Sunday, 21 March 2010

The Major Oil Leak That Wasn't

Last November I set off in my van to do a 200 mile trip up to Manchester. However, after 40 miles or so she sprang a major oil leak and I ended up being towed home by the RAC. It's taken me a while to find out and understand what went wrong and it turns out to be an embarrassingly stupid mistake on my part. Rather than keep it to myself however, I thought I'd write it up in some detail, in the hope that it benefits somebody else.

As you can see, my van's engine, like most, is not entirely stock. For one thing it has a progressive carb with a paper air filter, and for another the heating system is not connected up. One of the first things I did when I got my her was to block up the gaping holes in the fan shroud where heater pipes would be attached. Given that the Manchester trip was to be a significantly longer drive than I'd ever done before, I'd decided to attend to a few other things too, including blocking up the holes where said heater pipes, and a stock air filter's warm air intake hose, would go through the rear tinware.

All of the above is as it should be but I'm mentioning it here because it gives context to the mistake that I did make. The fact is that if you look around you'll see a lot of VW engines with these orifices left gaping; and they shouldn't be. The ones in the fan shroud will result in air being blown back into the engine bay rather than being sent to cool the cylinder heads. Gaping holes in the tinware will result in warm air from the lower engine being sucked back into the engine bay.

So what was my mistake?

Well, the oil filler neck has a connection which, on a stock engine, has a hose connecting it to the air filter; thus, you might think, as I did, allowing the crankcase to breathe filtered air. Replace the stock air filter (often done when a non-stock carb is used) and you might not have a place to connect this hose. Have a look at a few dub engines with non-stock carbs and you'll see that the breather on the oil filler neck is often left unconnected to anything. This did not strike me as being a good thing and in my bid to close up 'unnecessary' orifices, I put some tape over it to stop any crud getting in there.

As I discovered later, the crank case is in fact more inclined to breathe out though that tube as it takes air in through a (surprisingly to me) unfiltered opening behind the pulley wheel. The tube on the filler neck connects to the stock air filter not to supply it with filtered air but so that the oily vapour it breaths out goes into the carb; to be burned up in the engine rather than dumping it elsewhere. Block the pipe on the oil filler neck, as I did, and the crank case will breathe its oily breath out behind the pulley wheel. Result: the pulley wheel flings the oil all over the engine bay.

Combine my faux pas in closing that vent with topping up the oil to the max (she always leaks a bit so I expected to lose some on the trip) before I set off and I was all set for the incident that followed. This part of the story is worth telling because it helps to show why it took me a while to find out what went wrong. So, in a nutshell:

I pulled into a service station, smelled oil, and when I went around the back I found that there was oil sprayed all over the back of the vehicle (it must have been hitting the hot engine and vaporising) as well as all over the engine bay. In a bid to save a potentially dry engine I grabbed a can of oil and glugged it in fast. Well, most of it went in. However a good deal didn't so by the time the RAC man arrived there was additional oil, spilled by me, all over the place making things look even worse. It's also important to note (we'll see why shortly) that because I just glugged it in, there was now way too much oil in the engine.

So the RAC man arrives and a can of degreaser and a shed load of paper towels later the engine is somewhat cleaner and we're trying to work out where the oil came from. We drive down the road half a mile and take another look. This is where having glugged too much oil in the engine plays it's part in the story because of course it's immediately been forced out of the vent behind the pulley and thrown all over the engine bay.

Of course we didn't realise at the time that this is what was happening so we conclude that there's a major leak somewhere that we can't see. The greatest concentration of oil seemed to be on top of the tinware over no. 4 cylinder (where I've marked an X on the photo accompanying this post) and as we could see that it wasn't coming from the oil pressure switch or anywhere like that, we figured that the oil cooler was a likely candidate, it being hidden away, up top, on that side of the engine. Given that accessing the oil cooler is an engine out job we concluded that my trip to Manchester wasn't gonna happen and the RAC man towed me home.

I've already explained what the problem turned out to be but it took me several weeks of research to find and piece together the parts of this puzzle.

One of the first things I did was to post the photo shown above on VZi but I felt fairly sure that the oil cooler was the most likely cause of the problem and was kinda distracted by the idea of swapping the engine with the one in my (project) Beetle to get myself back on the road ASAP. So nobody thought to question my diagnosis and it wasn't until a while later, when watching the Bug Me Video on stripping/rebuilding an engine, that I began to realise that oil from the cooler is unlikely to end up on top of that tinware. Of course with hindsight it's obvious why there was a concentration of oil there. Clue: consider the direction in which the pulley wheel rotates and where most of the oil it flings/flicks is going to end up.

My first breakthrough came when I stumbled across some information about a "sand seal". For those who don't know, and to air my new knowledge, this is something that's needed on dune buggies to prevent sand from getting into the crank case through the vent behind the pulley wheel. WHAT? There's a vent behind the pulley wheel?

This in turn lead me to find an article about crankcase ventilation over at
Rob & Dave's Aircooled Volkswagen Pages which pretty much describes the problem. Oh how I wish I'd found that sooner but I have to say that when I did I was sceptical that the amount of mess I'd seen in my engine bay was down to just that. However, having cleaned up my engine, unblocked the breather, and syphoned out a litre of excess oil that I'd glugged in when I panicked, she's working just fine.


You can get little "breather filters" (SSP part no AC115551) to go on that filler neck connection. I've heard they can leak oil but they've got to be better than nothing and certainly a hell of a lot better than what I tried. On closer examination however I found that the rectangular filter on top of my carb had a connector for a hose. The filter was fitted with this hidden away around the back; which is why I hadn't seen it before. I've turned it around however there's still an issue in that the most direct path for the hose would be at risk of fouling the fan belt. This would not be the case with a stock filter.

For now I have a long tube, taking a path over the generator and around the back of the carb to connect the breather to the filter. However I'm also investigating other possibilities ranging from returning to a stock set up, to installing twin carbs and a breather box. More about that in a future post.


Glenn Newman said...

Lol thanks for the education. I have had the same problem with my bug and have not yet been able to figure it out till now. Thanks

LuAn said...

Glad it helped you Glenn. We can't be the only people to have fallen foul of this. :-)