2001 montana antifreeze mystery

[eaglehawk]

I recently had my 01 montana overheat and realized the overflow container was almost dry. I stopped and bought some 50% for all cars at walmart and filled to the hot line.
The car continued to overheat in idle only but would cool down when moving. My mechanic pressure checked it and added a couple of quarts to the radiator. He did say he blew air out of system and found no leaks. It seems to be ok but after a couple of weeks it looks like the level has dropped very slightly in over flow and I cannot seem to loosen the cap because of cross bar over the top. I am getting ready for a 1200 mi 2 day trip from fl to in please advise update The trip went fine with no noticeable loss of antifreeze. The only time the temp rose sharply was after a brief fuel stop while i was accelerating on the entrance ramp and then it dropped back down quickly. my mechanic replaced the sensor and the thermostat when i returned. i was finally able to open radiator cap and it stayed full from start to finish. i watch the gauge religously and it fluctuates +/- 5 degrees.

new development, my mechanic cannot locate the leak. if i let it stand in my garage for several days i get a puddle of antifreeze on the floor but not enough to lower the level significantly in the over flow. it seems to be coming from the rear area of the engine. at first i thought it was on the driver side but the longer it sat, about a week, there was more on the passenger side than the driver side. it might have run in that direction due to floor slope. he wanted me to pinpoint the region as closley as possible. any ideas?
sometimes +10 in idle comments?

[kcarlen]

Sorry to be the bearer of bad news....

cancel the trip dude.
Your vehicle is about to enter into phase 2 of the issue...
Cylinder head failure, overheating...it all starts from here.

Keep us up to date.

[rockwood84]

a bad radiator cap will let the radiator lose coolant.a bad intake gasket will gradually lose coolant. the cross bar can be moved out of the way to get at the rad cap.you say it overheats while idleing are the fans coming on? the first should kick on a little over 1/2 on the temp gauge if the temp keeps climbing the second fan will kick on at 3/4 or if the a/c is on both fans should kick on. take the cap and get it tested. but if the cap checks good i would think it is gonna be the intake gaskets leaking and i don't think i would use the van for the 1200 mile trip.you would be better off renting a vehicle.the cooling systems on the 3.4 holds air there are two bleeder screws so you can bleed the air.one is on the top of the heater hose right above the water pump. the second one is on top of the thermastat housing. the center turn to the left to bleed until coolant comes out.good luck