‘02 auto forester gets hot on hills

[el_freddo]

My mother inlaw’s 2002 auto forester with the EJ251 gets hot when climbing hills at speed in warm weather. Towing a light trailer exacerbated the issue at a lower ambient air temp (9°C lower at ~26°C). 

As you climb a decent long hill, not a mountain by US standards, you can almost watch the engine temp gauge go to the red, backing off and babying it will hold the temp gauge there or have it drop a tiny bit.

So I ruled out the engine being the issue for the following reasons: 
- I did the HGs two years ago, shaved the heads, lapped the valves and used the MLS HG units recommended by GD 
- top of radiator was hot, lower core was cool, lower tank was hot 
- RHS fan pulling really hot air, LHS fan pulling less hot air that was substantially cooler 
- auto fluid lines into the radiator felt quite hot with marginal difference between the two lines 
- lower rad hose seemed almost as hot as the upper rad hose 
- temp gauge drops to normal operating temp as soon as you crest the hill, it would generally be back to normal about halfway down the other side 

I’m thinking there’s an issue with the auto. There’s no AT temp light coming on and no other lights when this happens. I’ve only just thought about pulling code for the TCU but don’t know if that’s a thing or how to do it without a scanner. 

It’s got 370,000km on the clock from memory, it could be 340,000km... either way it’s “up there” by most Aussie’s standards. 

It drives as you’d expect, no issues there. I don’t know the age or condition of the ATF as I haven’t looked since doing the HGs, at which point it was still “good”.

What thoughts do you guys have and what should I be looking at? 

Cheers 

Bennie

[lmdew]

My 2000 OBS does pretty much the same thing. It's fine unless I'm in the mountains pushing itl

When the temp gauge starts to increase, if I turn off the AC it helps.  If needed I turn the heat to high and open the windows.  As soon as the load is removed it's fine.

I've replaced the radiator with a full metal aluminum one.  It helped some but did not correct he problem.   I've changed the thermostat, no change (Subaru thermostats).  Otherwise fine.

I have not pulled the water pump as to me it's just not worth the time right now.

[forester2002s]

You didn't mention it, so I have to ask: Are there any bubbles in the radiator overflow-tank?

[1 Lucky Texan]

our 03 H6 OBW shoed the same effect on a trip once. One thing I wish I had experimented with, and you guys could try it, was selecting 3rd gear. The rpms going up may  help spin the water pump faster and maybe help?

[el_freddo]

On 2/21/2022 at 3:22 AM, forester2002s said:

You didn't mention it, so I have to ask: Are there any bubbles in the radiator overflow-tank?

No bubbles, no boiling coolant. I didn’t have my infrared thermo gun with me at the time so no solid temp readings either. 

The fact that you could literally watch the temp drop back to proper operating temp suggests to me it’s not the HG.

Changing gears down didn’t help, but what did help was getting a run up on the flat just before the hill then ease off the throttle a little as we climbed the hill, putting only a little amount of load on the auto and engine. 

Cheers 

Bennie

[Numbchux]

Sounds very much like the issue we were having with our 04 Outback VDC last summer. Slow temperature creep under load.

 

A very thorough cooling flush solved it. 2 chemical flush treatments with a drain/fill. And back flushed the engine, radiator and heater core independently with water. While the radiator was out, I used cleaner and hose to rinse any dirt and debris out of the outside of the radiator and condenser cores.

 

The hot lower hose is a good sign, as it means you have circulation. But it's just not getting rid of the heat.

[el_freddo]

Thanks @Numbchux - the radiator is an unknown to us as it’s the one that came with the car. Will look at replacing it before our next summer, so November-ish. It won’t be doing any big runs like that in the heat from this point on, and certainly not towing a trailer for some time if ever again. 

Cheers 

Bennie

[1197sts]

I have found this to be a common issue on 2nd gen Outbacks, most likely the forester is similar. If the oat is above 90 to 95f, going up a long hill with the A/C on the temp can rise even if everything is working normally. As others have mentioned turning off the A/C usually helps. If it goes up under these conditions on a small hill I would suspect the radiator. Of course you want to verify your cooling fans are working.