Beware of alternators purchased tfom the likes of Kragen/O'Reilly, Autozone, etc., as some will come with the wrong regulator module; this will leave you with a warning on that dash that will not go away. Denso has a factory exchange program which is fairly reasonable. I got my exchange unit from Autohaus AZ (Yes, I know it sounds German, but they deal in Jag spares as well as the Kraut stuff).

 

Step back from the ledge! Don't jump! Head gasket? Alternator? Thermostat? Prepare the parts catapult!

The preceding was industrial-strength humor to make an important point. Figure out what is actually happening before lobbing parts towards the car in hopes of a fix.

Is the engine truly overheating? Or is this simply an indication problem?

What's going on with the low voltage? Is this consistent now or intermittent?

Are the low voltage and high temperature still appearing together? On one hand, that would point towards an electrical issue affecting the temperature indication. But on the other hand, maybe the serpentine belt is slipping, and reducing the performance of both the alternator and water pump.

So many possibilities, It's hard to know where to start. Maybe establish a baseline temperature reading with an infrared thermometer. With the engine at normal operating temperature, maybe 200F on your scanner, take an infrared reading near the temperature sender or the radiator inlet. Say you read 185F there. That's your baseline, 185 at a certain spot equals 200 on your scanner. Now go for a test drive and try to duplicate the conditions where the scanner value goes up. Quickly hop out (stop the car first, in case I have to be specific) and point your spiffy infrared thermometer at the same spot as before. This should help determine if chasing an actual overheat problem or simply an indication issue.

And please oh please oh please resist the temptation to simply start changing parts for now. We don't need to introduce any new issues just yet, such as a new thermostat bad from stock, etc.

 

I hear ya and appreciate the replies. I have a new serpentine belt and thermostat handy so I'll throw those at it eventually regardless. The heat gun sounds like a good idea. Somehow I think its related to whatever caused the overheating 6 or 7 months ago which changing the fan resolved. One of these years I'll get to the bottom of it. Just pretty odd that it runs solid for an hour or two before the coolant temperature rises past 110°c(sorry scan tool is in Celsius)and not sure if it correlates with the voltage Dipping but the battery was replaced last summer.

 

Finally got some time this weekend to investigate this overheat issue on the v8 and it appears a mini 10 amp fuse has resolved it. Fuse 1 engine compartment controls aux water pump and air conditioner clutch which was blown. Didn't mean to hijack the thread but I'm also still getting low volts usually after a good hour drive. Belt seems tight so maybe I'll bring it to my alternator guy and have him check it out.

 

Please post back with what he discovers. The timeframe is really odd, and makes me think the fault is heat-related because it takes an hour to appear.

One thought is to check the battery temperature. If you haven't got one yet, splurge the $30 on an infrared thermometer. It doesn't have to be a fancy model. Even an El Cheapo brand will do.

After running a few minutes, measure the temperature of the battery as a baseline. Go for a long test drive and wait for the low voltage to reappear. Check the battery temperature again and see if it has climbed significantly. Just thinking out loud, but wondering if the battery is getting too warm and the internal plates are warping, or something odd like that.

Do the same for the alternator temperature, too.

 

Ok kinda going crazy trying to figure out why after changing the heater hose which split in half does this overheat issue suddenly come back. I have purchased a new fan last year which resolved the fan spinning extremely slow. Now for the life of me I cannot figure out how the hotter the coolant temp gets the slower the fan spins. Only once I shut the engine off does the fan start spinning faster. It's like the car is behaving backwards. The hotter the coolant temperature the slower the fan spins until of course I shut the engine off than it spins full speed. Somewhat similar to venkos issue except mine is a 02 v8. Wonder if it's related to the ac compressor/ aux pump fuse as the 10 amp keeps blowing. Completely stumped because i can drive 75mph on the highway for hours and the coolant is locked in the low 90 degrees Celsius range but soon as its stop and go temp starts rising.

 

Fixed it! Loose coolant temp wire. For now I’ve held it up with a zip tie. Going to run it more this weekend and see if the cracked connection was heating up and disconnecting the fan. Man it makes me want to put an extra fan in these cars. Someone even mentioned how brittle the plastics get after time. Thanks for all the help. Still need to sort the low voltage but I’ll get to that eventually.

 

Literally spit out my coffee laughing at this.

Love you Karl. <3

 

Starting to run out of patience with these fans. The ole 02 4.0 has once again started overheating. Tested everything 100 times with same result everytime. Car reaches 89°c and fan starts to spin extremely slow even once 115°c is reached still spins slowly. Shut car off at that point for obvious reasons and fan spins full speed. This is the only time it spins enough to pull air through the grille. Why when the engine is off does it decide to work? Might throw one more fan at it because i simply cannot let the car die out when its still such a fun car to drive, at least until it sits idle in stop and go traffic. Could it be that I bought a fan on its last legs?

 

Can anyone confirm if these 02 fans have three speeds ? Looks like its either running extremely extremely slow or medium speed and when I get er real hot and shut the car off it ramps up to fast as hell speed.

 

Hmm, I must have missed your mention of the model year. The OP started this thread about an '03, which has a totally different style of electric motor and controller.

Does your '02 look like this?





If so, more details here, including how to inspect and rebuild the motor:

https://www.jaguarforums.com/forum/s...repair-248595/


As you have considered, it's very possible your motor only operates properly when commanded to run at full speed. It may not be responding properly when lower speeds are commanded.

 

Yes this is the same fan. My 02 v8 and 01 v6 use the same fan. I wonder if I should take a chance and swap em. Third fan the car has seen in its lifetime and this one runs well one out of the three or four times I drive the car. I keep thinking I've fixed the issue by swapping out the ect sensor, relay or thermostat or securing some wiring but it just comes back. Might take a gamble and see what happens but I really don't wanna touch the 01 its pristine, low miles and would torture me if I break a connector or mess that fan up (decent ones are becoming rare). Also seems like refurbishing it is a little too much for me to handle might honestly set up an aftermarket fan. I'll test the one I replaced this one with. I also noticed the fan doesn't ramp up when I turn ac on either.

 

This cord is cracked and held with a zip tie so I'll probably change it. Don't wanna install it backwards since the replacement wire is different colors it’s using black and red and the car shows white and black but I think it can be wired either way right? Literally makes no sense that it’s the fan because when I shut the car off its spins fast for 5 min.

 

Hello again,
can anyone tell me in s-type '03 3.0 v6 if I start the engine and then disconnect the coolant temp sensor (located in the middle above the engine, below the throttle body) is the fan supposed to spin at full speed?
Cause when I do that on mine there is no reaction at all.

 

I have no idea what reaction you should see, if anything. You'd lose the computer input and display on the dash, of course, but that may be it. Strictly a guess, but the computer may default to a medium fan speed to compensate for the missing control input. Once again, I'm just thinking out loud.

But as far as isolating a problem with the fan? The results from disconnecting the sensor may not mean anything.