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OBD2 coolant temp readings


NAXJA Forum User
Any of you using an OBD2 adapter to keep track of coolant temps? If so, what's the temp range that you see when she's all warmed up and pushed to the max (sitting in traffic, AC on, 90+ out)?

Mine fluctuates from 194-226 (max since replacing fan clutch is 232 but that was only once) most of the time it's at 210 or less but creeps up to 222-226 at stoplights in 95*F and direct sunshine on the hood. Nothing modified on the cooling side. New 195* thermostat, temp sensor, and radiator recently flushed. My dashboard gauge moves from the 2 in 210 to the 0 but doesn't really show the actual temp when it's at 222...if anyone were to look at it they would say it's 212...but the OBD2 output says different.

At what temp does the electric fan kick on?

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I have a obd 1 so I can't check my computer, but those temps are well within normal operation parameters. Xj gauges are notoriously unreliable though, I have a mechanical oil pressure gauge teed inline and both gauges rarely agree.
The coolant temp gauge value matches well with the OBD2 reading in my 2000 XJ. With a stock 195F thermostat, both the OBD2 reading and gauge sit at 210F during driving where the cooling system can work effectively, e.g., cruising down a flat highway at 65 mph. The efan kicks in at ~222F. If you're coolant temp rises much past 222F for any length of time, it might be time to start considering cooling system updates/mods.

The currently available replacement XJ fan clutches can vary significantly in their cooling performance. I started a thread on this about a week ago. The USMW fan clutch sold by Derale and also currently sold by Autozone under their Duralast label spins the mechanical fan much faster than the current NAPA/Oreilly/Advance Auto fan clutch. Also, the ZJ fan clutch (NAPA 272318) may spin the fan even faster than the USMW clutch.

There are differences in efan performance as well. The strongly curved blade fans with many blades (such as the TYC on Amazon) significantly outflow the straighter blade or straight blade efans with fewer blades (such as the the current offerings from Autozone, Dorman or NAPA).