Temp gauge and cooling system testing? (it's too hot)

[RastB]

02 QX4. After doing the very unpleasant job of replacing both primary cat converters, I have another issue. Haven't driven this car very much before the cats, but only noticed that the temp gauge never went above the halfway point. But after putting new coolant in, flushing bleeding burping etc, I connected live data scanner to monitor actual coolant temp. Was quite surprised to see that on this vehicle anyway, I can be below halfway point on the gauge while my coolant is actually near 220f. Went for a short drive tonight (40f ambient) and the car I think, tho not overheating really is running warmer than it should be. I mean COOL ambient temps and after a 10 mile drive my actual coolant temps were approaching 220f as I rolled it into the garage? I have full heat in the heater system, and I am sure I'm circulating coolant through the engine because with one of those no-spill funnels, if I rev the engine up a little it will quickly push all the coolant out of the funnel. Also, I'm almost positive i've got nearly every bubble out of the system, with the funnel, the air bleed tube, hose squishing etc... no bubbles appearing anymore but it seems I'm still getting too hot, can imagine what would happen if this were summer weather. I looked inside the radiator, looks clean but don't know anything else about the system as it is. So I have options but would prefer not to just throw money at it, are there any diagnostics I can do on the cooling system to narrow things down a bit, far as what to replace? Would rather not do the water valve right now, is there any way to tell if it's opening or not? Crack a particular hose a little and look for pressure? Btw 170k miles on it, have no reason to think the rad has been replaced, should I just do that and get it over with? Guess I can at least take the front thermostat out and boil test it. Thanks for any advice and sorry for the long winded post.

[mdmellott]

Your '02 QX4, like my '02 Pathfinder, has an engine coolant temperature (ECT) sensor and a temperature gauge sending unit. This second temperature sensor is strictly for the dashboard temperature gauge. The ECT is the critical engine control sensor, which is the one you are reading in the live data. Since your dashboard gauge does not go above half way while the ECT is indicating near 220F, then one of those two sensors is wrong. I don't have the resistance specs you should measure on each sensor to see which one is off but that is the first thing I would check before spending money on anything.

[RastB]

Your '02 QX4, like my '02 Pathfinder, has an engine coolant temperature (ECT) sensor and a temperature gauge sending unit. This second temperature sensor is strictly for the dashboard temperature gauge. The ECT is the critical engine control sensor, which is the one you are reading in the live data. Since your dashboard gauge does not go above half way while the ECT is indicating near 220F, then one of those two sensors is wrong. I don't have the resistance specs you should measure on each sensor to see which one is off but that is the first thing I would check before spending money on anything.

Ah, so my live data could be wrong. I hadn't considered that, thank you. Though I did read, here (i believe) on the forum that the factory temp gauge on these were basically "useless" and didn't even start to move until 175f? Do you happen to know what halfway on the gauge should roughly equate to, temperature wise?

[mdmellott]

I don't know how accurate or what the specific temperature values would be relative to the gauge indicator but I do know that when I reach normal operating temperature of about 180F, my gauge indicator is less than halfway of its full range. Your ECT may be fine, just reading at the high end of acceptable. Measuring the resistance across the the two pins of the ECT sensor will tell you if there is an issue or not with that sensor. Measure it when the engine is cold so that you know the temperature should be very close to the ambient temperature. On page EC-225 of the service manual, the temperature values with respect to resistance is shown on a graph. https://www.nicoclub.com/service-manual ... 2%2FEC.pdf You can plot the measurement you get onto this graph and see if you are in the ballpark or not.

[RastB]

I don't know how accurate or what the specific temperature values would be relative to the gauge indicator but I do know that when I reach normal operating temperature of about 180F, my gauge indicator is less than halfway of its full range. Your ECT may be fine, just reading at the high end of acceptable. Measuring the resistance across the the two pins of the ECT sensor will tell you if there is an issue or not with that sensor. Measure it when the engine is cold so that you know the temperature should be very close to the ambient temperature. On page EC-225 of the service manual, the temperature values with respect to resistance is shown on a graph. https://www.nicoclub.com/service-manual ... 2%2FEC.pdf You can plot the measurement you get onto this graph and see if you are in the ballpark or not.

Thank you, mdmellott. My sitting water temp was exactly 50 degrees which corresponds to 4k ohms and that's what it read. I have an NTK sensor coming tomorrow, wonder if I should just leave the oe in place. Was only 9$ so ordered it even though I wasn't yet sure if it needed replacing. To the point tho, I was measuring my various coolant temps- engine block via obd2 and my misc heater/cyl head hoses via IR gun. I could clearly see that my block temps were significantly higher than the lines that went to my various heater hoses. So since the purpose of that valve is to block water flow from the block I figured that was what was happening. I actually had a small leak in the rad appear on close exam (gots new one), but still tore the plenums off (all three) and plunked that "valve" in a pot of water and sure as heck that bleepin thing won't open no matter how long I boil it. Doing lots of vacuum lines and such, PCV, plugs etc but I'm very tempted to gut that dirty little rat and just let it flow and never have to think about it again (?) I realize there's some repercussions to doing that, still tempted