Overheating?? What could be wrong??

Hello, I have a 2006 mustang GT at 106000 miles. Fairly stock, JLT air filter tuned, with straight and SLP mufflers. I have replaced the fan, radiator, coolant, water pump, and thermostat. I hooked up my sct tuner and as I'm driving it stays between 198 and 208 degrees in 1st through 4th gear. As soon as I hop on the freeway and throw it in to 5th it will reach 230 within 10 minutes and climb to 236. I will pull over and let it cool down and continue to drive. I do not have a clue as I have changed everything I think is associated with the temperature. ANY ideas or suggestions will help, thank you for reading.
 
  • Sponsors (?)


I see that you have replaced the cooling system, but have you verified coolant flow through the radiator ? as well as air flow across the radiator? Have you checked for a leaking head gasket?
Checked to make sure the new fan is actually turning on ?
 
Head gaskets would be my first guess, but as Ragged says above, make sure your fans are turning on. Check the fan relays first and then hotwire the fans to make sure they run. Have you checked for exhaust in the coolant? You can purchase a tool here that can help you to determine if you have exhaust in the coolant:


If you determine there is no exhaust in the coolant, then I would do a complete system flush. Sometimes a clogged heater core can slow down the flow enough to cause the type of overheating you are talking about. Once you are in high gear, the engine rpm slows down which also slows down the water pump speed, and at that point, if it is, in fact, a heater core, it might not have enough to overcome a poorly flowing or clogged heater core.
 
Checked the fans, fans are running well. Checked for blowby and no blowby, also checked for coolant in the oil, no coolant in the oil. So I don't think it could be the head gasket. Coolant stays at the sake level, no leaks or coolant coming out of the water pump's weep hole. I will do the coolant flush as you suggested and give an update. Will also do a radiator pressure test.
 
Coolant doesn't have to be present in the oil to have bad head gaskets. They might be leaking coolant directly into the cylinders or outside to atmosphere and not going into the oil gallerys. Does the car smoke at all? Can you smell antifreeze at the muffler tips? Are the tips greenish colored around the outside edge? These could all be signs of head gasket failure without it pushing coolant into the oil.

I would have a pressure check done on the entire cooling system and listen very closely to see if you can hear it in the intake. If you can, then it's leaking into the cylinders and not the oiling system.