Ok so just a little background on whats going on here. I've been on these forums for 2 decades(lost original account pw)and have received tonnes of help from yall over that time especially from Jagv8, kr, jag genius(changed my window regulator for a small fee in real life when I was a rookie wrencher)and nbcat. In that time I've accumulated an 01 v6, 2002 v8(purchased in 04) and a 2003 v6. The 4.0 v8 is nearing a quarter million miles and its by far my favorite car I've owned and I've had plenty cars. Last summer I had a minor issue where the car overheated I shut it down fire er back up and all was well. Since then I've only really had time to drive it on weekends so not much stop and go traffic. Around Christmas I noticed a coolant leak which was followed by similar overheat issue. I decided to replace the water pump, heater hose(was fun), radiator(also fun), fan, ect sensor, thermostat and housing only to run into the same overheating issue. I'm willing to throw another 2 decade old fan at it but at this point I'm thinking its something shorting out because the fan spins extremely slow as Temps climb only for me to shut off the car and then it spins full speed. If I then start the car as the fan is in high speed it then stays in high speed for however long the engine is on. Very strange issue because after this shut down and restart the car is perfect and can idle in traffic fine. Haven't decided whether to install a secondary fan before the scorching heat of summer arrives or continue monitoring the Temps and when it gets close to 110°c, shut down wait 20sec restart and continue my cruise. Keep in mind the car is just a toy at this point (daily for 18yrs) the other two s types my sons drive. I have a caddy as my daily so the car running kinda funky isn't the end of the world. Any thoughts or insight would be appreciated also wouldn't mind installing a better temp guage if anyone out there has done that yet lmk.

 

The issue may be caused by a sticking thermostat, or a faulty coolant temp sensor. The ECM/PCM controls the cooling module fan speed.

The engine temp under normal conditions should range from ~88 C to 93 C.

 

Thanks for that info. I have three thermostats so I can try switching that again as well as 3 ect sensors I can try switching also. I’ve done a lot of testing and I’ve pretty much narrowed it down to this module on the fan shroud

or the pcm because at any speed above 40 mph temps stay in the mid to low 90s Celsius. Might look into an after market fan because when I send power direct to the fan it blows like a tornado. For now I may just add a small fan to compensate for when the puller is being lazy just for ***** and giggles. Also I’ll do some testing on the spare fan I have and see if there is a way to bypass it to always stay on full blast. At least until summer is over or until I can source a puller that can spin fast enough to keep er cool. Tbh I’m having too much fun tinkering away and it gives me a good excuse on the weekends to spend my time working on the ole beast mobile.

 

You could try one of these
universal radiator fan switches and a bog standard relay. They do them in different temperature ranges to suit your motor. Cut the wires to your original fan and connect them to your relay instead of the ECM. I did this last week to my Citroen. It works a charm.

 

Looks like a good idea except the issue i may face is that even if hot temps are reached the fan doesn’t necessarily want to kick into high speed. Honestly I may look for a setup that runs it full speed when the ignition is on or use a switch. Luckily the spare fan can be used to splice away and get it right so I don’t gotta keep yanking the thing out.

 

Before doing a bodge on the car, why not test the thermostat, and coolant temp sensor first?

The ECM/PCM may be receiving a bad signal from the coolant temperature sensor, or the thermostat is failing.

 

I have changed the thermostat(opened on stove) and ect sensor(beck and arney)a few times already. First I changed the ect sensor to a brand new one then I tried a new thermostat. Not that the old ones were even old. They were both only a few months old. Hence why I have three thermostats and three ect sensors. Definitely don’t mind swapping them again but starting to look like I cooked some wiring or a computer module. Or the used fan I got was on its last legs which kinda still means a module since it would be the fan module. The car is a tank is all I can say. It’s seen about 20 brutal Chicago winters and a few humid Orlando summers. I drove it during hurricane sandy and a number of other harsh weather events including some crazy downpours. If I have to install an aftermarket fan I will, if I fry the head gasket in the process so be it. However it gets parked in my garage when Im home but sometimes I ain’t home for a while.

