Noticed something new today and not sure if this is normal or not.
Replaced thermostat this weekend and all appeared to be OK. While running the engine to purge any entrapped air, noticed the cooling fans coming on and cycling on a regular basis but duty cycle was probably less than 25%. Today I noticed that every time I came to a stop the cooling fans would come on immediately and stayed on until I was moving again. I live in a somewhat rural area and no stop and go driving 40mph or more is quite easy. Weather is cool (60°) & wet. Even had the heater on low. I don't think the fans were acting this way before the repair but recently weather has been warmer that today.
New thermostat is stock temperature and temp gage is reading in the same area as before.
Thought was maybe due to ambient temp the AC was coming on with the heater to dehumidify the air but checked and AC is not running.
Did you have the defrosters on? The defrosters will activate the AC to dehumidify the air and to make sure that the seals stay oiled during the winter months.
Water level has stayed consistent for last several days. Have even pulled a small vac on the radiator and saw no drop in fluid level due to entrapped air.
Defroster wasn't on yesterday and I did mention AC compressor not running.
Anyone know the temp that the cooling fans come on at? Possibly that temp is so close to the thermostat that there is almost no difference and fan could come on at any time.
On the other hand I'm wondering why fans were coming on within a second or two of stopping and why never shutting off as long as I'm stopped. Why no cycling of the fans like is normal?
Need to find the reason for this operation as I don't want to find myself in a overheated situation.
Since none of the "usual suspects" seems to be your culprit, it may be time to swap out the radiator sensor that turns on the fan(s) and see what happens. My experience is that when the sensor fails, it usually causes the fans NOT to go on (overheating) but that doesn't mean yours couldn't be going the other way.
OTOH, it's STILL possible to have air in the system, even though your overflow tank's not going down. When you purged the system, did you have the car on an incline (front wheels on ramps or whatever) to make sure air could get out? My Subie's not so bad about this, but I had a Toyota that would take a month to get all the air out after a coolant change. PITA!
Cooling fans are controlled via the ECU with input from sensor in the coolant manifold atop the engine. Manual says signal from sensor at 85°C should be
1-1.4v.
I placed a thermocouple in the coolant and ran engine while fully warm at various speeds for several mins. Temps ranged from 175-185°F and fans were on full time. This is the temp the thermostat starts opening. Further test is still needed but hope root cause isn't the ecu.
Maybe my continual post will help others or latecomer will see and have the answer.
Got to work on this problem yesterday and what I found was interesting and thought some others might find it useful.
I had the chance to get over to my son's house where we had some test equip. Was able to see some real-time readings from the ECU via the OBDII port and laptop computer.
From physical observation I noted with the car stopped and cooling fans on, within a min or two I could hold my hand on the upper radiator hose or top of radiator and it didn't feel that hot. Also noted the air coming off the radiator fans was cool and not what would be expected when engine temp was close to 93(200). After seeing this I switched the heater on full blast. Within several mins the measured temp had dropped to the point where the fans went off and they stayed off. This indicated to me the problem most likely was with the thermostat.
The measurements: The stk thermostat is rated at 78 (172) and I expected to see the engine running close to this but what I saw while driving was the engine was running between
92(198) - 96(205) depending upon driving conditions, much higher than expected. Taking some other readings I found the cooling fans come on at 96(205) and shuts off at 91(196).
As stated in original post the fans were coming on almost instantly when I came to a stop. Now I can see why.
I pulled the new thermostat expecting to find is not functioning correctly but what I noted instead was the flow passage on the new thermostat was a lot smaller than on the original part. I took a couple measurements and did a quick calc. What I found was the original part had an opening of 1.43 sq in and the replacement part of .85 sq in. New part was Only 59% of the original. These number were based on area of opening dia not including restriction of the center support. Looking at the difference in the support design I would guess the new part actually was only flowing 50% of the old.
Putting the old part back in and going for a drive I saw a 15-20°F drop in temperature. Back at the house the car idled for another 5 or so min before the fans came on.
The replacement part was a Beck/Arnly, made in Germany, almost $20. I would have expected this part to be of high qlty in all respects but the reduced flow just won't cut it.
Will have to drive to nearest city with a dealer so I can purchase a factory spec't replacement.
Hope there is a lesson in here for all to learn from.
Thanks for the update! Looks like ANOTHER item to add to the "OEM works best" list! Not sure why Subies are so picky about factory vs aftermarket parts but they sure seem to be. My dealer parts guy jokes that aftermarket parts for Subies are all guaranteed: not to fit or work right! Several experiences of mine make me think he's right.
Got the factory replacement part put in on Tues and took it out for an instrumented run. At speed engine temp was running 183-185F. Big difference than seen with the Beck/Arnley which had the car running at 198-205F.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.