I am not sure what the other reviewer's problem was with his unit.

Because of his review I purchased this with some hesitation. However, I've used it now for a couple of months and it works.

It is not the best quality in the world. However, it is more convenient than having to install a tank heater, and, it works just as well.

The other reviewer may have received one that was not properly manufactured. On the other hand, he may just not have read the directions.

First, you must plug this in and place it in the oil reservoir while the oil in the vehicle is still hot. That is a tradeoff for the economy of a unit that consumes only 90 watts.

This is perfect for my tractor here in the San Juan Mountains.

When a storm is coming in, I always start up the old tractor to make sure it is working, then, shut it down and hook up the charger to make sure the battery is fully charged. After hooking up the charger to the battery, I remove the dipstick and insert this unit into the oil tube. It maintains the oil at a safe operating temperature of about 100 degrees. The heat seeps from the oil reservoir (under standard principles of fluid and thermal dynamics) into the surrounding metal.

The result is a tractor that starts immediately during a raging storm.

The 90 watts is 1/10th the cost of heating up the tractor if I used a tank heater (usually around 1,000 watts), and, it works just as well, and, the heated tractor is ready to work immediately (as opposed to a demand tank heater that takes (usually) at least a couple of hours to warm an engine).

Admittedly, this technology is from a bygone era. However, "if it works . . . . don't fix it."

I received the 20" Dipstick Heater and it only worked once. The second time I used it the unit never heated up. So as you can imagine my review is not a postive one.