Fine when running, hot when stopped - Subaru Outback - Subaru Outback Forums
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post #1 of 62 (permalink) Old 08-27-2010, 04:10 PM Thread Starter
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Fine when running, hot when stopped

Hello to all,

I've been reading this forum for a few months now as I'm getting to know my 98 Outback. I've had it for about 8 months now and it ran fine while the weather was cool, but through the summer it's been overheating occasionally. I'm only just now posting because I know lots of people have had similar symptoms and I wanted to figure it out without re-posting a problem that you guys have already addressed. I'll talk you through my thought process so far and I'm curious to hear any feedback you have to offer...

First off, it ONLY ever overheats when the tach is below ~2k and usually only when stopped at a light after the car has been running for a while. I drive 35mi one way on an interstate for work and when I hit the light at the exit after the drive it almost always gets warm. As long as I give it some gas while I'm stopped I can keep it cool. Others have mentioned this problem and I can completely relate.

More details: no bubbles in the overflow tank at temp, hot or otherwise. Cooling system has been flushed and tstat and radiator cap were replaced at the local Subie dealer and problem still remains. Drivability is still very good and I'm still driving it every day (albeit gingerly).

My plan at this point is to pull it apart and replace the timing belt, water pump and head gaskets. I don't know the history to know if they've been done recently and with 180k it's probably time to have them done again even if they were done in the past. What I'd rather do is JUST the water pump and timing belt. Can anyone offer some wisdom on my symptoms and path moving forward? I don't have a lot of the classic HG problems, but I can't figure out why it gets warm unless the water pump is just failing slowly and rev'ing the engine gives enough flow that it can keep up.

Thanks to any and all for your thoughts, hopefully we can figure this one out!

Cheers,
Chad
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post #2 of 62 (permalink) Old 08-27-2010, 04:19 PM
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Sounds exactly like a bad fan. Given the age its probably a bad fan - search on failed Fan or Fan not running lots of recent threads on people sorting out bad fan motors and relays and solving this very same issue.
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post #3 of 62 (permalink) Old 08-27-2010, 04:37 PM
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While I thought it was the fan on first reading your post I picked up on the fact that if you keep the revs up when stationary you can keep it cool. Usually, if the fan is dead then revving the engine while stationary doesn't usually help if the car is only fitted with an electric fan (i.e. has no direct engine driven fan) as the problem is a lack of airflow through the radiator.

So I think you have a water circulation issue (which of course will be helped by keeping the revs up) - a partly blocked radiator, partly stuck thermostat, pump drive bely slipping, etc). In any event it's a work of a few minutes only to ascertain if the fan is operational once the car is warm.
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post #4 of 62 (permalink) Old 08-27-2010, 05:00 PM
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Originally Posted by Colin M View Post
While I thought it was the fan on first reading your post I picked up on the fact that if you keep the revs up when stationary you can keep it cool. Usually, if the fan is dead then revving the engine while stationary doesn't usually help if the car is only fitted with an electric fan (i.e. has no direct engine driven fan) as the problem is a lack of airflow through the radiator.

So I think you have a water circulation issue (which of course will be helped by keeping the revs up) - a partly blocked radiator, partly stuck thermostat, pump drive bely slipping, etc). In any event it's a work of a few minutes only to ascertain if the fan is operational once the car is warm.
Your thinking too hard. Ramping up the RPM's will impact many things increase coolant flow - possibly increase fan speed given more juice and of course it will run cooler for a while till the entire coolant supply has had its temp raised.

Start simple and cheap first its almost always the cause - FAN's are not working correctly! I would put money on it.

Here is why - when your driving your car your putting more load on the engine it generates more heat - but your moving so the radiator is getting cooling air over the fins. If the water pump was bad you'd have heat issues regardless of moving or stopped.

Check the FANS grasshopper its the Fan's I tell ya
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post #5 of 62 (permalink) Old 08-27-2010, 05:36 PM
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Well, It's even cheaper to back-flush the radiator than change a fan or fan switch

If the car hasn't been properly serviced as regards rad flush and coolant replacement then 12 years is about the right time for a partly blocked rad.

So place your bets now!
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post #6 of 62 (permalink) Old 08-27-2010, 07:09 PM Thread Starter
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Thanks for the feedback guys - of course I forgot to mention that both fans are electric and both seem to be running well. I suppose there's a chance that one/both are running below spec, but since they are on/off I wouldn't think so. I have hopped out in a parking lot when the temp is slowing rising and checked to see them running even in an over temp situation - that's why I suspected the water pump or a blockage. I have considered hot-wiring the fans for a few days and seeing if that makes all the difference, but I shouldn't have to do that long term of course. I've also suspected the radiator fins, but the front of the radiator looks very clean and straight - especially for it's age.

The radiator has been flushed by the dealer as mentioned, but maybe I should pull the thing out and have a radiator shop refurb it - or replace it.

Only reason I have even thought of the HG route is that it seems that others who mention similar problems go through this exact routine replacing everything in the cooling system only to end up at the HG issues.
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post #7 of 62 (permalink) Old 08-27-2010, 07:14 PM
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HG can be caused by running hot doesn't take much of a bump in the temp gauge to have the engine in the really hot range. HG blown can also blow out the coolant resulting in low coolant levels and thats generally when people learn they have a blown HG because their car over heats.

Your situation sounds like bad fans or radiator given your only getting it at low speed or stopped situations and the fans are "running" I bet the fans are not running at full speed.

Search on fan issues in the OB forums there were two threads which were very good. both cases they found the fans were not working right and in one case they thought they were running when really only the small fan was running and the main fan was toast.
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post #8 of 62 (permalink) Old 08-27-2010, 07:21 PM Thread Starter
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Awesome, I'll definitely have a look. That would be great and certainly easier than tearing into the engine.

Thanks again!
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post #9 of 62 (permalink) Old 08-27-2010, 09:10 PM Thread Starter
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...just did a quick check of the fans when I got home tonight. When I turned off the engine it was very apparent that one fan slowed faster than the other one - this could be the culprit indicating bad bearings or motor. One other thing I noticed is that one fan has five blades, but the other has FOUR! Is this typical? Might be, just thought I'd check with the pros. I'll plan on checking them thoroughly this weekend...

Cheers
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post #10 of 62 (permalink) Old 08-28-2010, 05:05 AM
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One thing. Just pop the yellow lid on the coolant reservoir and take a sniff. If it smells like the tail-pipe - like combustion products - then you may well have a HGF. If it just has that slightly sweet smell of anti-freeze then you don't (well not one that's across the fire-rings - between the combustion chambers and the cooling system - anyway).

Might as well get that established one way or the other fairly soon.

Back soon (off to fix the brakes on my daughter's Ford Ka )
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