Cooling system layout.
Existing radiator with current alternator location.
https://ej0ffw.ch.files.1drv.com/y4m...&cropmode=none

Dual radiator setup from an Audi turbo 100 or something similar
https://ej0cfw.ch.files.1drv.com/y4m...&cropmode=none

http://https://ej0dfw.ch.files.1drv....&cropmode=none

A mystery outlet at the bottom of the new radiator, not sure what I'm going to do with it yet.
http://https://ej0ifw.ch.files.1drv....&cropmode=none

New radiators from another view
https://ej0dfw.ch.files.1drv.com/y4m...&cropmode=none

Mystery outlet at the bottom of the new radiator.
https://ej0ifw.ch.files.1drv.com/y4m...&cropmode=none

Existing alternator alignment to the front pulley. For some reason this picture is not showing.
https://ej0ofw.ch.files.1drv.com/y4m...&cropmode=none
http://https://ej0ofw.ch.files.1drv....&cropmode=none

Front pulley of 2.4TD with existing bracket which should fit the alternator relocation.
https://ej0pfw.ch.files.1drv.com/y4m...&cropmode=none

Turbo's side by side, D24T on the right with the four bolts for the exhaust downpipe flange, no way these will be interchangeable which I was hoping for.
https://d50hfw.ch.files.1drv.com/y4m...&cropmode=none

T-handle wrench for headbolts and this one injector. '85TD Jetta in the background.
https://d50gfw.ch.files.1drv.com/y4m...&cropmode=none

End of day one, head's coming off tomorrow, oil pan and oil pump as well.
https://d50jfw.ch.files.1drv.com/y4m...&cropmode=none

https://d50ifw.ch.files.1drv.com/y4m...&cropmode=none

Water flow pictures with questions to follow
Outlet from the block which goes to the heater core, also showing the threaded fitting for the temp sensor which appears to be in/inside a larger threaded fitting in the head.
https://d50ffw.ch.files.1drv.com/y4m...&cropmode=none

Return line from the heater on the left, I just had it looped when I test ran the engine.
https://d50cfw.ch.files.1drv.com/y4m...&cropmode=none

Here's a picture of the thermostat as it sits in position viewed through the water pump hole.
https://d50efw.ch.files.1drv.com/y4m...&cropmode=none

And here's looking in the thermostat mount hole.
https://d50pfw.ch.files.1drv.com/y4m...&cropmode=none

So here's my question, and this has been discussed here before.

With the thermostat cold, as shown in the first picture, the back of the t-stat is not closing the hole in the block which allows cold coolant to be sucked out of the head (as shown in the second picture), apparently close to where it's being pumped into the block. If the heater is off, the cable operated valve being closed, there's no coolant coming out of the back of the head/block, thus the coolant would seem to pool up and heat up at the back of the head and block while the circulating coolant around cylinders 1, 2 and 3 heats up more slowly.

In the second picture you can see the hole coming down from the head, which is where it's pulling the water from, so there's circulation near the first three cylinders and the corresponding part of the head.

When the coolant is hot the problem appears to be even worse since the back of the thermostat closes that hole and the only flow has to come from the back of the block, which wouldn't happen if the heater is off. I may be too tired and have missed something; is there another passage coming out of the block??

So my question is: how does the coolant circulate to and through the back of the head/block when the heater is off?

I'm considering plumbing in something so there's ALWAYS circulation to/through the back of the block/head even when the heater's off.

Has anyone done something similar?

Good to know you have a lot of that era's engines. I remember ordering some Bosch nozzles from somewhere and giving you a tip on where I got them. I also bought that spare D24T turbo, which is in the picture, from you. I thought it would work on this engine but not to be.

I really like the simplicity of the 1.6, 2.0 and 2.4. No computer. There's value in that for me!