98 suburban block heater

can someone tell me if the block heater is heating the coolant or the oil in the engine ?
i always thought it heats the oil but someone just told me otherwise.
TIA
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It's in the cooling jacket so heats the antifreeze primarily. Larry

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There are two types, there is the old electric dip stick that heats the oil. But they are not very effective. The best units are the type that either are located in the lower radiator hose or in the block in place of a freeze plug.
Brian
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He's asking about the factory installed unit. Larry

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