Itinerant Air-Cooled

There was a film of oil on the inside of the throttle body when I removed my S boot the other day. Upon further inspection, it was coating the inside of the S boot as well.

Where did this oil come from? My first thought was that it had to come from the oil breather tube. Re-examining the S boot seemed to corroborate this, as there was not a film of oil at the top of the boot, nor any sign of oil on either side of the AFM.

A dim memory of a looong thread over on the other board popped up in my brain. As suspected, it was still there. SGKent wrote that if the little hole in the top of the breather cap holds a vacuum when you apply it, that the diaphragm in the valve is good, otherwise it is damaged. So I cleaned it up as best I could and put a small vacuum to it and the vacuum was not held.

What i did not find on any of the seemingly 72 pages of that thread was anyone saying that this failure would cause oil to get into your S boot. Seems like it would drop the pressure and cause more air to flow to me, but I'm not supremely confident in that prediction. Does anyone have an opinion, theory, or emotional outburst about this?

Anyway, I was able to locate a good one in my stash and install it. Just would like to know if it is related to the oil problem.

Thanks!

Glad you had a spare valve to work with; they're not made anymore, and none of the modern VW replacements have the correct mounting flange. And I think you found the cause of your oil-coating. ANY combustion that sneaks past the rings (mostly) or the valve guides (to a lesser extent) will temporarily pressurize the case, and if the PCV diaphragm is ruptured, boom. Oil in the intake.

A malfunctioning PCV system can also act like a small vacuum leak; combustion blow-by is almost inert as a gas, so if your A/F ratio is way off the mark, you could have a slightly leaner mixture because of it.

A few people on the Shop Talk Forums in the last decade or so, have been dealing with the ruptured valve in a different way. Instead of allowing a diaphragm to occasionally meter the crankcase venting, they drill a small hole in a metal plug, and plug the crankcase vent hose with it. This allows a more constant metering of the crankcase pressure, keeping a slight vacuum on the case during operation. The size of the hole is dependent on how much metering your engine needs. I don't claim to be an expert on this, but the information is out there if you're curious and want to learn about roadside fixes for your issue.

Look on the bright side, I don't think your throttle body will be wearing unevenly like some FI throttle bodies tend to do without occasional lubrication. :)

Robbie

my GUESS is that (1) oil is present in the engine compartment and it condenses inside the S-boot and AFM over hundreds of thousands of miles. (2) the blowby goes into the S-boot at the hose from the breather. When the engine is running it gets sucked into the plenum and then into the engine. The CO and hydrocarbons get burned. The rest is inert. When the engine is off any oil fumes evaporating still go up that hose and fill the inside of the S-boot. The throttle is closed so the only way out would be the air cleaner side by leaking past the AFM flap. Very small amount but over a hundred thousand miles the build up is there. Unless the AFM door is sticking I would not worry about it. The problem however with a blown breather is that if the S boot sees say 18" of vacuum then the inside of the case will see the same and that can suck in valve seals, cause more blowby etc., cause the AFM to act weird. I would make sure I was running a good breather. A NOS one was on E-bay recently and one on the Samba. Both were outrageously expensive. The samba one appears gone. Maybe someone bought it and marked it up on E-bay. I paid $35 each for the two NOS ones I found. Hoody paid about $60. These were over $100 and one close to $200 with shipping. If you are not in a smog state you could meter the flow like Robbie suggested, or add a PCV valve some how for about a 2L engine, or vent it to a catch can.

Thanks fro the responses!

Just to make sure I am following you Steve...

You are talking about the breather box itself, right? Not the valve on top. I am confident that my old valve was ruptured and that I have replaced it with a good one. I have not done anything to check the condition of the breather itself, and would not know how to for that matter.

I found a pool of oil in my throttle body today. My PCV valve must be well and truly shot. I will test and if it is I guess I'll be making a metal plug.

Edited to note that I removed this throttle body no more than 200 miles ago to change it's gasket. I cleaned it then.

drober23 wrote: ↑

Mon Jun 12, 2017 12:04 pm

There was a film of oil on the inside of the throttle body
Does anyone have an emotional outburst about this?

JUST DRIVE THE DAMN THING!
Colin

(oil appearing is a natural consequence of increasing blowby as the rings give it up)

That checks all the boxes! Opinion, theory AND an emotional outburst. Thanks! Seriously, I have not had to mess with the PCV/Breather before. I get a bit nervous about things I don't know much about.

When was the oil last changed? What timing are you running on the engine?

sgkent wrote: ↑

Thu Jun 22, 2017 10:50 am

When was the oil last changed? What timing are you running on the engine?

I can answer that, now that I have visited the engine in question.
Timing, spot-on 28@ 3,400 rpm.

With the timing dead on, unless there is a vacuum leak into the motor case (valve covers, dip stick, etc) there should only be normal blowby going thru the PCV valve. If oil continues I might do a smoke test on the case to see if there are any air leaks. The PCV valve, unless it is perforated, allows the case to close off the PCV source when the case pressure is equal to ambient air pressure. Otherwise if there is a perforation it allows a vacuum to be drawn in the case which can pull more blowby past the rings, and oil into the S-boot. A slight coating of oil will always be present the way the stock system is set up. PCV valves are pretty much NLA right now. The last NOS one on e-bay about 30 days ago was $180 which is way outrageous.

sgkent wrote: ↑

Tue Jun 27, 2017 9:54 am

The last NOS one on e-bay about 30 days ago was $180 which is way outrageous.

Like . . . way TOtally, you know . . . outrageous. Did we mention that this is a Raby engine?
Colin

considering I built the equal for about $6500 - $7000 using the same suppliers for many of the items, yes. BTW if it is a CSpecial then check the end play. In his early threads he was pushing for something like .006" to .008" endplay which is way too much IMHO. The main difference is that mine is simply a type IV VW bus engine built by Steve's Racing and Engine Blueprinting. BTW, that is a real business but we don't build engines these days for others.

Did not check the end play while the engine was out.

I am confident that it has a good PCV valve now. I'll keep an eye on the boot for oil at the next change.