<E34> Overheating problem

["Curtis A. Ingraham" <ingraham@xxxxxxxxxxxxxxxx>]

In BMW Digest v09.n1918 Ashley R M Cox <acactus@domain.elided> wrote:

> Well then, out for a weekend drive in my 1989 520i E34 and have noticed 
> that the temperature gauge that normally sits on exactly 1/2 way shot 
> up to > when I began to climb a hill in low gears. I thought the engine 
> seemed to perform less at this point- could be mixture though (we've 
> been getting some really bad fuel), but later was back to normal. I 
> pulled over & stopped. I did what you should never do & eased the cap. 
> Not greatly hot, but a little coolant raced up & overflowed. Screwed 
> the cap on and with nothing else amiss, carried on. Seems this only 
> happens on hills under load through the gears. On the flat its dead 
> steady at =. Really scared of cooking it and would appreciate any 
> feedback. Had the thermostat & cam belt replaced 3000km ago. Could it 
> be: radiator, water pump, head gasket (gulp)? What order should I get 
> these things looked at? Is a TK test any good for diagnosing a blown 
> head gasket? Can a genuine BM garage diagnose easily & how? Any simple
> tests I can do? Have Haynes manual.

If the temp gauge normally sits at a certain spot near mid-scale, your
thermostat is working correctly.  If your head gasket is blown, you will 
lose coolant, either slowly or suddenly; check the coolant level daily 
when the engine is cold.

The fact that the temp rises when climbing a hill suggests that your 
cooling system can handle moderate driving but can't dump the greater
heat load of climbing hills.  The likely culprits are the fan clutch
and the radiator; both are easy to diagnose.  To check the fan clutch,
bring the car up to normal operating temperature, then try to stop
the fan with a rolled-up newspaper or magazine.  If it stops easily,
the clutch is bad.  

To check the radiator, shut off the engine, then feel different areas 
of the radiator fins and the inlet and outlet hoses.  If you find cool 
spots, the radiator is clogged up, something which is not too surprising 
for a 12-year old radiator.  If the radiator is the problem, a new one
is the best answer.  It's also possible that the front side of the
radiator is blocked with leaves, bugs, etc.

Water pumps seldom fail in a way that reduces coolant flow.  Either the 
bearings wear out, making the shaft wobbly, or the shaft seal starts to 
leak.  Some techs routinely replace the water pump as part of the cam
belt replacement.

To make a radiator last a long time, flush the cooling system every
two years and put in a fresh 50/50 mix of BMW coolant and water.

Curt Ingraham
72 2002tii
Oakland, CA
Improved 2002 Radiators

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