What does it mean if the truck IDLEs warm then cools at 2200+ RPM

[BrianSD_42]

So my truck is not overheating or anything but it does IDLE at 200-204 in traffic pretty often. The temps here are 70-90F but it doesn't seem to matter if it is 60F or 90F outside.

When I'm sitting in traffic it idles warm (but still normal) at 200-204 but if I rev it up for 30 seconds to 2200+ RPM it cools down to 197.

Is there some part that is slowly going bad? I remember a year ago it would idle at 198 pretty consistently.

Also I don't think it is going up to 204 because of engine heat / stress since reving it in drive or idle causes it to go back down to 197.

BTW if there is some basic explanation for how engine cooling works that I'm missing here please chime in. I'm no expert on auto-mechanics - this website is always a learning experience for me.


Any thoughts? Like I said no codes and its in the normal temp zone.

 

[BlackCat914]

Think of it this way, the faster the engine speed, the faster the water pump is spinning. If the truck runs warm at idle, I would first check the fan clutch operation, as it's main responsibility it to pull air through the radiator and condenser when idling or very hot out.

 

[LittleCaesar]

Original radiator? How dirty are the fins?

As BlackCat mentioned above, how about the fan clutch? T-stat?

Did you ever know the usual operating temp before you replaced your heads?

I am wondering if this may pertain or is relative to your sporadic CEL.

 

[BrianSD_42]

I don't think it pertains to the CEL as that happens once every two weeks an this is just normal for every drive.

It was the same on my trip all the way to UT and back. 195-ish freeway, 200-202 at a stop on the trail.

I think its been this way a long time. I only recently started keeping a closer eye on it with the scanguage. It has never gone over 205 and as I understand it that is well within normal ops range but still some people get 190s in town so I was curious if something like fan clutch is getting old.

Another thing ... It doesn't keep getting hotter, its not low on coolant or anything, it just goes up to 202 when stopped in traffic and levels out. I guess I'm just wondering why it doesn't level out at 195 since some people are reporting that. How about you guys?

 

[Skinfaxi]

205 at idle isn't high. As long as your radiator isn't clogged and the clutched fan is engaging you are fine. 210+ is about the threshold where something would be failing.

 

[LittleCaesar]

I usually run 190-195, 202 after filling up at a gas station or the like. I have yet to change the original water pump and timing belt for a close to 16 year old car so that time is fast approaching. With only 105,000 miles, my fingers are crossed. Not my DD though.

I can only say that unlike American autos, these Japanese autos love OEM, or at least the manufacturer. I will say that before replacing the OEM radiator with the Koyo, I used to run at 190-191 all the time, five years later the temp reaches 195 at a light sometimes but will come down to 191 thanks to the two year old Aisin fan clutch.

In thinking out of the box I once had a coolant temp sensor go bad on me in my Acura. It made the ECU think that the coolant temp was much higher than it was, thus putting the car in limp mode. No code to correlate its demise. Seeing how corrosion had built on it, I changed it out and the Acura was back to normal. From that time forward, when I change out my o2 sensors, the coolant temp sensor gets changed as well. OEM always.

How about the radiator cap? New/OEM?

What coolant temps does your Lexus see?

 

[BrianSD_42]

Radiator is Koyo about 20k miles old. So is WP and cap. It may have been like this for years.

The Lexus is a hybrid with Prius engine/system (CT-200h) so it might as well be a space rocket - I have no idea what the temps are.

 

[4Running Daily]

I'm pretty sure Toyota running specs are within 5 degrees of 200.

 

[LittleCaesar]

Ah, the Lexus is a hybrid. That's right.

Try putting it in N and see if you get the same drop in temp as if you would when revving it.

If the fan clutch is original, save your pennies for a new Aisin one.