Started having a problem with my 2010 grand caravan c/v 3.3L, 206,000 miles.
After driving for a while, the reserve tank fills to almost overflowing, and the radiator is empty.
Temp gauge fluctuates between center and 3/4...
After sitting overnight, the reserve is still full, and there is slight pressure in the radiator when I open the cap.
A few bubbles go into the reserve....
I can empty the reserve back into the radiator and drive it, and the process happens again.
No visible leaks at hoses or pump.
I have noticed though, that it will start overheating when a strain is put on the engine, such as going up hills, etc...
Normal flat driving short distances and the coolant stays low in the tank.

New radiator, new radiator cap (tried 2 of them), new thermostat, new radiator hoses, new lower hose tube.
Have not done water pump yet, but the upper hose is getting hot, fan is coming on just above halfway on gauge.

When I got this van, the cooling system was very dirty brown. I have flushed it about 4 times now and it's getting cleaner using Blue Devil.

Getting ready to drain and flush one more time today...
New water pump is coming, but not sure if I even need it.

All that's in the van now is water and flush chemicals.
If I do a final flush and put distilled water and antifreeze back in, will it even fix the problem?

I've read here and there it could be a head gasket....??
How to confirm that? I do have a compression tester.

I actually just drove up from Virginia 680 miles last thursday, and the temp didn't go over 3/4, but the tank was full all the way.

Any help is appreciated...

 

Before I read the whole post, my mind said, "Radiator cap," but you said you tried two of them. Then, you mentioned head gasket. You can rent a head gasket checker from the local auto parts store. It comes with blue fluid and you mix it with your van's current antifreeze, and if there's exhaust gasses present, than the fluid will change green--indicating there's exhaust gasses present in the cooling system.

Also, if you haven't replaced ALL of the hoses, I've heard of sellers purposely plugging return hoses so that it masks a problem. Check for obstruction in the reservoir return hose put there by the seller.

 

But even if it was a head gasket leak, shouldn't the antifreeze be drawn back into the radiator after cooling down? I did notice this morning that here was still slight pressure in the radiator when loosening the cap. A few bubbles went into the reserve tank...
Going to get a leak detector...

 

If it is a head gasket leak, that could ruin any vacuum, which occurs when the cooling system cools down. That vacuum would normally lower the radiator cap's one-way valve, thereby not allowing coolant from the reservoir to return to the radiator.

 

Tried the leak detector...
Even after draining the radiator a bit, the coolant started coming up into the detector and overflowing it.
The first minute or so was ok, and the fluid stayed blue.
I guess I need to drain more antifreeze and try again.

 

Definitely turned yellow the second time... darn...
Has anyone had experience with the Bar's leak head gasket sealer?

 

That sucks. Which bank is it?

 

not sure...
I saw a video where you remove spark plug wires one at a time for each test and it should point at the location of the leak

 

Maybe if you bought one of those inexpensive inspection cameras that plug into your phone, to use the phone as the display, you could pull each spark plug and look into each cylinder to check for a piston top that is much cleaner than the others.

 

I tried the Bars Leaks repair, and within 15 minutes of running, the aeration stopped. Will drive it more today and let you know the progress. I think I just had a minor leak and it sealed it quickly.