Straight Eight dip stick blow by

I have an oil leaking problem with my engine and I'm not sure if there is a solution. I'm hoping that one of you may have a unique solution. When I drive the car, oil blows out the dip stick tube which is about 1 inch in diameter. It makes a mess. The inside of the dip stick is just a hollow shell

ricosan

If your road draft tube is not plugged the solution is probably an engine overhaul. You obviously have a pressure build up in the crankcase. By the way what is your vehicle?.

You need to start thinking about an overhaul.

Hey tinindian,

It's a '32 Marmon. So this is an indication that an overhaul is needed? What's happening in the engine that is causing this problem? Is it because the rings are going bad. I don't have any smoke. What is the road draft tube?

ricosan

Hey Restorer,

Other than this blow by, The engine runs good, no smoke but it is a little tired. What's causing the oil to blow out of the crankcase?

ricosan

Check to make sure your road draft tube is clear.

Since your oil filler cap has a filter in it there must be an outlet from the crankcase somewhere. On common cars it was a tube that exited the valve cover and went down beside the engine almost to the level of the bottom of the crankcase. The end was cut on a bevel so the flow of the air as the car moved forward helped suck the oily blowby from the engine. There is always some combustion that leaks past the rings. If there was no way to relieve this pressure you would blow all the seals on the engine. Some cars had a pipe that went into the aircleaner to draw the polluted air back through the cylinders. Your modern engine has a pcv system (positive crankcase ventilation) that is supposed to cut down on pollution.

If your tube is plugged or too small to release the pressure it is a sure sign that your rings are worn and most likely the valve guides as well.

My engine actually was blowing oil out past the rear main bearing unless I was driving about 45mph. I knew my power was going down perhaps quicker than you might because my horses were smaller and a lot fewer than yours are.

With the engine running check if there is pressure there. Hold your hand over the hole.

If there is pressure, it is a sign you have a lot of blowby and/or the crankcase ventilation system is plugged up. As others have said, check the road draft tube.

It is also possible there is supposed to be a baffle to stop oil being thrown out by the moving parts, and this baffle is missing. I don't know what Marmon used but most cars have a baffle of some kind.

As the rings wear, and the cylinder walls wear, more of the gas/air mix in the compression stroke leaks past the rings, and the high pressure of the power stroke will leak a lot past the rings, exhaust not as much. On the intake stroke, eventually some oil will be drawn up past the rings and get burnt with the gas/air mix. I may not show as a blue cloud behind the engine until the leakage is quite bad.

Run you compression test again, this time with each cylinder, squirt some motor oil on the piston top, around the edge if you can. Use the same amount in each cylinder, I use two full squirts from a pump oil can with a plastic hose that I position near the cylinder wall. Then run the compression check again. You should see an increase in compression because the oil seals the rings for a short while..

Are you doing the compression test with the throttle wide open? or at least not closed at idle? the engine needs to 'take a deep breath' and take in as much air as possible to give a representative compression pressure. At idle the air getting past the throttle plate is very restricted.

If there is no change in the compression numbers, then the valves have some leakage, but this doesn't cause blowby.

One of your valve covers or the front timing chain cover will or I think should have a ? 3/4" or 1" tube coming out of it, and aimed down at the ground. All big engines have some blowby, and it stinks. So most car manufacturers either vented it down near the ground, or hooked the pipe to the intake before the carburetor, usually a tube on the airfilter housing after the filter. This drew in the stink when the car was being driven slow, or stopped for traffic etc. My Pierce Arrow cars all have the blowby pulled into the carburetor.

GLong