Engine overheating/fans not coming on

Asked by Sep 15, 2016 at 05:10 PM about the 1998 Subaru Forester Base

Question type: Maintenance & Repair

Recently I was stuck in standstill traffic on
a hill for a while and my engine began to
overheat. I turned on the heat full blast for
a bit as I learned to do when one of my
fans died in the past. However this time it
wasn't working. I pulled off the road and
looked at the engine and realized the
cooling fans were not working. However, if
I turn on the AC, they both come on. They
were both changed in the past year. The
temp gauge in the dash seems to work
correctly. Is there a relay or something or a
sensor that might be bad so the computer
isn't telling the fans when to come on
under normal operation (without AC)
perhaps? Thermostat? Any suggestions?
Thank you!

1 Answer

6,910

Fan switch and temp gauge sender are separate. If not acting in consonance it's usually due to percolated combustion gases trapped in the cooling system and migrating to the temp sender area, superheating the sensor...but NOT sending a signal to the ECU for the fans operation. This is the classic indication of high pressure head gasket failure, the repair of which on the 2.5i DOHC motor is usually NOT durable. Sorry. It is UNLIKELY that an OE t-stat has failed (although an aftermarket smaller one COULD cause similar symptom overheating...but fans SHOULD come on, as it's just the coolant that's gotten hot from poor flow...NOT superheated exhaust gas bubbles infiltrating the coolant bath). Likewise an obstructed radiator can cause overheating...but NOT without cooling fan op. So have a good wrench check for PERCOLATION before you start wasting money on a t-stat or radiator. Again, unlike the subsequent 2.5i SOHC motor, the earlier DOHC is prone to internal failure after head gasket replacement. It may be time to move on....

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