Blue Loc-Tite is like a girlfriend... your stuck with her, but you can get rid of her if you want to. Unlike Red Loctite. You put Blue Loc-Tite on a bolt that is prone to losening from vibration, or one that you don't really want coming loose, but it may be a little more work to get the bolt out later. I've had the TPS Sensor loosen on me twice before, so it is a good candidate. Now if it is seriously critical that the part not come loose, then you want Red Loctite.