In automobile talk what is blow back and what is the term's relation to the PCV Valve or Valve Cover Gasket?

Question

I have a 2000 Pontiac Grand Am SE. I went to get an oil change and I was about 2 quarts short on oil and the term "blow back" was used on my print out. I called up to the place and the technician said it could be a bad PCV Valve. The oil change before that, there was some oil under the top of my 2.4 Liter Quad 4 Engine. Some of the oil had gotten on my spark plugs and made 2 of the 4 bad. I had to replace the coil housing (which includes the 4 spark plugs). They told me that the valve cover gasket and one other gasket located under my timing chain was worn and needed to be replaced. I also have skipping when I idle and the engine is working harder to go uphill as if some of my plugs are shot again. It has never put me on the side of the road before and I keep it in the shop anytime I hear or feel anything irregular. I know the PCV Valve is cheap, but the other work we cost me some serious labor. Someone please enlighten me on this situation before I put any work into this car.

Answer 1

Some blow-by (see below for definitions) is normal on most engines, and (for the last 40 years of so) is taken care of by the PCV (positive crankcase ventilation) system. When the degree of blow-by is too great for the PCV system to handle, the mixture can foul the air cleaner and spark plugs. While the best fix is to repair the engine (ie, check and replace PCV parts (cheap), replace worn rings (expensive), etc), it is also possible to install a drain system (cheap) that will divert the blow-by emissions. This may allow you to put off doing the more expensive repairs until a better time -- or never.


Blowback or Blow-back: 1) Because of a sticky valve or the intake valve closing late, some of the air-fuel mixture is blown back through the carburetor.
2) The return, at low speeds, of some of the induced mixture through the carburetor of a gasoline engine; due to the late closing of the intake valve during compression, or by worn or sticking valves.
3) "blowback" is sometimes confused with the term "blow-by"
result: backfiring through the carburetor

Blowby or blow-by: The mixture of oil, fuel and air which is lost past the piston rings and causes fumes that form acid and sludge in the crankcase and smoking from the oil filer hole. Generally there is a loss of engine power. Most are removed through the PCV system.

Answer 2

OK-Time to set the record straight concerning Blow-by. ANY ENGINE, EVEN BRAND NEW, BROKE IN, OR WORN OUT HAS BLOW-BY.
The only engines I can possibly think of that don't have blow-by are the high-dollar racing engines.
Blow-by needs to be controlled for a couple reasons-the combustion chamber gases mix with the oil vapors from the crankshaft splashing around and form sulfuric acid., which eats away at the bearings.So it needs vented out, and since we can't vent to the atmosphere, it gets put into the intake manifold and burned via the Positive Crankcase Ventilation System.
If the blow by isn't vented, it will force the oily vapors, under pressure, out through the various seals and gaskets.
It sounds to me like there is oil getting into the spark plug wells, the tubes the spark plugs go into. And, yes, excessive blow by can cause that.
There are several things that can be done to help an engine that has blow by, if the rings and cylinders aren't completely shot. I've had good luck with the BG chemicals-the additives to clean the crankcase up. The oil control ring should actually rotate around the piston, and if the oil changes weren't done as they should have, the chemicals really help.
We also had a Toyota smoking so bad the fire department showed up, and used Restore in it. It quit smoking and the customer drives it-still not smoking-to this day.

Answer 3

The gas in the oil is caused by a failed diaphragm in the mechanical fuel pump mounted on the engine. Replace it and change the oil and filter. replace the paper fuel element located in the carburetor where the fuel line is attached. I also recommend adding an inline filter to the line going to the pump. Replace the pcv valve AND the grommet. The grommet will be hard as a rock by now and is probably leaking oil too. Replace the valve cover gaskets - as you said "they are leaking" - nuff said. If the idle problems persist there may be trash in the carb that got past the old paper filter in the carb. They didn't work very well. Gas in the oil will make it burn oil/smoke since it is thinned out.

Answer 4

Blow by is usually caused by oil getting past the rings causing oil use and a dirty exhaust pipe among other things.
It can be caused by high mileage, bad PCV valve, plugged cat converter just to start.
A good thing to do is when the engine is stone cold, run a compression check of each cylinder and compare numbers to specs. wide variances between cylinder readings will paint the picture for you...you want no more than a 5% variance.

Answer 5

Is called "blowby'' rings wear out let oil past them, oil goes out tail pipe. You may need an engine rebuild. BUT, before you do that get some stuff called " restore" at local parts store. This stuff may save you some hassles. PCV is usually found in valve cover. Replace vc gasket.

Answer 6

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X 2 on the bad fuel pump. Alcohol laced gasoline eats these pumps up. The Hone is likely coked as well. Buy a can of AC DELCO "Top Engine Cleaner" and follow directions on can. I'd bet the EGR valve/port is also coked with carbon.

Answer 7

Engine Blow Back

Answer 8

Worn piston rings can cause blow-by or blow back.

This is causing the engine case to become pressurized and blowing oil out of your PCV. I would first replace the PCV as it may be stuck.

Answer 9

I've heard of "blow-by" but not "blow back"

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