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

[AuroraGirl]

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?

With a radiator having rust like that, I would use a chemical flush like Thermocure

https://www.oreillyauto.com/detail/c/thermocure/evapo-rust-thermocure-cooling-system-rust-remover/eva1/tc001

It IS aggressive, so be mindful of using it with super high mileage.. might just start a leak in a heater core if your coolant was neglected for a long time.

But the removal of the thermostat, running your hose through your entire system, that means heater core, block both directions(which requires putting the housing back on without the t stat) , and do it tills its clear. Once its clear, you should use DISTILLED water and cheapest anti freeze concentrate you can get to fill your system up, equal parts. Then drive it (you can have the t stat back in for this part), put like 2 weeks on it, while checking every few days. if you see its getting dirty again then do another flush. As mentioned, block drains are good but theres a chance they are occupied by a knock sensor, but I could be wrong.

 

[slow_c1500]

Yes, the passenger side block drain has a knock sensor on it. I already took both drains out, I had to poke the hole with a screwdriver to get it to drain lol.

Dumb question but if the rust in there is hardened and solid enough, (I have no idea how long the previous owner neglected the coolant), would it be better to just leave it alone than risk stirring it up and having more particles flowing through the system? I will still gently flush the motor with a garden hose to get the loose bits out, but maybe it’s better to leave the really solid, hardened rust where it’s sitting?

 

[JDGMC]

Since you are at the point where chemical flushing would be easy to do and looks like it could use it - I would flush it.

 

[JDGMC]

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.

I think Dexcool is a well formulated product under ideal conditions. It's just too darn delicate when it comes to non ideal conditions that often occurs for the average vehicle that's semi maintained. The impact to the system usually requires more work and cost to fix.

 

[JDGMC]

DI is "de-ionized" I wouldn't even know where to get that. Distilled would be fine.

Walmart, but it's 9X the price of Distilled.

 

[slow_c1500]

Since you are at the point where chemical flushing would be easy to do and looks like it could use it - I would flush it.

would I just pour the thermocure into the thermostat hole, have the block drains screwed in and lower hose blocked off, let it sit for a few days, and then drain out later? I can’t run the motor.

 

[454cid]

Thermocure is something that you have in the cooling system with the engine running/driving. It may not be effective just letting it sit, and you'd likely need a couple quarts of it.... so kind of expensive. It seems to be about $25 a quart. It might be a better option to keep it simple and just flush it with water with the block drains pulled, and call it good.

 

[slow_c1500]

Thermocure is something that you have in the cooling system with the engine running/driving. It may not be effective just letting it sit, and you'd likely need a couple quarts of it.... so kind of expensive. It seems to be about $25 a quart. It might be a better option to keep it simple and just flush it with water with the block drains pulled, and call it good.

That’s what I’m saying, it may be better to water flush out the loose debris and leave the heavy deposits where they are, not really causing any issues. It has never had problems overheating. Also I am heading away to college soon and I don’t have time to do multiple flushes. I just wanna get her the way she was running before, but with a fresh radiator/Tstat/upper n lower hoses, and non mixed coolant lol.

 

[termite]

That’s what I’m saying, it may be better to water flush out the loose debris and leave the heavy deposits where they are, not really causing any issues. It has never had problems overheating. Also I am heading away to college soon and I don’t have time to do multiple flushes. I just wanna get her the way she was running before, but with a fresh radiator/Tstat/upper n lower hoses, and non mixed coolant lol.

FWIW, the most involved I have gone with flushing one, including the 4.3 blazer I got with overheating issues, was flushing a few times with water from the garden hose. This included pulling the block drains at least twice, one of which was right before filling with coolant.

 

[slow_c1500]

I figured while I had the coolant out I would flush the heater core and heater hoses, long story short I don’t remember what order the rubber o rings and plastic gasket rings for the heater inlet tube go. I can’t remember if it goes: plastic, rubber, plastic? Or rubber, plastic, plastic? Anyone know? I can only get the quick connect to fit back in if I do the rubber, plastic, plastic order. (Meaning rubber o ring going onto the inlet tube first, and being furthest away from the intake hole. But I don’t know if that’s correct. Anyone know?

Should I consider changing the fitting to something non quick connect while I got the coolant out, or not even risk breaking the fitting?

F*ck quick connect