2005 Dodge Neon SXT 5 speed manual. The coolant is not returning to the radiator when the engine cools off. I thought It might have been a pin hole leak in the heater core, bypassed that and that did not fix the problem. The radiator cap was bad, that the cooling system wasn't building any pressure, replaced that. Spark plugs look good, none looked steam cleaned and NO coolant smell in the exhaust. Parked it on a clean concrete slab overnight and no puddles under the car the next day. Oil looks good, no milk shake there. So I don't think its a head gasket. I can't find any leaks. Re-connected the heater core and burped the cooling system tonight. I'll take it for a ride tomorrow to see if that did anything. Any other ideas? It's driving me nuts I can't figure this out.

 

Are you sure there is enough coolant in it? The radiator should always be full. As it heats up, it will expand to the coolant expansion tank and as it cools, it will pull it back. A crack in the tank or even a pin hole in the hose to the tank will let coolant leak and then suck air back.

 

Yes, the system was completely full. I used one of those coolant burping kits that has a large funnel that connects where the radiator cap would go. Waited till thermostat opened and all of the bubbles stopped coming out. The hose from the rad to overflow tank is good. I used a Mityvac hand vacuum pump to empty the overflow bottle and it pulled the coolant out just fine through that hose and the tank.

There has got to be a leak somewhere that I just can't find. I'll replace the thermostat housing next since it seems like those are prone to failure and mine is still the original and its only $20.

 

Invest in a UV test kit. This is a black light pen or flash light and a pair of safety glasses. Be sure to use the glasses. Clean everything up and then add the UV dye for water based systems. Drive it for a bit and then use the UV light to look for leaks. The dye will show as green streaks leading to the leak. I've tracked many leaks this way over the years. Usually oil, but coolant too. You may find a loose clamp or maybe your water pump is leaking. The trace will tell.