A Cloudy Windshield Often Means Bad Heater Core

Dear Car Talk

Dear Car Talk | Aug 29, 2017

Dear Car Talk:

I have a 2015 Yukon XL with a cloudy inside windshield. It looks perfectly clean until the sun or oncoming headlights shine on it. I have tried to wash it with glass cleaner, and also plain water. When I go to dry it, it streaks really bad. One time, when I took it in for service, I asked the service representative if the manufacturer had put some kind of film on it. She said, "It's coming from the defroster, and there is nothing I can do about it." The only way I have found to clean it is with a dry cloth.

I like to drive with a clean windshield inside and out. No one smokes in my vehicle. I have been driving for 56 years and have cleaned a lot of windshields. Do you have any ideas? I live in northern Ohio, so I can't just stop using my defroster. But I hate having to clean my windshield every time I use my defroster. What's wrong? -- Judy

Well, these are classic symptoms of a leaking heater core, Judy. But your car seems to be too new to have a bad heater core.

The heater core is a second, small radiator that provides heat to the passenger compartment. When you call for heat, coolant from the engine circulates through it, then the fan blows over the heater core and transmits heat from that hot coolant, through the vents, to the car's interior.

But if the heater core is leaking, coolant mist can get blown by the fan, along with the warm air. Coolant is greasy, and guess what it does? It leaves a film.

It also has a sweet taste, but it's toxic, so I don't recommend that you give it the taste test. You might want to give it a sniff, though, and see if it smells at all sweet to you.

If you were writing to me about a 2005 Yukon, I'd feel pretty certain that a heater core is what you need. But it's odd to have one fail on a newer car.

The only other possibility is that the vinyl from the car's dashboard and interior parts is outgassing. That's what most of us know as the "new car smell." But it's actually the sublimation of vinyl particles into the air, which can leave a film on your windshield, too.

But you say the film appears every time you use the defroster, so I'd have to lean toward a heater core problem. You're probably still under warranty, Judy, so go back and ask them to fix it. If they say, "It's related to the defroster," ask them how. The only way I can think of is that the heater core is leaking coolant, and it's blowing onto your windshield.

If they have another explanation, write back and let me know what it is. Maybe we can use it to get rid of some of our troublesome customers. Good luck, Judy.

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