Since replacing the engine on the 01 Outback I am getting an intermittent code 128. It says coolant temp below threshold? The water pump and thermostat are new. Car runs perfect doesn't over heat or leak. It only happens if I crank it up and take off. If I let it set and warm up for 2-3 minutes it doesn't happen? I am clueless on this malfunction.

might have air in the system.

 

Where is the temp gauge once its hot?

Just below the middle after a 61 mile drive at 80 MPH ( my daily commute one way) . If I warm it up for a couple minutes before I go, it doesn't pop the code and CEL? I know I should always warm it up a bit. But sometimes I just crank it up and take off ( reasonable throttle settings until it's up to temp of course).  I let it run with the cap off after I changed the water neck several days ago and had the heater on hot until all the bubbles in the radiator stopped so I figured I had it bled, but it was doing this before I discovered the water neck leaking and changed it?

Does it have a Subaru thermostat?

Yep, brand new one done with the motor change about 1000 miles ago. I let it warm up for 3 minutes today before driving off and no CEL. Drove 61 miles averaged 75 MPH and no CEL or codes when I checked them after the drive??? So long story short, I will continue to monitor it closely. I get a CEL for code PO 420 about every 500 miles, I think due to aftermarket Cats. I erase all the codes when that happens and press on... thanks for the replies...

Edited October 21, 201411 yr by 01 Outback

Will your code reader read live data?

I am unfamiliar with the terminology you are using.I don't know what live data means? I checked and reset the code with the engine running while driving at 75 MPH 3000 RPM . I was merging onto the interstate after about 10 minutes of operation and the CEL came on just as the engine came to temperature.

Edited October 21, 201411 yr by 01 Outback

Update:

I am thinking it was trapped air as the CEL now only comes on every 4-500 miles with PO 420 as it has since I owned the car. The coolant and oil levels are unchanged in the 2000 miles put on since oil change at 1000 miles after the motor was installed.