# engine blow by



## sst1226

Hi again, I also want to mention that the "check engine" light is always on. The mechanic checked the sensors and said they were fine. This prompted his response about the "blow by"


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## A#1

blow by is when the piston rings have lost their tolerance to seal the compression of the power stroke...thereby allowing enging oil via the oil pump to be pushed out on the power stroke...or even the exhaust stroke...hence having smoke from the tailpipe...usually blow by on the power stroke leaves oil residue in the intake filter pan...where your air breather filter is located...so if your experiencing one or both of these problems...piston rings are shot...and or cylinder bore has become slightly egg shaped...(out of true round)...due to normal wear of a vehicle having 200,000 miles on it


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## sst1226

Thank you A#1!! I will look into that.


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## Wrench97

Blow by is excessive crankcase pressure, many years ago before emission controls it would vent out of the road draft tube now a days it usually ends up in the air intake piping/air filter assembly from a hose connected to a valve cover or directly to the crank case in some cases. It can be caused by defective rings, piston, valve guides, or a blown head gasket in rare cases. If you have a MIL(Check Eng Light) illuminated a scan tool will give you a code or codes if the light is there isn't any guessing involved if your mechanic can't give you a better explanation then what you got it's time for a new mechanic.


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## A#1

if you have an auto parts store nearby that has loan a tool with deposit...get a compression gauge...it has an adapter with threads like a spark plug... disable the distributor my removing the coil wire...you will remove each plug one at a time...screw the attachment into the spark plug hole and crank the engine a few times...there is a pressure gauge on the end of the compression check tool...this will show you the compression in each combustion chamber...check for specs for you engine...and you will find out if this is your problem...usually there is a set pressure with a built in +/- tolerance...and also standard deviation between combustion chambers...such as if an 8 cylinder...all are around 90 psi and one is 70 psi...the 70 psi would be out of standard deviation


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## bruiser

Since when does "blow by" set a malfunction code?


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## A#1

bruiser said:


> Since when does "blow by" set a malfunction code?


with the internal pressure of the engine allowing super heated gases to pass by worn piston rings...and possible past some type of computerized monitoring EPA standards...could be the sensor is alerting that polluted gasses are traveling where they are not supposed to...


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## Wrench97

A#1 said:


> with the internal pressure of the engine allowing super heated gases to pass by worn piston rings...and possible past some type of computerized monitoring EPA standards...could be the sensor is alerting that polluted gasses are traveling where they are not supposed to...


Well then there would be a code for it.


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## A#1

on the lighter side i have a 1993 GMC Safari Van...check engine light comes on and goes off at it's own desire...had a mechanic check it out with diagnostic equipment...couldn't find anything wrong...reset the code...within a week back to the light having a mind of it's own...the van has almost 200,000 miles on it...i change the oil at regular intervals...burns about 1 quart between oil changes...never fails to start...always runs w/o any problems...some mechanics will tell you anything just to rape you out of your money...i'd get a second opinion...as i mentioned before...with a local parts store loan-a-tool for a returnable deposit...loan out a code diagnostic check tool...


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## SABL

Years ago I did own a car that suffered "blow by" with no apparent effect. The car still ran rather well but the small white cloud emanating from under the hood was something that I really did not wish to see. The cause is generally worn compression rings or cylinder wear and most often occurs after a "valve job" in which the valves and seats are ground to provide a better seal in the "top end" of your engine. Like A#1 stated the biggest effect will show with a compression test....no real cause for alarm....your engine is just showing signs of wear. If it runs....drive it!! If it's so bad that you can't see where you are going...park it.


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## A#1

rite u are SABL...unless your wanting to unload some cash for a prob that's not worth what the cost are...if you start with the valves like SABL said...the next weakest link in holding compression will take the load...unless your a bonafide...shade tree mechanic...with a Phd in color'd injuneerin (no racial disrespect)...leave it be...taking it to a shop for the work...prolly cost more than the car is worth...


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## BEZ4

Hi every one I need a little bit of advice I have a dodge neon 96 76,000 miles and about 2 months ago it broke down on me I thought it was the timing belt because when I was driving it skipped to the next gear revved up then it just shut off all together so Im not all that grate with cars so that’s what I assumed it to be but when I went to the mechanic he told me that I needed a new engine I don’t believe that so I wanted to ask what are signs that your engine is about to blow? Someone told me knocking sounds. is that true? And what are any other signs


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## sst1226

Hey guys, I had the car fixed and the "light" is now off. It was the Mass Flow sensor. That is what they told me. They repalced it and now all the codes are gone. 

Thanks for all your input!!


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