Mountains Garage: Dealing With Crankcase Pressure!

Added: 2026-05-21

[00:00:09]Hello and welcome back Sean Hammond Mountain Garage on a warm Tuesday evening.

[00:00:17]It was I observed 97 degrees today. The humidity wasn't terrible.

[00:00:23]But who knows what tomorrow will bring.

[00:00:26]Tomorrow is going to be similar to today.

[00:00:28]And then the weather's going to go back to my kind of weather.

[00:00:32]Temperatures that start with a six or a seven.

[00:00:35]Makes me happy.

[00:00:37]Tonight I have been picking through this bucket of fittings. All fittings that weren't black.

[00:00:45]Buddy mine bought me.

[00:00:47]Sadly the remaining contents of a local speed shop, the fitting department. And uh I end up buying the all the fittings that weren't black. And I'm just sorting sorting them by sizes.

[00:01:00]And it's kind of fun. You never know what you're going to find.

[00:01:05]Or even how you're going to classify it and put it in bins. But I don't want to end up with a hundred bins with every different style. So basically just by size.

[00:01:15]Uh but tonight we're going to talk about uh crankcase ventilation.

[00:01:21]I went to the car show, local car show.

[00:01:24]Probably the biggest one we have all year last weekend.

[00:01:28]Weather was perfect. Uh record number of cars apparently.

[00:01:32]And as I'm walking around as usual um just observing things.

[00:01:37]The usual suspects uh wiring plumbing and in this case tonight we're going to talk about crankcase ventilation.

[00:01:47]And always got to start simple and work up.

[00:01:51]For a lot of years.

[00:01:53]Since cars were invented.

[00:01:56]Pretty much up into the late '60s.

[00:02:00]The crankcase pressure or vapor it occurs after combustion, certain amount gets past the rings on the piston and ends up in the crankcase.

[00:02:13]It's just going to happen, no matter how efficient or tight your engine is you're going to have some crankcase pressure. Then you have the bottom of the pistons which are sealed off going up and down acting like a pump.

[00:02:27]So it's going to be there and you have to do something with it. Well, for the first what 50 60 years, there was just a metal tube or a tube outside the engine hooking up on the top of the engine somewhere and dumping out on the ground.

[00:02:46]All the vapors just went into the atmosphere and nothing removed moisture from the oil, but that's all we knew.

[00:02:57]In a lot of ways some things never change, but in the late '60s um probably spurred by emissions. Now, people think this is where it gets uh odd and the thought process disrupted it's not all bad.

[00:03:24]So the PCV valve, positive crankcase ventilation I just stuck one in this valve cover right here.

[00:03:33]It is your friend. It's doing you no harm in the right circumstances. This uh example is you're going to street the engine most of the time, you're going to be idling, driving hours on end all that moisture is in your oil and nothing is going to remove it.

[00:03:53]A PCV valve will. Yes, you suck it back through the engine. The engine doesn't care. It is very small amounts over a long period of time.

[00:04:02]It's not hurting a thing. If anything, if there's a little oil mist in your intake air, that's probably a good thing.

[00:04:12]Obviously, if you have a severe engine problems, you're getting a lot of blow-by, that's different. But the PCV valve system completely misunderstood.

[00:04:22]Let's explain.

[00:04:23]In this scenario, in uh all times with high vacuum, that is idle, light cruise, cruise in general, anything but full throttle because you have all these pistons sucking air.

[00:04:41]And with the throttle blades closed, they can hardly get enough air, so it produces a vacuum. That's why a diesel engine with no throttle blade doesn't have any vacuum.

[00:04:54]The intake is just open and there's not there's no restriction.

[00:04:58]It's you know, putting your thumb over a whatever, something that's sucking, a straw or whatever.

[00:05:03]With it wide open, there's no you know, sucking. You get what I'm saying.

[00:05:09]>> [laughter] >> So, all the periods that you're not wide open throttle, the fresh air is entering through the breather.

[00:05:20]Again, I'm it's it is a breather, but in this case, it's breathing in.

[00:05:25]Fresh air in.

[00:05:27]That's why if you remember on my 377 small block, I went to the trouble doing like the factory did, I used a piece off a Corvette, but I hooked the valve cover to the as a big air cleaner, a 14-in air cleaner. I went underneath, so you're always drawing fresh air. This has a a filter in it, so you're still draw in fresh air, but it's if it happened to share the one with the engine, that's okay cuz most of the time fresh air is going in and it's getting sucked through the PCV valve because you have vacuum on it and it's going back through the engine.

