@Wino Yes it is possible if one removes the black cover piece in the middle. Then it is possible to remove the flap first. It needs to stand perpendicular to be able to pull out. It is connected to a shaft which is flat at certain location.

 

The plastic piece in the middle is just glued down there, it can be pried broken carefully or cut open perhaps. If it is not removed, the only way to extract the flap is by pulling the arm with smaller spring back with some sort of tool so you can open the flap perpendicularly. The arm with smaller spring goes inside the arm with larger spring. I bet VW has a tool for it at factory...

 

After that if the thermostat pin is completely inside the thermostat, it is possible to push it out carefully. If the pin is out, then you can freeze the part to get it back in. But also it is possible to dislodge the screw piece to go behind the pin and then push out thermostat. Much more difficult that way. But I managed to also get it back in.

 

Actually I could just pull out the pin from the thermostat and filled it with molykote 111 compound and it somewhat works now. It is able to push the spring about 5.5mm when I heat it with hair dryer. I shall experiment with it a little bit more

 

... makes me realise how much effort I've saved shutting the flap in the cold position. Also why would Škoda send cars to subtropical climates with such airbox design. Contemporary Mk4 Golfs with the BAH engine had the same airbox without the flap. 

@Wino I managed to remove and insert the thermostat. There are 2 things which help it.

1- Remove the small plastic cover in the middle.

2- It is much easier if thermostat is totally retracted (eg. cold)

 

My thermostat was moving about 5mm between cold and hot. But it is not enough, I put some o-rings and a heat-shrink collar around them to lift the thermostat slightly. Although this makes inserting things back slightly more difficult but not impossible.

Now from 45C-50C, the temps went down to ~30C. Not sure if it can go any lower as housing takes air from right lower corner, next to battery. I should perhaps put a wireless thermometer there and measure the intake temps next to that hole

 

What I need is a replacement thermostat. The borg-warner thermostat is not easy to find. Aren't there any other model/brand vehicles other than volvo which use similar thermostat???

 

@Wino I also found your post here, you seem to have exactly same construction.

 

Some good work there my friend, I don't know which other cars may use a similar arrangement, but I suppose there must be some.

@Wino your flap seem to have this red lip around the flap which I did not have. Although it looked like there was something but it crumbled away...(see attached picture)    I made a silicone border, but I like your flap more... I guess your cover part number is 036129607CS ? http://www.oemepc.com/vw/part_single/catalog/vw/markt/RDW/modell/PO/year/2009/drive_standart/253/hg_ug/129/subcategory/129015/part_id/0/lang/e#sec_1

 

I have 036129607CN but it was discontinued in end of 2003 and new model is 036129607DP I wonder if it has the nicer looking flap like yours. That is just an expensive part due to a small thermostat, so annoying... These boxes seem to range from 100euro to 300euro from vw/seat/skoda. If I buy Volvo thermostat it costs 50euro with shipping...

 

Apparently there are many vehicles using similar thermostat but none has thermostat as a replaceable part. Even in some cases thermostat is outside the air filter housing. Like 1.2 engines with cover 03D129607K... it is a huge oversight to not make the thermostat a replaceable part I think....

 

 

@wino volvo thermostat solved the issue :)

https://evren-yurtesen.blogspot.com/2020/11/golf-mk4-air-fillter-box-heated-air.html

I still don't understand how you managed to change thermostat without removing the little black rectangular cover in the middle of the spring mechanism. Very strange stuff :)

Nice write-up. 

 

All I  can remember is considerable force being required to do whatever it was that I did. It's possible that our airboxes were slightly different.

Edited 3 November, 20205 yr by Wino

When I acquired my 1.4 BBZ a couple of months ago, the flap was stuck on hot air the whole time and it would not pull the skin off a rice pudding regarding acceleration, especially on a hot day.

I also run a mk 4 GTi and an S3 8P, both with open cone filters as they are tuned up to stage 2/2+. No issues whatsoever changing from the standard air box set up.

In fact for a while, my BBZ ran with an open cone filter Jubilee clipped to the top of the throttle body by the previous owner. It pulled strongly, sounded quite racey with an induction roar but suffered a very bad resonance type vibration that could be heard and felt in the car. However, no issues with not having a thermostatically controlled flap to warm up the intake air quickly.

So in a bid to obtain as much air flow as possible, I removed the thermostatic valve from the engine cover and used araldite to glue the flap in the always open position! 

I looked at the diameter of the throttle body and then the diameter of the air intake by the front side of the air box and it was much smaller. So out came my Dremel, and I cut out the blind end of the engine cover opposite to the air intake and I removed the plastic baffles along that side of the cover channel smoothing everything as much as possible. Now, you may say that some of the air being sucked in is not from the direct cold air feed  from the grill. What I can say is that additional air is being sucked in and so now no restriction. The car performs as well as when it ran the cone K & N style filter but with none of the vibration. It also sounds quite sporty from about 3K revs and above.

