Which of the following are types of coolant heaters?

The types of coolant heaters are categorized primarily into two main types: circulating and immersion.

Circulating heaters function by circulating coolant through a system to maintain or raise its temperature. They are designed to ensure that the fluid moves through and is heated effectively, which is particularly important in applications where consistent temperature is required throughout the entire coolant system.

Immersion heaters, on the other hand, operate by being directly immersed in the coolant. These heaters transfer heat directly to the liquid they are submerged in, making them efficient for quickly raising the temperature of the coolant.

Both types serve the purpose of improving engine performance, enhancing fuel efficiency, and reducing emissions by ensuring that the engine reaches optimal operating temperatures more quickly and efficiently.

The other options presented do not align with the classification of coolant heaters. Electric and gas represent power sources rather than types of heaters, while conventional and instant describe methods of water heating rather than specific types of coolant heaters. High and low pressure refer to operational characteristics or conditions of a system rather than types of heaters themselves.