Engine overheating/fans not coming on

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....

Not sure if this was resolved or not. But we've a 2007 Forester that just had both heads machined and new head gaskets installed. Cooling fan operation is intermittent to say the least. I monitor the temps with a scan tool as well the dash gauge. On the highway going into work this morning: 176-178.... In town it averages about 205-210 or so. It's gone as high as 215 (verified on the scan tool of course) and the cooling fans do not come on. If I turn on the A/C? Then the right fan only spins up. The left one does not. When I was trying to figure out an unrelated issue, the car did fire up both fans (issue was with the VVT servo not functional and a few other issues after we installed the engine back into the car) So I know the computer CAN turn the fans on.... Just wondering what the criteria is and the control side of it. She's clearly not overheating as the scan tool is keeping a close real time watch on the temps. Wondering if progress was ever made on this one.

First interchange fan relays with a clone to see if it's a simple relay problem. Also, what does the dash GAUGE say? Does it run above average? Is cooling system absolutely purged of all air (this is NOT trivial)?

I'm having a similar issue, changed head gaskets, water pump and timing belt, thermostat and it seems the fans just don't want to kick on as the temperature gauge reaches the red zone is there a different sensor responsible for the fans and another one for the dashboard temp gauge? If so could someone please post pictures of the two? It would mean the world as this is my mom's main source of transportation and I'm stuck trying to fix it for her.

Did you use a large bore OE size t-stat? This is important. Are you sure you've purged all air from the system? If an air bubble gets stuck near the temp sensor it won't allow proper fan triggering. Let us know....Ern

Hi Guru, I am having the same problem. Both fans not going on. How do I purge the cooling system from air? and specially, how to avoid air bubbles onto the temperature sensor? Thanks for your help!

To purge tougher cases: elevate front of Subie. Mount funnel tightly to radiator top hole; fill with water. Start car and await cooling fans onset to establish isothermal running. Wait for all bubbles to purge from top of funnel surface (adjust as necessary to get a nice big visual "puddle" to watch). Drive on highway and repeat as necessary. If you absolutely cannot get all air to purge then indeed have a HC probe to sample the bubbled gases to assure they're not percolated cylinder exhaust. If so, you need new HGs. Good luck. ern

Hi, purge is done and lots of air came out. Thanks for the tip but still fans not switching on. How can I test the Main Fan relays? The is a big grey one (how do you take that off???) and a smaller one. Is there a bypass way to keep them both going all the time? otherwise, where more to look for? Thanks again for your help!

Most relays are interchangeable, so rotate to test logically. Don't bypass as you'll never get up to operating iso-thermality in the winter!

The car is in Haiti and it never gets below 15 ...

Red herring. Not having fans in the tropics is even worse!

so, as the temperature never goes down, could bypassing be an option, even if not within "the rules" ?

No. The system is carefully balanced to operate isothermally. As an example, reducing t-stat temp results in insufficient heat in cooler climes, as well poor fuel eco. Running fans full-time simply extends the warmup time perhaps indefinitely except in the tropics. Removing fan operation risks dangerous (blown head gaskets) in all climes.