I have a 2007 Silverado 1500. It has the 4.8L engine. Here is the problem:

After I have been driving for about 10 minutes the temperature will get to about 235, and then the fan kicks on and it will lower back to 210. Once it does that it will be fine. If I come to a red light etc. it might or might not decide to start getting hot again, but it never goes above 235.However, it doesn't do this all the time. So, since this doesn't happen all the time i am confused as to what might be wrong.

I have read that a bad sending unit will make the gauge do crazy things. At first I suspected the thermostat, but I don't just want to go changing parts unless I know it'll fix the problem. Also, if it is the sending unit would that show up as a fault code if someone were to hook up the computer to the truck?

Any and all help is greatly appreciated.

 

Did you check the coolant level? it would be a good idea to flush the system and refill with new coolant.

 

I have checked the coolant level and it is fine. I've never had the system flushed. I have had the truck since it was new, so I know it has never been done. It might not be a bad idea though. Thank you.

 

Sounds like the gauge is reading OK.

Low hanging fruit:
#1: is there enough coolant?
#2: is the system holding pressure. Pressure test the system and the cap. Or just buy a new rad cap (OEM).
#3: make sure the radiator is clean and not plastered in leaves and bugs.

 

Okay, this is embarrassing, but I just went out and checked it after it has been sitting for about 6 hours. The coolant in the reservoir was nowhere near the cold fill line. I had a gallon of coolant in my truck tool box and I filled it up. I leave work in about 3 hours so I will see if that was the problem. I am going to feel so stupid if that was the problem. I do appreciate your response.

 

i know my 94 used to sky rocket to around 230 then fall back down and stay around 180 till i topped off the coolant. then it works normal. think it has to do with the thermostat not opening at the right time because its not surrounded by fluid

 

So, I feel like such a moron. I went out and filled the coolant up to the cold fill line and it fixed the problem. I guess when I checked it a couple days ago I couldn't tell exactly where the coolant was sitting.

I thank everyone who took the time to answer. It helped a lot.

 

The LONGEST flush interval I've seen is 5 years. Your truck should have have had at least two flushes by now. It's probably getting pretty nasty inside your engine.