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2008 Outback 2.5L
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Discussion Starter #1
So this may be lengthy, but I wanted to give a full picture of what's going on with my 08 Outback. It currently has ~112,000 miles on it. I had the timing belt replaced(and water pump) at 108,000 miles about 6 months ago. A few months later, the radiator started leaking, so I had it and the hoses replaced. Like an idiot, I didn't request the thermostat be changed at the same time. About a month ago I was sitting in stop-go traffic, when the temp gauge started going up. It never made it to the red, and as soon as I started moving it went back to normal, never moving again the rest of that trip. It has continued to do that sporadically ever since, a few times getting to the red. When it first happened, I thought maybe there was air in the system from the radiator being replaced, but my attempts to burp the system didn't stop the issue. The coolant level has not dropped a bit, in either the radiator or resevoir. My second guess was the fans not working, but they were cycling on as they should, or at least I thought. Everytime I checked them, they were working as they should.

So one afternoon last week while driving home from work, the gauge started creeping up while stopped at a light, and at the same time the a/c compressor sounded like it was trying to cycle on but was stuck or something. The air coming out of the vents wasn't super cold at the time, but as soon as I started moving again, everything went back to normal. When I got to my destination, I popped the hood and left the engine running, and it started doing the same thing. A/C trying to cut on, temp gauge creeping up, and then I noticed the fans cutting off and on. I cut the engine off before the temp got to the red. I haven't driven the car since. This morning when I went to start the car, it turned over really slow when I first turned the key, almost like the battery was low but it is an almost brand new battery. I cut it off, and turned the key again and it started like normal, however the temp gauge went to the red and stayed there. The engine was also running a little rough. I turned it off immediately, and re-started it. Engine ran better, but temp gauge still pegged in the red, staying there. I turned it off, and drove another car to work.

I'm almost thinking I have some sort of electrical problem, but the rough running engine this morning has me more concerned a head gasket has blown. I have been monitoring them, and there has been seeping of oil on one of them, but no leaking and it's only lost maybe 1/2 quart between oil changes. Mechanic I use hasn't been worried about it. I do think my a/c system needs a re-charge, but can't imagine it being low affecting anything else, but maybe I'm wrong. While driving on the interstate a couple of weeks ago on a really hot day, the a/c did stop blowing cold air for a few miles, but eventually returned to normal. The CEL has been on, but I've only been getting the catalytic converter code.

Any ideas? Seems odd the temp gauge would show an overheating engine right after a cold start.
 

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Lawn ornament XT
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14,366 Posts
Sounds like an electrical problem all right- one that may be preventing your cooling fans from operating or reaching peak airflow. With most of the observed overheats happening at a standstill, the fans and the electrical system feeding them are rather suspect.

I would write off the cold start instant overheat as a direct electrical problem- something prevented the meter from giving an accurate indication. A secondary problem. However I think your other overheats were likely real, and may have a common electrical flaw.
 

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03 H6 OBW & 06 WRX Sportwagon
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interesting set of symptoms. could be a coupla problems at the same time though electrical could be responsible in some way?

Nothing wrong with a thorough test of the battery and charging system. Did the accessory belts get refreshed when the TB work was done? Are they properly tight? The odd starting symptom - check for tight battery connections. Also, sometimes battery cables can 'wick' under the insulation and become corroded.

Intermittent fans have been reported in the past, certain generations are more prone I think.

On your car, pretty sure the rear O2 sensor error code is more important than older generations - it may actually be used to adjust the A:F ratio instead of just a 'nanny' light for the cat conv.

The ECU needs accurate info from the Engine Temp Sensor - it shares a housing on newer cars with the Temp Gauge housing on the crossover pipe - it 'may' be one of the first areas to get a gas or air bubble so, until this is solved, be hypervigilant on coolant level. Don't rely on the overflow tank (but keep it at the proper level), you must check inside the radiator.

Any chance rodents have been chewing on wires?
 

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2008 Outback 2.5L
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19 Posts
Discussion Starter #4
Rodents could be a problem, but I haven't seen any other evidence to suggest that.

And they only replaced the TB, along with the pulleys and water pump. No other belts replaced.

Towing it to the shop tomorrow morning to have them do a thorough check on things. The engine running rough after start this morning has me pretty concerned. Don't see how that relates to electrical problem, but I'm far from an expert. Battery was replaced when the radiator was 2 months ago.
 

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A bit off the wall, but it might be interesting to consider that all the symptoms could be caused by one electrical fault.

The temperature gauge being high when the engine is clearly cold might be the clue.

The coolant temperature sensor is connected to the ECM. The ECM translates the voltage from the sensor to a temperature value; it then sends this to the instrument panel for the temperature gauge, and uses the temperature value to control engine fueling and timing.

If the temperature signal seems to be indicating a warm or overheating engine when in fact it's cold, the engine might not start well, or not run well once it does start, because the ECM is fueling for a warm engine rather than one that is cold (and there is a distinct difference).

Similarly, if the ECM is interpreting an overheating engine, (even when the engine is actually at normal operating temperature) it not only turns on the radiator fans, but it can shed engine load, including turning off the AC compressor.

The combination of symptoms could therefore suggest a fault (electrical) in the engine cooling temperature sensing system.

The temperature sensor is a negative coefficient resistor; i.e., the higher the temperature the lower the resistance and the lower the voltage signal to the ECM.

There's two wires to the sensor; one is a ground, the other goes to the ECM. If the sensor or the wire to the ECM develops a conductive path to ground, or if the sensing element itself changes characteristics, that could lower the voltage signal to the ECM and send the temperature gauge to the top. An intermittent short, such as might be caused by a wire that has frayed against something else that's grounded (or, as suggested, rodent damage), could be quite intermittent, varying with temperature and even engine movement.

Perhaps one test would be to check the coolant temperature that the ECM is "reading" (accessible with a scanner at the OBD data port) with the temperature measured with another device, e.g., an infrared thermometer on the water (aka crossover) pipe in the vicinity of the engine coolant temperature sensor. Obviously, if the engine is cold and the gauge, and scanner are reading a high temperature, that's a bad start to begin with. Might as well try to find that cause; it might just clear up the other symptoms.
 

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2008 Outback 2.5L
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Discussion Starter #6
Interesting, and that all makes sense. The car did sit in my driveway a couple of weeks when the radiator was leaking. I thought I was going to change it out myself, but ended up sending it to the shop. It's possible a rodent took up residence while it was sitting there.
 

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2008 Outback 2.5
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Typical symptoms of an intermittent or bad fan. The fan keeps the coolant cool when you're stopped. It also cools the refrigerant in the A/C. The fan should go on.

Compliments of Porcupine73 from a post back in 2009. It's from a 96 Outback but many electrical pans have similar logic. Either a high speed fan setting and a low speed fan setting or a main and aux fan setting:

 
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