I know this has been asked several times before and I've had a look over the various threads, but still very much undecided between an actual air-lock, sender fault, thermostat fault or the dreaded water pump!

So, my symptons are having recently changed the coolant and water the engine temp will rise to 90 quite happily on the drive when idling, however when I start to drive it will drop to between 50-60 and rarely move unless I come to a stop when it'll return to 90.

The fans are working fine, and the top hose, bottom hose and rad are all hot.

I had the MIL come one when I went to Swindon and back, but no other problems and this just gave a fault code stating tempreature indifference, which I've reset and its not returned!

I'm hoping it is an airlock. When I bled the system I did so from the little tap underneath the rad by the bottom hose and only about 4litres of water came out.

Any ideas, greatly received!

Thanks

Matt

Soz m8 classic sign of the thermostat stuck open

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Stuck open?? How would that affect things?? Surely we want the stat open??

At least thats better news than the water pump!!

If its stuck open then water is constantly flowing through the rad whereas you only really want it opening when the engines hot enough to need it. Hence the gauge never gets above 60-70ish.

You'll find your fuel economy suffers a bit as it will inject more fuel because the engine is running colder

This is why you are only getting up to temp when stationary, I had this problem a few months back and a new stat cured it. It's something best done now before the colder weather sets in or your car's gonna be freezing as the heater won't produce enough heat

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Right, well despite the whether, I put on my waterproofs and went for it!!

I've drained the system, removed the temp sender and blown into the header tank to remove ALL the water. Having replaced the temp sensor, re-connected the bottom hose and closed the tap I replaced the coolant and water.

Started the engine and let it run....topped it up and after about 20minutes, the top hose became hot, then the rad and then finally at 90degrees, or just after the fans started!!

Header tank cap replaced and a quick spin around the block and it seems fine!!

Final test will be to work tonight, so fingers crossed!!

Cost so far....wet jeans!! lol

Yep sounds like a stuck stat.

But to make sure you have all the air out of the system. Put the heater on full hot take the header tank cap off & bring the car up to normal temp then hold the revs upto at least 3000rpm for 10 mins or so. Turn off allow the engine to cool down & check coolant level.

Well, I got to work OK....25minute journey and it maintained a steady temp of 70. Only when I got to work and parked up did it rise to 90!! GRRR!!

No MIL light this time though. Removed the header tank cap, and only a small amount of pressure....nothing to make it steam or errupt everywhere.

I'm guessing then time to go for the stat????

Yep i'd go for the stat. You can check if the old one opens and closes or not in a pan on the hob before deciding to replace it.

lol told ya it's the stat if you're removing the old one you might aswell fit a new one as they do wear out.

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Mmmm......Just to help convince myself, how would a faulty stat (which I can only presume is stuck open) cause these problems??

If the stats stuck open you are getting water flowing through your radiator all the time, so when you're driving the car and cold air is hitting the radiator and cooling it your temp gauge doesn't go up above 70. When you come to a standstill though the rad is not being cooled by airflow so the temp then does go up to 90.

On a car thats working properly the coolant will start off only circulating round the block then the stat is supposed to open when the coolant gets hot enough, at that point the hot coolant will flow through the rad and rad pipework as well and start cooling down, then once it's cool again the stat should close and the cycle starts again. Its a self-controlling loop. This keeps the coolant temperature around 90 degrees (it doesn't sit at exactly 90 it varies a lot but the dash dial is damped so it should stick at 90). In traffic the rad fans will also cut in to cool the coolant in the rad so it doesn't get up near 100 and boil.

Basically your car is running with the coolant flowing through the radiator all the time which means it never gets up to temperature. The ECU will inject more fuel as the engine block is colder than normal and you may also get problems trying to get the blowers to blow hot air.

Plus, if it had an airlock it would be giving intermittent OVER temperature, rather than under.

Replace the stat.

Perfect!! Great explanation chicken! Thanks very much!!

