I have an '04 Allroad with the 4.2 (timing chains) and NO timing belts. The engine overheats after operation for 30 to 45 min. The temp gauge will slowly move past the center mark, and the oil temp will rise to just below 250 degrees...... The thermostat and WP are new (50 miles) as are hoses, coolant res tank and cap. The main (large elec fan) was replaced first as it appeared to not come on at temp. Both fans work fine, and at temp. Trying to discover what else in the cooling system could cause this?? NO bubble in coolant, no coolant in oil...... Thoughts???
Be sure to bleed the system of air properly to prevent cavitation and air pockets.
Run the car at idle once its warmed up with heat on high, ac compressor off.
Then rev the engine to about 2000rpm for about 30 seconds. If it gets significantly warmer, check coolant level when cold or re-do your bleeding procedure.
Do you have an inferred thermometer? Take the temp of the coolant hose coming out of the engine. It should be generally close to the sensor reading. (say about 20 degrees F)
Compare the temp of the upper hose and the lower hose going to and from the radiator. There should be a big difference.
Does it overheat when driving above 40mph? If so, id suspect a faulty thermostat or blockage.