Discolored coolant? We're betting it's colored with either rust or oil.

Dear Car Talk

Dear Car Talk | Oct 01, 2003

Dear Tom and Ray:

My mother recently bought a used 1999 Daewoo Nubira. It looked shiny and new, and it ran pretty well. When we inspected the engine compartment, we noticed that the coolant was brown and had an awful smell to it. I recommended that she get it serviced, so she went to the local quick-lube and got her fluids changed. About two weeks later, we checked it again, and once again, the coolant had turned brown and that old, familiar smell came back. What could be causing this? Please help my momma! -- Josh

RAY: Josh, it sounds like you "checked the engine compartment" AFTER you bought the car. Switch the order next time, OK?

TOM: It's possible that the car has a blown head gasket and that what you're seeing in the coolant is oil. That's hundreds of dollars to fix. So you want to rule that out first. A good mechanic can rule it out for you with a head-gasket test.

RAY: More likely, however, is that she's just got rust in the cooling system. If the previous owner never changed the coolant, the rust inhibitors would eventually wear out. And then rust could build up inside the radiator and cooling passages. That would explain the brown color and the foul odor. Most people don't know it, but rust stinks. Big time.

TOM: So if the head gasket passes its tests, I'd get the cooling system power-flushed. That's where they pump a cleaning solution through the system and try to flush out any loose rust particles. It might not get everything. In fact, she might have to do it several times before the coolant clears up. But it beats replacing the head gasket, Josh. And next time, be a good son and have any used car checked by a trustworthy mechanic BEFORE your mom buys it.

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