Throwing 20w50 around SW England and night-vision NW France

[woodman]

Greetings from Quimper, Brittany. You didn't think I'd go on holiday and not get in touch?!.....

The trip from Sheffield to Plymouth went very well, Magnus running like clockwork, cruising happily at 65-70mph, pulling up the hills nicely, sounding very healthy. Performance-wise the only limitation I found was on a long steep climb on the A38 after Exeter, just after it splits from the A30: I floored the throttle and it kicked down into 2nd at about 50mph, and though it just about held on to the speed there was a sense of hesitation like an occasional misfire. Other than that, perfect.

However, there is one big problem - the engine is throwing out about a pint of precious oil every 100 miles! Most of it appears to be coming out of the air filter body and all over the inner wing and steering column, plus a bit out of the filler cap and the rocker cover.

Now, the perplexing thing about this is that I've completely overhauled the crankcase breather system: cleaned out the flametrap, changed the PCV valve and the hoses, and also put in a fresh air filter (which by now will be drenched in oil again). If anything, I would say this has made the problem worse instead of better.

I'm certain that very little of the lost oil is being burned - not a trace of blue smoke and if you hold your hand to the exhaust gases your hand stays totally clean. And performance is great, plus I'm getting 27mpg on this trip so far. So things like valves and piston rings being culprits seem unlikely. And it only seems to throw oil when the oil is seriously hot on motorway runs. Basically I think it just gets hot (though water temperature is absolutely fine) and pees up the breather pipe from the oil filler cap into the air filter, suggesting (I think) that the oil pressure in the engine is substantially higher than the supposed positive pressure in the breather pipe.

Can anyone shed any light on this?

Speaking of light, one other (scary) event. Driving through Brittany in the dark, enjoying the foot-operated dipswitch which seems so much more functional than a modern column stalk one. A car approaches over a brow, we play beam-dipping brinksmanship with each other and end up dipping simultaneously.....except that when I dip my lights the headlights go out altogether and I am driving into total darkness with a pair of lights coming towards me. I brake in a straight line to an almost standstill (fortunately nothing behind me) and then press the footswitch again, and the dipped beam comes back on. Press again and the main beam comes on. Back to normal. Another hour of night driving ensue - another twenty-odd uses of the dipswitch completely without problem or drama. Frightening and totally perplexing. The only time the lights have ever played up. Has this ever happened to anyone else?

Off to buy some oil now, well after breakfast, anyway....

[Derek UK]

The ventilation system should flow from the filter to the filler cap so in theory oil shouldn't get anywhere near the filter. The other pipe should flow from the side ear to the inlet manifold. Check that you have the PCV valve the right way round. It's likely to have an arrow on it and should point towards the manifold. As a stop gap you could pull off the pipe at the filter and swivel it round to the fuel pump side. Stick in a plastic 1l bottle lashed safely out of the way of the fan.

Foot dipswitches can get cranky and best replaced for safety reasons. Dip early, you know it makes sense, especially when driving on the wrong side of the road.

[woodman]

Spent a while with a Frenchman today who used to race Amazons many years ago. We verified that the PCV valve is the right way round, and he also recommended pulling out the oil filler to air filter pipe and routing it into a bottle - which I'll do tomorrow. At least it means I can put the lost oil back in. But when he saw an otherwise healthy-seeming engine with oil dripping from the air filter body he just kept saying "C'est bizarre. Ce n'est pas normale." So we were agreement, but we were none the wiser.

I'm still trying to think this through. As far as we know, the crankcase to manifold bit is working correctly. When you open the oil filler cap the engine note changes markedly, so the air filter to filler cap pipe must be sucking when the throttle is shut. But when the throttle is open I'm thinking that that pipe is not sucking, and that the flow of air through the air filter and into the carb is creating a reverse draw that's sucking oil into the air filter. But why? Why does the PCV valve not prevent this from happening?

[Alf ista]

Not sure if you have a B18 or a B20 but the pcv hoses are different between the two engine types. See here, this is from Ron Kwas's site which shows the difference:

http://www.sw-em.com/pcv_diagrams.htm

[woodman]

Thanks Alfa Ista. I've seen those links before but they make a little more sense each time I read them.....

This time I've gleaned that the PCV valve might be in part responsible for my variable idle speed. But it is a new PCV valve, it works and it's not clogged. I wonder if variable vacuum at idle is causing the PCV valve to wander up and down, for example because the air filter to carb housing doesn't have a great seal?

The real question is, do I rig up things to stop all this oil fouling the air filter, eg external bottle to catch oil, separate filter on filler cap, or do I try and address where the oil's coming from eg start delving into piston rings etc in an engine that seems to be otherwise performing well?

[Steve121]

Had oil coming from the air filter housing on my Amazon's first 'spirited' run after buying it....

turned out to be broken piston rings in 2 cylinders!!! it made quite a mess of the engine bay. checking the compression on each cylinder would be my first port of call

perhaps another related thing you may have mentioned is excess oil pressure. I have a 1970 Lotus Europa with Renault 16 engine which was 'prepared' for racing. The builder foolishly shimmed the oil pump relief valve spring with washers to up the pressure. This upped it to the extent that it just kept on building and the relief valve no longer relieved pressure, and oil was dripping out the air filter via the breather hose! in the end the oil filter exploded.. nice.

