So I got my truck (96 5-sp discovery) back in late november, and have been getting no more than 15.5 mpg, but my average has been a solid 15 (always running 92 or 93 oct), and I thought that must just be normal.

Then I got my Ultra Gauge in the mail yesterday, and my temp has been reading between 183-192. I thought "hey, that looks great", but then i get two alarms: Cat Bank 1 is over temperature limit, and the other is a P-0125 trouble code. So after searching the forum I know I need a new temp sending unit, and that also what is probably what is causing my 15mpg average. Is that also making the catalytic converter run extra hot to burn off the excess gas the ECU is giving what it thinks is a cold engine?

So I am getting this part Sensor Temp (Ects) (Part # ETC8496) - Land Rover sending units from Atlantic British

But could it be something else causing the problem?

 

"Cat Bank 1 is over temperature limit"

This is a known bug when using an UltraGauge on a D1. Ignore it. You can disable the alarm for that specific item.

If your CAT was actually the 8000 or so degrees it says, it would vaporize. In other words, there isn't an element on the periodic table that wouldn't melt at that temperature.

The rest of your diagnosis sounds correct. Just replace that sensor.

 

15mpg is the average for these trucks, most of us get less, shut up and be happy with your 15.
As already stated, turn off the alarms on the Ultra-Gauge, the U-G can only see the info the ECU gives it and cat temp's ain't one of them.

 

I'm not worried about the MPG, and fuel efficiency was the least of my concerns when buying it.

The PO had a new water pump and t-stat put in 2 years ago and I am thinking that I might as well put in the sending unit, a 195* tstat and change the coolant all at once.

 

Thats good that you're not worried about MPG, I was just busting your *****.

 

The P0125 code is related to cats and temperature, but it is triggered by engine taking too long to reach closed loop fueling (90 second limit if engine is started at 20 degrees C.). See attached page from ECU manual. Obviously, if you are staying in open loop, mpg will be poor. You can also get an idea if ECT sensor is way off by comparing readings at cold start to ambient, it should not be -40F in the garage, etc. ECT is one on right, gauge sensor is one wth a single wire.

 

I replaced the ECT unit on Thursday and the ultra gurgle has been reading 172-179 . Is that still considered running too cool? I cleared the P0125 code and it has not returned after driving it 600+ miles this weekend. The previous owner put in a new water pump and a 180* thermostat 2 years ago, so maybe it is time for me to put in a new 190* tstat?

 

Yes that is running to cold, I'd step it upto the 190.

 

Thanks spike, I am buying the 190 tstat today and am going to replace it this weekend.

Just last night on the way home from work the P0125 was thrown again (with the new ECT...) I have digital infrared thermometer and took a reading on the sensor and it was between 188-196, and the ultragauge was giving me 174-178. Could it be a couple of bad sensors, or a problem with something else entirely (or just the bad thermostat)?

 

Could also be a ground (rubbed or skinned wire) on the ECT circuit, dragging the computed value down below the actual value. You might also find that the existing stat has a vent hole drilled in the flange, if too large that can pass enough water to slow initial warm up. The style with a jiggle device seem to just pass bubbles in the coolant, not a steady stream.