PCV / Oil Catch Can Trouble

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ApexArbitrage
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PCV / Oil Catch Can Trouble

Post by ApexArbitrage » Mon May 06, 2019 5:09 pm

Hoping someone here can help me out. I did search the forums and wasn't able to find my exact issue. Really appreciate the help!

When I bought my Datsun a few months ago it had an oil catch can that was sitting between the engine and the intake/air filter, per the below picture:
IMC-47.jpg

I noticed that some oil would pool beneath the air filter. After I had the valves adjusted which made the engine run better I found more oil pooled there after driving the car for a short while.
Note: I don't actually know if this was a coincidence or not, just saying in case there is a possible connection. It's also possible the old catch can just got full.

My mechanic suggested that we install a bigger catch can with a breather and not route it to the intake at all. We did that, per the below pic:
Image from iOS (4).jpg

This created two new problems - first the breather let out enough oil vapor to make the top-down riding experience less than pleasant and second I drained almost 3/4 of the 750ml tank after about a 10mi drive (never going over 6k RPM). The oil that came out of the catch can was black, but the engine dipstick still shows a normal level of clear oil. Pics:
57878987734__D0C1B2FD-D896-447D-8FB9-0EA0D8421BAF.JPG
Image from iOS (5).jpg

So... Should I just go back to the original setup and deal with some oil accumulating below the air filter, or is that a recipe for disaster down the line because dirty oil is going back into the engine?
Is there a better breather oil catch tank I should use? Or something like this Mishimoto?
Some way to prevent the oil from draining out of the air filter?
Lastly, is there a potential problem with the engine? It was rebuild by the previous owner and he was a very thorough and honest guy so this is not my base case.

Thank you for your help!
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nismou20
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Re: PCV / Oil Catch Can Trouble

Post by nismou20 » Mon May 06, 2019 5:32 pm

How many miles have you put on the car since purchasing? You’ll have to keep an eye on miles driven vs oil consumption rate to really know what’s going on. I had 3 out of 4 top compression rings broken on mine and burning thru oil like crazy. After a 30 mile drive my dipstick would be half low. But even then my catch can never filled like yours. Is it possible that maybe the PO filled the crankcase with excessive oil? Did you find that 3/4 full catch can of oil since you acquired the car? Try replenishing oil to top level mark, empty catch can and then start measuring your oil loss. Hate to think that you have that much blow by going on. Does car run good? Power? Your dipstick looks to be closer to half full too. If you notice your oil turning black very shortly after replacing it, that’s a good sign of carbon from blowby too. Fingers crossed!
Last edited by nismou20 on Mon May 06, 2019 5:35 pm, edited 1 time in total.

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Re: PCV / Oil Catch Can Trouble

Post by jrusso07 » Mon May 06, 2019 5:34 pm

Stock set up goes from cam cover to air filter assembly On my two SU cars there is never any oil in the filter housing or underneath it.

I believe (if memory serves) there is a sheet metal baffle in the cam cover to prevent oil from just spraying out through the vent. Have a look underneath the cam cover and see if it is and is present.

Other than that you might be getting oil blow by at the piston rings

I found a pic of the baffle on line
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ApexArbitrage
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Re: PCV / Oil Catch Can Trouble

Post by ApexArbitrage » Mon May 06, 2019 5:57 pm

nismou20 wrote:
Mon May 06, 2019 5:32 pm
How many miles have you put on the car since purchasing? Is it possible that maybe the PO filled the crankcase with excessive oil?
I've maybe put 50 miles on it, changed the oil right when I got it. Got a valve adjustment shortly after.
nismou20 wrote:
Mon May 06, 2019 5:32 pm
Did you find that 3/4 full catch can of oil since you acquired the car?
The original catch can was close to full, but replaced it so all that oil is just from 10 miles of driving.
nismou20 wrote:
Mon May 06, 2019 5:32 pm
Does car run good? Power?
Yup, no issues other than the excessive blowby and some minor oil leaks elsewhere that I knew about beforehand.
jrusso07 wrote:
Mon May 06, 2019 5:34 pm
I believe (if memory serves) there is a sheet metal baffle in the cam cover to prevent oil from just spraying out through the vent. Have a look underneath the cam cover and see if it is and is present.
Yup it's there. Nowhere near as much glues as that pic though.
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nismou20
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Re: PCV / Oil Catch Can Trouble

Post by nismou20 » Mon May 06, 2019 6:22 pm

I would venture to say while the dipstick oil looks to be clearish it is basically the same as what you caught in the catchcan. It’s darker than you think it to be. That is some blowby! Do you see blueish smoke out the rear on launch? My car ran great even with 3 broken rings! When you pull the plugs for inspection are the threads oily? Wet piston tops? All signs of blowby. Compression check in order? Your car car looks to be really nice from the pics. Hope I’m wrong.