Stat it is then!!

I'm already impressed with my fuel economy at the mo, so will be looking forward to seeing more miles for my £!

Will update after new stat fitted!

Doh was a stat from the start!

lol I'm not worried!! Its been driving fine and hasn't let me down, so I'm not worried. And for a couple hours work and a £10 part, I'm quite happy.

Very pleased and impressed with the help and support from members, so thank you.

Here's an oldie from the archives to help you - pretty useful to have the right tools

http://www.briskoda.net/forums/topic/150282-thermostat/

Spot on chicken.

Well having discovered the loss of PAS fluid last night as I turned out of the road and nearly into a load of parked cars, I found the cause to be that the PAS oil pressure sensor had sheared off!!

Anyway, I took the time to replace the stat today. Easy enough job HOWEVER I STILL have the same problem, if not worse now....and to make matters even more complicated, I tested the old VW genuine part and found it to be working fine.

So, the latest prognosis is that the rad took FOREVER to get water and when it did, it was hardly hot.

Water is pump is working fine. MUST be an airlock but I can't shift it for love nor money!!

So, my method of draining and re-filling is as follows:

To Drain -

Remove cap on header tank

Undo bleed tap at bottom of rad and bottom hose....about 2.5litres comes out so I'm guessing this is just the rad.

When I took the stat out, more water escaped. That was my efforts in draining the water.

To re-fill

Close tap at bottom of rad

Fill header tank with water

Start engine

Blower at full and hot

Wait till thermostat opens and keep header tank full

Wait till fans start then replace header tank cap - only issue - fans didnt start today.

So - what next???

Fill header tank

Edited 14 October, 201213 yr by matt1471

These engine can be a pig when airlocked. Allowing to cool properly overnight usually settled the most. Squeeze a few coolant hoses several times repeatedly and see if the level drops.

I'd advise changing the CTS as a precaution if you haven't already, for a GENUINE part.

Have you put the stat in the right way round, and in the correct orientation. Get it the wrong way round and it wont open properly if at all, get the orientation wrong and will stick fully open.

When I did mine I flushed clean water through the block when the stat was removed and flushed clean water through the rad as well, then just put it all back together again, filled the coolant via the header tank until it was up to the line, ran the engine with the header tank cap off until there were no bubbles then let it cool and topped it back up to the line again.

As mentioned above it could be the coolant temp sensor playing up but if this happens you usually get unrealistically high or low readings (e.g. the gauge sticks at zero or in the red when the coolant is only lukewarm). If you have a VAG-Com you can log the temp readings on Block 001 and if you get something stupid like -70 or +170 then you know it's duff.

If it was an airlock I'd expect your temps to go high every now and again rather than being constantly cold. and if the water pump has failed, again you would be running hot as the coolant just wouldn't be circulated properly

As stated 1.8T's can be a pita to get air locks out.

Header tank cap off, heater set on hi temp. Bring engine up to temp holding the rpm up at 3000/3500 ish keep it there for 10 mins or so, a second pair of hands squeezing top & bottom rad hoses often helps. Let engine cool down & top up with G12 if needed. Always worked for me. Have a look at the CTS & if it's the old black type or not genuine VAG, replace with genuine green VAG CTS.

I don't think the housing allows for the stat to be fixed any other way?

I checked it this morning and the water in the header tank was empty, so topped it up but haven't had a chance to repair the leaking PAS pump.

Turns out that the pressure switch appears to be a dealer part and as I've realised of late....Skoda don't seem to hold anything of use in stock so gotta wait till Wednesday for that to turn up.....at a cost of £25!!

I did try ECP and GSF but they only do engine oil pressure sensors and yes they fit, but for some reason the one I got to put in temporarily ****es fluid when the engine runs.....so I lost another 2litres of PAS fluid on the driveway today!! Great!!

FIngers crossed for Wednesday, the correct part, no leaks and a working cooling system!! Just the MOT to face then!