At the end of the day, I can always buy another cover from Ebay for about £15 but as mentioned already, the thermostatic valve might be equally knackered. However, the car performs so much better now then when I first took over ownership. 

Very interesting - you would nearly think that this device is redundant in a fuel injected engine as the management would decide on air and engine temps and compensate !

 

Well if it's jammed on hot then that would have a detrimental effect on performance !

 

In Mk3 Cavaliers this device was in the airbox to stop the fuel in the caburettor from freezing in cold weather ! 

 

Just my 10p I  the ring sorry lads !

 

 

 

 

 

1 hour ago, VanhireBoys said:

Very interesting - you would nearly think that this device is redundant in a fuel injected engine as the management would decide on air and engine temps and compensate !

 

Well if it's jammed on hot then that would have a detrimental effect on performance !

 

In Mk3 Cavaliers this device was in the airbox to stop the fuel in the caburettor from freezing in cold weather ! 

 

Just my 10p I  the ring sorry lads !

 

You've misunderstood the purpose of it, because these engines use port injection, the warm air is to help the fuel stay atomised in suspension rather than partially condensing on the cold metal surfaces and trickling into the cylinder as a liquid which doesn't burn and blows straight out of the exhaust. It's why port injection engines use more fuel on cold starts.

The issue no longer exists on modern direct injection engines because the fuel isn't injected until the air in the cylinder is partly compressed and already very hot.

5 hours ago, sepulchrave said:

 

You've misunderstood the purpose of it, because these engines use port injection, the warm air is to help the fuel stay atomised in suspension rather than partially condensing on the cold metal surfaces and trickling into the cylinder as a liquid which doesn't burn and blows straight out of the exhaust. It's why port injection engines use more fuel on cold starts.

The issue no longer exists on modern direct injection engines because the fuel isn't injected until the air in the cylinder is partly compressed and already very hot.

 

Thanks for taking the time to explain that - Very interesting.. Every day is a school day ....! 

9 hours ago, VanhireBoys said:

Very interesting - you would nearly think that this device is redundant in a fuel injected engine as the management would decide on air and engine temps and compensate !

 

Well if it's jammed on hot then that would have a detrimental effect on performance !

 

In Mk3 Cavaliers this device was in the airbox to stop the fuel in the caburettor from freezing in cold weather ! 

 

Just my 10p I  the ring sorry lads !

 

 

Not quite. It was to stop water vapour in the air from freezing and blocking up the carb.

 

One purpose here is similar, to prevent blockage of the throttle body parts by ice. The risk of freezing is much less with injection engines, but still present in high-humidity, low-temperature conditions (e.g. fog).  Fuel vapourising nearby made things much worse with carbs, the latent heat (cooling) of vapourisation adding to the expansion cooling of air passing the butterfly into intake manifold.

 

Some engines use engine coolant pumped around the TB metalwork to do the same job, instead of pre-warming the air. Had an old MPI Vx Omega with such plumbing. 

 

Another part vulnerable to freezing is the PCV valve, as it passes (and depressurises) blow-by gases which contain lots of water vapour. It contains a small electrical heater on the 1.4/16v engines to prevent such freezing from blocking it. These recirculated vapours add to the moisture in the TB airflow in older designs where the PCV re-entry point was upstream of the TB (AUA, AUB?).

 

It could be that the pre-warming system is designed to fail in the 'all hot' position, because the converse might cause more problems, in some climates/conditions.

I think both our 1.2 Fabia and my 1.4 Polo have fully wedged shut warm air feeds now, with no noticed issues though.

 

I was a little surprised to find the original airbox thermostat still working correctly on my 'rescue car' last year (another 1.4/16v Polo). Will leave that one alone for now but try to remember to check it periodically. 

 

Edited 6 November, 20205 yr by Wino

Thanks again lads for the explanations- I find all this very interesting - There is a reason for every component to be there ! 

 

I am in the middle of rescuing of all things a 1983 Porsche 924 at the minute- she is Bosch K Jetronic. So it's great for me to have this info just so I can have a better understanding

 

I am learning as I go and you know there's a feel good factor ! Sorry for the tangent lads !

 

I

K Jet is a purely mechanical injection system built like a swiss watch so getting the fuel distributor alone reconditioned could be very expensive, all those tiny seals will have age-hardened and it'll be leaking like a sieve.

You'll find a few folk with good knowledge of k-jet over on clubgti.com forums, as the early injected Golfs used it. 

I just realized last week that the flap was stuck half open again. Knowing that the springs were really strong in there, I was experimenting with replacement springs.

Now I put another volvo thermostat and I changed the springs with softer ones. Now the thermostat is able to push against the spring easier to close the hot air port.

Stainless steel springs seem to be softer in general. Let's get back to this in a few years