Thanks again for the input. I tried the same test again with the engine hot, and found the same difference of 40 degrees between actual and indicated. The IR thermometer puts my open road coolant temp around 185 at the sensor and 180 at the top left corner of the radiator near the inlet. The sensor should show up today or tomorrow in its way to familiar AB box.

Still no loss of coolant or waterfall sound from behind the dash.

I'll post the results once I know what they are.
N

 

So were your previous comparisons based on OBDII scanner data, or just the point and shoot IR thermometer?

 

The tests were based on what the obd scanner read compared to the IR thermometer reading when pointed at various bits. The obd consistently reads 40-45 degrees hotter than the IR on the manifold near the sensor, the radiator, or any of the hoses (closer to 50 on the hoses)

 

Try to compare when cold engine the coolant temp and the IAT reading (intake air temp), both should be close on the OBDII port. Sensors can have some calcium buildup, which usually works like an insulator, plus if you have a steam pocket the senasor will be cooler than the water. Kinda like you can hold you hand over a pot of boiling pasta, but when you stick your hand in the pot things get real hot real fast.

We all hope that it is a sensor - and not something more sinister.

 

i appreciate your fair wishes. At this point, I am reasonably well convinced that the sensor is the issue, or at least an issue. I think the radiator would be the next step on this ladder, I hope it does not come to that.
I'll check the IAT once the beast has a chance to cool, but I'm not sure if my scanner will show that data point real time.

Thanks again for all the help.
N

 

Scanner, if it shows coolant temp, should also show IAT. See pix with both temps, and note position of temp gauge in background. While this is a D1 with an analog "slow" gauge, the D2 has a gauge controlled by computer to always show center point unless beyond normal temp limits. So when it starts to move, you are already hot.

 

The new sensor arrived, in a box marked Lucas, they are known for unquestionable reliability, no wait, the other thing...
The new sensor reads within 3 degrees of actual, which is inside the margin of error for the IR thermometer, so that problem is solved.

The IAT on the other hand is reading about 110 degrees from what it should, so on to the next gremlin. I have this sinking feeling that it is a part of the MAF, someone please tell me I'm wrong.
N

 

Nope, you are correct, same unit.

 

Final update, the problem is solved. coolant temp sensor replaced, and reading a number that I am much more comfortable with, and the IAT sensor reads right while the engine is running, just read high with the system on and the engine not turning.
The coolant sensor was a serious pain to get at, I had to buy a set of crows feet to get at it without pulling the upper intake manifold.
Back to waiting for the next thing to break.
Thanks again for all the moral support and what not.
N

 

Yippy SkippY! What kind of temps are you reading now in digital form?