My Subaru overheated while towing and while I read some other threads about overheating, there isn't much written here about towing, so I thought I'd start a new thread.
I live in Switzerland with an EA82 MPFI 3-speed Automatic GL Wagon (Leone II) with a hitch. No A/C, no turbo. About 130,000km on the original engine.
As scheduled maintenance in February I had replaced the HG's, intake manifold gaskets, sealed the cam towers, valve seals, Mickey Mouse seal, etc. I also replaced the plugs, plug wires, dizzy rotor and dizzy cap at that time, and topped off the driveline lubricants. It seemed to be running perfectly, quietly, and consuming little oil and less fuel than before.
On paper it has more torque and more Horsepower than my old Land Rover, so I tried towing our 800kg/1800lb camping trailer last week on vacation over some big mountains. The car also had 4 bikes on the roof and 2 adults/2 kids inside.
Wife at the wheel, doing 4500-5000 rpm up a 10-12% grade in 1st gear and 35C/90F outside temperature, it boiled over.
After it cooled, I recovered the green cap from the overflow canister (it was down in the bodywork), put in about 2L of coolant (!) and we continued, only to overheat and blow the green cap off again and need another 2L of coolant. The electric fan was working. There's nothing blocking air through the grille.
Returned home to swap cars and now I'm back from vacation figuring this out.
1) the car has been normal when not towing anything.
2) It has always pinged like mad under load (steep uphill, 2 adults/2 kids). I had the timing checked by a Subaru garage and they said it's fine.
3) Before leaving with the trailer, I filled the coolant overflow tank. It was empty. I had not been aware of coolant loss as it's my wife's car and I'm not on top of the day-to-day situation. I didn't know at the time that an empty overflow tank meant I should also fill the radiator. Thus it COULD have been low on coolant from the outset!
5) After it overheated, we noticed a weep of coolant from the thermostat housing gasket. I had never replaced that gasket.
So what am I looking at here?
Was something wrong with the Subaru to have caused overheating, or would you have expected the overheating under this much load?
It overheated even when I re-filled the radiator and overflow tank. So it being low on coolant wasn't the cause of overheating.
Does the repeated overheating indicate that I have perhaps warped the heads? Might they have cracks?
Could a malfunctioning thermostat cause this?