Coolant issues help please

[BennyG_UK]

Its a weird issue. Coolant temp keeps dropping whilst im driving but will reach 90c no problem stood still/slow driving.

So I though ok itl be thermostat (ive already replaced sensors at this point). So new stat is on. Same issue.

But last night I noticed after my commute home when I took the cap off the coolant bottle there was NO pressure even thought the engine should have been hot.

So I let the engine get back up to 90c put the cap back on and left engine running for good 30mins. Took cap off again expect a huge TSSSH, but just a little TSH so I guess it is keeping pressure.

Going to get it pressure tested tomorrow but has anybody else got any ideas?

Water pump is working fine as when the engine is rev'd you can clearly see coolant flowing through the bottle so im not sure what else it could be.

Engine is not over heating at all and fans kick in after a sprinted drive (even though temp reads 60c) so somethings fishy.

Oh and since this issue was there before thermostat change also, I thought Id test the old one. The stat is open when cold and closes when hot. I have another spare one from ECP which was leaking and we didn't end up using, that behaves the same so Im guessing this is correct? Im at whits end

Any ideas? Its a 2.0 TFSI Quattro

 

[fangio]

'Stat should open when hot - unless they've changed them since I last did one?

 

[BennyG_UK]

That's what I thought. Il try get another tomorrow to confirm what it should be doing. But my original one closes on hot water and opens on cold. So it's not exactly stuck as it moves perfectly fine and instantly. I've seen a post buy someone saying dsg's have three thermostats one main one, one turbo and one dsg. Don't know how true it is but that's only other thing I can think of (the turbo one, mines not a dsg)

 

[BennyG_UK]

http://www.audi-sport.net/vb/a3-s3-sportback-8p-chassis/199956-2-0-tfsi-temp-gauge-low-reading.html

This is where I saw it. Incidentally my old stat looks exactly like the one on this page. Then moves up when hot water is added, and back down again when cold. Just checked and it deffo blocks off the bottom connection when cold so my old one will most likely have been ok I guess?

Argh won't have much hair left soon!

 

[BennyG_UK]

Anyone? tested my old thermostat and it operates perfectly fine and the issue was there before the new thermo. really running out of ideas

 

[BennyG_UK]

Anyone? tested my old thermostat and it operates perfectly fine and the issue was there before the new thermo. really running out of ideas

Right getting a bit further, logged with VCDS on my commute home, engine will get up to temp no problem.

Once up to temp the fans come on full blast and cool the car right back down! They don't just come on for a few seconds they will stay on rest of the journey

So even though the car has barely just reached 90c they will stay on until I turn the engine off regardless of temp.

Anyone had this issue before? Not sure where to go from here, no error codes at all. Fan controller or fans? Thing is fans will cut in and turn off perfectly fine if the car is stood still. Start driving and theyre on full blast

 

[BennyG_UK]

Just to update people on this incase anyone has the same issue. New stats from VW (main engine one, and a turbo one) all new temp sensor and she's all good again.

Even though old stat opened and closed fine, it was opening at a much lower temp then my new one so was probably just weak