As matt0091 suggested, it sure seems like these cars don't like to sit. For the first 5,000 miles I owned mine not a single problem. After sitting for about six months (for no particular reason) it seems everything is on the verge of failure!

After some repairs and four days of pretty intense driving (see my emissions thread...) everything seemed a-ok. Then, yesterday on the way home in 110 degree weather I looked down at the temp gauge just in time to see it rise pretty dramatically and flick on the red over temperature light. Good times.

A brief moment of panic and a choice: Shut it down and back up traffic or use the open road in front of me and ease it up to speed and stay there for a little bit. I did the latter, and within less than a quarter mile the light was out and the temp had dropped significantly. I took a couple small roads that don't have stops to get to my place and I shut it down and popped the hood.

The scanner showed 246 degrees at the ECT (OUCH) but the cooling system was holding, just a normal burp into the overflow tank. What was not happening was anything from the fans. Gee, shock. I know factually they were working the day before as they ran after I parked, but you can't hear them with the engine running so I have no knowledge of them running since.

Turns out one of the fan fuses had blown - I think 12 but maybe 14. Doesn't matter. Put a new fuse in it, fan started right up, all good. I came back several hours later (ambient temp = 100 degrees, engine temp = 200 degrees) and started it up just to see if it was okay. Sure seemed like it. Slept better.

This morning at 9a (82 degrees ambient, FML) I drove it to work watching the ECT and everything seemed fine. Held 180-190 most of the way, crept up to 205 after a freeway drive and a long stop at an intersection. It does not appear anything was damaged and that now everything is working. I checked the fuses again after parking, still good.

TL;DR, any guesses on whether my blown fuse is just a random occurrence or a symptom of a greater problem with the fans or fan control module? Do those things typically fail? The situation makes me pretty nervous - I have a number of older cars (30-50 years old) and as such I am not one of those never looks at the gauge types. Old cars don't stay running if you don't pay attention. There isn't a lot of time between "all good" and "too hot" as reported by the Jag's gauge (stupid lying gauges!) and not really any good indicator of the fans behaving themselves.

I am considering investing in WhiteXKR's gauge modification, but I really, really don't want to put any more money into this car right now. I really need to justify its existence with more miles before it gets more of the car budget. Maybe a better short term fix would be a small LED powered by the fan 12v run to the cabin... I wouldn't know if the fan was actually running, but I'd know if the fan system was working. Maybe a ScanGauge or something temporarily, til faith is restored?

 

I use an OBD II reader and leave it plugged in all the time. Need to hit enter three times and it begins to read data real time once the engine is running.

actron cp 9575 was cheap and did the trick. But there are also apps for smart phones, I read somewhere.

You might also clean the line connectors at the fans and check for frayed wires that caused the fuse to blow.

 

I am going to clean the grounds and the connectors this weekend for sure, although being a California car it's very abnormal to find anything wrong there. It's about the only thing I can think to do short of waiting it to have another issue. Honestly, I don't remember the last time a fuse in a car popped, so while as much as I'd like to believe it was a fluke, I'm more inclined to believe it is symptomatic of a greater problem.

For monitoring the coolant temp - which doesn't really change my actual problem - I think the options on the table are:

1. $60 Ultragauge that reads OBD2 data, but is kind of ugly and a dumb shape
2. $150 Scangauge that reads OBD2 data, and is quite compact and nice looking
3. $15-$60 smartphone solution, and I have at least a few spare iPhones I can dedicate to the purpose. This is tempting if I can talk myself into wiring up connectivity for music playback.
4. Plenty of way more expensive solutions from Innovate, PLX, etc.
5. Realgauge, which falls into the middle price-wise and is by far and away the most convenient, attractive solution.


Anyone have any other tools I've overlooked?


Edit:


6. $60 PLX Kiwi MPG - Only displays seven OBD2 parameters, but one of them is coolant temp. Quite compact!

 

My only guess is a lazy fan motor, after sitting for 6 months then called into action it or they blew the fuse. Nice to see it's a simple fix, can understand the mild panic when the temp light pegs.... I had a crank pulley problem last summer in similar conditions and had thoughts of valves seats dropping out - they can do that on these engines if cooked!

 

It could very well be just that, although the fact that it worked for days before failing gives me pause. It could be the fuse got stressed from the first few times and then failed when pushed I suppose, but who knows? The fans rotate smoothly and are quiet when spinning - I've definitely had way worse behavior from engine cooling fans!

I have looked at the wiring diagrams and do not see where the fuses come into play - are they between the battery and the fan relay (control module, whatever you want to call it) or between the fan and the relay? The former seems less likely - but the diagrams don't seem to call out fuse locations for this system. I'm wondering if maybe the relay is what's having an issue and high resistance is causing a voltage drop/amperage spike?

Does anyone know the resistance value of the ECT at the temperature when the fans are supposed to come on? Does anyone know even what temp that is?

 

OBD II Scanner - CAN & OBD II Deluxe Scan Tool

It's big and ugly, and hard to get it communicating with the XJ8. $80 bucks all day long, with a 20% discount coupon which are easy to come by, will net you $64 and tax.

Can't really say I recommend it for the Jag, but it DOES work, and does all it says. Doesn't do ABS. Certainly does coolant temp real time, along with fuel trims and such. Sometimes it picks up communication right off the bat, but usually, you have to unplug 'n replug it several times before it starts talking to the Jag. There's no communication problems with my other vehicles, though, so there's that.

That's what I use for now anyway. If I ever upgrade my phone to a new fancy model, I might go the bluetooth/smartphone route.

 

I have an Autel MD802, which is a fine scan tool and handles all of the car's modules from the instrument cluster to the climate control. I'm looking for something a little more compact that I can leave in it, and maybe mount it in a useful location. I really don't like clutter and things floating about in the cabin.

 

how about an Elm bluetooth obd and torque app?

 

If you are not after a multipurpose OBDII device, RealGauge also has a few features which are not that well known:

-Audible alarms for high coolant temperature and low oil pressure (yes, even on the coolant temperature only version) to alert you if you are not paying attention to the dashboard.

-A 'history' feature that automatically plays back the maximum temperature from the last 60 engine runs on demand, to let you see if there are trends indicating a worsening problem.

 

Yep, #3 in my list.

I saw that and thought it was pretty badass! My MIL's PT Cruiser had a similar malfunction (cooling fan connector failed) and I got a nice chime when the temp got too high. I was very appreciative to see that Realgauge offers that feature. Seems like a no brainer, but other cars don't do it. Beyond that, I like the idea of directing money towards enthusiasts who help enthusiasts.

I am neither after a generic nor a specific device, but it's a lot easier for me to justify spending money on a generic solution that might come in handy later vs. a specific solution that only has one application. Had I not just thrown over $500 into this car - including removing and replacing the cluster - I'd be far less hesitant about this. In two years I've put 5,000 miles on the car, so that's not a very favorable miles:dollars ratio.

I am going to pull apart connectors and such this weekend and throw a little more research at the scenario and see what I come up with. I'm hoping to find a melted relay or a corroded connector that just explains it all.