Quote:
Originally Posted by slogfilet
To redo this experiment would require several nights with consistent outdoor temperature:
Day 1: run heater for 15 minutes, crank engine to mix coolant, check temp.
Day 2: run heater for 30 minutes, crank engine to mix coolant, check temp.
Day 3: run heater for 45 minutes, crank engine to mix coolant, check temp.
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Day X: run heater for 15*X minutes, minutes, crank engine to mix coolant, check temp.
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Done! Over the last two years I've been collecting data and I've finally crunched the numbers. I recorded the plug in duration, outdoor temperature and coolant temperature when it stabilizes 10-30 seconds after starting the engine. I did not record the data when something could have skewed it, for example if the car was parked in the sun, or if the engine had less than 12 hours to cool off.
As a reminder: I have a 550W coolant heater (no pump) and a 125W pad heater stuck to the oil pan. My lower grille is blocked year round, during the colder months so is the upper grille and then I have a piece of cardboard with aluminium foil insulating the engine from the top. Underneath is an OEM undertray. Coolant temp was from my ScanGauge, outdoor temp was always from the same digital thermometer.
I collected a total of 89 datasets, of which the first 9 where before I installed the pad oil pan heater. The graphs below show how much warmer (°C) the coolant was after how many minutes.
This surprised me: the oil pan heating pad helps much more than I expected. I thought that it would shorten warmup time
after starting the engine, but it turns out to help with prewarming too
Also, I was was expecting the curve to flatten out much sooner. I usually plugged in for 1.5-2h assuming that longer time had diminishing effects, but the few times I've plugged in for up to 3h show that the engine is still keeping most of that heat
Notice how large the variation is between datasets with the same plugin time: 2 hours can increase the coolant temperature by anything between 22 and 33°C. I thought that this depends on the outdoor temperature (losing more heat when it's cold?), so I plotted the data in four outdoor temperature ranges: below -5°C, -5 to +5°C, +5 to +15°C, and above +15°C:
As you can see, this does not effect the wide temperature spread. There must have been other factors effecting how the coolant heats up, maybe wind?
Sometime in the future I plan to add some more insulation to the engine bay. When I do I'll start recording data again to see the effect on prewarming.