I've looked around in the forums for answers for about an hour now and I can't seem to find what I'm looking for... maybe I'm just dumb... but here's my issue at hand.

I just got a coolant flush about a month ago, checked the heater core and blower and radiator... everything was fine.

This just started happening about last week: My heat stopped blowing hot, and then my engine started to overheat while driving on the highway and I didn't even notice until the light came on and I saw my temp was at 260... and all the sudden it cooled itself down and my heat worked again for about 5 minutes.

I thought it was the t-stat and maybe it was just stuck closed. But then i found another issue.

Checked my coolant levels and my reservoir was basically dry. Refilled it and 250 miles later, it was dry again and my engine overheated. No apparent sign of leakage on the ground and no smoke coming from exhaust.

I've noticed a "knocking" sound coming from behind my dashboard, and as soon as I hear that sound my heat will come on hot and the engine will cool down.

Would this be a water pump issue, thermostat issue, clogged heater core, all of the above? Some help would be awesome.

 

start with the easy stuff. thermostat, fan clutch, air flow. I never do a radiator back flush. I prefer the dump and fill. I have less problems this way. check the lower hose, they can collapse at highway speed. see if its way soft to squeze. might change radiator cap.

 

ok awesome.

now i just need to find where my radiator fluid is going... it's apparently just disappearing

 

possible over heat issue caused overflow bottle to over flow. then when it cools it draws fluid out of overflow back into radiator.

 

What does your oil look like?.....could be loosing coolant internally thru a cracked head/gasket.

 

one thing you can do is go to autozone and have them pressure test the system. they will hook up a hand pump to the rad and pump in air to see if there are any leaks. If there is a leak you may get lucky and be able to see it. Please dont get you new parts such as themostat or rad there. trust me spend the extra money and get it from the dealer.

 

The #1 symptom of a cracked 0331 cylinder head (which is what 00-01 XJs come with from the factory) is unexplained coolant loss.

You also have symptoms that correlate with a cracked head.

Have you performed a comprehensive search (get underneath with a hot engine and a good light) for a leak?

I hope I'm wrong here, but I think it is time for you to educate yourself about the 0331 cylinder head defect.

Here is a thread on the 0331 that is required reading for all 00-01 owners.

http://www.jeepsunlimited.com/forums...d.php?t=391831

Let us know what you find......................