Anyone had this issue with heater/coolant?
 

I have a 4.8L 2001 Silverado that has been needing a coolant top off every few weeks for years. The oil is never milky in any way, so the head gasket seems a very remote possibilities. I cannot find any obvious exterior leaks, but I did replaced my water pump as the truck is well over 200K and there was some slight yellow staining under the water pump's weep hole, however, this changed nothing. Thing is, every time I get in and start up the truck, the heater core gurgles a bit, so I'm thinking the leak might be in that area. Has anyone had this issue? Thanks in advance for any assistance so I don't just part swap over and over.

Thanks so much in advance!!!

My coolant issues
 

In my 2004 Sierra coolant was leaking out the weephole in the pump, but only if it was in the perfect position. There would mostly be no sign of a leak, then one day there's a puddle. Another issue I had lately, with a new reservoir cap was it was leaking. T test I fed the overflow pipe int a soda bottle. After a week of driving, there was 1/4" of coolant in the bottle. no cap on the radiator seems weird.

In my 2004 Express I was using about 1/2 gallon coolant per week for a few years. No one could find the issue till one Mechanic took a risk and pumped the cooling system pressure tester way past the recommended pressure. Suddenly the pressure would drop and indicate a leak. Water, oil were all fine. When he took off the head and cover, it was covered in a thick black gunge. Blown gasket. [If i recall correctly, maybe16# pressure was the recommended pressure, and it stayed constant for hours indicating no problem. At 20# the pressure would slowly fall back to 18# before leveling out]

"To test I fed the overflow pipe int a soda bottle. After a week of driving, there was 1/4" of coolant in the bottle. no cap on the radiator seems weird." This is interesting, I'll give this a try. And I agree, a flush topped, sealed radiator is a new thing for me too.

"When he took off the head and cover, it was covered in a thick black gunge. Blown gasket. [If i recall correctly, maybe16# pressure was the recommended pressure, and it stayed constant for hours indicating no problem. At 20# the pressure would slowly fall back to 18# before leveling out]" I'll see if the mechanic I know well has this testing ability. I hope it isn't a head gasket. I have heard head gaskets on certain GM products are common and some very much uncommon. Have you heard such stereotypes?

Thanks for your thoughts and experience!

Had a similar issue on my '22 Silverado last year. The fix was pretty straightforward - my thermostat was stuck closed and needed to be replaced, but a tech I know said it's also possible the coolant level sensor was faulty.

You can't just fill the reservoir and think the radiator is full. Pull the top radiator hose where it goes into the top of the motor, fill that house with coolant until it starts coming out of the goose neck. Carefully put that house back on to the goose neck, trying not to spill much. Next, take the same hose off of the radiator and fill till it's full. The reattach to the radiator. Now fill the reservoir to full. Shouldn't have any problems after that. It's easier to fill with a funnel in your hose.

Interesting, if the thermostat was stuck closed, did your truck run hot at all?
And... the coolant level sensor? I know nothing about that and I feel the '01 doesn't have one at all. And, even if it did, I do have lowering coolant as it's going somewhere.

Thanks for your thoughts!

I went through my truck overheating for 2 yrs until I learned how to fill the radiator. Pull the top hose* and follow my instructions.

Your not getting the radiator full, so it's overheating. It won't fill the radiator full with the reservoir. It leave a space.

I put a bottle on the overflow hose and it has about 1/4" of coolant after driving it around a bit. What was the issue with that? The cap on the coolant reservoir?
Thanks again!

When you you fill the reservoir up, it does fill the radiator completely. It leaves an air space in the radiator, which causes it to over heat. The over heating is what builds the pressure to push the coolant out of the overflow. Pull the top radiator hose at the gooseneck first. Put a funnel in the hose and fill with coolant until it starts to come out of the gooseneck. Reattach the hose and then go to the other side of it where it connects to the top of the radiator. Put a funnel in that side and fill till you can't put anymore in it. Reattach and then fill the reservoir to the proper level. You won't have anymore overheating problems.

Hello; I have had two slow leaks with my 2004 Silverado with the 4.8. Took a while to find the first. I had to remove the plastic belly pan so I could see. Was the O-ring gasket where the water pump mounts to the engine block.
Just found the second leak a few weeks ago. again removed the plastic belly pan. turns out to be a Y shaped hose which runs to the overflow tank. it is seeping at the Y connector.