Btw if I IR gun the water neck how close to actual water temp is the reading?

 

Again, how long have you had your car? And, has it always behaved this way?

When I sit in summer, stop-n-go, FL traffic, my temps run toward the top of the indicated range...95* to 100*. When the fans kick on high, if I'm simply sitting [not moving] in traffic, my indicated temps don't move much, if at all, either. Never have...in 15 years.

Heat is the enemy of electronic components...high junction temps result in decreased reliability/accuracy and lead to component failure. I'm sure [from decades of duty cycles] my indicated temps are in error, on the high side, due to corrosion/resistance across the signal path(s).

Well, in that situation, I would hope the temp [indicated or not] drops. Ponder this for a moment...what is driving the water pump? The cam belt bone. And what is the cam belt bone connected to? The crank bone. Ergo...more RPM, more volumetric flow through the water pump.

 

Ok I verified the belt is not slipping.

That leaves air in the system, a defective WP, or may be a defective thermostat not opening up all the way. Would revving the engine to get it to cool be indicative of that?

Mel- I don't disagree that it may be normal but I need to verify.
Just so I'm clear you are saying that in the summer, at a red light, you temp goes up, your fan comes on, and your needle does not drop?

Also I realize revving the engine moves more coolant in front of the radiator, but it's in from for,a,much shorter time. Wouldn't that cause less cooling of the coolant at idle?

 

Clean the grounds at the back of the engine if you haven't. That bought me ~1/2 a division on the temp gauge. Still fluctuates a bit like yours, but at half a division lower, it'll sure seem more normal.

Does your gauge jump when you turn on your headlights, defroster, or AC? Another symptom of ground resistance.

 

I have cleaned all the grounds in the car. I did not see a change, but none of the grounds were bad though. They looks like new actually, but I cleaned them to be safe anyway.

 

No worries...verify away.


Correct. At a light, when the high speed fans come on, my indicated temps may drop from 98* to 96* before I leave the line.


Less heat transfer from the coolant, to a certain extent...yes. Keep in mind, the temp sensor doesn't take its reading from the radiator...it takes it from the head.

1. On one hand: higher revs = higher flow rate = less time spent in the radiator = less specific heat transfer per molecule of coolant.

2. On the other hand: higher flow rate = higher cumulative heat rejection from the engine/head.

While someone like Harvey or Van would have a more accurate answer, I'd venture to say/guess that, at idle, the water pump flows enough volume to empty the radiator in 10 seconds, or less. At speed, 3000 RPM, I'd say that drops to 5 seconds, or less. Under normal driving conditions, 2000-4000 RPM, coolant simply doesn't spend a lot of time in the radiator.

So, while revving the engine at a light results in #1 above [less specific heat transfer per molecule of coolant], it also results in #2 [higher cumulative heat rejection from the engine/head], which is precisely why your indicated temp drops.