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'99 Chevy Lumina Radiator Work


I recently did a radiator flush with my '99 Chevy Lumina 3.1L today since it started running close to overheating. The previous owner had it sitting in Ohio during one winter and then here in Arizona before I bought it for God knows how long. That being said, there’s rust build up in the radiator which is why I performed a flush. That actually fixed the temperature issue but now I’m not sure exactly what the part is (pictured below) but I am almost sure it’s leaking because after I shut my car off, there’s sizzling hot dirty water chilling right under the intake manifold area. Circled in red below is what is believed to be leaking and/or cracked.

Pictures of issues via Imgur

What part is this? I believe it’s the “intake coolant line” but I’m not sure if that’s the actual name.


Guess: Possibly the “bypass coolant line.”

Chilling? and why do you have hot dirty water instead of coolant ?

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Yes, as shown in the pictures it’s just been sitting there. Even this morning it was still there and I’m in Arizona. Like I said, previous owner neglected it by leaving during the winter in Ohio which built up rust.

huh? how can hot water be chilling?

Sitting during winter does not damage anything. I routinely have multiple cars that sit unused for the colder months (~6 months). What does damage cooling systems is not changing the coolant. The rust inhibitors in coolant degrade over time…


None of you are contributing to the question I initially asked instead you’re trying to correct the way I’ve explained things or telling me what I should or shouldn’t have done. I didn’t ask that anywhere in my initial post. Secondly, chilling as in just sitting there… not chilling as in cold.

And how were we supposed to know that slang term meant fluid was accumulating from a leak ?

Because insightful already guessed correctly- it’s the bypass hose-

It’s always important to know the REAL reason something failed because then you can address all of the collateral damage as well. Imagine if you thought only the radiator was affected by the rusty water…

You may not want to hear this, but that rusty brown fluid needs to be completely purged from the system before considering this repaired.

Also, you cannot tell where that fluid is coming from without removing the plenum, if that’s what we’re looking at… although it looks like a cast part to me. You need to start doing some disassembly to determine the source of that fluid. And even if you find the path it’s traveling to get to the hole in the photo, it still may be coming from the thermostat or… and this is my real guess… … corroded steel parts inside the block (steel cylinder sleeves perhaps). Or perhaps inside the radiator, although the tanks are generally copper or plastic and the cores are copper.

Having said all that, I believe this system uses a radiator with two heat exchangers stacked, the lower being for the transmission fluid and the upper for engine coolant. You may have bigger problems than you realize.

If all you want to do is identify that part, that’s easy.
If you want to fix the car… that’s a far bigger problem.

Thank you for actually giving me an insight of what may be going on and how to go about identifying the problem. I stopped by a mechanic this morning and he said it definitely looks like the bypass hose/pipe is leaking but would need to pull the intake manifold off to get a better idea. He said if it is the pipe, he’d charge $200 to fix it.

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