 

Your standard fan will run at full speed if you take the power to it straight from a new relay instead of the ECM.

 

Yes this is the route I'll probably go. Will remove thermostat and boil it as well as change ect sensor one more time, just to make sure. My gut tells me sending power straight to the fan to make it run full speed is the route I'll have to go. Using the spare fan I'll test first. The car doesn't drive a whole lot so I'm not worried about burning through fans. Especially since they are only $50 at the wreckers out here.

 

Where's my 11-foot pole? Sometimes I wonder why I do this to myself...

Please elaborate exactly what you observed when you said the engine was overheating. Are you watching the temperature on a scanner and it climbed above the normal range? IIRC, that's 180-230F. What about the needle on the instrument cluster? Did it move to the right from the centered position? How about physical clues? Was steam venting from the cooling system cap? Any unusual noises such as knocking or hissing?

I'm asking all these questions to determine if you have an actual overheat condition, an indication problem, or even a combination of the two. The stock radiator fan in good working order will handle nearly any conceivable demand on the cooling system. Fitting an aux fan makes me cringe. That's like having a broken leg and deciding to permanently walk on crutches versus getting the bone fixed.

In your other thread, I strongly suggested getting yourself an infrared thermometer. I've seen no mention of having done so. Copy/paste from the other thread, and still applicable:

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.

End of copy/paste.

HF has a thoroughly adequate infrared thermometer for $25. Plenty of choices on Amazon, etc., if you'd rather not be seen shopping at HF.

The first time I ever saw one of those thermometers was roughly 1995, back when I still had hair. My car had an "overheating" problem and I threw more parts at it than you could imagine. My arms and back were aching from repeatedly loading the parts catapult (Pull!) in hopes of a fix. Radiator, thermostat (multiple), water pump, temp sender, and so on. The temp gauge showed normal 99% of the time, but when I worked the engine hard (such as accelerating up a freeway on-ramp) the needle would quickly move to the right. In desperation, I took the car to a radiator shop. The owner made a secret phone call, a flying saucer soon descended onto the parking lot, and an alien time traveler stepped bearing an infrared thermometer from the future. The alien took some readings of the cooling system temperature and immediately determined the indication system was misbehaving at the upper end of the normal range. He then got in his flying saucer and departed to points unknown. I stood there in awe. Okay, maybe it didn't happen exactly as I remember, but I replaced the factory gauge head and then all was good.

Now obviously replacing the Jaguar gauge will make no difference, as it is merely a repeater driven by a computer. But it is entirely possible for a temperature indicating system to misbehave in strange ways. Hence my questions about exactly what you're observing.

 

I'm watching the temp rise on an obd scanner. Maybe you missed my previous post. I mentioned this also in a different thread you responded to. So the car isn't your typical old lady driven vehicle. I purchased it in 2004 when I was 19 years old. It’s been all over the US and Canada, was t-boned by a drunk lady in 2012 (had to replace rear subframe)and has had its fair share of electrical gremlins. I don't exactly care to keep switching thermostats and ect sensors when I can blatantly see and hear the fan isn't spinning fast enough to cool a moped let alone a big ole quarter million mile v8.

 

Also as mentioned in a different post regarding heater hose, this winter I changed a bunch of worn parts including a blown up heater hose(would have changed the knock sensors but a theif smashed and grabbed em), radiator(leaking), fan(intermittent), thermostat, ect sensor, and water pump. The only thing still reoccurring is the fan isn't working full speed. I've narrowed it down to this. I know it seems like it could be alot of other things because this isn't a common issue but more then likely the used fan sender isn't switching from low to high or the pcm isn't telling it to run full speed. Strange thing is if I shut the car off and turn it back on it runs full speed. Yes I have a thermal gun but I haven't bothered using it as it probably won't make the fan start spinning faster lol. Also I get that you cringe at an aux fan, aftermarket or customized fan but I'm good with turning the car into a custom fabricated hot rod if I really get in the mood. To each there own. I'll probably just end up with an aftermarket fan or jump it to run full speed. I don't have a pic of it in this phone but it sits on 20'' wheels(second set), chrome mesh grille, suede headliner, visors & pillars, curtain in the back with a pioneer radio. Also a remote kill switch since auto theft has become rampant here. I'm hell bent on getting the thing to a quarter million miles. Will the car be recognizable by then ? Not sure

