Overheating engine

["steve.weighell" <steve.weighell@xxxxxxxxxxxx>]

Help me out with a bit of detective work.

My 1987 520i is running well and the tuning is good, according to the last
emissions check.  But it tends to overheat when idling.  This seems to have
become worse in the last few months, and now we are getting into an English
summer (?), it is getting to be a problem.  If I get stuck in traffic for 5
or 10 minutes, the temperature quickly starts to head towards the red zone.
As soon as I get up to speed again, the temperature drops within a couple of
minutes back to a healthy  "normal".

So what are the feasible explanations, and in what order should I check
things out?  This is getting urgent, as I plan to be driving in France in 3
weeks!!

My possible suspects are:

1. Radiator blocked (water side) - needs flushing or replacement.
2. Water pump badly worn ??
3. Thermostat not opening as far as it should.
4. Viscous coupling needs replacement ?
5. Radiator blocked (air side) - needs good hosing?

I have already cleaned the radiator and it does not seem blocked on the air
side or water side.  The fan coupling seems to have about the same viscous
drag as that on another 520i that I looked at in a scrap yard - I suppose
they could both have been in poor shape....

What do you think??

Steve
Darlington, UK

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