Bottom Line
Maintenance Q&A
Running hot

By Paul Abelson
senior technical editor


Q: I have a 2006 Freightliner with a 500 Detroit. I spec’d it for light weight, so there’s lots of aluminum including the radiator. A few months ago, I noticed it was running warmer than usual, and recently it started running hot climbing hills. Since it’s out of warranty, I took it to an independent repair shop to save some money. The guy that runs it says that because it’s aluminum, he couldn’t clean my radiator. He wants to sell me a new one.
Is he right?


A: The first place I went for answers was to the TMC Recommended Practices Manual. RP333A deals with Heat Exchanger Exterior Maintenance and Cleaning. Because aluminum does require special handling, aluminum radiator maintenance is covered.

You may not need a new radiator. Yours can be cleaned if it hasn’t been damaged. Before replacing it, clean it thoroughly inside and outside. If you still have problems after that, then you can consider replacing the core or the entire radiator.

Start with the outside. Remove all debris from the air passages through all your heat exchangers: the oil cooler, air conditioning condenser, charge air cooler and radiator. They all must be open for air to flow smoothly and completely through.

Large debris such as leaves,  paper or even twigs collect on the heat exchanger surfaces. Smaller items like insects, grass, plant products, dirt, oil mist and corrosive chemicals tend to collect between the heat exchanger fins, which should be straight. Often, the debris passes through one heat exchanger and is trapped in the one behind it. Debris collects and restricts flow. It scrapes up fins and tubes, eventually bonding to them, which leads to overheating.

Fins and tubes are easily damaged. Harsh chemicals can remove the protective outer layer of aluminum. TMC recommends using a mixture of water and dishwashing detergent because it is gentle and effective. Use a soft brush. Avoid wire brushes or any tools that can bend fins. You don’t have to remove heat exchangers, but loosen them so you can get in between them to flush away debris from each one.

If you’re using compressed air to blow debris away, keep it under 30 psi. Be careful not to contact fins with the nozzle. Always work from the engine side out to the front, against the direction of the normal airflow.

Place a plastic sheet in front of each exchanger as you’re cleaning it, so debris isn’t forced into the one in front. You can rig a flushing tool to get into the narrow openings between heat exchangers. Get a watering wand at a lawn and garden store. Cut the tube to the length you need and then crimp the end closed with pliers. Drill small holes every few inches in a line along just one side. Put it on a garden hose and you’ll have a gentle, directional flushing tool.

Steam cleaning is also safe and effective. When you see what comes out of your coolers, you may discover what caused your overheating. But if that doesn’t bring your temperatures back to normal, the problem may be internal.

According to RP336A, Aluminum Radiator Maintenance, the use of high-silicate antifreeze or coolants developed for aluminum, along with standard supplemental cooling additives, may cause gelling problems and/or silicate dropout. When this happens, alkaline-based cleaners may be required. Only cleaners that specifically state they are aluminum safe should be used. Always follow the directions for the product.

If you are still having overheating problems after performing these cleaning steps, you may have to replace the radiator after all. LL


Paul Abelson can be reached at