Enigne block heater gel

The thinest possible coat of heat conductive grease or thermal grease is what is best. That is, just thick enough to fill in the gaps between the heater element and the block. When it's thicker than that it actually insulates.

Go to an electronics store or a computer store and ask for thermal grease (used in CPUs between the CPU and the heatsink). It's usually white or gray, the gray paste being the latest version. It's also called metal oxide silicone grease. And there is also now a version with no silicone oil. The silicone oil based type is probably best in this application (repels water best).

The thermal grease will lower "thermal resistance" by about 400%. It does two things on the Prius block heater. It lowers the thermal resistance, thus lowering the block heater temperature when it's plugged in (which will lengthen its' life). It also repels water, reducing or eliminating water induced corrosion between the heater and the block.

 

It won't loose a significant amount of efficiency. The 1st law of thermodynamics states that energy is conserved - so, whatever energy that goes into the heating element will get passed into the engine block.

What that goo does is increases the thermal transfer so that the heating element doesn't have to get quite as hot in order for the heat to transfer. If there's less goo, the element will just have to get hotter in order to transfer the same amount of heat to the engine block.

That said, the resistance of most metals increases with temperature, so the heater might pull less power (~5% or so).

In summary:

1) _ALL_ of the energy that you put into the EBH will go towards heating the engine - none of it will go to waste. You'll get as close to 100% efficiency as you get on our planet.

2) Because the heating element is hotter, it will likely pull less current, but all of the energy that it does pull _WILL_ make it into the engine block (see 1 above).

I hope this is clear enough yet detailed enough to answer your question.

 

Uhh... I might point out that if you, for example, plugged the heater into the wrong slot with little or no contact with the engine, it CAN overheat and burn itself out (happened to someone on this forum).

While I can agree that 100% of the energy is used, that does NOT mean that 100% of the energy is making it to the engine (and staying there). Air resists heat transfer, which means all your doing is warming up the air, and indirectly the engine block. This not not efficient because the engine block will QUICKLY lose any heat if it is not supplied fast enough.

While the heat will eventually make it to the engine, it make take several times LONGER for it to do so... which mitigates the effect of an EBH because the engine will lose heat fast.

 

1) If you put it in a slot with no contact with the engine, I can see how it might burn out. Because there isn't enough thermal contact, the heating element gets hot enough to melt.

2) If I understand correctly, when you put the EBH in the (correct) hole, the heating element is effectively contained, and there isn't any air in contact with it except the air in the self-contained area around the heater. Because of the increased temperature of the heating element, all of the heat from the heater will make it to the block. Now, if the heating element is flapping in the breeze, and it is possible for air to blow on it and then blow away, you're right. But, I think that the heating element is put into the hole and then sealed around the edge relatively well. Think of it like a light bulb - a light bulb has a heating element and a vacuum around it. But, if you put 100 Watts of electricity, it manages to get 100 Watts of radiated energy (heat and light) out of it - even if the heating element has to become incandescent in order to do it. If there's not good thermal contact with thermal grease, the element will get hot enough for the air to be able to transfer the energy. If there's no air, the element will get hot enough to radiate the energy (just like a light bulb does).

3) All of the heat put into the heater (subject to #2 above) will make it into the engine block - it won't take significantly longer (just the time that it takes to get the (relatively small) heating element heated up to a higher temperature).

If the EBH is put into a relatively sealed hole, then ~100% of the energy that goes into it will go into heating the engine block. Conservation of energy - all of the energy that goes into the heating element has to go somewhere. 1st law of thermodynamics - it's wonderful stuff!

 

Lets put it this way. If I put on a computer CPU heatsink without thermal paste, is it going to effectively transfer the heat? The CPU is only going to get hotter and hotter until it self-destructs. And the heatsink? semi-cold instead of hot, because it transfers what bit of heat it gets from the CPU at a much higher rate.

Same story with the EBH. Even if its in the hole, the EBH may just get hotter and hotter until it self-destructs because it can't transfer the heat effectively to the engine(heatsink). And the engine, semi-cold.

My point is, air is NOT a good way to transfer heat! Air insulates. Thats why winter jackets are so "puffy", because it takes a long time for heat to escape. (a vacuum is even better).

Air slows down the rate of heat transfer.

Otherwise Toyota wouldn't bundle the grease with the EBH.