[Vwdiesel] Coolant flow through stock oil cooler/heat exchanger

[Sandy Cameron]

At 06:13 PM 16/11/04 EST, you wrote:

>
>I get what you're saying about the double valve in the w/pump.  I will 
>reexamine.  Understand that I am talking about the diesel vanagon and not
rabbit or 
>jetta.  The coolant routing is different.  I will be doing more digging.
>Andrew

Yes, that may make a difference.

I expect, unless the water pump is completely different, the on-engine
piping will be mostly like the jetta system

The outlet from the front of the head between injector 3 and 4, will have 2
hose fittings, one headed directly for the radiator, and another that snakes
diagonaly down the face of the block to the water pump. That is the
"bypass", where most of the flow goes back into the pump until the temp
rises and  the stat "opens" and in so doing, clamps off the bypass with the
obscure disk. At the same time, the return from the rad, entering the bottom
of the pump, opens up, permitting flow around through the rad.

I suppose you could think of the pump trying to push water to the rad when
the stat is closed, but it takes the easier path through the bypass hose
until the stat opens, then the pump can also "suck" from the bottom of the
rad now.

Summary, water exiting the main outlet on the head goes down the bypass hose
until the stat moves to "open" then the bypass is shut off, and the rad
circuit is opened, and the flow now goes to the rad.

The heater circuit is it's own private circuit, not affected by the stat.
Water leaves the head by the end fitting and goes directly to the heater.
>From the heater, it returns to the pump by the steel tube, and the oil
cooler if fitted, into a separate inlet on the pump, always open, not
controlled by the stat, Flow in this circuit is steady as long as the engine
is running, and the water pump is turning (no broken belt).
The fluid from the heater return line wafts over the control element of the
thermostat all the time, and "modulates" the thermostat position, to keep
the return fluid from the heater circuit at a constant temperature. This is
known as a closed-loop servo

The thermostat housing in the water pump is a bit like a half a heart with a
chamber (the pump suction) with 2 inlet valves(one from bypass hose, other
from bottom of rad),{one is always open when the other is closed} and the
heater return in between. This is where the fluid mixes as it enters, and
this is where the sensing element of the T-stat is located, and it realy
does work well. The Tstat will settle at a partly open position, modulating
it as load and speed require, to keep the temperature constant as some
coolant goes to the rad for cooling, and some goes down the bypass to keep
it from getting too cool.

My old jetta warms up quickly, the heater could roast you out of the car,
and the temp gauge never moves off the white dot as long as I'm driving.

Sandy