[00:06:03]And your oil if you ever pulled your valve cover off after you just started your engine on a cool morning and didn't run it in half an hour going to burn all the oil out of the water out of the oil, you got a mess under there. Looks like Well, it looks like a baby's diaper. In situations where you're full throttle, obviously the PCV valve has no vacuum on it. It has a little valve and it's even going to close.

[00:06:28]And then you're going to get the vapors out the breather.

[00:06:33]If it took to the air cleaner, now you're going to suck it through this way, which is good.

[00:06:38]Again, a little oil vapor in the intake air is not going to hurt a thing.

[00:06:43]There's little or no downside and that will always be my opinion. I've seen engines both ways and that's the way I, you know, at least prefer to have mine.

[00:06:54]Now, on a race engine, let's talk about, for instance, I usually default to drag racing, but let's talk about circle track.

[00:07:06]They typically have a valve cover like this and if they're turning left, they put it on the left side cuz all the oil wants to go that way in the engine.

[00:07:15]It's naturally going to go up that way.

[00:07:17]And you might get it out the breathers on this side if you're turning left.

[00:07:23]Much less likely to put oil out here.

[00:07:26]Uh the tubes are baffled.

[00:07:30]And then you have a probably a pair of these breathers.

[00:07:34]Might even have a shield facing forward because you might have a lot of air coming through the grill and at speed you don't want to be, you know, causing a jet stream to suck the oil out for any reason.

[00:07:45]Uh depending on the condition of your engine, you may see rags wrapped around these as the engine gets a little looser, these might start putting oil out on the exhaust, ruining your race. So, a lot of times you'll see a rag wrapped around these, too. Again, depends on the shape of the engine, I guess.

[00:08:05]Drag racing, same thing. You pretty much with a dedicated drag car, you're going to drive through the staging lanes, and then you're going to spend most of your time, or at least half of your time, full throttle.

[00:08:18]You can run just [clears throat] breathers, but you can expect to mess up your valve covers quite a bit cuz you're at full throttle, that oily air has to go somewhere, and it's going to come out the bottom here.

[00:08:31]And again, often times you see a rag tied around it.

[00:08:34]Uh it was real popular, you don't see it as much anymore, but to put another early emissions piece, there was a one-way check valve in the exhaust for the air pump, but that one-way check valve was already ready to hook to exhaust, it's half-inch pipe.

[00:08:53]You'd weld a nipple into the header collector, put that one-way check valve in there, and you'd get a breather with a hose connection on it, and when your engine's at full song, you have a lot of exhaust, and you put the nipple this way, so the exhaust is going to pull on it, forming, I wouldn't really call it a vacuum, but a draw, and it'll draw your oily vapor, and just it'll get burnt in the exhaust. That was pretty popular for a long time, and that system still works just fine. If you watch drag racing at all, the latest trend you typically see a stove pipe coming out of the trunk, And when the car's like on the starting line spooling up or whatever, you'll see a pretty steady rush of air coming out of there.

[00:09:45]They plumb it all the way from the valve covers through tubes into the breather tank, and that's actual pressure from the engine pushing the air out, but the tank itself is going to collect any oil, most of it anyway, from ending up anywhere you don't want it. It ends up in the tank, and you have to drain the catch tank.

[00:10:08]Along the same lines, a lot of like turbo LS engines and stuff, they they people will buy a catch tank, little small one, route a hose from each valve cover into it, and the catch catch tank itself has a breather.

[00:10:27]And the vapors will find their way over there.

[00:10:31]Oil and some of the mess will get out of there. Nothing is going to clean your engine up. Again, this white residue from moisture in your oil is always going to be there unless you drive it a long time, which you can do. You can probably drive your oil clean.

[00:10:47]However, it's not the greatest situation, and lately, they're manufacturing these little catch cans with a PCV valve in the top of it, right back to where we started. That hooks to your vacuum, and just like this system works, majority of the time, your oil vapors are going back into the engine. So, you can't smell it cuz if you have a open breather under the hood, it smells like oil.

[00:11:14]Uh side bar for a minute, diesel trucks, over-the-road trucks and dump trucks, etc., up into the '90s still had a draft tube or road tube, like the cars did for the first 50 or 60 years.

[00:11:29]And that would come out by the bell housing, and every time we service the truck, the additive package in the oil had a distinct smell to it when it got warm.

[00:11:40]And we'd get a lot of complaints from the guys, "You must have changed the oil in my truck. It stinks again."

