I recently did a coolant system flush on my XJ. I replaced the thermostat housing so I waited 24 hrs for the rtv on the gasket to cure prior to putting the coolant back in. I put the coolant back in and when I started jeep there is a loud screaching from the engine. Upon further investigation, I noticed that the lower pully attached to the block is locking up and the belt is what is screaching. Anyone have any idea why pully may lock up after coolant flush?

 

It decided it was its time.


Replace it.

 

Probably something else locked up. That big pulley at the bottom is the Harmonic balancer and it is attached to the crankshaft in the engine. It powers the belt. If you got the engine going then that pulley was spinning. The harmonic balancer pulley can come undone but the crankshaft will keep on spinning.

With the engine off, take off the belt and turn by hand every pulley in the drive path of the belt. You should be able to turn every pulley by hand except for the Harmonic Balancer. The one that is stuck is the culprit.

Also check the Harmonic Balancer and make sure it is not wobbling or rubbing up against the engine; this would indicate it is about to come apart.

Had this happen to me recently. I shut down the Jeep for a few weeks for axle maintenance and then when I turned it on again the alternator had seized up. Would not turn. Had to replace it.

Good luck.
Remember to take note of the belt path so you can reinstall it. Take a picture or follow the diagram on the fan shroud.

 

Just did as you suggested and removed belt. The alternator pulley wont budge. Think it got pretty wet with all the flushing and prob seized. Thanks so much for the advice. Will be changing alternator this weekend.

 

Don't know which year you have, but on mine the alternator had to come out from the top. Had to remove battery and battery tray. Still had to fight to wiggle it out. Then to install new one, I had to nudge the engine up a tiny bit by placing the jack under the oil pan (X mark on it is where you want to place the jack contact, a piece of wood in between helps to displace the force). Just lift it a very small amount and very slowly. I only pushed the handle on the jack down an inch or two. This bought me the clearance to wiggle the new one in.

Good luck.

 

Out from the bottom in from the top and no jacking required.

 

RTV. Why use it on thermostat housings and wait a day?