Question on oil breather cap

[jawn101]

Just throwing this out there as a general curiosity. I was at the junkyard with Clint today and picked an oil breather cap off an 88 Premier. The cap makes a much tighter seal in the oil fill neck, and fits the hoses to the airbox and intake manifold perfectly (I already have it installed on my car)

The question is, this cap doesn't have the weird filter media inside. It's just an empty space. What's that media really for, anyway? Does it make a lick of difference if it's not present? This cap looks way nicer and fits much tighter so my preference would be to keep it, but if there's a reason not to I won't....

[Dangermouse]

Funny, I was just wondering the same thing about how tight this should be.

Mines pretty loose and I was gong to get a new O ring to see if that improves it, but I wanted to make a trip to the scrapyard anyway.

[jawn101]

Funny, I was just wondering the same thing about how tight this should be.

Mines pretty loose and I was gong to get a new O ring to see if that improves it, but I wanted to make a trip to the scrapyard anyway.

That's exactly why I hate the OEM one, but we haven't had much luck finding O rings that fit it! They are a weird, huge size.

[Farrar]

I had a hard time finding a proper O-ring even at my local Ace hardware store which has lots of oddball stuff around. In the end I got one from John Hervey piggybacked onto another parts order. I though perhaps I had a vacuum leak there with an ill-fitting O-ring, but I didn't notice any change in running when I got one that sealed better. Go figure.

[Kenny_Z]

There's no vacuum in that area. It's just a spot for the engine to breathe. The only thing you have to worry about with an ill fitting cap is debris and dirt getting into the valves and cam.

[Ron]

Actually it is not supposed to breathe...it is a closed crankcase system under vacuum. Check out where the two hoses go- breather AND cold start tube.
(Something to consider when setting CO...)

The media is there to filter the crankcase vapors...helps oil vapors condense and drip back into the crankcase...

[Jonathan]

Interesting.

Ron, I was looking at Dermot's other thread where this was being mentioned too and had a couple questions.

- So if the vacuum is being pulled, is it being pulled from say the charcoal canister, through the tube that connects it to the cold start valve and then from the other port on the cold start valve and then to the one connection on the oil filler cap? So the direction of flow (if you will) would be from filler cap, through the tube to the CSV, from the other port on the CSV to one of the connections on the charcoal canister?

- With that pulling direction in mind, what about the other connection on the filler cap, the one which goes up to the air filter housing? Is there air/vacuum being pulled towards the filler cap from this air filter housing as well? Part of that question is related to whether there is a proper installed direction for the oil filler cap? Not where it sits in the hole of course, but whether it matters which tube you have on which end? I am thinking in terms of the way a check valve often has an arrow shown on the side of it saying which direction the flow is. Wasn't sure if that applied to the filler cap or not. The second part to that is trying to understand the significance of the air filter housing (is this what is called the breather, btw?) connection and why it is there? Mostly because I think it was a photo or two of someone with a modified and cosmetically nice version of the air filter housing, but I don't think it had this tube going from the corner of it over to the filler cap. I don't understand the purpose of it so can't say whether it is necessary or not.

- The odd thing is that the vacuum routing diagram doesn't show this tube going from the oil filler cap to the air filter housing. It might be left off for simplicity or clarity or perhaps because it isn't needed. Not sure myself, so that's why I ask.

- And final question... what is it that generates the vacuum? If you want to produce pressure, such as moving water for example, you use a pump. I often work with centrifugal pumps in our water treatment systems. We also use vacuum pumps to do something very similar but instead of pushing water, they pull vacuum (air). We would use them on a "vacuum degasifier" type technology. They don't have the exact same centrifugal impeller like you would see on the water forwarding pump, but they often have a rotary lobe type design that accomplishes the vacuum pulling. What pulls vacuum in our engines? Is it this rotary lobe type idea of the crankshaft rotating and how the chamber in there is designed?

Thanks for the lessons professor :)

[jawn101]

...Part of that question is related to whether there is a proper installed direction for the oil filler cap? Not where it sits in the hole of course, but whether it matters which tube you have on which end?

This much of your question is an easy one, the tubes are two completely different sizes :) And I'm also pretty darn sure there's no valving inside the cap at all. The one off the Premier motor is just a totally void space inside and I doubt the one for the D will be any different, except for the goopy, nasty filter media.

As for the rest of your questions... I dunno :)

I did notice the inside of the Premier cap was caked with oil residue which I cleaned out. It obviously served the same function as the D's cap, collecting and condensing vapors back into the motor.

[Dangermouse]

Goopy?

Mine just looks like a ball of black wire string.

[jawn101]

Goopy?

Mine just looks like a ball of black wire string.

That's a good description of the media itself, but it's all coated in a film of oil.

[DMC5180]

Jonathan,

Without getting into Professorial detail, The Internal combustion engine is a big Air pump that requires a fuel/air combustion process to keep it moving.

As the piston moves down during the intake stroke, it creates a LOW pressure condition which draws in (atmospheric pressure) based on the differential of HIGH to LOW. Within the intake system there is a Throttle plate that causes a measured restriction in airflow. Upstream of the throttle is the Filtered Intake or air inlet. Downstream of the plates is the Upper deck (manifold pressure side). When the pressure is LOWER on the Manifold side of the throttle plates it creates a vacuum that can be utilized for auxiliary purposes ( all vacuum ports) are downstream of the plates. When the throttle plates are closed you are at maximum differential, creating strong vacuum. Engine RPM plays into this too. Think high RPM deceleration. Attached too the manifold side of the intake is the emissions system, evaporative fuel vapor and Crankcase vent (Blow by recirculation) and a vacuum tank storage system with a CHECK VALVE too smooth out the transitional process between open throttle and closed.

