My 2003 forester overheats running on the highway. Changed coolant, and thermostat, didn't help. I'm not loosing coolant, no white smoke, no air in the system. Don't over heat running around town. Im out of ideas in this one.

Replaced radiator? 

Cheers 

Bennie

Use a scanner to view live data and see what temperature the ECU is reporting while driving.

2 hours ago, mikestrick1 said:

My 2003 forester overheats running on the highway. Changed coolant, and thermostat, didn't help. I'm not loosing coolant, no white smoke, no air in the system. Don't over heat running around town. Im out of ideas in this one.

My 2004 Legacy has been doing this lately and I would also like to know why. My ECU reports 220-maybe 230 max.New TS, coolant for me too. Rad is original.

make sure you look in the radiator itself - never trust the overflow bottle to reflect actual coolant level when there is even a HINT of cooling problems.

Radiator is full.

@Rampage, I have an Android head unit and either run torque pro or dash command at all times. The ECU was showing 226-237. The ac would quit blowing cold when it got to 230. The radiator is original I think, but from what little I can see looks like brand new inside .

Is the Tstat oem or Stant 48457?

Bubbles in overflow bottle?

Have you been using Subaru's "conditioner"?

Dried antifreeze at head seams?

Unfortunately, it sounds a lot like HG.

You are going to cook your bearings driving like this.

 

O.

Stant, no bubbles, coolant looked like new when I drained it to change the t stat. It only run that hot on the highway. Which I didn't know till I was 100 miles from home. I am well aware of cooking the engine. But what puzzles me is it runs normal temp around town. And no conditioner. I've turned wrenched all my life and this shows no sighs of a head gasket to me. No white smoke, not boiling over, and not loosing coolant.

@mikestrick1  I am having very similar symptoms, new OEM Tstat, radiator looks fine, only hot after a highway trip. My HGs were done 20k mi ago and I do notice some slight coolant loss but no white smoke or any oil contamination. No wetness on the bottom of the heads either. I am trying to sell mine and pretty much refuse to deal with the HGs again. I'm sticking with EA engines from here forward!

Has the water pump ever been changed?

O.

Also, do you still have the air dam section under the engine that mounts to the bottom of the radiator support panel? 

Not having this can effect the airflow through the radiator at high speeds. 

For those that still have factory radiators that are getting old, replace them! I learned this the hard way with a freshly rebuilt EA82 cooked when the side of the (looked good internally) radiator blew out. That was in 2007. I don’t trust plastic end tank radiators for long anymore. 

Cheers 

Bennie

47 minutes ago, ocei77 said:

Has the water pump ever been changed?

O.

Last year

 

Scratching my head here.

Try changing the coolant temp sensor ..

O.

Im going to change it, just to try.

You may want to flush the heater core.

What temperature thermostat did you put in?

Are the fans running properly.

Edited August 10, 20205 yr by Rampage

M@Rampage

3 hours ago, ocei77 said:

Scratching my head here.

Try changing the coolant temp sensor ..

O.

 

@Rampage, I guess you think your talking to an idiot that don't know the difference between a lug nut and muffler. I'm a seasoned mechanic, that don't use these boards unless I'm stumped. Yes the fans are working properly, yes it was overheating before is the reason I changed to a 175 thermostat. I'm not loosing coolant, no air in the system, the heater core is not stopped up, because I can switch to heat and cool the engine back down. I'll put a new radiator on it and go from there. Thanks everyone for the help. 

has the car been run offroad? anyway, look between the rad and a/c condenser for buildup of debris/grass/bugs etc. Outbacks sometimes have partial blockage in that area.

soob thermostats have a large wax capsule. most typical thermostats will lead to problems. Also, the circuit thru the heater core is important to the cooling system, but seems like that may be OK.

 

Almost certainly going to be a head gasket. 

GD

6 hours ago, 1 Lucky Texan said:

......soob thermostats have a large wax capsule. most typical thermostats will lead to problems. .....

just an FYI The Stant 48457 and the Subaru are exactly the same...

O.

 

Edited August 9, 20205 yr by ocei77
add

I've been fighting a similar problem, '01 Outback EJ251 auto trans. It only happens during very hot weather, 95 F and up, and usually only up hill with the A/C on, but the temp will creep up, I can control it by turning off the A/C and crank the heater full blast if needed. No external leaks, doesn't seem like a headgasket issue (fingers crossed). Both fans are working.

Yesterday I replaced the t-stat with an new oem unit, removed the radiator and blew it out, particularly blowing out all the mud from my son's off road adventures. Blew out the AC condenser while there. Installed new radiator hoses and coolant, etc. Cap looks good, but I ordered a new one just in case.

Took it for a test drive and all checked good, I don't really trust it until I've driven it more but so far so good.

 

50 minutes ago, 1197sts said:

I've been fighting a similar problem, '01 Outback EJ251 auto trans. It only happens during very hot weather, 95 F and up, and usually only up hill with the A/C on, but the temp will creep up, I can control it by turning off the A/C and crank the heater full blast if needed. No external leaks, doesn't seem like a headgasket issue (fingers crossed). Both fans are working.

Yesterday I replaced the t-stat with an new oem unit, removed the radiator and blew it out, particularly blowing out all the mud from my son's off road adventures. Blew out the AC condenser while there. Installed new radiator hoses and coolant, etc. Cap looks good, but I ordered a new one just in case.

Took it for a test drive and all checked good, I don't really trust it until I've driven it more but so far so good.

 

Radiator clogging will over heat under specific conditions like hills, temps, AC, towing. 
 

headgaskets will as well - On that hear, particularly if they’ve already been replaced. 
 

check or replace radiator check for hydrocarbons in the coolant. 

5 hours ago, ocei77 said:

 

 

 

ah, I missed that earlier

The headgaskets have been replaced, I did them myself with OEM MLS gaskets they have about 45K since it was done. I have done lots of them with no failures but this could be the first. I'm curious, is there a reason they're prone to this kind of problem after HG have already been replaced? Thanks.