Block heater performance data

[Diesel_Dave]

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.

[GRU]

so would you say 6 hours is about enough to be plugged in because past that time there doesn't seam to be much difference?

[Frank Lee]

http://ecomodder.com/forum/showthrea...-warm-817.html

Darin's leveled out at about 1 1/2 hours.

http://ecomodder.com/forum/showthrea...iency-609.html

[Olympiadis]

Thanks for your testing.
To me, 750 watts sound too low even for a four cylinder in a cold climate.
Does your coolant heater also circulate the coolant?
If so you might want to consider how much heat you lose through the night from the radiator fins.
If you're going to be checking under the hood in the mornings anyway, then you might consider putting a couple of large ball-valves on your main radiator hoses . If your heater circuit dumps to the heater-core return line and goes directly back to the radiator ( like some cars do ), then of course you'd have to splice the heater-core return to another area on the engine-side of the ball valves, - not the radiator side.
I just thought I'd throw that idea out there, and I hope it was understandable.

[Diesel_Dave]

Originally Posted by GRU

so would you say 6 hours is about enough to be plugged in because past that time there doesn't seam to be much difference?

Yeah, past about 6 hrs there's certainly diminishing returns. Sure, I could probably get another 5 degress or so, but it would take another 3-4 hrs to get it....probably not worth it.

[Diesel_Dave]

Originally Posted by Frank Lee

http://ecomodder.com/forum/showthrea...-warm-817.html

Darin's leveled out at about 1 1/2 hours.

http://ecomodder.com/forum/showthrea...iency-609.html

Yeah I saw Darin's data, but I knew mine took much longer to warm up. It's pretty much a matter of scale. He was using a 800W heater on a 1 liter engine. I'm using a 750W heater on a 6.7L engine that weighs over half a ton. Plus his was a circulating heater, which is better than my immersion heater, which I don't think leads to much circulation.

Granted the block heater is there for a starting aid and it looks like it's sufficient for that. If you can get a 60 deg F temperature rise from ambient, then -40 F goes to +20 F. In addition, my truck has the intake grid heater for the air. So if you're just worried about getting it started, the 750W heater looks like it'll do the job.

[Diesel_Dave]

Originally Posted by Olympiadis

Thanks for your testing.
To me, 750 watts sound too low even for a four cylinder in a cold climate.
Does your coolant heater also circulate the coolant?
If so you might want to consider how much heat you lose through the night from the radiator fins.
If you're going to be checking under the hood in the mornings anyway, then you might consider putting a couple of large ball-valves on your main radiator hoses . If your heater circuit dumps to the heater-core return line and goes directly back to the radiator ( like some cars do ), then of course you'd have to splice the heater-core return to another area on the engine-side of the ball valves, - not the radiator side.
I just thought I'd throw that idea out there, and I hope it was understandable.

It's an immersion heater in the block. It's not a circulating heater per se, although I'm sure some natural circulation takes place. I don't think there should be too much heat loss through the radiator, because the thermostat is closed so I don't think there would me hardly any circulation out to the radiator. Frankly, I'm not sure where the heater core returns the coolant.

[Frank Lee]

I found a university test on large diesel block heaters such as tractors and semis once; can't put my finger on it now IIRC their results were similar to Darin's in that the temp rise levelled off in only a couple hours- I want to say three hours but am not sure.

I shoot for 1 to 1.5 hours plug in time. I've never bothered to try to measure the temp rise.

[Diesel_Dave]

Some of the folks over at Cummins Forum are noting warm up time quite a bit quicker and to higher temps (using a scan tool to read the stock sensor). I'm thinking my warm up looks a lot slower than others because of where I measured it. The stock sensor is right by the heater so that should show a quicker rise and higher temperature than where I measured it down by the water pump inlet.

Snd now that I think about it, since I was measuring at the water pump inlet, there's not really a good way for the coolant I was measureing to mix with the coolant near the heater (it'd be blocked by the pump).

[ron]

it looks like 3 hrs is the optimum for the heaters you might try on of those clock timers to turn it on before you get up,im in cali and on the coast so no hard freeze here, might need more time the colder your area gets