Used car prices finally dropped after years of high demand, short supply, and high prices. According to car buying site CarEdge, this is due to purchasing incentives for new cars and high interest rates. However, two mechanics from Dave’s Auto Center (@davesautocenter) in Centerville, Utah, recently warned people who are car shopping about one glaring red flag they’ve noticed in used cars lately that anyone can check for.
“We’ve had a rash of used cars that have issues, and we got one here this morning,” Dave says before handing the mic to Miles, president of Dave’s Auto Center. Their explanation received over 221,000 views as of publication.
What’s the issue?
Pointing underneath the hood, Miles explains that the red flag is a car’s overflow bottle (or coolant reservoir) being black instead of clear, “especially on diesels.”
“If you see your overflow bottle that’s black, don’t let a used-car dealer or somebody say, like, ‘Hey, we can just clean it. It’s just dirty.’ That’s wrong,” Miles says. “It’s not just dirty; it’s full of exhaust and, especially on a diesel, that exhaust is really sooty. If you see your overflow bottle black like this, it is an indicator that you have a blown head gasket or exhaust getting into your cooling system, making the bottle black.”
What is an antifreeze overflow bottle?
According to AutoZone, a coolant reservoir, or antifreeze overflow bottle, is “a regulating component to the excess coolant that’s produced from the heat in your engine” that catches heated coolant overflow. After a turned-off car cools down, the coolant is “sucked back into the radiator.”
New tanks versus old tanks
At the end of the clip, Dave shows viewers why a black overflow tank is a red flag by comparing two more antifreeze overflow bottles. He shows a new one with clear plastic and an old one with yellow discoloration from age to demonstrate that a black-stained bottle means there’s “soot crap inside the antifreeze overflow.”
@davesautocenter Warning ⚠️ Don’t buy if you see Black #autoshop #autorepair #usedcar #usedcars #enginerepair ♬ original sound – Davesautocenter
Some viewers added some extra issues that a black bottle could indicate.
“Don’t forget oil contamination. oil cooler failure. danger is a correct term,” one said.
“That looks like an eco diesel with a bad oil cooler. (Oil in the coolant) common issue with the eco diesel,” a second added.
Most thanked Dave and Miles for the shop’s series of red flag warnings for people shopping for cars. Their videos include topics like “What to check before buying a new car” and how “shoddy jobs” lead to A/C contamination.
“Great advice and knowledge,” a viewer said.
“Finally an honest mechanic shop,” another agreed.
The Daily Dot reached out to Dave’s Auto Center via the shop’s contact form and TikTok comments.
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