The Folly of the Temperature Gauge
 

It's simply a philosophical issue I suppose. The engineers programming these things believe, or are told to believe, that someone who spends 100k on a car does not want to be bothered with gauges that don't look perfectly normal all the time. When the red blinky light comes on or it doesn't go any more they'll call a tow truck and send it to the place they bought it from because it is under warranty and not their problem. :icon_naughty:

Fast forward to the post warranty years and those of us that bought something we could work on and keep running ourselves for the low low price of 10% of sticker. Given the information and the eye candy formerly known as engine gauges, we will be needing something more for diagnostics, or in my case, normal everyday running. After all, these are spectacularly great cars that with some good ol' TLC will go the distance. :icon_confused:

To wit: the Engine Temperature or Coolant Gauge.
It climbs normally up to the 50% mark where it resides steadfastly through a seemingly spectacular range of temperature. Then it continues on apparently into the red zone. I should say that I have no data to support the trend line above the 50% mark save for my own memory in the heat of the moment. :icon_laugh:

Attached are some pics of my '97 XK8 engine temperature gauge with my ScanGaugeII along side. I also included a little chart that shows the "flat line" in the middle of the range. Some would say I have some maintenance to do on my cooling system and I agree. Just gettin' 'round to that. :icon_bump1:

One last thing, as a Control Systems Engineer, programming a gauge to do this is very easy when it's built like any late model car. This is no different than what we can do on any industrial man-machine interface.

..and now for more wine...

Please explain how the chart works.

We're waiting for WhiteXKR (The JagWrangler) to invent the workaround for this ridiculous temperature display (I won't call it a gauge).

You ARE working on that for us, right Jagwrangler? I'll be your first customer. :icon_wink:

Nice to see a plot of actual and what the guage is saying
Great work with that plot
Wow it sure says 50 percent for a wide temp swing
Which I was suspecting
It is a very nice analog looking guage but it is just that
Eye candy and does not tell you much but now at least with the chart when it climbs to 60 percent the coolant temp has gone up !!!!!
If there is a work around that would be great
But I guess an aftermarket one may be possible which I was asking about in a previous post

Hats off again for the graph

Howard

Skid-
The graph shows on the horizontal axis the gauge swing from 0% to 50% to 100 %.
The Vertical axis shows the temperature readings from my scan gauge that is plugged into the OBD-2 port.
The pictures is where the data table on the chart comes from through 220 degrees F. Above 220 degrees is from my memory.

The scan gauge reads what the computer (ECM) sees from the engine temperature sensor.
The reading on the gauge is the PROGRAMMED output on the ECM channel the gauge is wired to.

Coupe-
The way to properly fix this is to change the programming. Any of the aftermarket ECM re-programmers could do it if it was worth their time ($).

Mike

I wonder if the gauge could be reconfigured somehow and paired with a bluetooth receiver to read the coolant temp from a bluetooth sender connected to the.OBDII port.

After all, my Droid can do this with the Torque app, and we could bypass that ridiculous ECM temp programming altogether.

Or just buy a aftermarket gauge.

The way the gauge behaves is worse than an idiot light. At least with an idiot light there is no mistaking there is something wrong.

The whole time it is creeping up from 180F to 220F, time that the driver could have used to decide to pull over, it is lying.

First off thank you OregonJag for drawing a clearer picture of the behavior of the coolant gauge.

From the architecture of the system, my expectation is that the ECM is always putting out the correct temperature over the internal network in the vehicle. It is the computer in the main gauge cluster that 'filters' that data and then drives the stepper motor type gauge. I would be surprised if many 'tuners' had the tools to reprogram the instrment cluster computer.

In my view, the easiest way to make a correct reading gauge (and easy is a relative term) is to disconnect the gauge from the speedometer cluster and monitor the analog temperature from the temp. sensor with a small microprocessor and have this small microprocessor drive the gauge stepper motor directly.

I currently have quite a backlog of products I am developing, but I think there is enough interest in this, so I am going to add it to the list. It is going to be a while though :icon_snow:

If enough of us pester you about it, perhaps you could move this particular product towards the top of your list. After all, great as your other products are, this one can help save fellow enthusiasts from inadvertently cooking their aluminum engines. That's important stuff! A rare opportunity to combine profit with a public service.

Public opinion will win here...I'm listening :)

OK everyone, you heard the man.

Those of you who would like WhiteXKR to develop a product that turns your current temp gauge into something USEFUL, post up your interest here!

I'll go first...please do it!

Don't feel bad, BMW does exactly the same thing. My 330 trip computer could be made to read the real temp digitally, while the analog indicator gave you the "feel good" reading.

As an Aircraft Maintenance Engineer, specializing in electronics and instrumentation, this is unforgiveable.

Not as bad as some Fords I've had, where the oil pressure indicator is really an idiot light, showing pressure or no pressure.

Those of us that participate on these enthusiast boards are the true 'geek' owners that represent maybe .1% of the total. Almost all temp gauges on cars operate exactly as described by Oregon to suit the 99.9% that don't know, understand or care what the indication means. If you think of why many cars have idiot lights instead of gauges, if I was an OEM I'd do the same thing.

There was a post not long ago from an owner that drove his car with the gauge pegged until the engine seized. The original engine on my vintage Corvette went bye-bye because the owner at the time thought the oil pressure gauge was an oil quantity gauge and he had enough to get him another few hundred miles or so.

Jaguar starting going to the "idiot gauges" in the mid-90s. My '95, for instance, has idiot gauges for both coolant temp and oil pressure. And, yes, many other car builders have done the same.

I was a bit disturbed by this at first but eventually shrugged it off. The oiling and cooling systems, on the old X300s at least, are virtually dead reliable...so I became a member of the placated "if it still runs everything must be OK" masses :-)

I find it amusing that Jaguar left the voltmeter as an actual functioning instrument, given that we're not entrusted with the truth on the other two :-)

Cheers
DD

Agreed, sign me up for the first harness after Coupe! :icon_toast:

Thanks, got it now!

I do agree that the gauges (oil pressure and temperature) in this car are nothing but placebos. I hope you can find a fix.

Ditto.:icon_smile:

Is the ScanGaugeII (SG-II) fully compatible with your car? It seems that the Ultra Gauge (UG) has a compatibility issue with the XK8/R that they do not wish to address; however, the UG works great in my S-Type so it was not a total loss. I would like to know more about your SG-II and any issues you have with it. Also your temp chart was it a download from the SG-II or did you create it?

Do the measurements shown by the graph mean that the normal operating temperature range is from 181 to 230 degrees F ?

Also for over temp or low oil pressure, will the ECM prevent the driver from damaging the engine?