Blow By

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anthony cox

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1965 Doge Dart has blow by from the oil filler cap and the PCV cap. I believe it's leaking oil from the oil filler cap. It's runs very good, I drove the car 30 miles at 70mph without any issues. Any suggestions on what this might be?

It was setting up for a few years before the oil was changed and the fuel system components replaced.

Thank you,
Anthony
 
Do you mean after this oil change it started, or is this bringing it back after many years off the road? Sometimes a thin oil on an older motor will cause you some problems. It might be some rust on the cylinder walls and it might work in some.
 
Check the PCV system. It is common for the PCV passage in the carb to get plugged up. If it is, just remove the carb, and clean the passage, through the tube, and up from the base (makes a 90* turn) with a 1/4 inch drill bit, by hand.
 
Well, my 65 Valiant wagon had bad blow by,it got so bad I had to keep the windows open and hook a vent hose from the oil fill cap to the air cleaner just to drive.The day before I pulled the motor to put in a known good one I had it on the interstate going 70 mph. She ran like a top. After I pulled it I tore it down to see what was causing it. Results : #1 cylinder has the top edge of the piston melted away and 2 broken rings , on 4 of the other cylinders I found broken rings as well. The thing just wore out ! She had 350,000 miles on her and still ran like a top with all this going on inside. This is how strong these things are ! You'll probably find similar stuff inside your motor if it has high miles as I suspect it does.
 
You shouldda seen my slanty idling with a hole in the side of the block and the broken rod doing the crazy dance.
that was not blow-by, but rather; blow out.
Edit:
were they tough?
Apparently not tough enough.
I've never windowed a SBM

A friend of mine at a bush-party, once bricked a 318 gaspedal at WOT . After 20 minutes of listening to that thing roar, somebody flipped the brick off. It stalled and would not restart. I bought the car for $50, and pulled the heads off. Hyup there was the evidence; the valves had hit the pistons and were bent.
A couple of hours later, with different heads, and she was back in action.
 
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My old slant in my 71 had such bad blow by, I couldn't keep the hose from the breather connected to the air cleaner. It would push so much oil into the air filter it would clog up. I finally ran a long hose from the breather down to a container by the frame rail. After a long drive on the highway I'd pour the oil from the container back into the engine and keep going!
 
340doc said:
My old slant in my 71 had such bad blow by, I couldn't keep the hose from the breather connected to the air cleaner. It would push so much oil into the air filter it would clog up. I finally ran a long hose from the breather down to a container by the frame rail. After a long drive on the highway I'd pour the oil from the container back into the engine and keep going!
Click to expand...
I was not as smart as you,lol. I ran the hose down below the oil pan and oiled the road. 4 quarts of oil to a tank of gas.
 
Rust on the cyl walls, that's an oil burning cause...the rust doesnt just wipe smooth...and if it rusted at the ring..there is now a groove the circumference of the cyl where it rested those years. The surface can leave small pits for blow by

Could have already had many miles on it to boot.
Burning oil under load/throttle. Rings
Burning oil only at start up, seal and guides.
 
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PCV on a 65 Dodge was just a mild vacuum source for the crankcase to promote a constant ventilation of oil vapor into the carb base to prevent sudge and moisture condensation. The oil filler was a slip fit cap with a brillow pad filter in it. I dont think a plugged or lack of PCV on a 65 would cause blowby control issues as its already vented to atmosphere through this large opening. Also the umbrella valve seals are probably long gone and are already in the oil pan as black plastic gravel.
 
It's not smoking out the exhaust because all that crankcase smoke that blow by is is making it's way past your rings and past your valve guides into the top of the head and also down into the crank case and coming up as the crankcase gets filled with the gas that's passing the rings and worn out pistons & cylinder walls . The motor is tired and worn out. This is how they die
 
My slant has had blow by the entire time I've had it. (3 years) I've put on about 15,000 miles in that time.
Your muffler is probably full of carbon which is why you're not seeing it too bad from there.
Mine also runs like a champ at 70 mph. I've tried everything under the sun, re seating the rings, adjusting everything again and again. I think the rings are just bad and I am gonna pull it later this summer and rebuild it.
 
Holy wow, and here I was worrying about the blow by in my 225... and it's nothing like what you guys are describing. Just some oil in the air cleaner after thousands of miles.

On another note, have you guys heard of the cap dance test? It's something diesel guys do to check for blow by. You loosen your oil filler cap and let it just sit there on the valve cover with the engine running. If the cap stays still, you don't have much blow by. If it dances around and or completely flies off the cover, you've got a lot of blow by.

Does this apply to gas cars too? My cap doesn't move at all, but I feel I still have blow by.
 
I'm currently driving a high blow by engine in my latest rescue car which has unknown mileage and sat for 8 years before the rescue. At 30-50mph doesn't use hardly any oil. Cruising from Tucson to Los Angeles, about 600 mi at 75-80mph, I used a quart of oil per tank of gas. After seeing the increased oil consumption I had a friend follow me on I-10 to check for tail pipe smoke figuring I must be putting out a cloud at highway speed even though I'd never seen one. Surprised when he said he only noticed a small puff of blue smoke when I'd lift up on the accelerator to slow down but none under acceleration. I've so far driven this motor about 40K mi. in this condition. Runs fine and idles smooth regardless. As others have suggested checking the maintenance items like the PCV is the best place to start. But if you have a high mileage oil burner just keep it full of oil and you'll be fine.
 
Keep in mind that it's not enough for the PCV system to be apparently intact and giving suction at the end of the valve when you test it with your thumb. It also has to be the correct PCV valve or you'll oil down the air filter (on a '64-up California/'68-up everywhere-else system where the breather's ducted to the air filter) or be driving in a permanent cloud of blowby (on a car without a ducted breather). See here for gory details.
 
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