Is my compression low?
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From: Cleveland, WI USA
Is my compression low?
I have a 73 460 in my 78 F150 that's blowing oil out of the dipstick. I was told that it could be a "bad rings" problem. A compression test shows about 130psi in most cylinders and one at 110psi. Is that bad/avg/good? Where can I find out what it's supposed to be?
Thanks!
Kevin K.
Thanks!
Kevin K.
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Is my compression low?
Cranking compression pressure should be 140 psi.
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Joined: Jul 2001
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From: Gainesville, FL
Is my compression low?
kj,
130 psi is wonderful! You Rock! 110 is a bit low though. Compression test should not vary more than 10% from one another. This means that the average is 130 your lowest cylinder should be 117. Your close, so let's not worry about it. Check your PCV valve. If you don't have one, install one. Remove your EGR, unless your emmissions are regulated/monitored, in that case, just disconnect it.
Is your motor burning oil? It should be, according to what your telling me. If it's not then your good to go.
My Way is the Highway
KingFisher
130 psi is wonderful! You Rock! 110 is a bit low though. Compression test should not vary more than 10% from one another. This means that the average is 130 your lowest cylinder should be 117. Your close, so let's not worry about it. Check your PCV valve. If you don't have one, install one. Remove your EGR, unless your emmissions are regulated/monitored, in that case, just disconnect it.
Is your motor burning oil? It should be, according to what your telling me. If it's not then your good to go.
My Way is the Highway
KingFisher
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From: Cleveland, WI USA
Is my compression low?
PCV valve is working fine. Good vacuum! Oil only blows out when the stick is in and I'm on the road at high RPM (as far as I can tell). If it idles in the drive for 45 minutes, I get no oil blowing out. Drive it around the block and it's pretty messy. Just seems like a lot of crank case pressure.
Thank you for the insight.
K.
Thank you for the insight.
K.
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Is my compression low?
hey kevin what you need to do is a dry comppresion test and a wet one ck cylinders dry and then squirt some oil in the cylinders and ck it again comp will probaly be quite a bit higher wet. You could also find a proffesional shop and get them to do a cylinder leak down test this will give you a real good idea what shape those rings are in. hope this helps some. i
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Is my compression low?
[updated:LAST EDITED ON 20-Feb-02 AT 07:00 PM (EST)]When your motor is running there air inside there is like a fine oil mist. Any place that crankcase vapors can leak out will let fine droplets of oil out too.
The pcv valve is only open at high vaccum levels which is at idle or very low rpms. As you rpm up the motor and open up the throttle your vacuum goes down and the pcv should shut. If you have a weak dip stick tube seal it may not be sealing up very well where it goes into the tube and that will let it slip off and leak once you rpm up the motor. Oil mist will vent out and it doesn't take much to oil down your motor. A crack in the handle right above that cap seal will also cause this leak. Just put a couple of turns of electrical tape around the dip stick right where it goes into the tube and tape it to the tube to hold it shut. It may be time for a new dip stick.
The pcv valve is only open at high vaccum levels which is at idle or very low rpms. As you rpm up the motor and open up the throttle your vacuum goes down and the pcv should shut. If you have a weak dip stick tube seal it may not be sealing up very well where it goes into the tube and that will let it slip off and leak once you rpm up the motor. Oil mist will vent out and it doesn't take much to oil down your motor. A crack in the handle right above that cap seal will also cause this leak. Just put a couple of turns of electrical tape around the dip stick right where it goes into the tube and tape it to the tube to hold it shut. It may be time for a new dip stick.
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From: Gainesville, FL
Is my compression low?
Kj,
There is still yet another possibility. What if the intake gasket is leaking and the exhaust gas port under the intake is pressurizing the crankcase? Is this possible? If it is, it's a dangerous situation. How could this be diagnosised? Rev up your motor in neutral and see what happens. Only about 2500 RPMs should do it. Could you smell the exhaust coming out of the crankcase? Would the oil filter the smell? If so, then the oil should be full of dirt. How long does it take your oil to turn black? Does it smell normal? What if an exhaust port is cracked and pumping exhaust into the case. This wouldn't effect a compression test and would only show up in a case like this.
Consider the diagnosis and keep it in mind as you go forward.
Good Luck, Have Fun,
KingFisher
If this is the case, your oil temp would be high and your water temp would be effected.
There is still yet another possibility. What if the intake gasket is leaking and the exhaust gas port under the intake is pressurizing the crankcase? Is this possible? If it is, it's a dangerous situation. How could this be diagnosised? Rev up your motor in neutral and see what happens. Only about 2500 RPMs should do it. Could you smell the exhaust coming out of the crankcase? Would the oil filter the smell? If so, then the oil should be full of dirt. How long does it take your oil to turn black? Does it smell normal? What if an exhaust port is cracked and pumping exhaust into the case. This wouldn't effect a compression test and would only show up in a case like this.
Consider the diagnosis and keep it in mind as you go forward.
Good Luck, Have Fun,
KingFisher
If this is the case, your oil temp would be high and your water temp would be effected.
Lead Driver
Joined: Oct 1999
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From: Kalispell, MT
Is my compression low?
Check for simple things first - my 351M did the same thing and it turned out to be an old collapsed hose on the crankcase ventilation system. The one opposite the pcv that comes out the air cleaner and goes to the valve cover. Even if the outside looks ok, they can deteriorate and come apart inside enough to block the flow.
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From: Cleveland, WI USA
Is my compression low?
DFisher1,
I never thought of the intake manifold, and the oil did smell like gas when I took off the valve covers. I have to pull the heads off this week so I'll redo the gaskets then - Thanks!
MTFlat,
I agree - simple things first. I checked all the hoses, valves, and the breather and they're all clear.
My temp solution is to follow Hottarod's suggestion - electrical tape on the dipstick tube to seal it a little better.
Thanks everyone! I'll let tou know what I find out.
I never thought of the intake manifold, and the oil did smell like gas when I took off the valve covers. I have to pull the heads off this week so I'll redo the gaskets then - Thanks!
MTFlat,
I agree - simple things first. I checked all the hoses, valves, and the breather and they're all clear.
My temp solution is to follow Hottarod's suggestion - electrical tape on the dipstick tube to seal it a little better.
Thanks everyone! I'll let tou know what I find out.