Dirty Oil- PCV Fail?

[SofaKing]

I drained the engine oil and collected a sample of strange looking, non-magnetic, black particulate matter from the drain plug. I drove the truck 12 miles and drained a sample of oil and it was black. I drained it again and drove it 6 miles and it was very dark. I have not driven it since the 4th refill due to time.

I have a 1936, 21 stud engine and driveline from a humpbackcar. It was assembled 2 years ago, has less than 5000 miles. It was thoroughly cleaned by machine and with bore brushes by me prior to assembly. It is stock with the exception of a pcv system. No oil filter. I am using 10W40 Castrol. My first suspicion for the source of the particulates is the clutch housing through the labyrinth rear seal due to the pcv. My pcv system has 15” hg steady vacuum available at idle from a 1” spacer under the carb. The pcv valve is located at the front of themanifold. The oil pan road draft is blocked-off. I put a vac/press gauge into the manifold pcv valve port and the crankcase pressure is ambient, abrupt throttle changes don’t cause the needle to move.

I checked, primitively, the clutch housing airflow with a3/16” wide strip of paper. The result isthat the paper, if held ¼” away from the top vent, oscillates to and away from the vent. Get it slightly closer and itis drawn into the vent suggesting a slight low pressure area inside the clutch housing. I did not plug the drain holeon the bottom or attempt to seal anything, it is in as-driven condition.

I have blocked off my pcv system and will drive it a whileto see if it makes any difference. I amnot real happy about this since the draft tube is blocked but will only be fora few months.
I mention this because it may be useful info to others considering a similar pcv set-up and I am looking for suggestions for otherpossible sources of the oil contamination, or testing methods. This is my first flathead so I have no basis for comparison.

The pictures show the concentrated particulates, dirty oilafter 6 miles, and the paper sticking to the clutch housing vent.

[alanwoodieman]

do you still have the breather on the rear of the manifold? If the previous owner used a non detergent oil, now you are using a detergent oil the results are you are removing sludge that has accumulated in the hidden areas of the engine

[SofaKing]

Yes to breather. Not sure what hidden areas you are referring to, I ran bore brushes through every oil passage I could access. Did not notice on earlier oil changes but longer interval this time.

[51 MERC-CT]

The PCV system will indeed produce a vacuum in the crankcase.
That is why all vents to the crankcase should be filtered.
It's hard to believe that so much dust could be drawn into the crankcase from the clutch housing in such a short period of running and is there an air path source that should not be there.
Perhaps running without the vacuum will verify it one way or another.

[SofaKing]

Originally Posted by 51 MERC-CT

The PCV system will indeed produce a vacuum in the crankcase.
That is why all vents to the crankcase should be filtered.
It's hard to believe that so much dust could be drawn into the crankcase from the clutch housing in such a short period of running and is there an air path source that should not be there.
Perhaps running without the vacuum will verify it one way or another.

I think the oil got very dirty on the second and third oil changes, 12 and 6 miles respectively, because of residual contamination that did not drain from the initial oil change. I plan to purge the system a couple more times in the next few dozen miles just to be sure.


It is certainly preferable that all air sources are filtered however I don't see how that is practical with the 21 stud rear main design.


When I tore this engine down it was full of sludge but that sludge did not appear to have particulates. I remember it being very smooth and a bit waxy like grease.


The pcv valve is located about 12" forward of the rear vent scoop atop the fuel pump stand. Unless the clutch housing is actually pushing air into the crankcase through the rear main, it seems like the pcv would simply draw air from the vent scoop across the lifter plenum and back out; rather than trying to draw it through the clutch housing, through the rear main and up through the oil drain holes into the lifter plenum and out. We are talking about a 3/16" ID tube. That's like a drinking straw compared to the engine interior volume which has a 2" hole inches away and the rear main just a bit farther.


It is simply not what I would expect. But if I had the answer I wouldn't be asking for opinions or attempting to test it myself.


The alternate air source is an interesting idea as well, wonder how I could check for that? Being in an "as-designed" configuration, except for the pcv and draft tube, hard for me to imagine the causes.

[JSeery]

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I would not be running a PCV setup on an engine that does not have a rear main seal. You are just pulling dirty air into the internal parts of the engine. Seems to be that is much worse than no PCV at all!

Another question would be what temperature is the engine running at?

