I have a 2005 Saab 92x Linear with 2.5 l engine..it is basically an Impreza WRX with a Saab interior.  It has been overheating on the highway only (speeds over 60 mph).  The heat gauge creeps up after 10-50 miles of highway driving, then jumps up as the car slows to a stop.  In-city street driving is no problem.  Thermostat, radiator and coolant temperature sensor have all been replaced.  My Saab mechanic is stumped.  Anyone seen this before?

were all those parts replaced trying to solve the problem? or was some of that work done just before the problem came along?

 

was the radiator cap(s) replaced?

 

is coolant being pushed into the overflow bottle?

 

was the timing belt changed?

Edited April 30, 201411 yr by 1 Lucky Texan

were all those parts replaced trying to solve the problem? or was some of that work done just before the problem came along?

 

was the radiator cap(s) replaced?

 

is coolant being pushed into the overflow bottle?

 

was the timing belt changed?

Yes, these were all attempts to solve the issue...the radiator cap has not been replaced.  I am not seeing coolant into the overflow bottle above the regular fill line.  Timing belt has not been changed.

Possibly the heater core is clogged.

Possibly the heater core is clogged.

Heat inside is working fine...

Are your fans coming on at temp?
Are you loosing any coolant?

you're a little over due for the TB (105 k miles OR 105 MONTHS). maybe it's slipping on the water pump.

 

how many miles on the car?

 

is the thermostat OEM-style or aftermarket?

Are your fans coming on at temp?

Are you loosing any coolant?

Fans are coming on, appears to be no coolant loss.

you're a little over due for the TB (105 k miles OR 105 MONTHS). maybe it's slipping on the water pump.

 

how many miles on the car?

 

is the thermostat OEM-style or aftermarket?,

110K.  This is where my Saab mechanic is at...water pump and TB replacement.  He and I are both a little reluctant to spend the $$ on a maybe.  After market therm, but then when that didn't help, OEM.

A cheapie thermostat could cause this problem. Cheapies don't work well in a Subie motor. Either go Subaru OEM, or most expensive aftermarket.

 

I have also seen where a bad water pump can cause this problem, even though it doesn't leak. If old, some don't pump well.

I wonder if there could be an electrical/voltage problem and the car isn't overheating at all? maybe the gauge or it's sender is incorrect.

 

or, the system needs to be 'burped'.

Edited April 30, 201411 yr by 1 Lucky Texan

Heat inside is working fine...

You can still have plenty of heat with a partially clogged heater core. The thermostat opens and closes at 170°F. You only need 140° at the core to make good heat.

 

The route through the heater core is a bypass route that brings hot coolant from the engine through the core then returns it to the engine just behind the thermostat. This stream of coolant is warm enough to keep the thermostat open when crusing on the highway or in cold weather.

 

With the thermostat in the inlet side of the water pump, it is constantly in a stream of coolant that is colder than its normal opening temperature. This causes the themostat to close, which blocks the flow of coolant into the engine. When coolant in the engine doesn't flow it begins to overheat.

The reason for the bypass coolant route is to keep warm coolant flowing to the thermostat. The coolant flows around the thermostat on the back side which keeps it open even if the incoming coolant from the radiator is less than 170°.

 

If the core or the hoses to it are partially clogged there will not be enough flow to maintain the temperature necessary to keep the thermostat open, which leads to overheating.

You can still have plenty of heat with a partially clogged heater core. The thermostat opens and closes at 170°F. You only need 140° at the core to make good heat.

 

The route through the heater core is a bypass route that brings hot coolant from the engine through the core then returns it to the engine just behind the thermostat. This stream of coolant is warm enough to keep the thermostat open when crusing on the highway or in cold weather.

 

With the thermostat in the inlet side of the water pump, it is constantly in a stream of coolant that is colder than its normal opening temperature. This causes the themostat to close, which blocks the flow of coolant into the engine. When coolant in the engine doesn't flow it begins to overheat.

The reason for the bypass coolant route is to keep warm coolant flowing to the thermostat. The coolant flows around the thermostat on the back side which keeps it open even if the incoming coolant from the radiator is less than 170°.

 

If the core or the hoses to it are partially clogged there will not be enough flow to maintain the temperature necessary to keep the thermostat open, which leads to overheating.

 

 

good post - for testing purposes, could that heater circuit be bypassed with a direct hose loop? If everything was good, then heater core would be the culprit right?

good post - for testing purposes, could that heater circuit be bypassed with a direct hose loop? If everything was good, then heater core would be the culprit right?

Yes it can. Bypassing the core itself is easily done with a u-shaped heater core bypass/delete hose which can usually be found at most parts stores, though it will probably not show up in parts listings.

 

There is a small L-shaped hose which WILL sometimes show up as "bypass hose" which is what connects the metal pipe from the heater core return hose to the side of the water pump housing. It is not normal for those to clog, but any coolant hose can deteriorate inside and block flow.

 

That hose shown here: http://opposedforces.com/parts/impreza/us_g11/type_19/cooling_system/water_pump/illustration_1/

Edited April 30, 201411 yr by Fairtax4me

The new theory with my Saab guy is head gasket replacement.  Any opinions about this?

Could be the head gasket, block tester from napa is like 30 bucks. Leakdown test could tell you too.

 

I definitely do not recommend a milkshake sealant, ick! But the rest is pretty spot on.

Edited April 30, 201411 yr by Ibreakstuff

If it were head gasket you would have bubbles in the overflow. Or the coolant would be very low.

The type of head gasket failure that produces overheating and bubbles inthe system is not common on this engine. But bubbles in the radiator or overflow are a dead giveaway.