Well it’s that time of year when everyone’s talking about the weather and turning up the heat. You might even need to replace your fan belts but what is the Viscous Heater and where is it fitted?

You will need to know this when ordering fan belts on certain Land Cruiser models, we often describe the belt options as “with or without” viscous heater fitted. This is because the length of the belt will vary if fitted.

What is a Viscous Heater?

A viscous heater (also known as Power Heater) on a Land Cruiser and is a pump bolted to the engine and is manufactured by Denso. It churns up a silicone gel inside the pump as it rotates when the engine is running, this in turn generates heat quickly through friction.

The heater then warms the engine coolant which passes through the viscous heater which in turn passes into the vehicles heating system and so warming up you quickly on a cold frosty day.

How is the Viscous Heater driven?

The viscous power heater is usually driven by a flat ribbed fan belt for greater resistance to slipping.

At the front of the pump it has a clutch mechanism, similar to what you find on an air conditioning compressor, this engages and disengages automatically as the sensors sense the temperature.

Once up to temperature the clutch disengages the pump, which in turn stops generating the heat and the vehicles normal engine cooling system flows through.

When the coolant temperature drops below the value set then the clutch re-engages the pump friction is generated and hey presto - more heat.

Where is the Viscous Heater fitted?

It depends on the vehicle model, but on the Land Cruiser it is usually found on the front of the engine, at the top near the rocker cover.

It is a very distinctive component that has a belt drive to the pulley and coolant pipes in and out.

Here is a good image of a Viscous Heater fitted to a Land Cruiser 100 Series, it can also be found on the 90, 100, 120, 150 & 200 Series Land Cruisers too.

Why do we need the Viscous Heater?

In very cold climates some diesel engines run cooler than others and cannot produce enough heat to keep the interior heaters warm.

By utilising a very effective and extremely reliable separate heat source Toyota overcome this problem. The system is also smart enough to increase your engine revs at idle when the pump is engaged.

Hopefully you will now be able to tell if you have a viscous heater fitted to your Land Cruiser.