AE86 Trivia: Viscous fan

June 23, 2009 in AE86 Trivia by banpei

As being an admin of AEU86 I’ve seen a lot of questions, facts and fun stuff about the Toyota AE86 (hachi roku). I also see a lot of questions returning even though we documented it on the FAQ already.

AE86 Trivia
This time we feature the viscous fan of the stock 4AGE!

So what use has a fan for the engine in general? Well, the engine heats up and is cooled through the water system. The water is cooled through the radiator and the radiator only works well when there is enough airflow (moving the heat from the radiator).

Most of the time when a car is driving it will have enough airflow to cool down the radiator, however during city runs and traffic jams the radiator won’t cool down enough. To overcome this problem a fan is mounted to ensure a airflow through the radiator. This can either be a fan driven by the engine (belt or clutch type) or an electrical fan.

The stock 4AGE has got a viscous fan installed on the waterpump. It is driven through the multibelt (crank, alternator and waterpump) and is driven through an internal clutch system. The clutch system consists of a small reservoir containing oil which reacts on heat. If the engine heats up the oil will get thicker and the fan will rotate faster.

4AGE 20v blacktop with viscous fan mounted
4AGE 20v blacktop with viscous fan mounted

The viscous fan of the AE86’s stock engine is driving the fan constantly, so even though you have enough airflow from driving it will also generate extra airflow from its fan. This is not an effective way of using a fan, but back in the early 80s a viscous fan was cheaper than an electrical fan with a thermostat controlling it. The thermostat is able to turn on the fan when it is needed, so 95% of the time it will remain silent! :)

Another reason for switching over to an electrical fan is an engine upgrade: all transverse mounted 4AGE engines (7 rib big and smallport, 4GZE, 20v Silvertop and 20v Blacktop) have a different waterpump. The waterpump of the transverse mounted engine has weaker bearings which will fail after a while when you mount the fan on it. So either you keep the waterpump and have the chance it will fail, you switch over to the old longitudinal mounted 4AGE waterpump or best option is to switch over to an electrical fan!

So upgrading your 25 year old system with an electrical fan is a good upgrade: it will save you fuel (not continuously driven), increase engine power (not driving the fan anymore) and will lighten up the engine (revving becomes a little bit faster).

4AGE RWD/FWD and 4AC waterpump differences
4AGE RWD/FWD and 4AC waterpump differences

Nowadays you can find electrical fans (and thermostats) plenty in the junkyards! For the thermostat the easiest solution is to buy an AE92 16v 4AGE bigport thermostat: it is external and easier to mount between the waterpump and the radiator. Also the 1988 Camry V6 radiator is a good upgrade of your stock radiator and already includes a big electrical fan!

4AGE AE92 thermostat adaption for AE86
4AGE AE92 thermostat adaption for AE86

However there are also some doubts upon the numbers of increase of performance: some people even claim 8 HP increase after switching over to an electrical fan. This is very unlikely: 8 HP of airflow is moving more than 10000m3 per hour! Also the viscous fan is driven by a clutch, so it probably won’t rotate too fast at the higher revs as expected unless the engine is overheating! If you get 8 HP increase after removing the viscous fan most probably the clutch system is stuck and the fan rotates at the same speed as your waterpump (or slows down your waterpump)! More likely it will be somewhere around 1 or 2 HP increase. But that’s still an increase of a few percent!

This one already got its viscous fan substituted by a electrical fan:

Images taken from:
[Club4AG]
[ Golberg’s 4age 16v Cooling Guide on RollaClub]

Other resources:
[Camry V6 radiator upgrade]
[Guide how to hook up an electrical fan to the 4AGE]

Thanks to Edgar for correcting me with the word viscous! :)