AAZ overheating issue

[RadoTD]

Alright, I'm stumped... not sure what's going on here.

The car is a 1990 Corrado with a 1.9L AAZ. Passat rad with dual fans.

The problem is that it's overheating. Under normal driving conditions, the coolant temp sits between 70 and 80deg Celsius, if I'm stuck in traffic on a warmer day or run it hard up a long hill, it climbs up.. highest it's gotten to is 110deg. The engine bay is very open so I'm not too surprised that it normally runs that cool, it should hang out around 90deg for a while though. No matter how hot my coolant is, the lower rad hose hardly gets warm...

First thought was the thermostat, so I swapped that out, flushed the whole system and put in G11 coolant. No dice (tested both thermostats, both seemed to be working fine)
My water pump has metal impellers that all look like they're in good shape, spins freely, so I don't think that's the problem.
Then I wondered if my rad was plugged and I got one for cheap, so I put a new rad in... that didn't help either.
I found a link to this thread here. His problem sounds similar to mine, so I swapped to a lighter spring but that didn't work for me either.

One thing that had me confused is how exactly the thermostat is supposed to open. In reference to the picture below, when I put it in hot water, the inside plate in the top (fat side) travels down, compressing the spring and the plate at the bottom also travels down. Is this how it's supposed to work? It seems to me like it's just pushing that bottom plate towards the block, keeping coolant from flowing down out of the block. I've got a picture of my thermostat fully open on my camera if anyone wants to see it.

Something else that Smokin Eddy mentioned is that I should have coolant moving through the small hose going to the top of my overflow bottle. When I pull that off, it takes a minute for coolant to start flowing through it and when it does, it's not steady flow... it just spits a bit out every second or two. Does this mean my water pump isn't working properly?

[macka]

is the small outlet going to the overflow blocked? just a shot in the dark, but sometimes a flush does little if a chunk o gunk is lodged in a corner or elbow.

[theman53]

Whenever I have had pumps go bad it seems that they didn't have a steady stream into the tank. Not saying that is for sure your issue, but that is how it was for me.

[RadoTD]

is the small outlet going to the overflow blocked? just a shot in the dark, but sometimes a flush does little if a chunk o gunk is lodged in a corner or elbow.

I think your shot in the dark may have just done it!

Got my fingers crossed hoping I get stuck in traffic on the way home today I just started poking it with a bike spoke and I seem to get much better flow into the overflow. When I get home from work, I'll pull that flange off and clean it out properly

[RadoTD]

Alright, so I've got a proper steady stream into the overflow tank now, increasing when I rev the engine... still overheating though.

I'm still not sure if my thermostat is working properly. Are both plates supposed to move in the same direction (both towards the rear of the vehicle) or are they supposed to squeeze in towards each other? Mine both go in the same direction

[macka]

whats flow like through the rad? if you had a gummed up water jacket, you may also have restrictions in its rad. Try the cheap fix first. Disconnect the hoses, plug the bottom hole and put vinegar in overnight. Drain in the AM and see how much crap comes out. If the DPO used stop leak products you will know for sure. IIRC Vince still has a rad for sale if you need to replace it.

[RadoTD]

If I stick a hose in the top of the rad, the water comes out the bottom as fast as it comes in the top.

That vinegar idea sounds good though, couldn't hurt