The Heat Is On in Greg's Dakota Sport

Dear Car Talk

Dear Car Talk | Jan 25, 2012

Dear Tom and Ray:

I had a heater core on a '99 Dakota Sport replaced, and I now have heat all the time without it being turned on. I was told that I was feeling heat from the engine because there is no insulation on the firewall. I didn't have this problem before the new core was installed. What, if anything, did they forget to do?

-- Greg

TOM: Boy, you're an understanding guy, Greg. They give you a song and dance like that, and you say, "Okey dokey," and walk away. We could use some customers like you!

RAY: That's not heat from the engine bleeding through, Greg. That's heat from the heater. And it's likely the fault of the guys who changed the heater core.

TOM: But before we conclude that they're absolutely to blame (we'll get to that soon enough), let's look at one other possibility. The heater controls in this truck are operated by engine vacuum. There's a check valve under the hood that helps the system maintain vacuum during hard acceleration.

RAY: Right. So if that check valve were broken, your blend doors (the flaps behind the dashboard that regulate how much heat comes into the cabin) can pop open during hard acceleration.

TOM: So if you're getting a surge of heat only when you're accelerating hard or climbing a hill, then this five-dollar check valve could be the problem.

RAY: But if you're getting heat all the time -- which is what you say in your letter -- then these guys screwed something up. Maybe they jammed a blend door so it can't close all the way. Or maybe they forgot to reattach a vacuum hose.

TOM: The reason they're trying to get rid of you is because rescuing the Chilean miners was easier than getting to the heater core in this vehicle. They don't want to do it again. For free. So they're hoping you'll just go away, or start driving around in your bathing suit.

RAY: So you're just going to have to be a little more insistent when you go back to see them, Greg. Bring a couple of large friends with you. Or a lacrosse team.

TOM: They don't want to take out the dashboard again, but that's what happens when you screw something up -- you have to do it again until you get it right.

RAY: Sure. Ask my brother about his years in eighth grade.

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