Intermittent Overheating

[Flicka]

This is for a 2WD 2004 Tahoe with a 5.3 engine and 165k miles.

The Tahoe is overheating on a daily basis. It goes to 235 degrees while driving but then goes back to 205. Sometimes it goes back to 205 while sitting at a stoplight with the a/c running and sometimes it will go back down while driving.

No leaks
Coolant level looks good
Oil looks good
Nothing blocking the radiator
As far as I can tell the hoses look good
No water pump wobble

A couple of years ago I replaced the water pump and thermostat and belt
Replaced the clutch fan this year when I started having issues as I should have replaced with the water pump but was cheap.
Had the dash cluster rebuilt shortly before having this issue. The speedometer was acting bizarre and they fixed all gauges. I hooked up my scanner to confirm the gauge temp matched the computer reading.

I don't think I have ever soon a car cool down while sitting at a light with the a/c on. Any ideas?

It is a closed system so ruled out radiator cap. Not sure how to check for a collapsed hose but they look fine.

 

[ccapehartusarmyINF.(ret)]

im actually having the same issue right know i have a 2002 and i replaced the water pump and Thermostat like a year ago i also replaced the fan clutch like 6 months ago
and since its been getting 110 plus here in arizona the last week or so is been overheating when im sitting still

---------- Post added at 12:02 AM ---------- Previous post was Yesterday at 11:55 PM ----------

last time i had this problem i replaced hte water pump there was a small leak on top of the pump and all the gunk and grime and dirt was soaking up the coolant

in order for your cooling system to function correctly it must maintain a pressure of 15 psi
water boils at 212dagrees farenheit but that boiling point is raised to 245 dagrees under 15 PSI so even the smallest leak=loss of pressure=overheating

 

[Flicka]

I will pressure test over the weekend but I have not had to add any more coolant to the system. Would a pinhole leak cause the temp to go hot then be fine? It never goes above 235 and half the time it stays right at 205, even while sitting at a light.

 

[ccapehartusarmyINF.(ret)]

okay yer overheating issue doesnt seem as bad as mine like if im sitting somewhere more then 5 to 10 minutes miy temp climbs up to like 235 240 but also i live in arizona and its been well over 100 dagrees for the last week and a stop light isnt long enough for it to start overheating.
a pinhole leak will cause a loss of pressure but not much
what happened with me last time when i replaced the water pump was a buildup of grease and dirt and grime was hiding a small leak so what i do is go the do it yourself car washes with high pressure and thuroughly clean the engine to expose any possible hidden leaks

 

[TheAutumnWind]

I will pressure test over the weekend but I have not had to add any more coolant to the system. Would a pinhole leak cause the temp to go hot then be fine? It never goes above 235 and half the time it stays right at 205, even while sitting at a light.

Yes.
That's exactly what I would suspect if temperature spikes like that
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