BMW E34 temperature gauge, thermostat and viscous fan clutch
Where should the E34 temperature gauge needle be?
With a warm engine the needle is roughly in the middle, usually vertical or slightly past it. On highway driving it may be slightly below the centre line. On old gauges the reading can differ, so the needle position alone does not tell you about a fault.
How do I test the viscous fan clutch?
With the engine off and cold, the fan should turn easily. When hot, a good viscous clutch resists turning. If you can stop the hot fan by hand or it spins completely freely, the viscous clutch is worn. Do not touch the blades while the engine is running.
Why does the temperature rise at idle or in city driving?
The cause is often the viscous fan clutch: silicone oil has leaked out and the fan does not engage. Other causes are a stuck or incorrectly installed (wrong way round) thermostat, air in the cooling system, low coolant, a clogged bleed hose and a radiator blocked by insects.
Why does the temperature gauge not rise to normal temperature?
The cause may be a thermostat that stays open, or a fault in the temperature sensor. The sensor's resistance can drift with age, in which case no fault code appears. Measure the resistance cold and hot and compare it with the workshop manual values.