So I took Jank the Jankity Haguar on a longish road trip for work yesterday. I covered approximately 340 miles. I learned a few things about the car on that trip.
1. I don't think too many other cars passed me on the highway yesterday morning. I was moving along at a pretty good speed. Only problem was the speedometer said I was only driving at 63 mph the whole time (when at highway speeds). I had reason to mistrust the gauge when passing Mercedes, Porches' and BMWs. I downloaded a speed tracker app on my iPhone and found that I was speeding slightly... 112.7 mph...
Has anyone experienced this with their speedometer? Do you know if there is a way to repair it short of replacing the gauge and then having to deal with the discrepancy in miles on the odometer?

2. My petrol (gas) gauge is untrustworthy. On a full tank it indicates approximately 2/3 full and empty is far past 0. I use the odometer to gauge my range. Up until before this road trip each tank was good for 100 miles. My highway travel at high speed (see above) yielded approximately 185 miles per tank!! That's a substantial improvement! Now keep in mind that I have only been driving this car since early December, so there were many times of starting the car and allowing it to idle and warm up to a good operating temperature, which burns gas without showing any miles (obviously), but a 75% improvement on mileage is nothing to shake a stick at!!
What sort of MPGs do you all find with your vehicles (4.2 liter XJ6 series 3)?

3. The electric fan on the front side of the radiator/condenser came on yesterday while driving. I noticed it when I stopped, turned the car/engine off and left it sit for a good while. I was thinking that it was a "run on" cooling fan, which it is, that would help cool the radiator after shutting the car off. But it kept running... for hours... I finally had to pull the fuse to get it to turn off. Then reinstalled the fuse right straight away after and the fan did not start again.
Does anyone know what circuit or sensor this fan is controlled by? Or why it would continue running long after the car had cooled down? I can fore tell a dead battery if I forget to pull the fuse!!

Thanks in advance for any advice, and I'm pleased to continue to learn things about Jank.

Cheers,

Tom

 

what year model ?? (you might put this info in your signature)

the good news:
1) your auxiliary cooling fan is good!
2) you know where the auxiliary cooling fan Fuse is located.

the bad news: look for the Red Relay at the driver's side above the radiator and replace it, it has gone bad. That's all.

 

OK, changed the relay on the DS of the radiator support. Fan still runs on. Next?

 

fan keeps going indefinitely? new and correct relay ?

the only other related component will be the Thermal Switch located at the bottom right corner of the radiator, (part number 13 in diagram), a pain to get to without removing the air filter assembly and even then, almost impossible. Check with a flashlight to see if the two black wires are connected,

ideally you would want to disconnect either wire of the Thermal Switch while the fan is running, to check the system, but it will be extremely hot to get in that corner. You might try to get to it from under the radiator.

 

Tom:


Two things on your post perplex me. where did the HP come from to drive that circa 3000 # beast at 112+ MPH? Secondly, where in your state are the roads that accommodate that velocity? Amazing!!! Oh, one more, no state troopers on that circuit?


Jose:


The complexity in that drawing amazes me. The low water indicator in my car, when it was DOHC powered failed me, as did the temp guage!!


Carl

 

Carl,
the drawing does not show some aluminum tubes that go around the top of the radiator from one side to the other, talk about complex.

 

JagCad,

It's amazing what happens when you push on the accelerator pedal with the right circumstances. I was lucky there were no state troopers along that stretch. My only defense to "Sir, do you know how fast you were going?" would have been "63 mph".

 

ohhhI see now, it's a Canadian speedo

 

A Canadian speedometer? As far as I know this car was sold in California, though it's possible that a "new" speedo was fitted at some point in its life. Can anyone show me a picture of a true USA/Federal spec speedo?

 

Looks just like mine. A CA car, first sold in nearby Vallejo, Ca.


MPH in white on the inner circle. KMH in smaller numerals about the outer.


Small letters show mph and kmh


Odometer reads mph's only!!


