compression check -- hot or cold engine?
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compression check -- hot or cold engine?
I am checking my compression tonight to see if I can verify a blown head gasket. (see post on the FE board) In this case, it probably doesn't matter, since I am looking for 2 cylinders lower than the rest. But, should I check the compression after running the engine for a while, or when it is cold? I have been told to check compression, then squirt a little oil in the cylinder and check again to distinguish between leaks on the upper or lower end.
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compression check -- hot or cold engine?
Check it both ways. Take the cold readings and then take the warm readings. If there is no change in the readings on any cylinder then I would say that there is a blown head gasket. Warming up the motor allows the rings to swell, like all metals do when they are hot, to fill the cylinder better. But if you have a blown head gasket you will find water in your oil or oil in your water. I have never seen one that didnt. As far as oil in your cylinder then testing?? Let me know how it goes, I would think that would be the same as a warm test unless your rings are really gone.
72 F250 4DR SB
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Joined: Apr 2001
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compression check -- hot or cold engine?
Hi,
Be carefull if you put oil into the cylinder's when doing your tests, I have seen things break from the pistons in the cyliners going "hydraulic" due to the better sealing caused by the oil!
My two cents,
-Brents
Be carefull if you put oil into the cylinder's when doing your tests, I have seen things break from the pistons in the cyliners going "hydraulic" due to the better sealing caused by the oil!
My two cents,
-Brents
Senior User
Joined: Feb 2001
Posts: 158
Likes: 0
compression check -- hot or cold engine?
>Hi,
>
>Be carefull if you put oil
>into the cylinder's when doing
>your tests, I have seen
>things break from the pistons
>in the cyliners going "hydraulic"
>due to the better sealing
>caused by the oil!
>
>My two cents,
>-Brents
Only use about a teaspoon to check if it's rings or a valve/head gasket problem... A teaspoon shouldn't make the pistons go "hydraulic". If compression goes up temporarily, it's the rings or cylinder... if not, it's most likely a valve/head gasket problem. Hope that helps.
Oh yeah... if you have two adjacent cylinders that are low, it's probably got a blown head gasket between those two cylinders, sounded like you already knew that though. Good luck...
Greg
67 F100 CCS 390 cruise-o
>
>Be carefull if you put oil
>into the cylinder's when doing
>your tests, I have seen
>things break from the pistons
>in the cyliners going "hydraulic"
>due to the better sealing
>caused by the oil!
>
>My two cents,
>-Brents
Only use about a teaspoon to check if it's rings or a valve/head gasket problem... A teaspoon shouldn't make the pistons go "hydraulic". If compression goes up temporarily, it's the rings or cylinder... if not, it's most likely a valve/head gasket problem. Hope that helps.
Oh yeah... if you have two adjacent cylinders that are low, it's probably got a blown head gasket between those two cylinders, sounded like you already knew that though. Good luck...
Greg
67 F100 CCS 390 cruise-o
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