my 1999 outback[185k miles] has recently developed an overheating problem. pressure testing indicates no problem with the head. the thermostat has been replaced twice. the car runs fine for a short time then begins to get hot. my mechanic let the car idle in the shop for several hours after a tune up and thermostat replacement and drove it 25 miles w/out a problem. I picked it up and drove 12 miles with no problems. 90 minutes later I drove it about 5 miles and it overheated again. I slid the heater temp control back and forth and it began to cool down. then it got hot again and no warm air would come out of the vents. it seems that there is some type of blockage in the cooling system. What next… do we pull the radiator, replace the water pump, pull the freeze plugs? can the system be purged and cleaned. HELP!!! I want to sell it but can’t with this problem. Any suggestions on where we go from here?
There are a number of possibilities. For starters it would not be unusual to need a new water pump at 185,000 miles. Is the radiator fan(s) coming on? One should come on with the A/C and the other when it is hot. It is also possible a hose is malfunctioning and look and feel OK on the outside. The inner lining can block the flow.
However the “I slid the heater temp control back and forth and it began to cool down. then it got hot again and no warm air would come out of the vents.” leads me to suspect some air in the system and that needs to be purged.
If you haven’t checked the coolant doing a test that detects for exhaust gases in it I would suggest you do that. Even though you had a pressure test done, the problem may be intermittent.