The Sizzla Posted April 4, 2015 Share Posted April 4, 2015 I picked up a pretty nice (not cosmetically) 91 Legacy L wagon on the cheap. It runs well but the thermostat is stuck open but it also blinks a code 21 for the coolant temp sensor. I know for sure the the thermostat is bad – it stays on cold forever if you just up and drive the car, but it will come up to temp if you stop and let it idle for awhile. I'm not sure what to make of the coolant sensor code because I thought it was supposed to run the fans all the time if it threw a fault code. Is the OBDI computer smart enough to throw a code if it takes too long to warm up, or is there a tolerance level between when it initially throws a code and when it goes into failsafe mode with the fans? I'm going to replace the sensor just for age's sake if nothing else, but I don't know if I'll be chasing some weird electrical problem afterward if it's supposed to be in failsafe mode when the light's on. Link to comment Share on other sites More sharing options...
lstevens76 Posted April 5, 2015 Share Posted April 5, 2015 First, is the thermostat stuck open or is "non-existent"? I don't like saying this, but I've seen a lot of people who will pull a thermostat on an overheating car just to sell it and then claim the thermostat is "stuck open". Never trust a car with a "stuck open" thermostat. It could be getting "erroneous readings" which means it is sort of working but not correctly. Either way it needs replaced and while your at it I would do the PCV as well since you have to disassemble those hoses. Around $30/$35 in parts and maybe an hour to do the work. You can verify the fans work with 2 green connectors under the dash. On my '90 they were close the center, but most places say they are to the left of the column. When you plug these together the fans should cycle on and off with the key on (I wouldn't recommend starting it this way). This way you know the fans are working. That video shows you it pretty good. A 19mm socket (deep as you can get), swivel, decent extension, and a ratchet. 1 Link to comment Share on other sites More sharing options...
The Sizzla Posted April 5, 2015 Author Share Posted April 5, 2015 I'm confident it's just a bad thermostat. I haven't pulled the housing yet (waiting on an OEM t-stat/gasket kit to arrive, stealership won't pricematch) but if I block off the middle third of the radiator it holds temp in the middle even if I do stuff like go uphill in 2nd while dragging the brakes. The fans trip on just fine. I really enjoy working on this thing compared to my wife's 04 Forester - everything is even more "right there." Link to comment Share on other sites More sharing options...
86 Wonder Wedge Posted April 8, 2015 Share Posted April 8, 2015 (edited) Edit: reading is hard. Glad you got an OE one. When I had big air bubble problems, it would throw the code 21 on my 91 SS. But the book defines it as an "abnormal" signal witch could be a bad electrical signal or a wildly varying signal as well. Check the harness on the driver's side by the battery for clean and tight connections. Edited April 8, 2015 by 86 Wonder Wedge Link to comment Share on other sites More sharing options...
lstevens76 Posted April 9, 2015 Share Posted April 9, 2015 I'm still learning the subaru computer's personality (every manufacturer's computer has its own). There is a possibility, after thinking about it, you could be getting a code 21 due to the lack of a thermostat, nothing more. The reasoning behind this might be the computer is looking for a specific temperature within a certain amount of time. If it's not getting it the system may be assuming everything else is correct, but the ECT is misreporting. I would replace the PCV regardless if you don't know when it was last done. It's a $1.99 and 5 minutes to change. I am curious now if the code clears and doesn't come back once the thermostat is replaced. Link to comment Share on other sites More sharing options...
The Sizzla Posted April 14, 2015 Author Share Posted April 14, 2015 (edited) I pulled the old thermostat - it had 4 big (1/4in?) holes drilled around the perimeter in addition to the smaller manufacturer bleed hole. I tested it on the stove and it's OE temp - it starts to crack open at 170 and is fully open around 185, but by the time it cracks open it's already flowing a lot of water with the extra holes. It also looks like the radiator cap is original - it has a yellow sticker with Japanese and English instructions and is flaking gray stuff off into the neck. Trying out a new cap and stat after a vigorous driveway bleed cycle tomorrow, hopefully this was just a dopey repair and not to mask something :X edit: world's smallest HG leak revealed! hee... Edited April 21, 2015 by The Sizzla Link to comment Share on other sites More sharing options...
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