It’s been 2 months now of researching, reading every thread I can, trying, monitoring with no success; I am now totally stuck and don’t see what else I can do to solve my issue, and this is driving me mad ^^ !
I have a Subaru Impreza Hatchback 1998, EJ15 GF1, manual, petrol, with now 190,000 km. Small engine, pretty well maintained, I change all filters and oil every 10k since I have it, the previous owner was taking care of it and I bought it after the cam belt and water pump were changed professionally by a garage., around 170k.
So one day (around 187k) I noticed the car smelled a bit like overheating engine. I checked under the bonnet and noticed that the fans were not working. After more in depth checking I noticed that the lower radiator hose was cold and there was no pressure in the radiator.
So bought a new thermostat and gasket (original Subaru) and new coolant, tried it with the new one and didn’t change a thing, the damn thing stays closed. Tested both thermostats in hot water, they both work fine.
I then tried to run the car without the thermostat, I get good pressure, the coolant is flowing, I could properly burp the cooling system and I could see the radiator was not clogged, but surprisingly the fans still did not turn on. So I bought new temperature sensor and sender and tried again, but nothing changed, the fans don’t turn on. I checked all the fuses, under the steering wheel and under the bonnet, tested the relays with the test wires under the steering wheel and both relays and fans work fine. (I also bypassed the relays with fuses and this turns on the fans, no problem).
The very weird thing is that when the thermostat is installed and the engine running, the temperature gauge comes up to the optimal position, slightly below the middle, and stays there, even though the engine keeps heating. I don’t have an infrared thermometer but I can tell by the smell and the heat, and the fact then the thermostat stays closed and fans stay off, that something is wrong and that the engine is too hot. It really smells like overheating engine and the hoses and engine are reeeeally hot.
Before this began happening, when it worked well, the fans turned on and off automatically and I could tell when the thermostat opened and closed, it was all fine.
I tested all sensors, new and old, with a multimeter and they all work fine, even the thermostats in hot water both open and close correctly.
I contacted a mechanic friend who checked everything, he used a pretty strong product to clean the cooling system in case there would be some kind of stop-leak or stuff clogging the system, but nothing, the circuit is clean. I even used a thin brush to try to clean possible depot around the sensor areas, but nothing came out, all is clean… I also cleaned the cooling system with my garden hose, I know it's not recommended but I was out of options, I confirm that water flows through everything and came out clean. (I rinsed with demineralised water several times after this and put new coolant).
I feel like I did everything I could, I don’t see what else to do. I am not sure this could be related, but (I think) this began happening the same month that someone tried to steal it, or at least I noticed this cooling issue like a month after. No big issue from these unskilled robbers, who just broke the door handle and damaged the ignition, but it took me like 2 weeks to fix this, but during this time I removed the battery from the car because I could not close it and I don’t have a garage. So the car stayed quite a long time without a battery. I thought this could have done something to the ECU (I have nearly no knowledge about this part of cars) but anyways, this should not impact the thermostat which is a purely mechanic part.
So Guys, I don’t knot what else I can do. I am pretty sure that the radiator is fine, I have been driving without a thermostat since, the engine takes longer to heat and the temperature tends to decrease at high speed and increase at idle and low speeds (no fans working, remember) which seem logical to me. Also the heater core seems fine, heat turns on and off, no problem.
If you have any idea what might be going on I’d be super keen hearing your opinion, this is getting so frustrating.
Cheers guys, thanks for reading !
Oh and it's not a head gasket by the way, already checked, oil and coolant are fine, I changed both.