Temp gauge rises hot in idle; 2500+ RPMs cools it back down

[howie]

1999.5 QX4

Coolant was flushed by Midas in the last year.

Issue: Temperature gauge showing "too hot" when idling, but running the engine brings the gauge back down.

I start the car from cold and let it run...
The temp will go to "in the middle" (9 o'clock, where I expect) and then keep rising to 11 o'clock within 5 minutes.
If I start driving at about--or faster--than 40 mph for a few minutes, it will drop back to "normal" (9 o'clock).
If I get stuck in traffic or sit at a long stop light and have to idle again, the gauge will rise back up to 11 o'clock or 11:30 within a couple minutes (varies...like 2-5 minutes).

Here's the twist:

If I'm idling with the gauge reading "hot" (11 o'clock) and I go into Neutral and press the accelerator to hold the engine at 2500-3000 RPMs, then the temp will drop back to "normal" within 2 minutes.

So running the engine seems to cool the engine off (or at least the gauge).

= = =

It's been about 80-90 degrees F outside here. I'm sure pulling air across the engine helps, but if simply running the engine cools it off, that seems a little confusing to me.

I've changed my oil & brake pads but not much else. Not sure if another coolant flush would help. Is this a problem with the gauge? I'm sure it needs to be fixed, whatever it is, but I'm not sure what the diagnosis should be.

= = =

Oh yeah, the running the heater thing...

Yes, I've been using the A/C.

Turning the fans on at the highest temp in the display (85 degrees F) and blowing at "four fans" through the foot and face blowers has not seemed to help too much but I have not explored it a lot, either... I know this is often suggested for engines overheating... this worked for my old '94 Mazda 626 sedan but I'm not sure if it works the same with the Infinity's computer / system or not, actually. In any case it's a short term solution and I really want to know what needs to be done to fix it at this point.

= = =

Thanks for any thoughts. I'll be able to answer any questions to provide more info as well.

[Towncivilian]

How's the coolant level in the overflow reservoir?

[howie]

Ack! It might be that easy!!

Engine was cold (well, as cold as can be expected when 86 degree sun is bearing down) and the coolant level in the reservoir was below MIN by a little.

I'll add some coolant.

Thanks! If you don't hear back, it probably was that simple.

[Chuck Tribolet]

I'm guessing a fan problem of some sort. Maybe the viscous clutch.

And check for something obstructing the radiator, including between the AC condensor and the rad.


Chuck

[ARKQX33V6]

Besides coolant, check if you have flow from the coolant pump, no flow no cooling. Is the cooling system under proper pressure? If coolant level is or was too low, where did it go? Look for leaks, head gasket, oil pan, may not hurt to do compression test to verify.