5kTQ overheating - need help

[Steve Sears]

Mike,
Thanks for the reply.
Actually, I do know where the coolant is going - out the cap (judging from
the coolant saturation of the hood liner and the bottom of the car on the
driver's side).  Pulled the plugs a couple of days before the trip - all a
nice tan colour.  Each time it overheated - it blew coolant out of the cap
as it boiled.  The A/C system is discharged and the condenser has been
removed so it is not to blame for overheating.  The water pump, however, was
changed about 3 months ago (the old pump was boring its way through the
t-belt cover) - I've logged a fair amount of highway driving with it
installed and no overheat.
It seems that there are two contributors to the overheating - the rpm of the
engine, and the load on the engine.  Here's a thermodynamics question: Would
the engine in a '87 5kTQ generate more heat in 5th at 120 km/h (~ 2k rpm)
than in 3rd at 95 km/h (~ 4k rpm), with a 30 km/h headwind?  Seems to me
that it would not, and the added cooling is from making the pump spin
faster, raising the coolant pressure into the radiator. (ok, I've
overstepped my schooling, as I know more about the response of clay soils to
added loads than I do about engines)  Would this not suggest that the
radiator is clogged?
Cheers!
Steve Sears
1987 5kTQ - hurtin' (heatin'?)
1980 5k - helpin' (got me to work)
1962 and '64 Auto Union DKW Junior deLuxes - oblivious
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