Howdy folks! First order of business for getting the truck back into tip-top shape this year: fixing the heat. I was tired of driving around in winter freezing my butt off. A dealership flushed the core for me a year or two back and it didn't seem to do much — but rather than pull the whole dash for a full heater core replacement (no fun at all), I decided to give it a real, thorough flush myself. Cheapest route first. Spoiler: it worked.
Confirm the Core Is the Problem
With the engine warmed up, find the two heater core hoses — one in, one out — at the firewall. If both are hot to the touch, coolant is flowing and the core is a good candidate for a flush. Mine were both hot, so it was worth a shot before tearing anything apart.
Disconnect the Hoses
Pull both heater hoses off their nozzles. Fair warning: this can be a bear. I used channel locks and regular pliers to squeeze the clamps back, and there's barely any room to get your hands in there. A handy trick on the tougher clamp — squeeze it open and slip a zip tie around it to hold it loose, so you can freely slide it back out of the way while you work.
Flush It Out
Thread a 5/8-inch barb-to-garden-hose fitting onto each heater hose (about five bucks each at the hardware store). Connect garden hoses and run water through to flush the system. Then put a funnel in the end, pour in some CLR (Calcium Lime Rust), and let it sit for about half an hour to break down the built-up scale. Flush that out thoroughly afterward — you should see sediment come out, which is exactly the sign you want.
Button It Back Up
Reconnect both hoses to their nozzles (the part you were dreading on the way out), top off with coolant, and let the system burp out any air. Then take it for a drive to test. In my case, the flush absolutely worked and I was thrilled — it saved me a lot of money versus a full core replacement. If you find yourself in the same boat, it's worth trying first; it might just save you some too.
The Tools & Supplies
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CLR Calcium, Lime & Rust Remover
Sits in the core for ~30 minutes to break down scale before the final flush.
5/8" Barb to Garden Hose Fittings
The cheap adapters that let you connect a garden hose straight to the heater hoses.
Automotive Funnel Set
For pouring CLR and coolant cleanly into the lines.
Channel Lock Pliers
For wrestling those stubborn hose clamps off in tight quarters.
Engine Coolant / Antifreeze
To refill the system once the flush is done.
Up next on the channel: I've got a diesel heater that needs installing — so stay tuned for that one. Until we meet again, Godspeed.
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▶ Subscribe on YouTubeDisclaimer: The information provided in this article and its video is for entertainment/educational purposes only. By following any advice from this article, video, or any provided links, you do so at your own risk. Please consult with a professional before attempting any automotive, construction, plumbing or electrical work.