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Discussion Starter #1
Guys need help my subbie outback 2016 2.5 is overheating when I drive above 90mph. The temp guage is normally on the middle but when I drive fast it starts to creep to the right side at the 3/4 close to the red zone. I have checked the radiator and have noticed that coolant is moving from the radiator to the reservoir tank after a drive. The car is not losing coolant, if I remove the reservoir tank and pour the coolant back into the radiator it fills the radiator and the reservoir tank remains with the quantity between the min and max. Is it a head gasket issue? Or thermostat or the radiator cap. The car is still new less than 40k miles. If i hook up an obd the coolant temp is around 109 degrees celcius when driving around 80mph. If I push it to 90 or 95mpg it goes to 110 degrees celcius. Thats when the temp gauge starts to move to the redline although i have not allowed it to reach the redline .Have removed the thermostat and drove it without but it still does the same.
 

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If you're in a hot climate, it may be due to the active grille shutters. I noticed that cruising around 80mph on a 115F day they would cycle open/closed alternatively getting worse/better mileage and the coolant temp dropping/climbing. If there's a cutoff speed where they remained closed, I could see how the coolant might get quite a bit hotter than desirable in a similar environment.
 

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Discussion Starter #3
thanx but the active grill shutters broke off when i hit a bird and i just left the motor, so its just open at the lower grill. The filling of the reservior bottle with coolant way above the max mark is normal???
 

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Its possible the 2.5i just has to work too hard against wind resistance at that speed. I saw similar engine temps when driving for extended periods of time at 85 mph though South Dakota and Montana in my 2.5i.
 

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It is possibly the radiator cap. If the cap is not holding pressure in the system, the temp will rise higher than it should.

Also the cap should allow the coolant to be drawn back into the radiator from the overflow as the engine cools.

Try a new Subaru OEM cap and see if this fixes the problem

Seagrass
 

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I'll bite.
Why are you driving 90mph ?

Sent from my SM-G960U using Tapatalk
I was thinking the same thing. Pretty sure it is not designed for those speeds. I would almost to expect it to over heat before it detonates.
 

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Next time the bottle fills, let the system cool completely (overnight or at least 4 hours) and see if the level returns to normal (or the previous level).

If normal, I'd say it's just the system compensating from a high load. The engine is out of it's comfort/efficiency zone at that RPM, so it will generate more heat.

If it stays high in the bottle, but low in the radiator, I'd say you have something displacing the coolant (like exhaust gas) and it would warrant investigation.
 

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Discussion Starter #10
levels go back to their normal when it has cooled down, I have checked. hahaha the outback can reach 100mph without an issue. Any recommended methods of improving engine cooling? like a bigger radiator or fans?
 

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2017 Outback Limited -2.5 CVT ---- 'Gone' 2014 Outback Limited - 2.5 CVT ---- 'Rehomed' 2012 Outback Limited - 2.5 CVT - Deep Indigo Pearl ---- "RIP" 2010 Outback - 2.5 CVT - Silver - So's my hair
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O.P. uses both metric temperature and miles per hour. What few places in the world use centigrade and miles?

Looks like he/she has removed the thermostat and screwed up the grill shutters and is worried about going from 109 to 110 degrees Celsius. Wonder if there is any real coolant being used. If using water only as coolant it's going to boil at those temperatures.
 

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levels go back to their normal when it has cooled down, I have checked. hahaha the outback can reach 100mph without an issue. Any recommended methods of improving engine cooling? like a bigger radiator or fans?
An old trick is to turn on the car's heater at full blast, to act as a small secondary radiator. This isn't a good permanent solution, but if your car's temperature is rising beyond the ability of the cooling system to cope, then this is something you can do immediately.

Also, does your car still have the plastic undertray? It's supposed to help air flow through the radiator, but I'm not sure of the aerodynamics at 90mph if it helps or hurts cooling. You could try running it with/without the undertray to see which works best for you.

If the bird strike broke off your active shutters, are you sure it didn't damage the radiator?
 

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Discussion Starter #13
I have 50/50 subaru oe coolant . sorry was converting but we use metric. The question was 109-110 degrees is too hot . i think its supposed to be 100 degrees celsius
 

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Discussion Starter #14
An old trick is to turn on the car's heater at full blast, to act as a small secondary radiator. This isn't a good permanent solution, but if your car's temperature is rising beyond the ability of the cooling system to cope, then this is something you can do immediately.

Also, does your car still have the plastic undertray? It's supposed to help air flow through the radiator, but I'm not sure of the aerodynamics at 90mph if it helps or hurts cooling. You could try running it with/without the undertray to see which works best for you.

If the bird strike broke off your active shutters, are you sure it didn't damage the radiator?
thanx , no the radiator is fine , yes the car still has the undertray
 

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OP's profile shows Namibia. It is summertime there. I think pushing a 2.5 at 90mph sustained speeds will just run the engine hot. It is using quite a bit of horspower at that speed.
The cap pressurization will not affect the temperature the coolant is at, but will affect the boiling point of the coolant.
When the coolant gets that hot, it will expand and push the extra volume out to the reservoir. As the system cools, it will draw it back in.
If the car has always behaved like this, I suggest nothing is wrong and it is normal behavior for running the car at that speed in the summer temperatures.
Change the coolant ratio from 50/50 to 70/30 water or even 80/20. Water has much more ability to transfer heat than the coolant. Use distilled water, not tapwater.
 

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Discussion Starter #16
OP's profile shows Namibia. It is summertime there. I think pushing a 2.5 at 90mph sustained speeds will just run the engine hot. It is using quite a bit of horspower at that speed.
The cap pressurization will not affect the temperature the coolant is at, but will affect the boiling point of the coolant.
When the coolant gets that hot, it will expand and push the extra volume out to the reservoir. As the system cools, it will draw it back in.
If the car has always behaved like this, I suggest nothing is wrong and it is normal behavior for running the car at that speed in the summer temperatures.
Change the coolant ratio from 50/50 to 70/30 water or even 80/20. Water has much more ability to transfer heat than the coolant. Use distilled water, not tapwater.
will try that thanx
 

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How hot is the fluid when driving at lower speeds? If the cooling system is operating properly it shouldn't creep above ~95°C/200°F at normal speeds and 80mph isn't really outside that range. It shouldn't be at 109°C by 80mph either way.
 

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Have removed the thermostat and drove it without but it still does the same.
NOOOOO!! Subaru uses a 'bypass' cooling system. Without a thermostat, the engine will likely run HOTTER than with one. (because there is no thermostat to block off the radiator 'bypass' when it is supposed to.)

With a thermostat installed, under ALL situations, the flow thru the ENGINE is continuous..... the thermostat only controls the TEMPERATURE of the fluid within the engine. The thermostat does this by controlling the FLOW thru the RADIATOR.

The bottom line is that the thermostat has SEVERAL functions.
1) Route the fluid AROUND the radiator for faster engine warmup (bypass mode)
2) Allow JUST ENOUGH flow thru radiator to maintain engine-temparture.(the rest of the flow 'bypasses' the radiator and goes back into the engine)
3) At high engine temps, the thermostat will BLOCK OFF the 'bypass' pipe and force all the flow thru the radiator.

In other words, without a thermostat, the waterpump will push the fluid haphazardly thru the thermostat housing instead of metering the flow thru the radiator based on position of the thermostat. (because there is no thermostat to block off the bypass pipe) It is likely that the flow thru the thermostat housing will 'bypass' the radiator when it is supposed to go THRU the radiator.
 
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