Yesterday I did a little experiment on my block heater performance. My main goal was determining how long I really need to plug it in to get the coolant as warm as it can get. I'd heard some folks quoting 2-3 hours. but all those numbers were based on relatively small engines.
The coolant temp gauge in my truck only goes down to 140 deg F and I knew that, no matter how long I left it plugged in, I never got to 140. Based on how long it took to get to 140, I could tell that leaving it plugged in 8 hours definitely warmed it up more than 4 hours or less.
So here's my experiment. I was about 3:30 PM and 38 deg F outside, and the truck had been sitting for over 24 hours. I have a little indoor/outdoor thermometer that has a sealed probe that designed to be used for the outside temp. I removed the plug at my coolant vent point and inserted the probe down the pipe about 18 inched or so. This should have placed the probe at right about the inlet to the water pump. This is on the same side of the engine as the 750 W coolant heater, which is about 10-12 inches above the water pump.
I also had my dual 150 W oil pan heaters on and an old blanket thrown over the engine compartment because this is my normal routine. Every 1/2 hour or so, I'd go out and write down the temperature. I did this from 3:30 pm until I went to bed just after 10 pm. I got up just before 6 am and took 4 more readings until I left for work at 7:30 am.
Here's the data:
Clock Time CoolantT AmbientT
- Hours deg F deg F
3:35 PM 0.000 38.8 38.8
3:53 PM 0.300 40.1 38.7
4:08 PM 0.550 42 38.7
4:25 PM 0.833 44.2 37.4
4:41 PM 1.100 46 36.3
5:11 PM 1.600 49.4 34.7
5:40 PM 2.083 53.4 34.3
6:13 PM 2.633 57.3 33.1
6:35 PM 3.000 60.2 32.2
7:03 PM 3.467 63.3 32.2
7:33 PM 3.967 65.4 31.6
8:04 PM 4.483 68 30.6
8:35 PM 5.000 70.5 29.3
9:10 PM 5.583 72.6 28.8
9:34 PM 5.983 73.7 28.6
10:07 PM 6.533 75.3 28.2
11:00 PM 7.417 - 26.6
12:00 AM 8.417 - 24.8
1:00 AM 9.417 - 25.7
2:00 AM 10.417 - 23.7
3:00 AM 11.417 - 23.7
4:00 AM 12.417 - 23.2
5:00 AM 13.417 - 22.8
5:56 AM 14.350 79.8 21.4
6:29 AM 14.900 79.1 21.7
6:55 AM 15.333 78.9 22.3
7:16 AM 15.683 78.2 22.1
And the plot:
So it looks like it takes 8-9 hours to get to equilibrium, and about a 60 deg F increase from ambient it about all I can get. I'm thinking a more powerful heater would be a benefit--I should be able to get higher temps in less time. Here's one I've been looking at:
http://www.amazon.com/Kats-13150-Alu...ar=1&carId=001
When I get a chance, I'm gonna try to do this type of experiment with my oil pan heaters as well.