer and an engine ignition timing light (timing light is to be used as a strobe light).

(4) Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner condenser). Use tape at the top to secure the plastic and be sure that the air flow is blocked.

(5) Be sure that the air conditioner (if equipped) is turned off.

WARNING: USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN A DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE CLOTHING.

(6) Start the engine and operate at 2400 rpm. Within ten minutes the air temperature (indicated on the dial thermometer) should be up to 88° C (190° F). Fan drive engagement should have started to occur at between 74° to 82° C (165° to 180° F). Engagement is distinguishable by a definite increase in fan flow noise (roaring). The timing light also will indicate an increase in the speed of the fan.

(7) When the air temperature reaches 88° C (190° F), remove the plastic sheet. Fan drive disengagement should have started to occur at between 57° to 79° C (135° to 175° F). A definite decrease of fan flow noise (roaring) should be noticed. If not, replace the defective viscous fan drive unit.

 

Newspaper test is easier.

 

Agreed... but mad props for salad... ive never read how to actually test a fan clutch... i dont have an FSM
either though...

 

Yep, salad covered it all and very well as usual. I forgot about the 209 efan off temp but "fan off" is kind of a non-issue number. However, 210 is never mentioned/referenced, not in section 7 of the FSM nor any other section of the FSM. There is no reference in the FSM to any number being "normal operating temp".

Our experience has been that the XJ doesn't even come close to the 218 efan on temp this time of year nor will it turn on for the next several months for that matter. We do have the benefit of a digital ScanGauge to monitor coolant temp.

Again, IMHO, the OP has a wacked gauge or something in/with the cooling system is wacked if the gauge is correct at 210+, in 40* ambient, using a 180 stat, with the efan on and most likely the heater is on as well. If it's correctly displaying 210+ now, chances are it really will overheat in 6 months. There's plenty of time to replace the shroud and a new fan clutch can be installed in less time than it takes to read/perform the FSM test procedure.

 

Could it be the sensor just needs to be threaded in more? cause mine does the same thing, but I didn't thread it in that deep.. So I'm thinking the outside engine heat is messing with the reading

 

Outside/external heat is equal to or less than coolant heat because of radiation to the atmosphere.

 

Mmm well for whatever the reason the temp at the back of my block is at or below 230 while at the front out the thermostat housing is at or below 200