SOLVED: Diagnosing/replacing a leaky radiator + flushing coolant (for the inexperienced GMT400 owner)

[rebelyell]

Since I flushed it while the truck was parked on a slight incline facing uphill, should I be worried about water being in there that never drained out? (Bumping the question because new page)

During your flush process, did you also remove the block drain plugs (2) located about midway fore-aft, either side of block just above pan rails ? --- that's where the rust-sediment and any unmixed coolant collects at bottom of water jackets. Of course, if you've been driving it, it has already mixed. Removing those drain plugs is both a basic & important step in flushing / cleaning coolant system.

 

[Erik the Awful]

Since I flushed it while the truck was parked on a slight incline facing uphill, should I be worried about water being in there that never drained out? (Bumping the question because new page)

It's a question of "perfection" versus "good enough". Are you trying to build a time capsule truck that will last fifty years of only Sunday driving and be pristine, or are you going to drive it and do truck stuff with it? Are you willing to perform routine maintenance?

If you're going to be using the truck and maintaining it, don't overthink it.

 

[slow_c1500]

Ok I filled her up and ran her at idle for about 25 min (maybe that’s excessive but I wanted to be sure I get out as much air as possible). Test drove her about 15 miles and the temp behaved normally, highest it got was a couple ticks before 210, just like before. Checked trans fluid, all good. I think it’s safe to say she’s drivable again

Im probably overthinking it, and it probably doesn’t matter since the temp was fine during test drive, but I didn’t fill the overflow until after the test drive and burping the air out. Would this matter at all? Is it possible for air to have gotten into the system from the overflow during driving? Before the drive, the coolant level was just under the overflow hole, then I installed cap and drove it.

 

[JDGMC]

No impact with that scenario. Just keep an eye on your coolant level and check for leaks over the next 100 miles or so. Good job!

 

[slow_c1500]

thank y’all for your help once again! I will change the thread title to something a little more relevant lol in case anyone ever looks back at it

 

[movietvet]

thank y’all for your help once again! I will change the thread title to something a little more relevant lol in case anyone ever looks back at it

When you change the thread title, you can add solved in all caps. Members looks for that to read the whole thread

 

[slow_c1500]

Ok it’s been a few days since the coolant refill, i noticed that the coolant level in the overflow has gone down. My guess is that some air has naturally found its way out of the system, and coolant from the overflow has come down to take its place. I think (and hope) this is the case since there are no external leaks and the oil looks normal so I am guessing no internal leaks either.

 

[Road Trip]

Ok it’s been a few days since the coolant refill, i noticed that the coolant level in the overflow has gone down. My guess is that some air has naturally found its way out of the system, and coolant from the overflow has come down to take its place. I think (and hope) this is the case since there are no external leaks and the oil looks normal so I am guessing no internal leaks either.

It's normal for this to happen as the last little bits of trapped air move from the far corners of the
cooling system to the top of the radiator. So when the hot engine is shut off, as the antifreeze/water
mix cools down, it contracts creating a partial vacuum, and pulls coolant from the overflow tank.

The next morning, you fire up the engine, you head to work, the coolant expands, and the air at the
top of the radiator is the first to be pushed out towards the overflow tank. And once you arrive at work
and shutdown, as the engine cools it again pulls coolant from the overflow tank into the radiator. It may take
2 or 3 trips to get all the air burped out to the overflow tank this way, but eventually there be zero air in the
radiator/rest of the cooling system.

If you haven't already done so, find the "Full Cold" molded line on your overflow tank and put a clearly visible
sharpie mark on that. What you want to end up with is the overflow tank that's filled right to that mark
when the engine is cold. And when your cooling system is healthy it is always at or above that mark at
all times, and never goes below. No coolant consumption = healthy motor with no leaky intake manifold
gaskets, blown head gaskets, or weepy water pump seals, etc.

Here's to a well-behaved cooling system that stays fixed.