Chrysler Repair: cooling system: fluid doesnt return from reserve tank, upper radiator hose, engine radiator

Question
Hi Roland, Still having the same problem and no mechanic has yet to diagnose it with any certainty. Two pressure checks showed nothing wrong. The last time I took it in the mechanic told me it seems to be building pressure after it begins to cool down. He said it is probably either a head gasket or the wrong rating of thermostat. Is there any way to positively diagnose this problem other than tearing apart the engine. I don't want to have the gasket changed and then still have the same problem. My plan right now is to try a sealer and see if that make any difference. If so I will asume its a gasket and start saving my penies. I apreciate any insight you may be able to give. Thank you much,  Randie
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-----Question-----
I recently purchaced a 1998 Sebring Lxi. The problem I am having is with the cooling system. When the engine heats, the coolant is going to the overflow tank but when it cools it is not being sucked back. I chnged the rad cap and thermostat and it starts to act right then returns to the same symptoms. Should I use a lower presure rad cap? The one in the auto is 16 psi. Thanks
-----Answer-----
Hi Randie,
The 16 psi cap is the right one. If it were an old cap the problem might be that the little vent valve in the center was stuck closed, but that shouldn't be the case with a new cap. You might check to see that it is moveable nonetheless.
The principle by which the fluid is returned is that a vacuum is created in the engine/radiator as they cool and the volume of the coolant decreases:
If the upper radiator hose collapses during cooldown, that would indicate that the cap vent valve is plugged, or there is some crud in the overflow bottle or its hose that is blocking the fluid from flowing in the reverse direction. So check that the bottle is clean and the hose is open. If there is a tight fitting cap on the overflow bottle make sure that its vent is also open so as to allow air to enter the system so the vacuum created by the cooling of the engine can be satisfied by the return of the fluid to the engine rather than maintaining the vacuum in the bottle.
If there is no problem related to the above, then I would wonder if the cooling system is airtight. Are you loosing coolant slowly over several days of driving? It may be there is a slight leak either in the radiator, hose connections, or internally in the engine (head gasket) such that when the engine cools the vacuum necessary to suck the coolant from the overflow bottle back into the engine is released via that leak. So look over the radiator, all the hose connections and hoses and finally observe whether you are seeing white smoke from the exhaust when you first start the cold engine or any cloudiness in the engine oil which would be signs of an internal engine leak. You did say that the bottle fills as the engine heats. Try letting the engine warm up while parked, and notice whether there is air (actually exhaust gas) bubbling into the overflow bottle also as that would also be a sign of a head gasket leak.
Those are the several possibilities that I can suggest you look into. Let me know if you find something that needs further explanation.
Roland

Answer
Hi Randie,
You haven't told me whether you are loosing coolant? I would try sucking up the fluid from the overflow bottle and returning it to the radiator so as to determine whether or not you are loosing coolant and at what rate. What about the other checks/observations I suggested?
About the only other check for a head gasket leak is to go to a radiator shop that has an exhaust gas detector and let them attach that in place of the radiator cap to see if they find any exhaust gas getting into the cooling system. Also you can check for white smoke (which has the smell of anti-freeze if you let is condense on the palm of your hand when held at the exhaust pipe, when first starting the engine from cold.) Doing these tests/observations is needed. Remember that if you have a V-6 there are two head gaskets to consider so if it is a leak it would be desireable to find out which one by looking for coolant on the spark plug tips before starting the engine or doing a compression check to see if one of the cylinders is low (another way to look for the leak). Then you don't have to remove both cylinder heads to find one leak.
I would be inclined to hold off on the sealer because it tends to coat the interior of the cooling system and reduce its efficiency. I would save that for an older engine or when you are out of options entirely.
Roland