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

[slow_c1500]

Hello all, the other day I noticed my truck was low on coolant so I topped it off at the overflow tank with some orange dexcool I had lying around. At the time I thought the existing coolant in the truck was compatible with dexcool, it was done by a shop a few years back. Turns out it actually had green coolant in it, and after driving it about 20 miles with dexcool mixed in there, I noticed a burning coolant smell. Popped the hood and saw that coolant had spat over the top of the engine. None of the radiator hoses were leaking, but the radiator was wet with coolant. I can only assume the mixed coolant is what caused this. I am obviously going to drain the system and replace with all green. My question is, should I replace the radiator? I see no other part that the coolant could have spat out of, but I’d like to hear any suggestions, or any kind of explanation for how mixing coolant can somehow cause this to happen. Thanks!

 

[termite]

Hello all, the other day I noticed my truck was low on coolant so I topped it off at the overflow tank with some orange dexcool I had lying around. At the time I thought the existing coolant in the truck was compatible with dexcool, it was done by a shop a few years back. Turns out it actually had green coolant in it, and after driving it about 20 miles with dexcool mixed in there, I noticed a burning coolant smell. Popped the hood and saw that coolant had spat over the top of the engine. None of the radiator hoses were leaking, but the radiator was wet with coolant. I can only assume the mixed coolant is what caused this. I am obviously going to drain the system and replace with all green. My question is, should I replace the radiator? I see no other part that the coolant could have spat out of, but I’d like to hear any suggestions, or any kind of explanation for how mixing coolant can somehow cause this to happen. Thanks!

I'd be looking for leak but wouldn't chalk it up to mixed coolant types. I'd first find and fix the leak, pressure tester would be helpful, then a flush-n-fill with ensuring both block drains were pulled.

 

[slow_c1500]

I already removed the radiator and flushed it, it was extremely dirty in there. I will do the block as well. Is there a good way I can test the rad for leaks while it’s removed? Btw some of the rad fins are bent but I don’t know if they were like that before.

 

[Komet]

When you flush it out, fill it back up with water first and try to figure out where the leak is coming from. Rad fins are extremely easy to bend. Fortunately, they're also easy to bend back.

 

[slow_c1500]

I filled the rad with water and held it up to see if it leaked at all. Turned it over to test the other side. No leaks. I’m really confused how the truck could spit coolant on top of the motor and fan shroud if the rad and its hoses aren’t leaking, even more puzzled if it was a coincidence or if mixing coolant caused this.

 

[1998_K1500_Sub]

Very interesting reading may be found in these Motor Magazine stories about coolant types and their additive packages, and how / why they vary from manufacturer to manufacturer and application to application:

Coolant Confusion: It's Not Easy Being Green ... or Yellow or Orange or ...​

https://www.motor.com//magazine/pdfs/082004_04.pdf


Relearning the Alphabet: Making Sense of the Cooling System Scene
https://www.motor.com/magazinepdfs/082010_08.pdf

Both these should be required reading for any shade tree mechanic, IMHO.

 

[smdk2500]

Are you putting it under pressure when you test it?

 

[Komet]

You're not really going to be able to test the radiator until it's under pressure.

 

[slow_c1500]

Can I do that by just attaching a running water hose to one of the openings, and closing off the others?

 

[1998_K1500_Sub]

Can I do that by just attaching a running water hose to one of the openings, and closing off the others?

That’ll give you water-mains pressure on the radiator (and coolant system, including engine coolant passages / gaskets / seals, water pump and heater core, if connected, which I have seen done)

It may not be a bad idea but I don’t think it’s a good one. Water mains around me run 50-55psi.

Get a coolant system test pump and use it to apply rated pressure (probably 15psi).