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Re: PCV / Oil Catch Can Trouble

Post by Gregs672000 » Mon May 06, 2019 7:29 pm

Ya, I hate to say it but I too think something is wrong. I have a catch can on my motor that vents to a hose under the car and it's never even seen oil (it has a clear tube to monitor oil level inside the can, I've never drained it). You changed the oil... 7 quart pan or five quart? How the heck is it pumping that much oil out the valve cover?! Is the engine pushing out any seals, like the oil pan gasket, valve cover gasket etc that would suggest excessive internal pressure? It has to be DUMPING oil into that tube. There's not even a vacuum drawing on that catch can now to suck anything out, let alone oil. Only thing I can think of is over full on oil, or something major broke as discussed (rings) that is pressurizing the block.
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Re: PCV / Oil Catch Can Trouble

Post by C.Costine » Tue May 07, 2019 5:49 am

I agree that you need a compression check as it is obvious that your crankcase is getting way over-pressurized. It could be a problem with the rings, but it could also be valve seals. Do you have receipts for the work done by PO? If the valves were done there should be a receipt from the machine shop. The PO's "rebuild" should have also included a refresh of the block, including magna fluxing for cracks, crank polish cylinder hone at least, but most likely a bore job, and decking. Since our roadsters tend to blow head gaskets, sometimes all that the head gets is a resurfacing and gasket, but the replacement seals in the kit don't get used.
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Re: PCV / Oil Catch Can Trouble

Post by nissantoy » Tue May 07, 2019 9:30 am

The first thing I would try is resealing the baffle inside of the valve cover, had the same problem when I first got my roadster. Scrape all the old sealer off and recoat with a good fipg.



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ApexArbitrage
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Re: PCV / Oil Catch Can Trouble

Post by ApexArbitrage » Tue May 07, 2019 1:14 pm

C.Costine wrote:
Tue May 07, 2019 5:49 am
I agree that you need a compression check as it is obvious that your crankcase is getting way over-pressurized. It could be a problem with the rings, but it could also be valve seals. Do you have receipts for the work done by PO?
Thanks! Looked through the papers that came with the car, only found receipts for the piston rings plus the compression test results over a period of a year. I will ask the PO about the valves. The last one from August 2017 was 130+ for every cylinder. Here's a link to the PDF if anyone would like to take a look. I guess I'll run another compression check and see if the values are off.
nissantoy wrote:
Tue May 07, 2019 9:30 am
The first thing I would try is resealing the baffle inside of the valve cover, had the same problem when I first got my roadster. Scrape all the old sealer off and recoat with a good fipg.
@nissantoy, I really hope you're right! I did notice that there was a lot less sealant than the picture that @jrusso07 sent...

Once again thanks to everyone for your help. I'm very new to the vintage car world, so appreciate you helping me out!
Max | Orange County, CA
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Re: PCV / Oil Catch Can Trouble

Post by Linda » Tue May 07, 2019 1:22 pm

Which sealant to use?
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ApexArbitrage
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Re: PCV / Oil Catch Can Trouble

Post by ApexArbitrage » Tue May 07, 2019 2:46 pm

Max | Orange County, CA
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2014 Porsche Cayman S "Fandral"
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Re: PCV / Oil Catch Can Trouble

Post by Gregs672000 » Tue May 07, 2019 3:00 pm

Numbers can vary when it comes to compression testers. Get a screw in with a long hose type, block the throttle open and hit it several times. I happened to have my manual out and remembered I had written down compression numbers post a stock rebuild, and compression after 500 miles was 150-155, solex cam. The compression now on the 11.7 to 1 compression motor is 205-210.
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Re: PCV / Oil Catch Can Trouble

Post by nismou20 » Tue May 07, 2019 3:15 pm

I’m hoping the PO had the cylinders honed proper. New rings on worn cylinders are usually a disaster. 130psi is really low. New oil should not turn black in 50 or less miles. Worn valve seals alone probably would not reflect such low numbers.
I just looked at your pdf and you have a big problem! 100 psi more with oil added? Are these numbers the PO gave you? Did he sell you this car knowingly?

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ApexArbitrage
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Re: PCV / Oil Catch Can Trouble

Post by ApexArbitrage » Wed May 08, 2019 10:29 am

nismou20 wrote:
Tue May 07, 2019 3:15 pm
I just looked at your pdf and you have a big problem! 100 psi more with oil added? Are these numbers the PO gave you? Did he sell you this car knowingly?
That first compression test on handwritten paper is from 2015, before the rebuild I assume. The final test is on the last page from 2017.
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Re: PCV / Oil Catch Can Trouble

Post by Gregs672000 » Wed May 08, 2019 11:23 am

Well, about now you're probably worried and wondering what you have and what you have gotten yourself into. I want to reassure you that whatever is wrong can be fixed. It is hard to know what was done to this engine regarding a rebuild, but we can guide you on what needs to be inspected and how, then you can make some decisions about what you want to do. We are here to support you and for you to enjoy your car. Sometimes that first requires some "bonding" time...
Greg Burrows
'67 2000 #588
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