<E30> Cooling system problem

[Mark Holbrook <holbrook@xxxxxxxxxxxx>]

My '89 325i w/ 95K miles overheats.  The temp gauge creeps up to 3/4
under normal driving (A/C off) in this warm weather, and will go higher
except that I turn the heater on full blast (directed out the windows,
of course!), which brings it back down to about 1/2, or slightly higher
than it sits when everything's "cool" <yuk yuk>

Got that?

I replaced the thermostat.  The old one was broken shut.  But there was
no real change in the overheating problem.

I replaced the fan clutch after "testing" it with a rolled up newspaper
when the engine was hot.  I could stop the fan and therefore declared
the fan clutch dead (95K miles, after all).  After installing a new one,
I got the same behavior.  Beginning to suspect the radiator at this
point.

(Incidently, at the same time I replaced the fan clutch, I had to
replace the broken auxiliary fan ($330, ouch), but this shouldn't really
be part of the problem or solution, except for when it gets really hot
and the sensor kicks it in.)

Sensors, switches, fuses, and relays check out.  Coolant is new and the
system is righteously bled each time I fiddle with it.

So what's left?  The radiator and the water pump, no?  I suspect the
radiator because of the fan clutch behavior, the fact that the aux fan
doesn't come on even when the engine is hot (non-circulating coolant not
hot enough to trigger sensor), the fact that the engine *does* cool down
when you crank open the heater (indicating that the water pump is likely
working, pushing coolant through at least the heater core), and the fact
that there's no noise or leakage coming from the water pump (although it
also is original).

So, I'm about the pull the radiator and take it to a shop to be
flow-tested.  However, I'm not absolutely sure that's the problem.  The
radiator and hoses all feel plenty hot when the car's running and
practically no crud has come out of the radiator, nor has the coolant
ever look cloudy or cruddy.  But I don't wanna do the water pump yet if
I can help it (I'd rather do it when I get to the next timing belt
change (due at 120K)).

Do you think I'm on the right track?

Is there anything I'm overlooking (like a funky heater control that
could possibly affect the radiator circulation?)

Thanks for sitting through this windage.  Any advice will be
appreciated.

- -- 
Mark (Holbrook@domain.elided)                    "Back roads. Period."
http://www.net1plus.com/users/holbrook/mark.htm

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