[Ggmac]

I wouldn't run a Pcv either .

[51 MERC-CT]

Originally Posted by SofaKing

It is certainly preferable that all air sources are filtered however I don't see how that is practical with the 21 stud rear main design.

Assuming that you do have a rear seal installed.
The pump stand filler cap/filter is where the air is (should be) drawn into the engine.
Although my system is on an 8BA the principals are the same.
This is a water column check for crankcase vacuum.

[JSeery]

51 merc, I think the issue is it does not have a rear seal, it is totally open air movement wise.

[Mike in AZ]

I didn’t know pcv system used vacuum. From valve to air cleaner where the gases were sucked thru carb along with regular air. The pressure from the crankcase opened the valve allowing the gases to go to air cleaner. Mike

[flatjack9]

No,, the vacuum from the intake induces the flow.

[SofaKing]

JSeery- I am not running thermostats so temps depend somewhat on the seasons. Seems to be 160-190 range.

Low temps may exacerbate the issue but probably not causal.

With engine being open at top and bottom seems like I have a choice between drawing clutch dust into crankcase to oil vapor into clutch housing.

[34PKUP]

Originally Posted by SofaKing

JSeery-

With engine being open at top and bottom seems like I have a choice between drawing clutch dust into crankcase to oil vapor into clutch housing.

Just wondering what exactly are these mysterious openings you are talking about?

[JSeery]

Nothing mysterious, early Ford V8s do not use a seal like latet models. They use a slinger system to keep the oil from running out around the crankshaft, but air can freely around the slingers.

[JSeery]

Originally Posted by SofaKing

JSeery- I am not running thermostats so temps depend somewhat on the seasons. Seems to be 160-190 range.

Low temps may exacerbate the issue but probably not causal.

With engine being open at top and bottom seems like I have a choice between drawing clutch dust into crankcase to oil vapor into clutch housing.

The lack of thermostats may be contribuating to the sludge buildup.

Most early V8 do not have PCV (and none should IMO) and do not have a big issue with oil getting on the clutch. Would guess there is something going on. Dirt being grawn into the engine would be a much bigger deal to me than oil vapor.

[SofaKing]

I am compelled to agree that putting a pcv appears to have been a bad idea. As I mentioned above, it is one of the reasons I posted photos, as a warning to others. I argued in other threads why it seemed to be acceptable. I was mistaken. Too bad because it really worked for keeping fumes out of the cab. I was considering a method of drawing fumes out of the clutch housing but that would entail oil vapors from crankcase transiting the rear seal and clutch, not great. It appears that the road draft will do exactly the same as the pcv, just less efficiently, draw dirt from the clutch into the crankcase. In short, the fix is a different engine. I can mitigate with frequent oil changes. I am still open to ideas but I am all out of them.

Regarding thermostats, if I put them in I lose my temp gauge until they open. It is a quirk of my installation. The 59a has the temp fitting in the middle of the head so the gauge tube is too short to plug into the water pump on the 21 stud. It is just long enough to go straight into the upper left radiator return line where I put it. Sure I could add a modern gauge but I bought an old truck to drive an old truck with old truck equipment.

[34PKUP]

Originally Posted by JSeery

Nothing mysterious, early Ford V8s do not use a seal like latet models. They use a slinger system to keep the oil from running out around the crankshaft, but air can freely around the slingers.

Got it. And a perfect reason not to install a PCV system on the early engine.

[JSeery]

The road draft tube type of arrangement does not really create much of a vacuum inside the engine. It is intended to provide a release point for the internal pressure build up and create an air flow from the inlet on top of the engine to the outlet at the road draft outlet. This obvious involves a lower pressure at the draft outlet compared to the inlet, but much less than a PCV system.

[Ggmac]

It's generally accepted that as much air moves thru the bottom of the engine as it does thu the top ( nearly as much ) so the crankcase has a lot of air being moved , the draft tube is a ford fix for dealing with the fumes and build up of pressure ( very low but still more than atmosphere but high volume )

[SofaKing]

I took my truck out for a 3 hour cruise after disconnecting the pcv. Decidedly unpleasant fumes in the cab. After brief consideration of my lungs and the absence of joy commuting in that malodorous interior, I have decided the engine is going to take one for the team. I am reconnecting the pcv, screw that schmutz. Oil is easier to change than either lungs or my disposition.