You're not going to believe this...or maybe you will.

[hh65flyer]

Well I just filled up the beast with its second full tank after the HG job. Got about 450 miles on it since the job was complete. She's been running like a champ, no issues...until this afternoon. I dropped my kid off for his music lesson then went to run a few errands. Pulling away from the school I noticed the temp gauge was at about 10:00. Really weird...ever since I got the rad work done the needle has been welded to about 8:30. Never have I seen it above 9:00. About the time it took my brain to process this horror the guage dropped back down to 9 again. It continued to cycle like this every couple of min or so. The needle never goes above the little themometer symbol and immediately drops. So I'm thinking (take a deep breath) it's probably a stuck or sticking t-stat. OK, that's not so bad. Then I started to hear the waterfall, gurgling noise behind the dash. I nearly drove it straight into a ditch at that point. There is no water in the oil. The coolant is exactly where it has been since I last filled it. there is no steam coming from the exhaust and the guage is 8:30 while idling, no gurgling behind dash. I'm going to pull the spark plugs and see if I see anything. I will stop by Napa and get a test kit tomorrow. Please make a sacrifice to the Rover Gods for my little green jelly-bean tonight.

[hh65flyer]

Pulled the plugs and found nothing unusual...one was darker than the others but not bad and certainly none were steam cleaned.

Also noted the coolant level was low now that the engine has cooled off (been sitting for five hours). Took about a qt to fill it back to the seam in the center. I haven't checked it cold in quite some time though. It's always been right on the center seam when I look at it (after running).

You know the Ford dealer has this really, really nice F450 sitting on the lot...

[EricTyrrell]

Could just be sticking stat and/or air bubbles in system. That would explain heating and gurgling.

[atancreti]

I would start with thermostat. Then burp air... burp again if needed....

[hh65flyer]

I really hope you guys are right. I've been driving it and running the heat continuously for a couple weeks now...thought the system would have been 'burped' by now.

The only thing different to my routine was two trips up to go skiing. It's a pretty long steep road to get to the village. Probably the most demand I've put on it since the HG job. I was watching the gauge the whole time though and it never moved off of 9:00 on either trip. I'm pretty sure I was able to see the gas gauge dropping though! ;-)

[ihscouts]

Two issues, the expansion tank and the expansion tank cap. Tanks split at the seam, caps will only last so long. Black tanks are original, clear or white are replacements. You lost coolant, besides a hose or the heater core or the unthinkable/unmentionable I don't know where else it could leave your system. Check your freeze plugs, even the ones you replaced......

[ihscouts]

Thought of something else......

Did you use sealant around the coolant ports on the valley pan gasket? See any coolant on the valley pan? The intake bolts loosen up quickly. I used Loctite blue on those because I got tired of torquing them down once a month. Almost all of them where loose while removing the intake after my hg went.

[Savannah Buzz]

If going into the stat, might consider replacing with a 180F, but not a 160 (too little heat). Even with a 192-195F, be sure it has a relief hole or jiggle device, mount that at the 12:00 position to allow the bubbles (and we also hope they are air) to pass by. If a steam pocket forms behind stat it will delay opening. A couple of extra stat gaskets are handy to keep on hand.

[leadfoot]

Originally Posted by hh65flyer

..... About the time it took my brain to process this horror the guage dropped back down to 9 again. It continued to cycle like this every couple of min or so. The needle never goes above the little themometer symbol and immediately drops..........

Continue to cycle like this...... means air in the system every time. Cheer up, no big deal, but some bubbles are really hard to get out. And, no, driving does not bleed the system.

[Savannah Buzz]

Might want to do a cooling pressure test, to find the hose clamp that is leaking, might not leak at idle, but at higher speeds/pressure. So you would not see it in the driveway. One owner kept having coolant loss and it turned out to be hose clamp under the coolant jug...