My UltraGauge arrived today. I seem to be running at about 208 - 212, consistently.
that's with the 180d thermostat.

I can't MAKE it get above 215 today. But it seems it oughtta run cooler. ?

 

That supports #2 or 3 of my initial response.

 

I think I'm sorta narrowing-in to the water pump. In my mind, it most fits the symptoms.

I'm going to hit the radiator with a thermal imager tomorrow, and we'll see what we get, but I flushed it pretty good, and was impressed with just how clean it was.

thanks everyone, for the continued aid in troubleshooting.

 

So:
today's commute (about 35 minutes at a sustained 65mph, and about 6 minutes at each end on surface streets) my UG read a coolant temp of 178 - 183. But the DASH gauge read PEGGED at HOT!

So which one do I trust?
I'm leaning towards the UG, because the truck shows no other signs of overheating. it's not pinging, and when I parked it, it didn't do that little 'tick'. It's running well.
So what gives?

And back to the cooling issue itself: why such a change from last night, when (similar ambient temps) the UG read around 212?

I'm confused.... and a little pissed.

In the meantime: it sounds like I've got an A/C compressor clutch going out on me, so I'll probably have the thing where I can replace the water-pump easily enough this weekend. (if they ain't made of gold )

 

trust ultra gauge, it uses data sent to CPU by coolant sensor. if a D1, you have a separate sensor that just drives gauge, unplug and check wiring. on disco 2 the CPU has one sensor only, but can have wire or dash cluster issued.

 

Savannah: I just added you to my Christmas card list!
I was HOPING I could trust the UG over the dash.

 

That dash gauge is nearly worthless. The UG temp and manual thermometer are the only ones I trust. If replacing the water pump doesn't do it and your radiator can't be acid flushed and rodded then try a 40/60 mix of antifreeze/distilled water with a bottle of water wetter. It made a big difference to my old inefficient radiator until I replace it.

 

Overheat scares me the most with the since they are Aluminum blocks. George brings a very good point that repeated overheats will do in the engine with slipped liner issue.

And Savannah does know these beasts a lot better than I do. I have been really lucky with mine so far as I have not really had to tear into much of anything major yet.

I am wondering on his latest thing with the UG reading boiling one day and only 180's the next day, what if the sensor providing the input to the ECM and UG is flaky?

 

The two sensors are shown in the pix, gauge is on the left, square top is the ECU sensor. A ground (skinned place) on the single wire can cause the gauge to read hot. Or green goop on connector. From RAVE:

The Engine Coolant Temperature Sensor (X114) has
approximately 136 ohms resistance when the coolant
temperature is low. As coolant temperature
increases, the resistance of the sensor decreases.
This varying resistance causes the current through
the sensor to change and the gauge to register the
temperature. When the coolant is hot, the resistance

of the sensor is approximately 17 ohms.

 

And back to the cooling issue itself: why such a change from last night, when (similar ambient temps) the UG read around 212?

Since 212 is boiling I would be very concerned.

I agree a shorted or skinned wire will give an overheat reading on the guage but he has a lot more than that going on. Very many more episodes of 212, that block will go really well with the round glass table top I have.