If you left a 400 watt inline oil heater plugged in overnight, how hot would the oil get?
There is no thermostat.
Can these oil heaters take running for excessive amounts of time.
My dart is in the trailer with antifreeze but temps are plummeting tonight.
I have a space heater in there but thought about plugging in my inline heater instead.

Inline ? ... or covering the pan or tank ? ..... don’t know if they still do it but some PS teams reportedly remove the oil and heat it externally

. I would imagine you would have a nice cozy Fire by the morning.. my oil tank gets scary hot after an hour.. that's 8 quarts

I agree with you but its 9 degrees in the trailer now.
I'm not sure if these heaters can work for extended periods of time.

You'll never get that oil hot enough. I was going to drain the water from the rad and block a few years ago after the season was over. The winter never came until late January. I had put off changing the water because of the mild weather. Wake up 2:30 AM and remember that I did not drain the motor. Next day, ice at the top of the rad and slush in the bottom. Panic!! Attached 2 block heaters and covered the motor with insulation. Checked every 2 hours. Next day, ice melted but the water was 34*. Dumped the water and pumped warmed antifreeze thru the motor. Let it circulate for 2 hours, thinking to melt any ice crystals that may have remained in pockets of the heads. Water temp 36*. Left the block heaters on overnight, water temp 34*. A cast iron block will always wick the heat to the ambient temp. If you prepped your motor before winter, than that cold cold oil means nothing unless you are trying to start it. I have 2 friends that change the oil to 0 W and they crank over the motor every week. As long as the water doesn't freeze, you are OK.

remove the oil and heat it externally

Heated on a big stove before being added to the crankcase: aero engines in 1914.

Leaving heavy oil in the car is harmless... until/unless you need to start it. Thick oil not only kills cranking speed, but when it starts it takes 3 weeks for the oil to reach that last bearing.