 

Okay, let us know what you find. We've still never established if you've got an actual overheat condition, an indication issue, or a combination of both. Pay attention to the low voltage condition, too, as it all seems to be related.

You seem to have a very unusual situation, with nobody here experiencing the same set of symptoms. You're in uncharted territory, so to speak. Keep us posted.

 

Indeed. I have resolved the low voltage issue. Looks like the remote kill switch was getting hot and loose like a lot of things around here lately and voltage was dipping. I think the cold weather and lack of diving the car in the last couple years has masked the issue for who knows how long. For sure when it’s real cold out and ram air goes through the rad temps stay down in the mid to low 90 degrees Celsius.. Now that I’m monitoring things it’s definitely the fan tripping up when it’s time to go from low to high. Thinking of painting a fan fin or two but even then I’d need a camera under the hood to see if what I suspect is taking place really is. It’s almost like as soon as the vehicle speed is reduced the fan speed slows. Might just throw another fan in there but honestly bypassing it to run full speed is mighty tempting. The 03 and 01 v6’s I own stay locked at 95c and 99celsius respectively. The steady spike in temps from the v8 when speeds are reduced or idle tells me it is definitely not an indicator issue. I know that v8 motor like the back of my hand and that fan isn’t getting to spinning fast enough when it should.

 

The following is offered in the kindest, gentlest manner possible. Picture Mr. Rogers lacing up his sneakers:

You may be your own worst enemy for getting to the root of the problem. I keep seeing attempts to make the clues fit a predetermined outcome.

My employer pays me good money to troubleshoot weird stuff like this. All conjecture on my part, but the vehicle speed may be immaterial with the climbing coolant temperature indication. It could be dependent on engine RPM. Could be something obscure like AC ripple from the alternator becoming more pronounced at low RPM and throwing off the indication you keep insisting is fine. Or maybe some other similar unusual factor is at play. (Edit) Forgot to mention the same odd power supply issue could also be simultaneously reducing power to the fan.

You have an infrared gun but insist it's pointless to even poke around with it. I have a high probability of being out in left field but experience (read: making mistakes) has taught me to revisit the basics when troubleshooting results don't make sense.

There's also a signal wire between the ECM and the fan controller. This would be well worth checking. A simple lack of continuity in this circuit could be the root cause.

Anybody else got anything? I'll be out back banging my head against a brick wall...

 

I hear ya about the thermal gun but it’s obvious that the engine is actually overheating. It feels 110 Celsius without me even opening the hood. I know the car well. Not exactly uncharted territory since I had a similar issue in 2010 and again 5 months ago. Both times throwing a new fan at er fixed it. This fan must have been shot too who knows. I get that you had a past experience where a thermal gun helped but I'll run the fan full speed and see if issue is resolved and let yall know. When Temps get close to 100celsius and I jump on the highway Temps immediately start dropping to low 90s as I mentioned before. Hopefully this weekend I can get it done.

 

Thanks. Worked like a charm. Will be putting lots of miles on er this weekend. Not sure I’ll ever know if it was the fan sending unit or the pcm but with it running at 92 Celsius and not a degree hotter it feels like a brand new engine. Makes me wonder how long the fan hasn’t been working properly and maybe the cold winter air mixed with a lack of driving it in stop and go traffic masked the low fan speed. Would obviously be nice to figure out exactly what got fried but with the beast mobile running this cool again I’m pretty stoked. Thanks again.

 

You’re welcome. I think sometimes manufacturers forget the KISS philosophy. Sometimes a simple replacement is easiest.