[00:11:46]And it would go away over time, but you know, that's how much venting it would do and it would drip on the ground, etc. Uh while we're talking about it, everybody as late as last night I was watching a video and this guy didn't know a whole lot about Harley Davidsons, but they always had a reputation for leaking and some of that's probably true, but did you know back in the day they took the crankcase pressure and vented it on top of the chain that connects the engine and transmission.

[00:12:18]So, that the oily air go in there to lubricate the chain and then it just dumped out on the ground. It was just That was the road draft tube. It just went through the primary case.

[00:12:28]So, every way you parked it, put it on the kickstand, oil ran out of it.

[00:12:32]And they got a bad reputation for leaking.

[00:12:34]The stuff was just doing its job. Now, we're working our way up the food chain, it became pretty popular in the early '80s, regardless of the oil system on your drag race engine, >> [clears throat] >> to put a vacuum pump on it. I remember seeing Warren Johnson's early attempts.

[00:12:51]He actually had an air pump off an emissions vehicle, you know, the little belt drive thing you used to see in the '80s.

[00:12:58]Well, they had a fitting on that and they would pull it out of one valve cover and I'm not sure they had figured out they needed to regulate how much they're sucking, so typically you have a regulator ingesting some air on the other side so you could adjust how much vacuum you're pulling on the engine, but the reason Warren Johnson was doing it, he wasn't worried about leaking oil on the ground necessarily, [clears throat] horsepower. When you take all that air and put it in a vacuum underneath the pistons, you just freed up some horsepower. So, didn't take long before everybody had a vacuum pump.

[00:13:33]And the positive side of note of that is when you put a vacuum pump on an engine, they don't leak anymore.

[00:13:42]Man, that thing is dry as a bone because you're sucking all that stuff out in anger and not just allowing the the vacuum of the engine to do it, you can adjust how much you have all the time. Pretty big hose, completely sealed. So, you're sucking on it other than the restrictor a regulator on the other side so you don't create too much pressure to suck your gaskets in.

[00:14:04]About 15 in is pretty good, maybe 20 at the most.

[00:14:09]And uh it'll really do some work.

[00:14:12]But it goes through the vacuum pump into a little tank with a breather on it and you have to empty that quite often, but that will remove Man, the water that comes out of that thing is pretty nasty looking. As the transition to dry sumps came along and I I reckon they I reckon I reckon they Chrysler Hemi was might have been one of the first to have an external oil pump. Not a multi-stage dry sump pump, but just a single oil pump. That's still pretty popular in some areas to have the pump external on the engine and combine that with a vacuum pump.

[00:14:48]That pump itself is not creating a vacuum to a point. So, they augment it with the vacuum pump I just talked about, but you have a multi-stage dry sump pump, you have one section that's sucking oil from the tank and pushing pressurized oil into the engine and the rest of them are sucking from different ports in the engine. You got two or three in the oil pan, you might put one in the lifter valley.

[00:15:12]You put one on your turbos and you're going to suck all that oil back, filter it, put it through the tank and then the pressure section of the dry sump pump, which is a multi-stage rig, three, four, five, six sections. You just bolt and keep adding sections to how much you want to do.

[00:15:32]And uh that kind of accomplishes both.

[00:15:34]That will draw our vacuum.

[00:15:36]And in most cases like that, you don't see a vacuum pump unless every last horsepower is necessary.

[00:15:43]It'd be pretty rare these days probably to find one. Not saying they don't exist. Back to the old car show, it was I got there early in the morning and pretty much the first thing people would do, they'd drive in, open the hood, get out a towel, and start wiping off the valve cover.

[00:15:59]Cuz they didn't see the genius in the $1.20 PCV valve, which is pretty much what they cost.

[00:16:08]If you can see this one, it has a 90° plastic nipple on it. That's a straight PCV valve with a little plastic adapter. If you want If I had longer hose, I just stuck a piece of hose on it that I had. Uh I could pop that plastic uh elbow off there and I could run the hose straight out of it and up to where my carburetor is. In this case, there's a convenient port.

[00:16:31]Uh I A lot of parts of the engine are functional and they're not necessarily beautiful. That isn't necessarily beautiful, but the function is. So, you won't see any of my street stuff having you know, run without it.

[00:16:49]That's just not going to happen. Even my race 55, uh I think the baffled catch can probably the best bet with the PCV valve sucking the stuff back into the engine. So, that's it for tonight.

[00:17:04]We covered most of it. If you got any comments, feel free to make them.

[00:17:08]And I'm going to go back to sorting fittings.

[00:17:12]Till next time. Take it easy.