2000 Ford Ranger Overheating Mystery

My son’s 2000 Ford Ranger, 3.0 V6 overheats. We have replaced everything (that we know of) except putting in a new engine. It started about a year ago when it overheated. Took it to our trusty mechanic shop. They replaced the radiator and thermostat. After it overheated again, my son replaced the water pump and the problem persisted. The mechanic then suggested it might have a bad head gasket. The mechanic put some Stop leak in as a temporary fix. It turned out to be drivable IF the truck was warmed up enough to open the thermostat (had to wait for the gauge to go up and then drop down and then level out in the correct spot). If you tried to drive it without a warm up, it would overheat as soon as the thermostat opened. Also, a low temp thermostat was put in. A couple of months ago it overheated after shutting off the engine (water and lots of bubbling noise came from the overflow reservoir. My son decided to change the head gaskets. The heads were resurfaced, new seals, exhaust valve seats and all looked good. The thermostat was again replaced. New coolant in place and it was ready to test drive. The truck was driven for about a half an hour from a cold start.. It didn’t overheat. Thinking we’ve fixed it, my son takes it out, stops by a friends house about a mile away to pick something up. He leaves the truck running and when he comes back out about 5 minutes later the gauge is pegged. At that point, the following parts were changed – radiator, fan clutch, coolant temp sensor, thermostat, upper radiator hose, and sensor elbow.

Again parts replaced and repaired since the first overheat include:
2 radiators
1 water pump
1 coolant temp sensor
1 elbow (coolant sensor attaches to it)
1 elbow (attaches to the smaller hose of the lower radiator hose)
6 thermostats
2 fan clutches
2 sets of upper and lower radiator hoses
Head gaskets and complete seal/gasket kit
Heads resurfaced and fixed with new exhaust valve seats
Head bolts and header bolts
2 Radiator caps

We’re out of ideas and need some help. Many thanks, in advance, if you’ve had a similar, resolved problem or think you might know what’s going on.

Answers for The Question

  1. Josh S
  2. kelly s
  3. bmwrider001
  4. rick29148