I thought that the rule of thumb on stock Engine Tempurature vis-a'-vis the T-Stat setting was T-Stat plus 15 degrees F. Goes to explain the stock operating temp of 210F.
Per my '98 FSM (pg 7-8), the Aux Fan comes on at 103C (218F) and goes off at 98C (209F). The values are given as "approximate" as the senders are close, but not exact. Hence, the value hedging. The off value makes sense for the standard operating temperature of 210F.
My system has a 185 T-Stat (warms up a tad faster and promotes better flow to the heater core) and the electric pump controller has a setpoint of 90 degrees C (194F) and it calls for fan 3C above setpoint (199.4F). What I get is the engine oscillates (slowly, but it changes in town...) between 195F and 201F as reported by the PCM. I have verified that the PCM is reasonably close to accurate via IR temperature probe shot at the T-Stat housing where the factory temp sensor sits.
The Ford fan runs on low speed with the ignition on and powers up to high speed on command from the EWP-115. The Aux Fan is wired to have the stock power delivered through the NC contacts of a 40A relay and fused power from the battery through the NO contacts. The relay coil is wired to the the power lead for the Ford Fan. Once the engine gets to 93C, the controller calls for fan and both fans operate. Going this way preserved the operation of the Aux fan when the A/C runs.
I am concerned that with a 200F setpoint, the fan will not shut down as I do not believe the engine will cool to under 200F with a 195F T-Stat.
The coolest I saw was 7F above the T-Stat which makes 205F possibly the best off setting. But keep in mind I have a 115 Liter per minute electric water pump installed. The mechanical pump has had it's impellor removed...
For those wondering, as an experiment, I did change the setpoint on the controller to 85C (185F) to see where the engine temp would go. The engine ran at 193F... This is with a CSF three core radiator, 72"sq of hood vent and the aux trans cooler moved out from in front of the radiator. Moving the Zux Cooler out from in front dropped the average operating temperature by 5F.
The end result was unstable so I moved the setpoint back to 90C. The controller only allows 5C increment changes in setpoint.
Also, keep in mind our alternators do not have much in the way of cooling which is why I run the Ford on low all the time. There is also an issue with the A/C head pressure going high if insufficient air is moving across the condenser which can cause the compressor to short cycle.
All told, I spent the better part of 6 weeks Summer before last ironing out my system with consults from the fine folks at Davies-Craig, in Australia. $80.00 worth of phone calls on my end plus what they spent calling me. I was the first, to their knowledge, to install in an XJ and they needed all the data I could provide.
