Biggest problems with these trucks.....
Blend door
Ball Joints
Transmissions are weak on V6 models
Head gaskets on OHV V6 (which you have).
Multifunction switch
Rear ABS sensor
I may have missed few, but these came off the top of my head.
Tuggey...I was in a rush when I posted this, so let me give you a little more detail as to what to look for regarding the problems I listed.....
Blend door - Make sure that the A/C is blowing cold or the vent is blowing the correct temperature air. Typically when the blend door fails it will blow hot air no mater what you put the temp on...Ok in the winter, but not fun in summer. There are threads on this site on how to fix it.
Ball joints - Definte issue with there trucks. Typical symptom is squeaking when going over bumps. Again, numerous threads on how to identify/fix this.
Transmissions - As I stated, the V6 trannys are known to have problems. However, if the transmission has been maintained well you should be OK (My 2000 XLT has 160K and the tranny shifts like new. However, I always change the fluid between 30K - 40K.). Check the dipstick for the fluid condition. It should be red and not smell burned. If it is brown then change the fluid.
Head Gaskets - The 4.0 OHV is a strong engine and should last well past 200K if well maintained. However, they are know to have issues with blown head gaskets. Check your oil and make sure it is not milky. Also check the coolant to make sure ther is no oil in it. Even if they both look fine, monitor your coolant level. If it is dropping that indicates you have a bad head gasket or a simple leak somewhere. Not trying to scare you and the vast majority do not have this problem, but just something to be aware of.
Multifunction Switch - These go bad on Explorers all the time. Luckely it is a cheap and easly fix for the DIYer. Symptoms include wipers that come on by themselves, smoke from the steering column when you put your turn signal and/or hazards on, lights not working, etc.
Rear ABS sensor - You will know you have this problem when the ABS light comes on. 90% of the time when the ABS light comes on it's the rear sensor. An easy fix (It's locted on the top of the rear differential).
Hopefully this helps. Overall, these are great trucks and are easy to repare for the most part. You are lucky you don't have the SOHC V6 as they have horrible problems with the timing chain tensioners/cassets (Mine has had a minor issue with this for over 120K, but keeps on going). Enjoy your new Ex and definely utilize this site as there is a wealth of information here and so many guys who are willing to help with any problems you may have!!!
