My 2003 Ford Ranger 4X4 overheats when climbing at low speeds. I can drive a steep mountain pass in summer with the AC on at highway speeds just fine–the temperature gauge stays m/l in the middle. But on a gravel or dirt mountain road climbing at say 5 to 15 miles per hour, the temperature climbs steadily until the “check gauge” light comes on. I first noticed this last summer & the dealer did a block test (which was OK)& replaced the fan clutch which was slipping. I just had the 90,000 mile service done which included a coolant system flush. And the problem continues. When I had the 60,000 mile service done a couple of years ago, they repaired the radiator. Not sure if this was a re-core or it was just cleaned out (It cost $150 at the radiator shop plus labor to install). The engine is a 4-liter V6. Anyway, I’m not sure what to do next. If anyone has a pearl of wisdom for me, I would really appreciate it! Thanks!!!
The first thing to check for is if there’s an air restriction at the condenser in front of the radiator. Things like bugs, leaves, and whatever. The condenser releases heat when the AC is on, and since it sits in front of the radiator, it effects the engine coolant temperature. If there’s not enough air moving thru the condenser/radiator because of poor air flow, the engine starts to overheat from the heat released from the condenser into the radiator.
For $150, nothing was replaced. I guess the shop cleaned the exterior of your radiator, which was probably loaded up with dirt and insects and plant life. When you climb a steep slope at a low speed, you intermittently use high torque at lower engine speeds (uphill) along with normal torque at normal engine speeds when the truck was travelling on flat terrain. All this time you are not doing what the truck was actually designed to do, which is to travel on clean, dry highways. Your engine is mostly cooled by air-flow. There are of course electronic fans to cool your engine if necessary while your truck is idling in a traffic jam or at a stop light, but these too depend on a basic principal, that enough air flows through the radiator to cool the fluid enough that the engine is cooled under any condition.
I think your truck is proof that a modern off-road production vehicle doesn’t exist. The truth is the advertising showed you potential applications that just don’t exist anymore.
I saw this same problem recently with a Chevy S-10. The problem turned out to be the cooling fan motor. The fan looked like it was running fine but the bad motor was only spinning at about 25 percent. A new cooling fan motor ($40) fixed the problem.