Hi everyone,

About 2 years ago my car was overheating. On the advice of the garage, replaced radiator, water pump and relay. No improvement. Changing the thermostat and burping the system properly cured the problem until now.

A few days ago the car was very hard to start and eventually when it did start, it ran horribly rough. OBDC showed P0118 so I replaced the engine coolant temperature sensor that sits under the throttle body. Started and ran perfectly and error code went away. Brilliant I thought. Ten minutes later the temp gauge rose almost to the red with no error codes!

Checked relays (only 2 fan relays in my car) - all good. Checked main radiator fan and it was dead. Replaced that and installed a genuine Subaru thermostat just in case. Idled for a while (up to 97C) and main radiator fan turned on and the aircon fan also came on when I turned the aircon on. After 15 minutes of easy driving the temp rose almost to the red (112 C).

I got hold of a head gasket leakage tester to plug into the radiator and ran the test. Fluid stayed blue so I'm assuming there's no leak. I'm aware that this is not 100% but I'm still hoping it's not the head gasket as the fluid level in the radiator doesn't drop at all.

I'm about to lose my marbles. Does anyone have ANY suggestions please?

Thank you.

 

You might need to re bleed the coolant system as you could have some trapped air?

 

Forgedmarco - I have tried 3 times, no bubbles, level doesn't drop and no change.

 

What method did you use to bleed/refill the system. There have been other users who have had issues and it was the bleeding method that was causing the problems.

 

You can't really bleed the coolant system of air - you need to stop air getting into it when filling. What procedure did you follow when replacing the coolant?

 

I used the long method described in the workshop manual:

1) Close the radiator (for turbo model, coolant filler tank) cap to start the engine and race 5 to 6 times at less than 3,000 rpm, then stop the engine. (Complete this operation within 40 seconds.)
2) Wait for one minute after the engine stops, open the radiator (for turbo model, coolant filler tank) cap. If the engine coolant level drops, add engine coolant to the filler neck position of radiator (for turbo model, coolant filler tank).
3) Perform the procedures 11) and 12) again.
4) Attach the radiator (for turbo model, coolant filler tank) cap and reservoir tank cap properly.
5) Start the engine and operate the heater at maximum hot position and the blower speed setting to “LO”.
6) Run the engine at 2,000 rpm or less until radiator fan starts and stops.

 

Technopug - Filled via radiator cap until full, then ran the engine and topped up as bubbles emerged or the level dropped.

 

You need to fill from the header tank on the engine. See post 3:

https://www.scoobynet.com/general-te...-question.html

 

Mine is the standard Impreza, not the STI, so I don't have a metal header tank on the side. Mine has the regular plastic header tank right next to the radiator. I did fill slowly and with the heater on.

This whole business is doing my head in! I know that if I take it to a dealer it'll cost an arm and a leg and they'll tell me the highest cost possible without really finding the specific problem.

Surely I should get an overheating error code if it goes above 100C?

 

Ive always burped the water system by leaving car to idle until the fans and come and gone off twice, never had a issue this way, cap off any header tank.
When the temp has shot up how firm are the radiator hoses?


edited to add : Car on level ground

 

Is the fault consistently repeatable?

Also, some more information - is it a 2004 or 2006? What's the mileage?

 

JDM Stig - I tried level ground and also parked on an uphill as someone said this helps. Hoses are hard when it's hot.

Technopug - Consistent after 10 minutes driving. From cold, standing idling (no matter how long), the fan comes on and the needle sits very slightly above the first mark as it always did. However, the fan doesn't turn off.
2004 with 210,000km

Appreciate the help guys!

 

Just had a look at the workshop manual which states that the non-turbo radiator cap should be 157kPa (1.6 kgf/cm). The cap on my car says 108kPa (1.1 kgf/cm).

Is this possibly the problem and worth me trying to find a higher rated one?

Cheers.

 

Post a picture of it.

 

Attached

 

Should be this one I think.

 

That's even lower pressure (0.9 vs 1.1) than mine so it would boil earlier and would make it worse! The manual says 1.6.

 

whilst it may not be correct unless faulty / damaged the cap on its own will not be causing over-heating issues in general........

 

that looks to be the testing pressure not the cap pressure?

 

Forgedmarco - You may be correct.

 

Check if you're getting heat from the heater - it's a fairly good test of whether the coolant pump is working. Or not.

 

There is heat from the heater but it's not like it used to be.
Tomorrow I'm going to pull the thermostat for some light driving for 24 hours and see what change it makes. At least then I can rule out the new thermostat that was installed.

 

Sounds like it could be the impeller slipping on the 'new' pump... 🤔
I did read somewhere on here that original Subaru waterpumps give no trouble and are better quality than replacement ones, something to consider when changing the cambelt..... in other words keep the old pump.!