RESOLVED - Thermostat fault issues 1.6 AEE

[SammoVWT]

This is more of an information thread really. I had some issues with coolant temperature after having my water pump replaced. Old pump had a couple of cracked fins. Never had an issue reaching and holding temperature previously.

After discovering on a motorway trip that my car was running about 75 Degrees C I thought I better see if it was an air pocket, bled the system. Then it started hitting 75 Degrees C at 30mph.

Started getting rough idle and stutter issues. Put it down to TBA after my battery died recently. Did TBA, cleaned TB (which was actually not that dirty), checked throttle cable adjustment all was fine. Replaced plugs to be on the safe side, cleaned up dizzy cap with contact cleaner and a screwdriver. Cleaned Distributor plug socket (hall sender), cleaned coolant temperature socket (both with contact cleaner).

Car idle improved slightly but still surging/idle stutter. It was doing my head in.

Bought a new thermostat and flange and fresh G13 coolant.

This is where I discovered more problems from the dirty cowboy re-builders who did my engine three-four years ago. I have never had to take the coolant housing apart or thermostat, only ever done a flushes with water and coolant changes every 2 years give or take.

When I took the old flange off I noticed black silicone plastered all over it. It seemed odd, as I checked ETKA for the fittings and it only showed an O-ring. From my little knowledge of plumbing the O ring when the right size is a good seal and no silicone is needed.

Closer inspection of the old flange showed that the o-ring was also caked in black silicone, i removed the silicone and found the 'old' o-ring was too big. Hence why they jammed it with silicone, much to my horror.

After checking the t-stat housing for more silicone and finding some white silicone stuck to near where the o-ring would sit inside the housing I had major worries that silicone was floating around my coolant system causing blockages.

After checking and not finding any more I fitted new t-stat and flange, refilled coolant and I had proper heat from the vents and temperature was solid 90 Degrees for a day. Next day, driving around it took over 30 minutes to warm up. Something was definitely wrong.

Initial thought, more silicone or bad t-stat.

Stripped the new flange and t-stat out again while the water was a bit warmer (maybe 40degrees). Felt inside t-stat housing again, found more silicone sticking up, pulled it and a huge lump of white silicone came out, it was partially molded to where
thermostat sits.

In their haste to seal it they used some nasty white silicone in the thermostat housing which obviously ran down and was sat in the bottom of the housing. F**king nightmare. I summarized that the silicone was not letting the t-stat close properly as it had a long strip getting stuck under the t-stat spring preventing it from closing.

Refitted new stat and flange again. filled with coolant again - took it for a test drive after bleeding air out. Put heater core to max heat max flow, drove down the road at 40 mph, temperature stayed at 90 for 40 minutes. Heat was back constant and very hot in the cabin.

So far problem solved.

Surging/stutter at idle has gone away. I think the coolant was getting too cold and was causing problems because the ecu was forever hopping between open and closed loop control. Overfuelling and such.

So far so good. I need to check water levels in the morning again before I go out for my last drive before christmas. I noticed a bit of condensation under the oil cap (very slight) due to the cold running of the engine. Dropped the oil as a precaution.

I'm quite glad I didn't throw all the parts in the world at the car just to find the thermostat was causing issues. Hopefully this may be a point of reference if someone has normal thermostat failed open issues.

I checked everything prior to this, battery, alternator, wiring between doors, earth connections and seals for leaking water. All came up OK. Even TBA/TB clean didn't cure it.

3 days of pain, but I'm glad I did it, i think if i left it longer the silicone would have completely broken up instead of just being loose around the hose entrance and would have started causing major problems with my cooling. Chances are the old stat was fine, but it was only a tenner so no great loss there.

[SammoVWT]

Small update: Checked water level this morning, dropped slightly, topped up coolant (assumed more air in system).

Took 6-7 mins to warm up from bloomin cold to 90 Degrees C. Temp stayed at 90 during drive. Let it cool and water level has remained bang on max.

Problem fixed. Lesson for the wise. If you need silicone to seal an o-ring system, something is broken. Don't use it!

[SammoVWT]

Second Update:

Was having days where continuous bleeding of the system was needed. Worked fine for the first few days/drives. Then the car was taking 20 minutes to warm up again, and temperatures getting 'stuck' for periods of time. Generally insufficient heat buildup.

Took went to take the flange off when I saw that the flange was not seating correctly anymore, and the self tapping screws (i'll get to this) appeared to have completely threaded the bolt holes. The pressure of the water had pushed the top half of the flange out by about 5mm. Tried to refit, but the screw had zero grip.

Checked etka for bolt sizes. Realised that they had put my radiator screws in where the thermostat flange bolts should have been and they had lost my thermostat housing bolts, hence why they glued it down with so much silicone and threadlock...

Luckily the there was enough meat in the plastic to re-tap the threads.

Retapped the housing thread to M13, drilled the flange screw holes slightly larger. Put in new M13 bolts, now holding coolant with no leaks, no more air pockets, no silicone and the VW o-ring again. Been like this for several days. So just be warned, if you see a self-tapping screw in your thermostat housing, the chances are its the wrong part.

Car now gets to 90 Degrees C in just under 5 minutes, even at -2 Degrees outside.