Plastics have heat cycles and stress cycles. You have to keep records of these items and have them replaced if needed before they fail on you.
In the older days a squeal or whistle would indicate you need to check/change your V-Belt, with the new belts being internally fibre reinforced they last longer but break without warning. Replace all belts every 45000KM or sooner if wear indicates.
BMW Plastics; Alternator slipper clutch pulley, Idler pulley, waterpump pulley and power steering pump pulley:
Plastic pulleys are used by BMW on many of the new generation BMW models. All BMW plastic drive pulleys are susceptible to minute stress cracks. Small chips and cracks around the edges are common especially after a belt failure.
Recommend these be checked or done with the Alternator belt; every 45000KM
Complete Tensioner Pulley
Not as easy to inspect this metal tensioner.
Few simple signs;
- with engine idling Listen for a dry bearing at the tension and idler pulleys
- With engine off. Check that all plastic tension pulleys are smooth and flat across the belt contact surface, make sure the tensioner is not sitting off position
- Sometimes the tensioner bolt was fails, some caught it early because I have no sounds upon start up.
Recommend this metal tensioner be change every 90000KM cycle.
See pic – attachment plates to pulley breaks – usual wear & tear
This you hear – and usually with the newer cars E90 E87 etc if this breaks then the belt breaks and you stuck, towed in
No tell tale signs – usually they just become noisy.
Clients come in (towed in) around 100000km to 150000km
The Radiator Expansion tank / coolant bottle
These bottles are made out of plastic and therefore have a heat cycle.
Cracks occur as a result of excessive thermal expansion & contraction.
You need to know when you have replaced it and keep a record of it. This part has no exact expiration date and there is no warning when the bottle cracks. Take note of what gets changed, images below might help.
Note: all the pipes and connectors become hard and brittle with age and heat. Those can be physically assessed
WE RECOMMEND YOU CHANGE YOUR WATER BOTTLE / RADIATOR EXPANSION TANK EVERY 80000km – 100000km (preventative maintenance).