Stag overheating problem - help!

[Mike Wattam <MikeWattam@domain.elided>]

Hi Larry

The gurgling noise sounds very ominous, but lets not jump to conclusions.

First, you say your temperature guage runs at half way across.  These are
not too accurate, but it sounds just a bit too high.  Does it rise further
when you turn the engine off?  

Do you have the correct thermostat fitted - with the disk under the sensor
bulb, and what is the opening temperature?  It should be happy to run with
a 88 degree thermostat fitted.

Is the expansion tank cap properly sealed, it could be that if it is not,
you have an 'open' cooling system which operates at just under boiling
point (at atmoshperic pressure) and the slightly increased temperature
which happens when you turn off the engine causing some after-boil will
turn hot water into steam and push water out of the expansion tank.  This
may be the gurgling noise.

Are you absolutely certain you have fully bled your cooling system.  You
will need to fill it (+expansion tank half full) with the engine ticking
over, then let it get cold, go through the procedure again ........... some
people raise the front of the car on a trolley jack to help get air out of
the back of the engine.  The heater valve should be fully open (hot) all
the while this is being done.

If the expansion tank is continually full of water, it cannot do its job
properly and should be half empty.

Check the water in your expansion tank.  Does it smell of exhaust gases, is
there an oily film on it?  With the engine ticking over hot, is there any
sign of bubbles coming through into the expansion tank?

Remove the radiator filler plug and rev the engine to see if there is any
depression of the water levle as the engine speed rises, this will give you
some indication that the water pump is turning.

Check the radiator top and bottom hoses for temperature differential.  Is
there a noticeable difference in temperature (should be about 20 degrees).

Is the exhaust reasonably 'clean' and stem/smoke-free?

Any evidence of antifreeze coming up the cylinder head studs/bolts?

Has the engine been re-bored, new pistons or rings?  If so, is the engine a
bit tight to turn?

The worst is that you might have a leaking head gasket or cracked
head/block - the latter two very difficult to find.

Hope the above is of help, and not too depressing.

Mike Wattam
Chairman - Triumph Stag Register