Boiling 525i

["Chris Northover" <chris.northover@xxxxxxxxxxxxxxx>]

Greetings.  I have a 1983 E28 525i with the M30 engine.  It has started
boiling after driving about four miles.  Very perplexing.  When it is
boiling, the radiator goes cold, as does the hose from the bottom of the
radiator to the head.  The top hose stays hot.  It boils out the overflow.
The water temp gauge reads a bit past the halfway point.  First I thought it
was the thermostat and removed it.  Still it boiled.
I reverse flushed the radiator, but nothing alien seemed to come out.  I ran
some cooling system cleaner through the engine, and flushed again.  Bled it
three times just to make sure.  Drove four miles tonight and it boiled
again.  This time I cracked open the bleed screw a little to see what
happened, and all that came out was steam.
I can't see where it is losing enough water to make this happen;  there are
no leaks.  The viscous drive on the fan clutch is not brilliant, but I don't
think it is that because it sits comfortably below "straight up and down" on
the temp gauge when it is coming up the hill before my home (no thermostat
at the moment).  It is only later that it boils.
I think the water pump is OK as well, because the radiator is warm all over
when running normally.  Also when running normally, it runs well, with no
misses etc.
Any ideas guys?

Chris Northover chris.northover@domain.elided
E28 525i
E28 525e
E34 525i


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