[Derek UK]

Remember that the PCV valve has to be the correct one, a random one off the shelf from another car is unlikely to match into the system. The valve pulses back and forth and has to match the engine. Too weak or too strong and it might reverse the flow when running reasonably fast. I'm not sure if the B18 has the metered adaptor at the manifold end but if that's needed for this system, that's critical too.
Correct PCV valves include the following. Listed on Brickboard so USA. Hopefully the usual (UK) suspects supply the correct one if you don't have a local parts factor that's willing to go through the books. They appear to be common on 60-70 USA GM cars so UK classic American parts suppliers likely to have them.
Fram FV112 ebay #120353900290
AC CV768C several on ebay but USA also
Standard V112
Niehoff PV280

[woodman]

Thanks Derek. I fitted the external bottle this afternoon and ran the breather pipe into that instead of to the air filter, then ran the engine. Result is a fairly consistent plume of thin smoke coming out of the pipe and into the bottle, both when cold and hot. I think, and only think, that it's exhausty rather than particularly oily. Not in puffs that you might associate with, say a leaking valve seal, so I'm definitely tending towards piston ring(s) as the culprit now.

Thinking ahead to when I get back from France, how much of a job are piston rings to do yourself on the B18, and should I do anything else while it's opened up?

Cheers.

[Derek UK]

I'd think that a compression and leakdown test might be your best bet for a starting point. Unfortunately checking the rings means a major tear down and lots of measuring, even if you don't find a broken ring or a scratched bore. Buying another known good engine minimises your off road time or rebuilding another in your own time over the winter might be another possibility if your current one turns out to be damaged.

[woodman]

On the one hand, I've tracked down a potential replacement engine and am tending towards taking Derek's advice by getting it overhauled and sweetened up a bit over the winter.

On the other hand, since I ran my breather intake hose into a bottle, instead of connecting to the air filter, the engine seems to have stopped throwing oil almost completely. Gave it a proper belting yesterday, cruising at 70, overtaking uphills, you name it..... a few drops around the rocker cover, the tiniest smear of emulsion in the bottom of the plastic bottle. Nothing at all coming out of the exhaust pipe. And the engine sounds and feels so well, it seems a bit bonkers to be contemplating taking it apart. I suppose at least this means my temporary fix takes the urgency out of the rebuild...

There is still thin smoke wisping from the breather hose, which means it's certainly still not doing the job it's supposed to, but my thinking is that running it to fresh air instead of to the air filter has reduced the overall crankcase pressure and thereby stopped it from pushing oil out of every orifice.

[Derek UK]

The early B18 just had a side breather going downwards combined with a plain oil filler cap. Both the cap and the plain side "ear" have mesh filters/restrictors which need to be kept clean, but the layout allows the engine to balance up it's own breathing. If the engine is in a reasonable state there won't be much smoke or oil mist out of either.
As said, a compression and leak down test would be useful. Compression test is easy but leak down needs a bit more kit, and someone who knows how to use it properly and interpret the results. If compression test is good there's probably no need to go any further.
When using the pipe to filter system it's essential that the cap mesh is clean, the pipe hasn't got a kink in it (very common) and the adaptor on the filter has a hole at least as large as the bore of the pipe. Adaptors fitted to aftermarket filters often have a very small hole through them. Not good.
Good to read you're driving it like a Volvo and making it work for a living.

[woodman]

Remember I'm still a novice where crankcase ventilation is concerned, but I've just had a thought. Before I re-routed the breather inlet hose into a bottle, there was a slight leak of exhaust on the manifold to downpipe gasket. After the re-route, that gasket leak has disappeared but there is this wisp of smoke into the bottle, which smells exhausty.

So, here's the thought. What if I've improved my oil leaks by relieving crankcase pressure, but the source of the crankcase pressure is actually exhaust back pressure being caused by, for example, an exhaust silencer that is falling apart internally? Hence my little bottle is allowing an alternative exit (past the piston rings and out through the crankcase) for a smallish proportion of the exhaust. When the breather inlet is connected to the air filter, the high back pressure is automatically balanced by increased inlet pressure, creating a build-up of crankcase pressure.

Or, to put it another way, would excessive crankcase pressure cause the manifold-downpipe gasket to leak if the exhaust system wasn't restricted? Might this explain why engine performance feels at least slightly improved since re-routing the breather hose?

Or am I making this up?

[Derek UK]

"Or am I making this up? "

Well you're thinking very hard about it. Yes you might be getting a bit of blow by at the rings. Theoretically you could have enough back pressure in the exhaust to maybe allow some exhaust gas to come up the valve guides if they were worn. Both of these sources of "smoke" can end up in the valve cover and out of the pipe. Engine wouldn't run very well with that much back pressure. You can fake that and also check your exhaust for leaks at the same time by holding a wadded up cloth over the tailpipe. No leaks and it'll be hard to hold it on there tightly and it will stall very quickly. It would also check your manifold joint. Take the oil filler cap off and put the palm of your hand over it when the engine is running. In theory it should be sucking in if your side pipe is open. It might pulse a bit and might smoke a bit if you check it after you've been out on a run. Although it should be minor, expect a bit more on a high miles engine.