2005 Outback: No Heat and Now Overheating

[lmelmed]

2005 Outback 2.5i. 79,000 miles. All standard service done.

Interior heat just wasn't coming on over past few weeks, but would then finally kick on after about 30 minutes (but sometimes never..or perhaps I didn't drive that far).

Then, driving home the other night in traffic but cool weather (40 degrees), temp gauge shot up to red. Putting on/off heat did not matter (at that time there was no heat).

Quick check of coolant level shows that it is ok and squarely within hi/lo. Have not seen any leaks but it is parked on street so tough to tell.

Going to take it in to specialty shop tomorrow but would appreciate any advice on what direction you might point the mechanics...

[AWDFTW]

The better: heatercore or thermostat issue. (Use a Subaru tstat ONLY)

The not good: head gasket, although on the 2000 and newer engines they usually fail externally and don't cause the temp spikes of the internal failures.

[Bimmer]

Originally Posted by lmelmed

Quick check of coolant level shows that it is ok and squarely within hi/lo...

You're doing it wrong.

You're looking at the coolant reservoir.

Look under the radiator cap (wait until it's not hot). It should be full of coolant, all the way to the top. If it's not, this is your problem.

If it's full, then maybe your water pump is kaputt?

Bimmer

[ETC]

Air bubble [has the cooling system had any work done ? flush ?]. If not, check that the radiator is full, if not, check the hose to the coolant bottle is tight on the radiator fitting and that there is no cracks in the hose, it flows freely and it is at the bottom of the bottle. You can i any of those cases suck air in to the cooling system and have symptoms like you describe.

Thermostat sticking [like awdftw said, use only oem]

Possible headgasket leakage -my 2000 leaked internally, similar symptoms but it would fill the coolant res to the top when it acted up and not suck fluid back in the radiator.

[Bimmer]

Originally Posted by ETC

Thermostat sticking.

But then the heat would still work, wouldn't it?

Bimmer

[ETC]

It should but the OP was a little "iffy" in his description "perhaps I didn't drive that far"

I'm thinking Bubbles in the system ... the question is why they are there. ?

OP- bleed the system of air [do a search on here], top the system off, run it up to temp, look for air bubbles in the coolant bottle [lid off, and you've already checked the integrity of the hose to the radiator] . Consistent air bubbles ever 5-15 seconds are a pretty telling sign of an internally blown head gasket.

[jimy]

I vote for thermostat sticking. You will get no heat at all and it will cause the over heating.

[plain OM]

I vote for thermostat sticking. You will get no heat at all and it will cause the over heating.

Just the opposite (as Bimmer noted). The Subaru heater is in a loop from the water (crossover) pipe on the top of the engine to the heater core and then back to the inlet of the water pump on the lower left side. There are no valves or controls in this circuit. As long as the water pump is working, coolant from the top of the engine (hottest) will be pumped through the heater core. If the thermostat sticks closed, the engine could overheat, but the coolant flow through the heater core would continue and would in fact be hotter than normal.

In 40 degree temps, the engine should still heat up fully in 30 minutes so that there would be warm air out from the heater, assuming that the AC isn't on at the same time inadvertently, and that the temperature (heat) control is set to max (on a manual HVAC). One thing that isn't mentioned is whether, in the example of a 30 minute drive (before the heat seems to kick in), the engine temperature gauge was at the normal position.

Low coolant in the engine cooling system could lead to insufficient flow through the heater core and/or an air bubble. Either could result in little, or no, heat from the heater.

As others have noted, the coolant level in the radiator itself should be checked when the engine is cool. The level should be up to the filler (rad cap) neck.

The OP should also notice that the level in the overflow reservoir goes up from its "cold" level when the engine reaches normal operating temp, and back down to the original "cold" level when the enginecools. A leaky or blocked overflow tube, or a defective rad cap, could prevent this important function from working properly.

If the temperature gauge "shot up to red" in virtually no time, while at the same time there was no heat, I think it's more likely a head gasket. (These are classic signs.) Because of the mass of the engine, and the volume of coolant in it, temperature changes in the coolant itself will not occur suddenly.