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Help Too much pressure

 
EZE-JR
I love my Chevy Chevette!
Posts: 1
Joined: 03/07
Posted: 03/20/07 05:40 PM

I had a buddy put my engine together and he noticed that there is alot air pressure causing an oil leak from my oil sender unit when i have the oil cap closed. so i bought an oil breather cap that would connect to the edelbrock air cleaner and no more leak from sender unit. but now i am getting oil along the inside of my air cleaner and filter gets ruined within a few hrs of use. is there something we might have missed doing? this is in a 1982 chevy truck with a 400 with an edelbrock 750 carb. any help would greatly appreciated.  

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55Guy
Administrator
Posts: 1153
Joined: 07/06
Posted: 03/21/07 04:56 AM

Man, sounds like the motor's making a ton of crankcase pressure. One problem could be the valve cover doesn't have the proper baffling to keep oil splash from being sucked up the PCV breather tube.

Another option is to try a venting style breath cap that doesn't hook up to the air cleaner.

How much oil pressure is the motor making when it's running?  

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oldbogie
V-6 Camaros rule!
Posts: 65
Joined: 10/06
Posted: 03/21/07 11:04 AM

Crankcase pressure will not cause the oil sender to leak. This is either a faulty sender or too much engine oil pressure. Messing with the PCV and the vents would have no effect upon the sender. While these events may have happened at the same time there s no relationship between the sender stopping leaking and any changes you made to the vent system.

Oil being pulled over the vent system indicates that there's too much oil circulating in the engine, the engine's clearances are too wide or the motor is worn out, or there is insufficient venting for the RPMs being turned.

Too much oil flying around inside the engine comes from too large an oil pump and or excessive bearing clearances. I'm not delving into a crack or missing galley plug leading to leakage. Too much oil circulating especially with wide bearing clearances makes for a flood inside the motor that the crank is whipping everywhere. This can result from wide machined clearances or wear that causes the same result. There is so much oil that the rings can no longer make a seal, or the rings can be worn out. In either case blowby is increased which raises the pressure in the crankcase. High RPMs can have a similar effect where the rings go into constant flutter and loose their seal. Blowby gets around them and the crankcase becomes pressurized, blowing oil out the vents. Race engines that see lots of high RPMs use vacuum vent systems in the headers to pull a vacuum on the crankcase keeping the rings in contact with the walls. You can also encounter this problem on a street engine that's running thin racing rings and or low tension rings.

Some oil blown into the air cleaner is OK but this needs to be a long way from leaving puddles of the stuff and soaking the filter.

Other issues can be broken rings, incorrectly gapped rings too much or too little, the failure is different but the oil and blowby result is the same. Incorrectly fitted/sized piston or ring set. You'd be surprised how often I've seen a thirty over bore with a standard piston and a thirty over ring set or other equally odd things people do to bores, pistons and rings.

Bogie  

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salba
I love my Chevy Chevette!
Posts: 1
Joined: 03/08
Posted: 03/28/08 08:06 PM

I have a similar problem. Same motor but was built by a guy I bought the car and engine from. He said it was his first small block he built but had built big blocks before. What did you end up doing?? Im afriad to drive my car because The mechanic said it might blow out my rear seal?  

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Ehbrown1
I love my Chevy Chevette!
Posts: 2
Joined: 03/08
Posted: 03/29/08 06:33 PM

Well, I hate to say it, but I believe you may have an extremely loose piston-to-bore fit, worn valve guides, or excessive ring end gap resulting in the amount of blow-by you are describing.  The oil leak from the sending unit is either poor thread sealing or a defective unit itself.  Excessive blow-by in an engine cannot cause the oil sending unit to leak.  If you are creating oil pressure that is enough to blow out the internal seal of the sending unit, you probably have an extremely oversize oil pump and/or the pressure bypass valve blocked and are going to find multiple distributor drive gear replacements in your future - unless you shear the gear teeth off or snap the shaft first.  I would perform a cylinder blow-by test, as well as taking an ACCURATE oil pressure test with a reliable gauge.  Those tests will determine your next course of action.  Either way, you'll be taking the engine apart to determine the EXACT cause(s) and the course of action that needs to be taken.  

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55Guy
Administrator
Posts: 1153
Joined: 07/06
Posted: 04/03/08 11:04 AM

Did you use a high volume or regular oil pump?  

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m_endymion
I love my Chevy Chevette!
Posts: 19
Joined: 04/08
Posted: 04/06/08 11:42 PM

I had a similar problem to this about 5 years ago it ended up that the piston rings on the #5 cylinder had split into 4 pieces. I was having to add a quart every 50-60 miles, because i was flinging oil out of the breather. You might want to check your compression on all your cylinders.  

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