I was taking the jaguar to Maryland on a nice drive 64389 miles and the temperature was fluctuating quite a bit . I do have an Obd mini gauge installed on my dash to see real temperature. I recently changed the temp sensor. Any clues to why this is happening. Thanks.

 

After fully warmed up, what are the temps fluctuating to and from reading on your scanner? Both fans working properly? Debris in front of the radiators?
Seeing as it’s easy, maybe start with a thermostat and gasket change to see if it’s sticking?

 

I will check , temp sometimes going from 203 to 167 to 185 , 197. Fans were working. I will have to check thoroughly.

 

203*F (95*C) is roughly full operating temperature. I wouldn’t get concerned about overheating until about 210*F (99*C). At that time I’d turn the A/C off and heater on full blast. It certainly sounds like you have a sticking thermostat with the low temps going on at times.

 

Thanks I hope I make it back home

 

As long as it’s dry inside the coolant temperature sensor electrical connector and the expansion tank is completely full of coolant, it should be fine. Just continue to monitor the temps.
There’s either three T30 Torx screws or three 8mm bolts that hold the thermostat cover on. If you can park at a steep enough angle with the nose facing up, you might not even lose any coolant. 😂 Ford would probably have the thermostat and gasket in stock.

 

Thermostat is not fully open until 215F on 5.0 cars,

​​​your temperature range seems fine.

 

Seeing as these are 98’-03’ (USA spec) 4.0 V8 cars, these cars aren't used to those temps. 203*F (95*C) is what I see on mine even with the double capacity intercooler radiator and overdriven blower. However, if I lived in the mountains and it was 100*F+ outside, yes maybe it would get to that temperature if I was going uphill with cargo and the A/C on. Fortunately I don’t.

 

Thanks to all when I get home a new stat will be installed

 

We hope the new stat cured the temperature range fluctuations.

 

I haven’t changed it yet , local driving so far it’s been okay , but I am going to change it before a long drive again.

 

I just did 300 miles to/from the Shenandoah Valley. In the flatlands the temp was what I consider normal. Outside it was upper ‘80s. On the Skyline Drive the OAT was 70-72, and the gauge read one hashmark lower with the AC off. I’m guessing all is well with my beast.

 

When I took my trip it was high 90s. An auxiliary fan would be great to keep the engine cool.

 

I live close to a mountainous area, about six miles, and it's not a maybe; it's reality. We both have close to the same mods and when I head up the hill when it's over about 95F the car will overheat at around two-thirds of an 11 mile climb, depending on how much fun I'm having. Sometimes the tourists are in the way and sometimes they get out of the way 'cause the -100 looks like a cop car when coming up really fast from behind. I have the Jag Wrangler's ECT mod which really helps in monitoring the temp so I don't blow a head gasket.

 

Because the J.W. ECT mod is on there, it’s going to actually fluctuate like a real gauge should. What I would want to know is, what is the actual temp when it’s up 2/3? Do you have the alarm set once it reaches a certain temperature?

 

Yea, it fluctuates like a real gauge and it gets a good work out this time of year. The mod is pretty accurate; it starts at 125F, the middle is 185 and the top is 245. I've had the scanner plugged a few times and checked the temp on the live data vs the gauge and it's spot on at the 185 marker. I only had the live data on once when I was climbing the hill and the alarm went off at 236F. (The mod instructions say it's set to go off at 230, so ??) The gauge was just below the 7/8ths marker, so that seemed to be a good reading.

 

You are a braver man than I! I don’t think I’d go over 220*F (105*C). If I was in a difficult situation where it wasn’t safe to pull over on the highway, A/C button *off*, windows down and heater on full blast. 🥵🥵🥵

I remember when I worked at a GM dealer in the late 90’s. The engine tech that worked next to me was a grumpy old man named Kent (Him and Mel Brooks looked like brothers) but, him and I got along well. His daily was a Yugo! Anyways, just about every quad 4 that came in for him needed a head gasket, water pump or the whole engine replaced. The reason is that the cooling fan wouldn’t even come on until about 225*F when it was controlled by the ECM. He would raise hell…every…single…time… one came in and needed a head gasket, water pump or the whole engine. 😂😂😂 You should’ve seen him replacing a GMC Typhoon engine! You’d swear his head would jettison right off his shoulders!! Poor guy…
This is why I wouldn’t get my engine to that temp!