Blowby and PCV
 

I have a stock 400 equipped '76 Trans Am and as of late, I have noticed excessive blowby. If I pull the crank case breather tube off of the breather, you can see smoke coming out of it and checking the little crank case filter in the breather, it is oil soaked. I removed the PCV valve hose from the front of the carb and there is oil in it and appears to be entering the carb.

I checked all the spark plugs and they look good; slightly grey in color with no black or sticky tar.

I removed the PCV valve and shaking it, it rattles so I think that is normal?! The hose being used for the PCV valve to the carb is a heavy 3/8 line and is not collapsing.

The other thing I noticed is a slight bit of smoke, from time-to-time coming out of the right rear exhaust tail pipe but that is very infrequent and I only noticed a few days ago while it was at idle.

The oil is not milky (head gasket leak) or watery (wash down) and it is not too full either.

I have been reading post about excessive blowby and PCV but I want to start simple and maybe replace the PCV valve but I'm not sure if it is bad or not. I currently don't have access to do a pressure test on the cylinders.

Any help is greatly appreciated.

What oil do you run?
The PCV system is as mother GM installed it? No mods?

I have had the car 9 years and always ran Castrol GTX 10W40 and this year I was running Castrol GTX 20W50. I thought maybe it had to do with the oil choice too so I am going back to 10W40. The reason I say oil choice is because I have had the car 9 years and never had an issue until I used the different viscosity this year.

The PCV system is stock.

Why such a thick oil for a stock engine..I would just use 10w30

I actually meant 10W30 and also completely agree; I don't know what I was thinking when I bought the 20W50. I'm doing some other work on the car right now so maybe I will change the oil before driving it again and see if that changes things.

following this...similar symptoms/issue

I put everything back together today and changed the oil back to 10W30 but unfortunately, the weather is crap so I cannot get it out today. Hopefully Lee does not come until Saturday like they said, and tomorrow will be decent enough to get it our for a quick run.

I tend to think thinner oil wouldn't help that situation if you're having a blow by issue, which is kinda what it sounds like.

If it were mine I'd do a leak down test to at least get an idea how healthy it is inside and if you see an issue with the test, it'll give you an idea as to why you have oil pushing out of your PCV and crank case breather tube.

More times than not when I see that it's typically crank case issues, ring seal going away, etc....and a leak down will verify that.

Smoking out the tail pipe at idle when at normal engine temps is mainly due to failed valve stem O-rings.
If the motor every ran on the hot side band then sat through a winter then there done!
I also think that the use of products like Rislone drys out these O-rings.

One thing you can try which does work to help ring seal is adding a can of a product called Restore to the motor, but be sure to install a new oil filter at the same time.

I agree about the thinner oil and I'm just just being optimistic that this will solve the issue.

It is not really smoke but looks more like steam so I thought maybe a head gasket so that is why I checked the plugs. It has no smell and I have gone through a head gasket leak before on a different car; you can smell the coolant in the exhaust. The car has never overheated and always runs between 165 and 180. Your comment about the valve stem rings could be correct, unfortunately.

I have never added any aftermarket products to the oil in the 9 years since I purchased it and have done consistent oil changes.

I just did an oil change and have not run the car yet so maybe a can of Restore is a good idea; I would just have to remove a bit of oil. Before I do that though, I think I am just going to run it and see if anything changed. If not, The car will go up for winter soon anyway so I will try the can next year.

If your smelling coolant from the exh then hopefully it’s just a failed head gasket and not a cracked head.

If you have a true duel exh system then when you see the white smoke from coolant out the back I hope it’s only seen coming from one tailpipe.

Is this the case?

Just to clarify, I'm NOT smelling coolant from the exh.

There is true dual and I have only observed it out the passenger tail pipe but it was there and then gone again.

If it was the unmistakable smell of coolant getting into a cylinder and turning to steam due to some issue, then such a condition just does not fix themselves unless you have added a sealant type product to the cooling system.

I would rent or buy or have a shop preform a coolant
system pressure test to see what might be taking place.
You do not want a leak to get to the point of hydro locking a cylinder.

Also if you are getting coolant into a cylinder the valves and valve seats are getting pitted which makes for low compression and a downward spiral in performance.

Well, I think that goes without saying. None-the-less, I see no evidence of coolant entering the cylinder(s).

One thing I did notice, and that is why I decided to do a few things, was that the upper rad hose was empty, even after driving for an hour; the car never got hotter than 180. To be safe, I changed the thermostat and gasket. I have not had a chance to get it up to operating temp. yet (valve train hitting valve cover:rolleyes:) to see if that resolved the issue. With that said, lets say it did not resolve the issue, what would cause the thermostat not to open? Is it solely based on the temp. of the fluid or pressure as well? I would guess both.[/QUOTE]

Yes, for sure.

Its not coolant, he said he doesnt smell coolant, that was mentioned happening on a different car....

T-stats open based on temp, if it was stuck closed the engine would overheat pretty quick, if it stays at 180 it sounds like its working OK.

Blowby is most likely caused by worn rings, if the engine is all original with unknown history theres a good chance thats the cause if everything else like PCV is working ok. Best to do a compression test, you can rent a tester from most auto part stores if you dont have one.

As for the restore additive, it wont fix shot rings but may improve the blowby a little temporarily if its related to worn rings/cylinder walls. I used it in my first car when I was 16, a 1977 firebird forumla with the factory sbc engine, had higher miles & burned oil, we did a comp test & found a few cylinders low, so I tried the restore until a basic rebuild could be done the next year... it did improve the oil burn smoke quite a bit.

Maybe I will see if the parts store I am getting the valve cover gaskets from has a compression tester.

When I removed the old thermostat, I could open it manually but I guess that is not a real test. :D

I should get some Restore today too when I pick up the valve cover gaskets. Although, I don't find it burning oil, per se, as you can usually smell that too.

Yes your right, he was talking about a different car.

After watching this John Kasse video again and the part about exh system rust harming a motor I am really starting to question weather letting a motor in a vehicle sit unused with any type of exh bolted onto the heads, and for any longer of a time period that it takes for rust scale to form is a good idea.

The easy way is to drop the t-stat into a coffee mug or pot of boiling water.

Dropping the thermo into boiling water, I knew. :-)

I have the car back together and let it run for quite a while and it appears that I am still getting the blowby so I'm going to try Restore.

The upper radiator hose still has nothing in it and the car has a 160 degree thermostat. It is cool here though so going to go for a drive and see what transpires.

I also pulled the radiator cap off and let the car warm. Once is was warmish, I revved the engine to 2000rpm and the coolant did get sucked down so that would indicate no flow restriction.

I'm going to go for a quick run with some WOT and see how the car acts, then let it cool and check the plugs (I know, not a real test) and also check to see if the coolant is low. If there is a head gasket leak, the coolant should still go into the rad because if it was leaking that bad, the exhaust would fog all the time and I highly doubt the car would run, right!?

Ok, so I went for a quick drive and it ran just fine but no fluid in the upper rad hose still. Car is not running hot either. I'll check the rad fluid in the next couple of days too since I topped it up.

The carb is acting up too but that is another issue.

Ended up having a smoke screen behind me because I decided not to tighten the oil filter as tight as normal since they don't need to be that tight. I'll go back out in the next couple of days and check the plugs....and tighten that filter.