Note: back in the OLD days before the invention of electric windshield wipers, they were vacuum powered. I always thought it was funny when driving my Uncles 1936 Dodge pick-up to a car show and having to drive through rain showers during the trip. Because there was no storage tank system to draw from, when you step on the gas pedal to accelerate or climb a hill and the one arm wiper stops moving due to loss of vacuum (throttle plates open). let off the gas to coast and it's back in action.

[Ron]

Jonathan,
First, yes the air filter housing is what is called the breather.

You have the direction of flow wrong. While the engine is running, the cold start tube is under vacuum from the intake manifold, created by the pistons on their downward stroke (exhaust valve shut, intake valve open...its port is connected to the intake manifold..). Also connected to cold start tube is the cold start valve (figures huh? nothing goes through it but fuel), a line from the charcoal canister, and a line from the oil filler cap (which also has a line to the breather, another source of vacuum. I'll get to that in a second). If the throttle plates are closed, crankcase vapors (simply combustion that gets past the piston rings, or blow-by) will flow to the filler cap, to the line going to the cold start tube, to the intake manifold (just like fuel when cranking cold) and burnt. Meanwhile vapors in the charcoal canister are being held. When the throttle plates are opened, a vacuum line connected to a valve in the charcoal canister opens, allowing them flow to the cold start tube, to the intake manifold and be burnt (higher RPM makes for cleaner emissions). [If you are wondering why the signal line didn't have vacuum on it, it is because it picks vacuum up on the other side of the throttle plates (ie upstream of the air flow)]. Here is where the other vacuum source at the oil filler cap comes in (relies on what Dennis posted, which should make all of this much clearer.) When you open the plates, blow-by at the filler cap will flow through the line going to the breather instead because it will have more vacuum than the line going to the cold start tube (Technically- It can handle more volume because of its size...it could go both ways...and the vacuum isn't necessarily greater, but almost always is when off idle...and a bunch of crap you don't want to know LOL).

[Ron]

Note: back in the OLD days before the invention of electric windshield wipers, they were vacuum powered. I always thought it was funny when driving my Uncles 1936 Dodge pick-up to a car show and having to drive through rain showers during the trip. Because there was no storage tank system to draw from, when you step on the gas pedal to accelerate or climb a hill and the one arm wiper stops moving due to loss of vacuum (throttle plates open). let off the gas to coast and it's back in action.
First, good explanation!

I've seen that before but it wasn't THAT long ago, on a school bus. It is weird. You probably remember Ford was plagued in the late 70s-80s with the AC and defrost dropping out when they took a load like climbing a steep hill (due to using vacuum activated/powered actuators) too?

[Jonathan]

Hey, cool guys! Thanks to both Ron and Dennis. I recall taking a combustion engines course in 4th year, but one of the lecture hours was bright and early on Friday morning and I'm thinking I might have missed a few too many of those time slots by hitting the snooze button, lol. I think I still have the text book lying around and I might just browse through it! :)

So... with the mention of the high RPM deceleration... would this tie in in some way to how the brake booster functions? I know it's not along the lines of an engine brake you might see on a big rig or something, but stronger vacuum if being utilized in the braking system may make it more effective at higher RPMs? Does that make sense?

[jawn101]

Wow, this has turned into a very informative thread.

Just a note on the premier cap, I just put on about 80 miles and didn't notice any difference, despite the much tighter seal. I do want to check out my dipstick though now, the seal around the actual stick has never seated into the tube, at all. Is the seal movable on the stick or is it fixed?

[Dangermouse]

Wow, this has turned into a very informative thread. ?

Hasn't it just!

I need to re-read it tomorrow with a diagram ;).

[Ron]

It's in the manual, but broken into two diagrams.....

[Dangermouse]

I had a hard time finding a proper O-ring even at my local Ace hardware store which has lots of oddball stuff around. In the end I got one from John Hervey piggybacked onto another parts order. I though perhaps I had a vacuum leak there with an ill-fitting O-ring, but I didn't notice any change in running when I got one that sealed better. Go figure.

Farrar, you don't happen to know the size you got that worked?

[Horsebox]

Farrar, you don't happen to know the size you got that worked?

Sorry for the epic thread resurrection.

I've just installed a 41mm ID 5mm thickness o-ring I ordered online from Simply Bearings in the UK I'm sure there is an equivalent in the US. They work out to be pence each if you order a bag full.

It's a much better seal than my old one, which had gone hard, but could possibly be improved if you can find 6mm thickness with the same ID. I think 5mm is far more common though.

[Rich]

That's exactly why I hate the OEM one, but we haven't had much luck finding O rings that fit it! They are a weird, huge size.

The vendors seem to have them. I recently replaced my original with one from Grady - now the original cap sits tight enough that it stays in place. Didn't expect any other changes, just a proper look and fit. The old o-ring wasn't tight like it used to be and it had a crack in it.

Nice that you got a better-looking Premier cap that does what you want, Jon. Creative, that.

[abiberacher]

Hi guys,
back in 2015 I had the same thoughts about my loose oil filler cap. Fortunately, I still had the opportunity to be supported by a large o-ring supplier who has sampled several possible sizes. At my Delorean it turned out that the perfect size is 43x5.5mm. The oil filler cap now fits perfectly. Very tight, as it should be.

[ed uding]

http://www.delorean.eu/catalog/advanced_search_result.php?keywords=102416&search_in_description=1&x=0&y=0

We have a good stock of the filler O ring.
Regards Ed
www.delorean.eu