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#1
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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. |
#2
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What oil do you run?
The PCV system is as mother GM installed it? No mods?
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frittering and wasting the hours in an off hand way.... 1969 GTO, 455ci, 230/236 Pontiac Dude's "Butcher Special" Comp hyd roller cam with Crower HIPPO solid roller lifters, Q-jet, Edelbrock P4B-QJ, Doug's headers, ported 6X-8 (97cc) heads, TKO600, 3.73 geared Eaton Tru-Trac 8.5", hydroboost, rear disc brakes......and my greatest mechanical feat....a new heater core. |
#3
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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. |
#4
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Why such a thick oil for a stock engine..I would just use 10w30
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#5
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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.
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#6
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following this...similar symptoms/issue
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Esquire '74 T/A 455 Y-code SD clone previously on Dawson's Creek: '74 T/A 400 '81 AMC SX/4 '69 FB 350 |
#7
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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.
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#8
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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. |
The Following User Says Thank You to Formulajones For This Useful Post: | ||
#9
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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. |
#10
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Would rings be the issue if she only blows when you hit it hard?
If its rings, then a minor top end rebuild is in order?
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Esquire '74 T/A 455 Y-code SD clone previously on Dawson's Creek: '74 T/A 400 '81 AMC SX/4 '69 FB 350 |
#11
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Like I said, typically when you have blowby with oil pushing up through the PCV and crank case vent, it's a ring sealing issue. Not always, but typically. A leak down will give you a better idea. If that's the case, it's really not a minor rebuild either. Short block will have to come apart. At a minimum a hone and re-ring will be needed and when I have them down that far it's steam rolls into just doing the whole engine and gets expensive quickly. If it has a bunch of miles I almost always find cylinders out of round, an overbore needed, new pistons.........you get the idea. |
#12
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Quote:
Rich |
#13
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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.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#14
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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?
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#15
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There is true dual and I have only observed it out the passenger tail pipe but it was there and then gone again. |
#16
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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.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! Last edited by steve25; 09-15-2023 at 07:35 AM. |
#17
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Quote:
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Yes, for sure. |
#18
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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. |
#19
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When I removed the old thermostat, I could open it manually but I guess that is not a real test. 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. Last edited by 79TA455; 09-15-2023 at 10:36 AM. |
#20
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The easy way is to drop the t-stat into a coffee mug or pot of boiling water.
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Greg Reid Palmetto, Georgia |
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