Cooling strangeness - maybe a thermostat or fan clutch?

[willinnashville]

Hey everyone. I'm having a weird issue in my 2005 Yukon Denali. It's not quite critical yet, but it's noticeable to me.

After I'm completely warmed up, if I get stuck in traffic, my coolant temp creeps up above 210 a bit. Normally, the temp hangs out at 190-195. If traffic is prolonged, it stays there long enough to make me nervous. Then it's like the thermostat opens and lets the coolant in and my temp drops.

Also, if I drive on the freeway on a day under 50 degrees, the temp sometimes runs cool, like 170-180.

I haven't noticed any difference in the heater, but I keep it chilly for the most part.

Like I said, it's nothing critical yet. I haven't seen it get hot to the point where it's over the big mark halfway between 210 and 260, and I haven't seen it run cooler (after warmup) less than the big mark halfway between 160 and 210. I just don't want to let it go and have a catastrophic failure that I could have nipped in the bud beforehand.

What should I check? Thanks in advance

 

[Tonyrodz]

How's the coolant level? Is the system pressurizing?

 

[willinnashville]

Coolant level appears fine. I can't say for 100% certainty that it's pressurizing. My understanding is that the only way you can really interact with the system is through the overflow tank. Is my understanding correct?

 

[rockola1971]

Squeeze your upper radiator hose with engine running and up to temp. Does it try to push back against your fingers? If it does then there is pressure. Cap to your overflow tank is your "radiator cap".

 

[willinnashville]

OK, I'll try it this afternoon

 

[SnowDrifter]

170-180 on the freeway sounds like a bad thermostat. Mine sits at 206 on the freeway, 212-214 in traffic(where the fans kick on).

IIRC 2005 models all came with efans. You sure that's just not the set point where they turn on?

 

[01ssreda4]

Fans dont run on the hwy, there is a preset mph that they disable (35mph on cars, not sure on trucks). Your temps seem normal (not overheating), and yeah in traffic the coolant likely settles at the temp the fan turns on at. Mine also doesnt run cooler in cooler weather, it reaches a point and stays there. Remember to take the gauge reading with a grain of salt as they are somewhat buffered so they dont swing around a lot and cause panic for judy the soccer mom.

 

[willinnashville]

I checked, and the system is pressurized. I'm not sure what temp the fans turn on. The high temp turn on, I can maybe believe that's just the point they switch on. Its been happening for a while now. The low temp on the freeway is new.

Should I even be worried about this?

 

[SnowDrifter]

It's not ideal for your engine to be running below temp. It's not designed for it. You'll get higher fuel and moisture dilution in your oil plus minor variances in mechanical tolerances.

Assuming the temps you provided are accurate, I'd start with a thermostat. It's difficult to diagnose anything else when such a core component of the system isn't functioning properly

 

[scrtcell]

Check your radiator when the engine is warmed up your radiator should warm from top to bottom if not it may be clogged you can flush it but it may be better to replace it and the thermostat along with the anti freeze lol....some people believe you should reuse the old stuff smh...