[Vwdiesel] overpumping

[Val Christian]

In exploring the potential causes of a block leak on a 1.6NA, a
local mechanic asked if I had seen eroded cylinder heads.  In his
business, he has seen more than one Al head sufficiently eroded
such that the water passages broke through.

None of those heads were VW heads.

I thought that I should pass this along.  With the signular exception of
the case where I had a thermostat failure (the rivet holding the valve plate
failed, causing the plate to obscure the impeller input on the waterpump),
I have never experienced water pump throughput insufficiency.  Therefore,
I would be disinclined to overspeed a waterpump.  (NB, cavitation is not
as likely on a pressurized cooling system, with the kind of flow rates
experienced even with a pully change.)  My experience base does not
include tropical operations at high ambient temperatures.  My experience
is also with NA VW diesels, which tend to run higher RPMs.

With regard to thermostat temperatures...I tend to like higher temp
thermostats.  It tends to help keep the crankcase dry.  I've never
really experienced a cooling system so marginal that it couldn't handle
the reduced reserve caused by a high temp thermostat...well at least
a system that didn't already have a problem.

My own daily commute distances are high, but in the winter, it's not
uncommon to have water collect in the crankcase.  Higher temps help
with that, and they help operational efficiency of the engine.
I avoid 80C thermostats, and go for the higher temp ones.  But based
upon my experience this fall, I would go for a quality thermostat
with a beefy valve plate rivet and backing plate.  Having that valve
deattach and get sucked into the waterpump is no fun!