Blowby

[JohnGunn]

Second Thought

After submitting my last message, it occurred to me that I don't really understand the connection between piston ring blowby and the presence of oil in the carburetor intake.

Is it that the air pressure in the engine sump increases and this causes more air to be pushed through the PCV valve into the carburetor intake?

But that is just air. How does that air come to carry so much oil? Or does this air carry the regular amount of oil, but there is so much more of it?

John Gunn
Coronado, CA

[Mike McKown]

After submitting my last message, it occurred to me that I don't really understand the connection between piston ring blowby and the presence of oil in the carburetor intake.

Is it that the air pressure in the engine sump increases and this causes more air to be pushed through the PCV valve into the carburetor intake?

But that is just air. How does that air come to carry so much oil? Or does this air carry the regular amount of oil, but there is so much more of it?

John Gunn
Coronado, CA

You're close. It's a pressure build up. The oil laden air though is not forced through the pcv valve, it's forced through the open fresh air breather hose and into the air intake to the engine. The air flow is supposed to be the other direction. Some of it will run back down the plastic duct to the air cleaner in a FI engine.

With good compression sealing, the pcv system should maintain a negative pressure on the crankcase during normal operation. Maybe 2-5 inches vacuum.

That's why engines that have a lot of blowby also have a lot of oil leaks. The crankcase pressure is pushing the oil right past the seals and gaskets.

[getnpsi]

How many miles on this engine? Depending on this answer will determine the steps I would take. 200k? You should cut your losses and b6 that lil guy.

resuwrecked - I was not stating that MMO will fix anything that needs to be replaced. Since I've only owned one new car in my life I've been dealt some ugly hands and carby cars when neglected get crudded up so more readily than their FI counterparts. With unknown history a compression test should be done for sure, and a good cleaning w/o R&R or disassembly should be considered.

[resuwrecked]

I apologize I didn't intend to come off as harsh. One way or another I'd put money on crappy compression #'s, be it from worn rings or stuck rings. Since the car is driven daily and all I'd say the chances of the rings being frozen are slim, and adding mmo might not do anything if they are stuck so bad that daily driving is not enough to free them. Sure its worth a try I guess. Either dump atf or mmo down the spark plug holes and let it sit overnight to soak the rings good if you like. ***IF you do this, CRANK THE ENGINE WITH THE PLUGS OUT to clear the oil from the cylinders!***
So, from here my advise for the quickest and easiest most direct route to repair of the problem would be to get another engine. Or another case of oil and a catch can :toothy10:

[JohnGunn]

You're close. It's a pressure build up. The oil laden air though is not forced through the pcv valve, it's forced through the open fresh air breather hose and into the air intake to the engine. The air flow is supposed to be the other direction. Some of it will run back down the plastic duct to the air cleaner in a FI engine.

With good compression sealing, the pcv system should maintain a negative pressure on the crankcase during normal operation. Maybe 2-5 inches vacuum.

That's why engines that have a lot of blowby also have a lot of oil leaks. The crankcase pressure is pushing the oil right past the seals and gaskets.

Thanks, Mike. This was very helpful. Since I have never dealt with a carbureted Festiva, it was difficult for me to visualize the flow of crankcase gases through the engine. Relating it to the fuel injection layout of my Festiva, makes it much clearer to me.

Based on this clearer understanding I have gone back and reread the thread and have some observations that are more likely to be of interest.

Before going on, it may be helpful if I describe the following picture from a carburated car, said to be a 76 350 Chevy, with a PCV valve installed.



This picture shows both the intake and output ends of the crankcase ventilation system. Inside the air filter you can see the breather through which air is drawn out of the crankcase through the PCV valve and into the carburator intake, while the hose going into the side of the air cleaner, under less vacuum pressure, allows outside air to be drawn into the crankcase.

Knowing this I would want to study very carefully which of these two ends is providing the input of most of the oil in the air cleaner. If the excess oil is coming from the hose connected outside the air filter, that is a clear indication of excessive blow by. If the oil seems to be entering from the PCV valve, that might be influenced by blow by, but blow by that the system was still able to accommodate without being overwhelmed.

This will be helpful when it comes time to evaluate the efficacy of the envalve you have ordered. With or without the envalve the ventilation will remain a closed system. That means no crankcase gases are discharged directly into the air. In that case, it would seem that the envalve would make little difference in the amount of blow by and the subsequent amount of oil found in the air cleaner. The only thing the envalve would accomplish would be to allow more air to flow through the PCV valve and thereby make most of the oil show up as coming from the PCV valve into the hose connected to the breather located inside the air filter.

I agree with resuwrecked when he says, "the quickest and easiest most direct route to repair of the problem would be to get another engine." But I also sympathize with your reluctance to do that before the car has had a chance to prove itself to you. I think I would also want to try and get the car stabilized for a period of time before deciding to spend more money and time on a car that has yet to prove itself.

Therefore, I would want to follow resuwrecked's suggestion on unsticking possibly stuck rings. I would experiment with different weights of oil, the timing of the engine (having it slightly retarded might reduce the pressure build up in the combustion chamber, and adjust my driving habits to lower blowby be treading lightly on the accelerator ( no heavy acceleration). I would also suggest that you make sure the hoses from the PCV valve, and between the valve cover and the carburetor are completely clean and open. I would want to remove the oil filler cap and place the palm of my hand over it to get a feeling for the pressures existing within the crankcase. For example, do you feel one strong pulse or are all pulses about the same, etc.

