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VW Polo / Golf breather system

Does your 1980s Polo or Golf burn a lot of oil?  Is the air filter saturated in engine oil?  Does the engine leak oil from every seal and gasket?  You may have thought that your engine is terminally worn, and be thinking about a replacement engine, or even scrapping the car.  Read this first - it could save you a lot of money.

This information definitely applies to all Mk2 VW Polos (1982-90) and 1.1/1.3 engined Golfs (1983-91).  Engines in question are carburettor fed 1043cc and 1272cc units.  It may also apply to the earlier 895cc and 1093cc units fitted to the Mk1 Polo and Golf, and to the later 1.3 motor fitted to the Mk3 Polo post 1990, and possibly even to the 1.4 motor in Mk3 Golfs.  However, I have no experience of these engines (apart from learning to drive in a Mk1 Polo).  It does not apply to the larger (1500cc and above) VW motors which have a totally different breather design.

Like any engine, the small VW motor has a system for getting rid of the gases that build up inside the engine when it is running.  The system consists of a dome shaped oil separator mounted low down on the side of the engine block, underneath the inlet manifold.  A rubber pipe connects this to the air filter housing, feeding the crankcase gases back into the carburettor where they are burnt in the engine.

When these cars were new the system worked fine, but it has a couple of major weaknesses.  Firstly, the oil separator tends to become clogged up over time, so that the gases are no longer able to flow freely through it.  This leads to a build up of pressure inside the engine, which will force oil past all the gaskets and seals.  The main weak spots are the camshaft cover gasket, the seal around the oil filler cap, the seals at each end of the camshaft and the seal behind the crankshaft pulley.  Significant oil leaks from these areas may indicate a blocked breather.

Secondly, there is a passage through the engine block, from the recess behind the oil separator down into the sump.  The idea is that oil droplets contained within the crankcase gases are separated out by the oil separator and returned to the sump via this passage.  However, the oil passage is a fairly narrow diameter, and over time it tends to clog up in the same way as the separator itself.  Oil builds up in the separator, and is forced up the pipe into the air filter housing because it has nowhere else to go.  It will then saturate the air filter and also end up being drawn into the carburettor, leading to excessive exhaust smoke.  This is especially noticeable when restarting the engine while it is still warm.

Finally, the oil separator itself is not very efficient.  Even when in perfect condition, it cannot cope with the volume of crankcase gases produced by even a moderately worn engine (75,000 miles plus).  VW recognised this problem and introduced a modified system with a second oil separator fitted in line between the first separator and the air filter housing.  I do not know when this system was introduced - possibly as late as 1990.

So my breather system is dead.  How do I fix it?

Before you start, it might be worth having a compression test done to see whether the cylinder bores are terminally worn.  There is no point spending any money on an engine which is about to die.  Likewise if the engine is very rattly you are probably better off replacing it.  BUT if you buy a second hand engine from a breakers yard, you should still follow the instructions below.  The crankcase breather is much easier to change with the engine out of the car, and any engine which has done more than about 50K will benefit from the treatment described below.

The first step is to replace the crankcase mounted breather.  The breather itself only costs around £7.00 from German & Swedish, but it is a pig to fit.  Access is very difficult, especially on the Polo where the brake master cylinder gets in the way, so you really need to remove the inlet manifold (complete with carburettor) before you start.  The breather itself is a dome shaped steel casing and is a tight press fit into a recess in the cylinder block.  Removing the old one is usually easy - you just need to tap a fine bladed chisel very carefully into the slot between the breather and engine block, until you can lever the breather out with a screwdriver.  However, to fit the new one requires a special tool - essentially a short, very large diameter hollow drift which bears on the flange round the edge of the breather.  If you hit the breather itself you will flatten it.

If you have a scrap Polo water pump, you will find that the aluminium pulley makes a perfect drift - you just need to cut a slot in it for the pipe that comes out of the breather.  However, even then your troubles are not over.  The new breather will be a very tight fit in the block, and on a Polo there is not really room between the block and the bulkhead to swing a hammer hard enough and precisely enough to tap the breather squarely into place.  The last time I replaced one of these, I ended up having to remove the engine to get the new one to fit.  For this reason, I strongly advise that you get a good independent VW specialist to do this job for you, unless you are an accomplished mechanic with a decent selection of tools and a lot of patience.

Before fitting the new breather it is absolutely essential that you clear the passage between the breather and the sump.  A wire coat hangar is just right for this - poke it into the hole and keep poking until you hit the bottom of the sump.  If you are getting a garage to do the work, make sure they are aware of this - most VW specialists should be, but some garages may not.  If you just change the breather and do not clear out the drain hole you are wasting your time (voice of experience talking here).  Make sure the recess in the block is thoroughly cleaned and degreased, and put a smear of a suitable silicone sealant around the edge of the breather before you fit it.  But don't overdo it, otherwise bits of silicone sealant will block the oil drain hole.....  It is also worth inspecting the pipe between the breather and air filter - if it is cracked or perished, replace it.

Now clean all the oil out of the air filter housing and fit a new filter.  Hopefully, with the reduction in crankcase pressure you will not need to replace all the leaking oil seals and gaskets, but be prepared to do so.  Clean up the area around them and see if any more oil appears.  Probably the two most important seals are the ones at each end of the camshaft.  If these fail you will get oil either on the cambelt, or inside the distributor, or both.  Check these areas for oil contamination - if the cambelt has oil on it, change it immediately.

I've done all that, and I'm still getting oil in my air filter.  What next?

As mentioned above, VW introduced a secondary oil separator on later cars.  This is a plastic canister, about 100 x 50mm, with a pipe stub at each end, and is intended to fit in between the crankcase breather and air filter housing.  The connecting pipework for this breather differs from the earlier setup.  The canister itself costs around £12 from a VW dealer, and you should be able to make up suitable pipework with a little ingenuity.  Just make sure that the pipe from the primary to the secondary separator is not kinked - the canister has to sit at an angle to clear the underside of the inlet manifold. 

Alternatively you may be able to salvage a complete system (canister and pipework) from a scrap VW of the correct age (try looking at 1990-91 cars as a start).  Clean the canister out with diesel, and it should be fit for further service.  If fitting this does not solve the problem, then the chances are that your engine is genuinely worn out.  In this case, a temporary fix would be to get a nice long length of hose, connect one end to the crankcase breather and the other to a plastic bottle secured somewhere in the engine compartment.  Empty the bottle regularly and start thinking about buying another car. 

To hell with this.  It all sounds too much like hard work.  I'll ignore the problem and see if it goes away.

Oil consumption on a VW motor with breather problems can be terrifying - as much as a pint every 100 miles (most of which ends up in the air filter housing).  Having an air filter clogged with oil will worsen fuel consumption and guarantee an MOT failure on exhaust emissions.  Every time you park the car on the street it will leave a pool of oil underneath, and you will be crucified by the local Environmental Health Officer.  And eventually the car will stop running, either because the distributor is full of oil, the cambelt breaks due to oil contamination, or you forget to top up the oil level before a long journey and the engine seizes solid on the motorway.  Polos and Golfs are faithful little cars, and deserve better than this.  If you are planning to keep the car any length of time, sorting out the breather system will save you a great deal of money and aggravation.

Finally, many thanks to Andrew Moorey and Rob Fleming, both regular contributors to the Back Room forum at www.honestjohn.co.uk  for their help and advice.