2003 Sierra overheats after coolant flush

[Nemesisdawn]

I did a coolant flush on my 5.3 '03 Sierra and changed the fluid from green to Prestone orange coolant. I had mild overheating issues prior to the flush, so I figured flushing the coolant and changing to orange Prestone might help (I did the same exact thing in my '04 GTO with LS1 and haven't had overheating issues since forever).

 

Now the temp always goes above midway, and here's the thing... It does the same thing even on the HIGHWAY with fans on high speed, and it sometimes goes down in traffic only (basically when I'm not giving the engine any acceleration).

 

I changed the coolant again with dexcool, and did an air bleed, changed the temp sensor and thermostat two months ago, and cannot see any leak from the pump but still nothing is helping.

 

I'll note that the green coolant didn't look dirty when it I flushed it out, and that it only heats up when I'm accelerating.

[diyer2]

Radiator?

 

[carkhz316]

So you had overheating issues before the coolant flush and exchange? Are you losing coolant regularly or any other issues? You should do a cooling system pressure test to verify. What about the coolant temp circuit? If you already replaced the sensor, the wiring can still be an issue.

[Colossus]

Plugged radiator and what brand of thermostat are you running? 

 

[pronstar]

Maybe an air bubble in the system?


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[Logan Lanfear]

Either a bubble in the system or you partially plugged your rad.  Wouldn't surprise me if it was both.  Could be a sensor or just an unrelated issue as well.  

[Nemesisdawn]

I'm positive it's not an air bubble because I changed the coolant twice and the issue didn't change. I tried splashing water on the radiator when it's cold to get any dirt out, still nothing.

 

But I'll have to note that the coolant temp sensor cable looks so thin and fragile, could it be that it's sending a wrong reading when the engine is accelerating?

[Nemesisdawn]

I swapped my clutch fan for electric OEM ones with a harness from JustChevyTrucks. What happens is that when I'm driving, the temp gauge suddenly goes above midway, and I hear the fans kicking on high, and then turn off after a while due to what I think is a shorting stopper that's in the harness, and then the car gets too hot because the fans are off. All this happens when I'm accelerating, or just cruising on roads.

[Nemesisdawn]

On 11/8/2018 at 6:00 PM, carkhz316 said:

So you had overheating issues before the coolant flush and exchange? Are you losing coolant regularly or any other issues? You should do a cooling system pressure test to verify. What about the coolant temp circuit? If you already replaced the sensor, the wiring can still be an issue.

No I did not lose coolant before, and no, there's no white smoke or milky oil. I've had mild overheating problems with the green coolant, but nothing that stopped me from driving the truck. I've posted a picture of the wire above, do you say it could cause all of the problems I'm having? I can see some exposure near where the wire meets the plug.

[carkhz316]

Well, since that is a thermistor circuit, a short circuit would show overheating temps, whereas an open (high resistance) would show cold, so if you suspect the wiring, I'd look for pinched wires somewhere. Also, I re-read your first post, and you mention that the gauge goes just above midway. Could it be that there's really no issue, or do you think it's still overheating?

[Nemesisdawn]

11 minutes ago, carkhz316 said:

Well, since that is a thermistor circuit, a short circuit would show overheating temps, whereas an open (high resistance) would show cold, so if you suspect the wiring, I'd look for pinched wires somewhere. Also, I re-read your first post, and you mention that the gauge goes just above midway. Could it be that there's really no issue, or do you think it's still overheating?

Well I bought a new wire with a pigtail that I'll install tomorrow, and I'll see if that fixes my problem. Whenever I need to push on the gas, or the car has to go up a hill or downshift, the gauge goes above midway, and I can hear the fans kicking on high but then turn off after a minute. And then the car gets seriously hot and lose all its power. The car behaves normal in traffic or idling, but whenever I'm seriously driving it the temp suddenly increases, fans go on high then turn off, and then the car gets seriously hot because the damn fans are off.

 

One thing I noticed is that when the fans turned off while it was still above midway, I fiddled with the lousy temp wire, and then the temp gauge suddenly decreased without the fans even coming on. I'm no coolant expert, but I don't think coolant can become colder suddenly in a running car with no fans.