Yesterday I drove my disco to work and back home. Got home picked up the wife and kids and headed to dinner. Park at the restaurant and my son say "whats that leaking dad?" I tell him its just the a/c. They do that. Don't think about it again. Head home and pulling into the apt. complex my wife says you are leaking alot of something. I look at the temp gauge and Oh crap I am nearing the top. Park it and shut it down. Pop the hood and it is coming from the cap on the reservoir. So I have no coolant in the oil, no white smoke, no fouled plugs, new hoses, and the white reservoir tank. I topped off about 2 weeks ago (and didn't bleed because I didn't realize the system was set up this way) so I am wondering if I just have air in the system or if the t-stat, water pump, or radiator are the problem. No prior symptoms. Has never had an overheat or boil over problem since I bought it in Feb. I was thinking flush the rad, replace the t-stat, bleed the system, and go from there. Opinions?

 

Air in the system should not cause it to blow coolant out of the overflow tank.
So it overheated because you were low on coolant.
About all you can do at this point is refill it and while in the driveway see if it happens again.

 

Mine did spew antifreeze after I topped it off a while back. I had replaced serp belt and done some other work on it and had the lower hose off for a while. So when I finished everything I topped it off and guess I put a litttle too much and possibly had some air trapped as well.

It never ran hot but it did spew a few times til it was happy again. So far my temp gauge is rock steady in the lower half of the range just below mid point.

 

Sounds like Spike is right and that you probably have a coolant leak. You might want to see if you can find it before doing the other work. Maybe one of those new hoses isn't tight or something simple like that. If you fill it up (and bleed) and run it in the driveway, and it overheats without a visible leak, then go for the t-stat. If that ain't it, maybe radiator is clogged. If it was the water pump it would probably be weeping from the weep hole in the bottom of the water pump housing near the shaft, or you might be able to hear the bearings squealing. Another possibily is the fan clutch. Try spinning it when the truck is cold. It should spin about once with a little resistance.

 

It will overheat if it is not bled right. That air pocket can stay in the heater core and pop out. When it does, it will shock the system and pop the cap. It is pressurized to keep the temp down, when the air comes loose, it will lower the pressure because you can compress air. This will jolt the temp up and cause you to overheat.

Clean it up and fill it back up. Make sure to bleed with the heater on high this time. Then check for leaks and start diagnosing.

 

So topped it back off today, bled the system (3 times), ran between bleeds with heater on high till she reached normal operating temps and no overheating. Checked for leaks and can't find any. I am really leaning towards the air pocket theory or water pump. I will know tomorrow. I will drive it 20 miles to school and back home. Will see how she does. I will watch the temp closely. Will update. Thanks for all the help guys.

 

So I was standing in front of the Disco thinking and staring at her and I had a lightbulb moment. A couple of days before the overheat problem I remember hearing a squealing sound, wasn't loud and didn't last long and I couldn't find what it was. Then the more I thought about it I remember hearing it the day she overheated. So now I am convinced it is the water pump. Do you guys agree? The two explain each other perfectly if I am not mistaken.

 

could be, and at your mileage, it wouldn't hurt to swap it out. watch the pulley while it is running and see if it wobbles.

 

When my original fan clutch went bad it put extra strain on the water pump and she would make noise, like a squealing squeaky noise.
Replaced fan clutch and noise went away, that was 2 years ago.

See if it overheats again and/or makes the noise again.