Hi Edward,
  Nice to see your good words.

   Might you have an idea of your heater circuit glow plugs are working
on your 2002  TDI ?

I believe that's an ALH ....which I am not all that familiar with.
I am pretty familiar with the AHU ...and those have 3 conventional glow
plugs at the back of the head, to heat coolant in the heater circuit,
since a tdi engine tends to run coolish anyway.

there's a fuse in the control box for those glow plugs too, or at least
there is an on AHU , like what would be in a 98 Jetta/Golf.

On 9/8/2012 1:03 PM, Edward Maglott wrote:
> Good explanation Scott.  This diagram from Ben helped me to
> understand the 2 way nature of flow in the system.  I agree it's very
> clever.  One thing has always impressed me (and others) about the
> water cooled VWs is the impressive heater output.  Not so much on my
> 2002 TDI.  In the winter it takes a while to get warm.  Once it's
> warmed, If I coast down a grade on the interstate, the temp gauge
> will actually drop off of the "normal" position.  I think all VWs
> have that marked area at the cold end of the temp gauge.  Don't drive
> it hard or use much heat until it gets above that level.
>
> Edward
>
> At 01:42 PM 9/8/2012, you wrote:
>> Perhaps something not being considered is the two door nature of the
>> thermostat.
>> When the main opening for rad flow is closed, the other part, for flow
>> in the bypass hose is open.
>>
>> that way.....when coolant is flowing out of the side connection on the
>> cylinder head ....it's trying to flow through the oil cooler to the main
>> return hose going to the t-stat...
>> but it can't since that main portion of the t-stat is closed.
>>  Similarily,  it can't flow through the oil cooler either , as that
>> coolant will run into the closed main opening in the t-stat also.
>>
>> Meanwhile, before the t-stat is open ...coolant runs around and around
>> through the bypass hose ...
>> from inside the cylinder head, where coolant is under slight pressure
>> from the water pump....through the bypass hose, and back into the water
>> pump housing ..around and around.
>>
>> gradually the t-stat closes off the bypass circuit and opens the main
>> circuit ..
>> thus allowing coolant flow to the radiator and through the oil cooler.
>>   Given the relative size of the hoses ..
>> the inside cross sectional area of the main radiator hoses and pipes are
>> 3 or 4 times larger in area than the inside of the oil cooler hoses and
>> fittings ..thus 'most' hot coolant will be pushed to the radiator and
>> eventually routed back to the thermostat inlet.
>>
>> Quite clever.  Means no flow through the oil cooler cirucit when things
>> are cold,
>> and 'some' ...like 1/3 of 1/4 of what's coming out of the side outlet on
>> the cylinder head, through the oil cooler when hot.
>>
>> and yes....as the main circuit starts to open the warm coolant also
>> helps to warm the oil ..
>> so the oil cooler is a heat exchanger helping to warm the oil at first,
>> then later, to help cool it. Very clever and always a good addition to
>> any engine really.    Other than the cost of the part, it's a 'free'
>> improvement affecting engine longevity in a good way.
>>
>> if it's not clear to some people ...the heater circuit is 'full time
>> flow' .... the hottest coolant in engine would be that coming out of the
>> cylinder head. If the heater valve is open ...there is un-thermostated
>> full flow in the heater circuit.
>>  And ..in winter .......it's not good to start out with the heater
>> full on.
>> This cools the engine enough that it takes much longer to get to full
>> operating temp.   What works is to have heater mostly off, of fully off,
>> for say the first 4 miles or so ..then turn it on some.
>>   Diesels to not produce much heat without a load. If your winter
>> driving mode is a long down hill run ..
>> that's exactly what you don't want. Ideally ...you start out with some
>> load ....level or slightly uphill .....keep heater off for a while, or
>> at least half off ..then as things get warmish, open the heater valve.
>>
>>   It doesn't matter too much, and I'd say it helps to think of the
>> water pump as pushing coolest,
>> and not sucking.  Water pumps push coolant.
>>
>> some might find this interesting ..
>> why I had to think about this so hard in the first place once. On jetta
>> cars the oil cooler is fed from a T in the bypass hose on the engine.
>> So I'm doing an AAZ conversion to a Syncro Doka ..and that T'd bypass
>> hose is already on the engine ...
>> so just leave that there, and the return from the oil cooler..
>> hey, return is return right ?  So I use a stock DV main coolant hose
>> that goes to the T-stat., with the oil cooler return T'd into that as
>> per stock DV.
>>   The rig overheats in about 20 minutes of driving on the level., or
>> gets too hot.
>> That's when I had to really, really look at what flows where and when..
>>  On a DV the oil cooler return is to the main hose going to the t-stat.
>> on a jetta it T's into the heater return hose.
>> Either layout works just fine, but you can't mix 'em.
>>   By using the DV return to the main t-stat hose and oil cooler feed
>> from the bypass hose, coolant was bypassing the radiator and t-stat
>> through the oil cooler ..which is why it overheated in a while.
>>
>> what fun !
>> Scott
>> www.turbovans.com
>