At present mine is nuts. GM signal to Jag speedo not quite compatible. I know how to fix it, but....


Anyway it is down now. bum starter out, new on the bench. Car on jack and stands awaiting my attention, any day now...


Carl

 

I found a couple speedometers on eBay that show both MPH and KPH (as usual). The MPH is in larger font and is white, the KPH is smaller (outer) and in orange (as usual). Only difference is that the ones listed go to 140 MPH vs mine above to 85 MPH. Plus, down at the bottom of the gauge face, to the right of the trip reset is printed FED CAL, while on mine NOTHING ("nothing" is not printed, there's just nothing printed there!) I may go for the 140 MPH speedometers and "clock" the odometer to match my total miles.
Anyone ever adjusted their odometer for the purpose of replacing and duplicating actual miles traveled? And no, not the old used car salesman trick to roll back the miles to get more money!!

 

A federalist joke at about that time. My 88 Tbird had a digital speedo. Floored on a wide open road, never more than 85!!! I know it's lively little 302 was moving it much faster.


It was a retired CA Budget Rent a Car. I got it for a good price in very early 89 with 10K on the clock. Immaculate as good as new condition. One of my better deals.


Carl,
Carl

 

OOOPs wrong bx...

 

There was a fed rule to limit the speedo reading below 100mph for a couple of years (intended to dissuade kids from trying to boast or some such nonsense), hence the 80 mph speedo. Utter govt crap

 

From Wikipedia-

"On September 1, 1979, in a regulation that also regulated speedometer and odometer accuracy, the National Highway Traffic Safety Administration (NHTSA) required speedometers to have special emphasis on the number 55 and a maximum speed of 85 mph (135 km/h). However, on October 22, 1981, NHTSA proposed eliminating speedometer and odometer rules because they were "unlikely to yield significant safety benefits" and "[a] highlighted '55' on a speedometer scale adds little to the information provided to the driver by a roadside speed limit sign."

 

I bought a used speedometer from David Boger at everydayXJ. Great guy! Inexpensive and super fast shipping. The speedometer is a little rough, but it's a FED CAL reading to 140 MPH. The odometer shows about 34000 miles less than my car has. Now I know what you all are thinking... but that really wouldn't do me very well as I just titled the car with 132000 miles. So I dismantled both gauges (my old one and the "new" one) and am in the process of running the mileage up to the desired reading of 133045. This works both ways if you all are interested to know that, though clocking a cars odometer back is highly illegal and morally reprehensible!! I believe in honesty in these matters. Besides, it's a badge of honor to be running a 33 year old car with actual mileage showing on the clock. More to follow...

 

another way of doing it is to save the old speedo that has the original mileage and just use the new speedo as is. If you were to sell the car, you can show the buyer the real speedo and the reason you replaced it. It is illegal to manipulate speedos but everybody does it anyway, just like removing airbags, I don't trust them so I removed them, so sue me all the way to the Supreme Court ha ha.

 

I combined the best parts of the two speedometers that I had, my "original" one showing 133045 and the "new" one with the FED CAL reading to 140 MPH. I shot a short video of my method for running the odometer up to where it needed to be. It took about 1 minute per 1000 miles! So all time running about 40 minutes!!


Though I guess I don't know how to upload a video yet.

Anyway, I put it all back together and got it back into the car, drove it to work this morning and, alas, no miles counting, neither on odometer nor trip. I suppose it could be the "new" wiring harness, or perhaps the "new" drive motor? The speedometer works for speed as this is essentially a different circuit in the speedo. My next step will probably be to swap the drive motors, the "new" one for my "original" one. After all, theoretically, the drive motor is turning at the same rate with the same shaft diameter with the same worm gear, so all things being equal it should yield the same turns to clock miles at the same rate... awfully confusing without know the right answer before trying all these things!!
Any help would be appreciated...

 

And why, when I upload a picture, does the text become so small? Am I doing something wrong? Picture size? I am using an iPad, btw.