Overheating after changing temperature sender

[stutaeng]

Hello guys, I hope someone can help me. So my temperature gauge on the instrument cluster has been reading low (about 1/4 mark) on my '00 K3500 with 5.7 for some time now. Everything else seemed to work well.

I finally had the time to swap out the sender by the exhaust manifold out. I lost about a gallon of coolant when I took it out, maybe more. Put the new sender and put water in the radiator and overflow reservoir and started it up... and it started overheating. I had the heater running. Shut is off by the 3/4 mark and the "check gauges" signal had come on.

I thought I had an air pocket and went and bought the fancy Lisle cone for bleeding the coolant system, and still did the same after bleeding. Radiator is pretty new, about 2 years old and had also replaced the thermostat at that time. I checked the thermostat this morning in boiling water and it did open.

The upper radiator hose does NOT feel hot. Seems highly unlikely that the water pump would have failed? Should I disconnect the upper radiator hose to see if there is coolant flow? I suppose the sender could be faulty? Is there another way to check the temperature of the engine?

I have a Innova handheld "scanner," but does not have live data functionality, unfortunately.

Edit: I went and disconnected the upper radiator hose and coolant does flow out of the hose...

 

[Texvet]

Hello guys, I hope someone can help me. So my temperature gauge on the instrument cluster has been reading low (about 1/4 mark) on my '00 K3500 with 5.7 for some time now. Everything else seemed to work well.

I finally had the time to swap out the sender by the exhaust manifold out. I lost about a gallon of coolant when I took it out, maybe more. Put the new sender and put water in the radiator and overflow reservoir and started it up... and it started overheating. I had the heater running. Shut is off by the 3/4 mark and the "check gauges" signal had come on.

I thought I had an air pocket and went and bought the fancy Lisle cone for bleeding the coolant system, and still did the same after bleeding. Radiator is pretty new, about 2 years old and had also replaced the thermostat at that time. I checked the thermostat this morning in boiling water and it did open.

The upper radiator hose does NOT feel hot. Seems highly unlikely that the water pump would have failed? Should I disconnect the upper radiator hose to see if there is coolant flow? I suppose the sender could be faulty? Is there another way to check the temperature of the engine?

I have a Innova handheld "scanner," but does not have live data functionality, unfortunately.

Edit: I went and disconnected the upper radiator hose and coolant does flow out of the hose...

Is it actually overheating, or is it just the gauge that reads high? Put the old sender back in and see what happens.

 

[stutaeng]

Is it actually overheating, or is it just the gauge that reads high? Put the old sender back in and see what happens.

Unfortunately, I cut the old one off, right at the sender. I put an O ring terminal on the new one.

I tried waving my hand over the engine to see if it "felt" like overheating. I can't tell if it's 200F or 260F, lol.

Id rather be cautious than blow the engine.

Now I do have 4.3 Vortec as my daily driver. I'll try swapping that one over to see if sender if off.

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[RawbDidIt]

While cold, "burp" the upper radiator line with the reservoir cap off. If bubbles come up in the reservoir, it's an air pocket in the radiator hose, keep squeezing the hose until no air comes into the reservoir. You've confirmed the pump works and the thermostat, so the odds are that's the issue.

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[88monteSS]

May not be feasible for you, but I've always had good luck parking on a steep hill, taking the rad cap off & letting it run for a bit. Seems to burp the air out pretty reliably every time.

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[alpinecrick]

You may have an air lock in the water pump. I always fill mine with the nose of the truck higher than the rear, and that has (almost) always worked to allow the air out. One time I squeezed the upper radiator hose a bunch of times to push the air out and apparently pushed air into the new water pump. The truck overheated as soon as it began to warm up. Never had trouble previously. I burped everything, shook the truck, but it overheated anyway. I knew I had an airlock somewhere. Finally pulled one end of the pump to manifold hose (the U shaped one that's friggin' hard to get to), and had to wait 2-3 seconds before coolant came shooting out. Air in the water pump.........

 

[90halfton]

"Burping" the upper hose with the cap off and topping off has always worked for me. OCD as it may be, when I need to fill the empty system I pull the temp sensor out of the intake manifold for an air outlet and fill the radiator til coolant appears at the temp sensor hole. Makes no sense as the heater core/hose should expel air.....but I do it anyways.

 

[Erik the Awful]

If you burp the air bubbles out of the radiator hose and still have the same issue, it's likely either a stuck thermostat or a freewheeling water pump.

 

[Kkortman112]

I have a 1993 4.3 and changed my sending unit on the side of the head as well as radiator and heater hoses and thermostat last weekend. I had the same issue as you. I ended up taking the upper radiator hose and thermostat back out and topping the block off with coolant there, reinstalling them and finishing filling the radiator. That worked for me.

 

[Pinger]

May not be feasible for you, but I've always had good luck parking on a steep hill, taking the rad cap off & letting it run for a bit. Seems to burp the air out pretty reliably every time.

Sent from my XT1254 using Tapatalk

Yep, nose pointing up hill worked for me too.