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

[JDGMC]

How much DEX did you add to top it off? You mentioned the system was flushed by a shop and just now discovered it was green. Did you contact the shop to confirm what type of “green” antifreeze they added? Napa offers an “Extended Life Cooling System Antifreeze + Coolant for All Makes All Models” and it’s green. When flushing the system I’m assuming you are removing the thermostat first? Just to confirm - the vehicle is a 96 C1500 w/5.7 correct? If possible can you post pics of the radiator fill neck, radiator cap (bottom view), and the thermostat port/jacket? Did you observe gel, chunks, rust, etc. in the old antifreeze?

 

[AuroraGirl]

As long as the system was properly cleaned out and the new coolant was used is good, new coolant, I wouldnt worry about anything. Asking the shop what kind of coolant they use is a good idea, because if they used traditional green , you can safely keep it until you need to service the truck again (2 years) and then go back to DEXCOOL if you want.
Or if you stay on it, you can use original green just as easily. But remember to stay on it.

Dexcool has benefits but it requires you bleed the system absolutely properly and ensure your radiator cap is sealing and purges/vents when it should.

 

[slow_c1500]

When flushing the system I’m assuming you are removing the thermostat first?

What is the benefit/purpose of removing the thermostat? Is that where I would pour (I emphasize pour, as in low pressure) water into when flushing the block?

 

[slow_c1500]

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Like I said very dirty. Idk how long it has been like this, or if the shop flushing my coolant did anything to help.

 

[slow_c1500]

Found my leak. Just as I suspected it was the radiator. Didn’t even need to get the pressure to 10psi and a little stream came out the front of the rad. While I wait on the new part I want to flush the block with water. What is the best/proper/safest way to do this, explained in 4th grade instructions because I’m new to this?

Also how urgent is it that I drain the block? should I be worried about water in there? So far I only removed the rad and flushed it separately, then reconnected it for the pressure test, then topped off system with water. After test I drained water out of plastic thumb screw and lower rad hose. Would there be any amount of water still in the block that would warrant draining it asap?

 

[termite]

Also how urgent is it that I drain the block?

I would pull the block drains, one on each side. There is a surprising amount of water that remains in there unless you pull them. In the 5.7s, I think at least one is a knock sensor in the drain hole.

At the least, I'd be sure to drain them before the final fill with coolant. And the knock sensor needs to be installed per FSM specs for torque. I'm not sure if there is a particular sealant that should be used. Others will chime in or can likely be found with a search on here.

 

[JDGMC]

Doesn't look to bad in there. My suggestion to pull the thermostat would only be necessary if large sediments are present. BTW when you get to the final fill, use DI water if possible.

 

[GoToGuy]

100% refined petroleum engine oil = Mineral base. Hybrid oil = semi -synthetic ; low percentage petroleum, high % engineered product = synthetic

Coal, Iron ore, Natural Gas, Crude oil = Mineral group.

 

[slow_c1500]

Doesn't look to bad in there. My suggestion to pull the thermostat would only be necessary if large sediments are present. BTW when you get to the final fill, use DI water if possible.

I figure since now I have the coolant completely drained out of the block, and while I’m waiting for the new rad to come in, Ill pull the thermostat and clean it, as well as the upper and lower hose. Maybe even flush the heater core again.

I am using premixed green coolant oriellys brand so no water necessary for final fill, but yes I have heard DI water is best if mixing.

Is there a specific way I should flush the block to ensure it gets cleaned good? Where should I pour the water in from? (Keep in mind radiator is removed.) And is it safe to use a garden hose as long as it’s a slower flow and not a jet stream at high pressure?

 

[454cid]

I figure since now I have the coolant completely drained out of the block, and while I’m waiting for the new rad to come in, Ill pull the thermostat and clean it, as well as the upper and lower hose. Maybe even flush the heater core again.

If you've got the money, and the existing parts are older, I'd go ahead and replace the hoses, and thermostat, since you're doing the radiator. Flushing the heater core wouldn't be a bad idea.

I am using premixed green coolant oriellys brand so no water necessary for final fill, but yes I have heard DI water is best if mixing.

That's the expensive way of doing it. I'd only use pre-mix if that's all that was available, or the cooling system was very small. DI is "de-ionized" I wouldn't even know where to get that. Distilled would be fine.