Mini experiments: 300w vs. 800w block heater warm up time

[MetroMPG]

Originally Posted by roflwaffle

the same amount of heat over a longer time will result in a better distribution of heat through the engine. The thermal conductivity of Fe also drops as the temperature increases, which could exacerbate this.

I think the inline or frost plug installation is best for that reason - heating the water jacket is the best way to spread the energy throughout the block as evenly as possible. My external bolt-on heater is probably the worst, in terms of uneven heating & the stresses that result (not to mention far less efficient).

If heating up quickly is a bad thing in terms of wear, then this 800w unit pales in comparison to simply starting up a cold engine.

I imagine both are better than nothing in the cold.

(I think you're saying the same thing there.)

Another point I often bring up: I don't use the block heater only for reasons of fuel / wear reduction. I really like being warm sooner.

[TomO]

Originally Posted by MetroMPG

Now that I've charted it, I can see that anything more than an hour and 15 minutes (#6) is probably not worthwhile in terms of return on time & energy invested.

This makes me rethink the amount of time I need the heater on for my VX.

Originally Posted by MetroMPG

Note that this probably isn't directly applicable to other cars. The 993 cc motor in the Firefly is a smaller heat sink. I'd guess that bigger motors may "level out" at a higher temperature (though they'll take longer to get there @ the same 800w).

Could you find the total amount of fluid in your cooling system? That would help to make a reference point for others to use in making a rough guesstimate of how long to run a heater in their car. You could also get the dimensions of the radiator and block in order to further the reference point.

Then Ben (SVOboy) could send me his SuperMID so I could do the same experiment in my VX and post results for the other VX owners. But now I might be going too far, lol.

[Frank Lee]

Good info!

I've always shot for about an hour of plug-in time, based on not much more than an educated guess.

roflwofl: Don't overthink it! What difference does a/t vs m/t make? They both have ECUs to control idle... I use it only for wear reduction- if the cold bothered me, I wouldn't live here!

[roflwaffle]

In an a/t the ECU/s prevent excessive load when cold by revving higher, which limits the peak force on the rings as well as heating them up faster via friction losses than if it shifted like normal with higher peak cylinder pressure and lower load. Seems to be significant compared to the m/t driver who short shifts IMO. Clearly not the be all end all, but something...

[MetroMPG]

More data!

I repeated the test with the 300w external block heater. This is a bolt-on element style unit like this:

Results:

Note: I didn't display the "temp before starting the engine" in this graph because the readings were all within a couple of degrees of the "after 30 seconds of idling" values. That's probably because the location of the heater element is much closer to the coolant temp sensor.

In fact, more often than not, the temp dropped a few degrees after start-up (which tells me the warm spot in the water jacket created by the heater was close to the temp sensor).

It's not shown on the graph, but out of curiousity, I left the block heater plugged in for another hour after it reached 101 degrees F. When I checked it after the hour (no idling during that time), the indicated temperature had actually dropped a five degrees. That suggests the heat generated by idling the engine for 30 seconds every 15 minutes to get stable temp readings was skewing things by about 5 degrees at the end of the test.

Reposting the 800w chart for easy comparison (less scrolling!)

[MetroMPG]

Originally Posted by TomO

This makes me rethink the amount of time I need the heater on for my VX.

What's the wattage again? (Sorry, being lazy - I know you mentioned it in your installation thread.)

Could you find the total amount of fluid in your cooling system? That would help to make a reference point for others to use in making a rough guesstimate of how long to run a heater in their car. You could also get the dimensions of the radiator and block in order to further the reference point.

3.9 litres / 4.1 quarts.

I wonder if a better measure for comparison's sake might be the weight of the engine. The Suzuki 1.0L mill weighs about 135 lbs.

[TomO]

Originally Posted by MetroMPG

What's the wattage again? (Sorry, being lazy - I know you mentioned it in your installation thread.)

400Watts

Originally Posted by MetroMPG

I wonder if a better measure for comparison's sake might be the weight of the engine. The Suzuki 1.0L mill weighs about 135 lbs.

This makes me think even more....does the firefly have an iron block and aluminum head? That 135 lbs. for a 1L 3 cylinder motor is really heavy! IIRC the 1.5L block in my VX weighs in at ~140 lbs. The block and head are aluminum with an iron sleeve pressed into the aluminum for the combustion chambers. Open block design as well.

It might not be a very measurable difference for the thermal conductance between iron and aluminum blocks especially when you have coolant in the mix as well.

Oh, Oh, just found some info:

Thermal conductivity of pure aluminum:

• Temp 68°F = 118 (Btu/(hr oF ft2/ft))
• Temp 200°F = 124 (Btu/(hr oF ft2/ft))
• Temp 400°F = 144 (Btu/(hr oF ft2/ft))

Thermal conductivity of Cast Iron, gray:

• Temp 70°F = 27-46 (Btu/(hr oF ft2/ft))

Thermal conductivity of Iron, nodular pearlitic:

• Temp 212°F = 18 (Btu/(hr oF ft2/ft))

Seems strange that they aren't really comparing the metals at the same temperature. I got the info from HERE.

[Frank Lee]

"The block and head are aluminum with an iron sleeve pressed into the aluminum for the combustion chambers. Open block design as well."

That's some crazy schnizz.

[MetroMPG]

Tom: I'm not sure if it's an Al or Fe block, but I suspect it's Fe.

More data!

This time I plugged in both heaters at once (1050w @ 120v, according to the kill-a-watt). And... blew the breaker! (I was also running a hair dryer at the time inside the ForkenSwift to defrost the windshield ).

So I unplugged the hair dryer, and this is what I got:

(EDIT : note the ambient temp was highest for this test)

I find the plateau @ 172F interesting. I guess the engine/cooling system had reached equilibrium with energy in & heat loss. My other thought was perhaps the local temp @ the thermostat caused it to open and permit cold coolant in.

[Frank Lee]

I like your tests.

Is it safe to say that, as a general rule, heaters should be plugged in from 45 min to 1 1/2 hours, regardless of ambient temp, no more and no less?