We both know none of this is likely to produce complete satisfaction, but once you fully understand what the problem is and can reduce it to a minimum, you can start driving it as you continue to evaluate what it will take to make it run to your satisfaction. What you spend on extra oil and air cleaners will be a small price to pay to have that clearly established in your mind.

This is what I would want to do.

John Gunn
Coronado, CA

[Mike McKown]

Thanks, Mike. This was very helpful. Since I have never dealt with a carbureted Festiva, it was difficult for me to visualize the flow of crankcase gases through the engine. Relating it to the fuel injection layout of my Festiva, makes it much clearer to me.

Based on this clearer understanding I have gone back and reread the thread and have some observations that are more likely to be of interest.

Before going on, it may be helpful if I describe the following picture from a carburated car, said to be a 76 350 Chevy, with a PCV valve installed.



This picture shows both the intake and output ends of the crankcase ventilation system. Inside the air filter you can see the breather through which air is drawn out of the crankcase through the PCV valve and into the carburator intake, while the hose going into the side of the air cleaner, under less vacuum pressure, allows outside air to be drawn into the crankcase.

Knowing this I would want to study very carefully which of these two ends is providing the input of most of the oil in the air cleaner. If the excess oil is coming from the hose connected outside the air filter, that is a clear indication of excessive blow by. If the oil seems to be entering from the PCV valve, that might be influenced by blow by, but blow by that the system was still able to accommodate without being overwhelmed.

This will be helpful when it comes time to evaluate the efficacy of the envalve you have ordered. With or without the envalve the ventilation will remain a closed system. That means no crankcase gases are discharged directly into the air. In that case, it would seem that the envalve would make little difference in the amount of blow by and the subsequent amount of oil found in the air cleaner. The only thing the envalve would accomplish would be to allow more air to flow through the PCV valve and thereby make most of the oil show up as coming from the PCV valve into the hose connected to the breather located inside the air filter.

I agree with resuwrecked when he says, "the quickest and easiest most direct route to repair of the problem would be to get another engine." But I also sympathize with your reluctance to do that before the car has had a chance to prove itself to you. I think I would also want to try and get the car stabilized for a period of time before deciding to spend more money and time on a car that has yet to prove itself.

Therefore, I would want to follow resuwrecked's suggestion on unsticking possibly stuck rings. I would experiment with different weights of oil, the timing of the engine (having it slightly retarded might reduce the pressure build up in the combustion chamber, and adjust my driving habits to lower blowby be treading lightly on the accelerator ( no heavy acceleration). I would also suggest that you make sure the hoses from the PCV valve, and between the valve cover and the carburetor are completely clean and open. I would want to remove the oil filler cap and place the palm of my hand over it to get a feeling for the pressures existing within the crankcase. For example, do you feel one strong pulse or are all pulses about the same, etc.

We both know none of this is likely to produce complete satisfaction, but once you fully understand what the problem is and can reduce it to a minimum, you can start driving it as you continue to evaluate what it will take to make it run to your satisfaction. What you spend on extra oil and air cleaners will be a small price to pay to have that clearly established in your mind.

This is what I would want to do.

John Gunn
Coronado, CA

First, what is an "envalve"?

The pcv valve in normal operation pulls crankcase vapors through a built-in baffle in the valve cover. It's a series of half open "gates", covered by a tin plate. If those baffles get plugged with sludge, then the pcv cannot evacuate crankcase pressure and vapors. In that event, all the blowby pressure will exit through the oil fill cap or through the engine gaskets and seals. If you remove the oil fill cap at engine idle speed and the engine is puffing oil vapors through the opening, you likely have too much blowby for the pcv system to control and/or a stopped up baffle in the valve cover.

One of my cars has an engine like this so I can relate to the symptoms here very well. I changed pcv valves. I tried the catch can, I tried the thicker oil, even used motor honey. None of that helped. I moved the timing back a little. That helped a little. The biggest thing that helped was cleaning the baffles in the valve cover so the pcv could do the job it was designed to do.

I've used MMO in a variety of uses. It's a very good solvent and cleaner. I don't see where it will hurt to try a quart of it at all. It may do some good.

The bottom line here though is the engine is probably on it's last legs and sooner or later, it'll be time to pay the piper.

[CaptHowdy]

We happened to find one right down the road from my parents' house. Motor is being swapped as we speak. Hopefully things go alright *crossed fingers*

[resuwrecked]

Awesome. Hang on to your old engine, You can rebuild it and keep it as a backup.

[CaptHowdy]

LOL, I ended up scrapping the entire junker car and motor. Got back 1/3 of what I paid for my entire Festiva. There is no blowby with the current motor. So, I guess the rings/pistons are sealing properly.

[odiekokee]

I'm in the same shape. Have a good lead on a $250 car with a bad body but "good" engine, with carb removed and sold already. trouble is it's 1000 miles away. I don't know anything about rebuilding engines, what it should cost or if my engine is worth building. We have basicly no festivas in yards here, they've all been crushed. Any suggestions?

[jawbraeka]

Did you? I think you should put 1-2 degrees in it.

That's why the whole process was Mentally challenged/challenging..

[odiekokee]

Whoa. Zombie thread. My festy is gone now....new owner who put some abomination of an engine in er, and i don't know anything else about it in a couple years.