The Ford Barn

German guy · 06-06-2025, 01:30 AM

My 30 Tudor has always dripped a bit engine oil...not much....maybe a drop every day or two and no obvious source is apparent. I installed a 6:1 head and it now leaks a LOT more. It seems that a fine mist of oil is coating the bottom of the oil pan as well as the underside of the transmission and eventually amounts to enough to drip. After a few days of standing cold the dripping is much less....almost stops Seems that heating up and thinning the oil when driving increases the mist and dripping. Can the increased compression exacerbate a slow leak at the oil pan seal? I inherited the car with an already rebuilt engine and it looks like silicon was used in lieu of gaskets across the board..including the oil pan....thin bead of red silicon around the joining edges at the pan and block. That bead is always slightly damp with oil...never enough to cause a noticeable drip, but you can always wipe a bit of oil off. Could increased compression force more oil out of that bead?

Bruce of MN · 06-06-2025, 04:00 AM

Maybe the vented oil filler cap is clogged and isn't venting the crankcase? Can you wash it out with solvent or see that the pipe is empty? I think I have heard of people putting mesh in the pipe to keep oil droplets from the cap.

nkaminar · 06-06-2025, 04:58 AM

Bruce has a good suggestion. If the engine has some blowby the increased compression will increase that and thus increase the pressure in the crankcase. If the breather and cap are restricting the venting then, yes, the higher compression head can increase oil leaking.

You could consider fixing the leaks too.

Bob Bidonde · 06-06-2025, 06:56 AM

Ditto nKaminar! Do a compression test. The cylinders should hold 90 to 95 PSIG.

johnneilson · 06-06-2025, 09:07 AM

The real test is leak down
This will help diagnose where the leakage is originating

The other question is are you driving it harder and exposing a weakness?

J

Richard Knight · 06-06-2025, 09:09 AM

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Clearly combustion gas getting into crankcase, blowby. If it is a rebuilt engine with not a lot of miles it may be that the rings are not fully seated.

katy · 06-06-2025, 10:02 AM

Quote:

Originally Posted by Richard Knight

If it is a rebuilt engine with not a lot of miles it may be that the rings are not fully seated.

Ditto

johnneilson · 06-06-2025, 10:39 AM

More than likely the driver is advancing ignition too far

J

06-06-2025, 01:30 AM	#1
German guy Senior Member Join Date: Sep 2023 Location: German/French border Posts: 104	HC head increasing oil leak? My 30 Tudor has always dripped a bit engine oil...not much....maybe a drop every day or two and no obvious source is apparent. I installed a 6:1 head and it now leaks a LOT more. It seems that a fine mist of oil is coating the bottom of the oil pan as well as the underside of the transmission and eventually amounts to enough to drip. After a few days of standing cold the dripping is much less....almost stops Seems that heating up and thinning the oil when driving increases the mist and dripping. Can the increased compression exacerbate a slow leak at the oil pan seal? I inherited the car with an already rebuilt engine and it looks like silicon was used in lieu of gaskets across the board..including the oil pan....thin bead of red silicon around the joining edges at the pan and block. That bead is always slightly damp with oil...never enough to cause a noticeable drip, but you can always wipe a bit of oil off. Could increased compression force more oil out of that bead?

06-06-2025, 04:00 AM	#2
Bruce of MN Senior Member Join Date: May 2010 Location: VA Posts: 1,808	Re: HC head increasing oil leak? Maybe the vented oil filler cap is clogged and isn't venting the crankcase? Can you wash it out with solvent or see that the pipe is empty? I think I have heard of people putting mesh in the pipe to keep oil droplets from the cap.

06-06-2025, 04:58 AM	#3
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 5,863	Re: HC head increasing oil leak? Bruce has a good suggestion. If the engine has some blowby the increased compression will increase that and thus increase the pressure in the crankcase. If the breather and cap are restricting the venting then, yes, the higher compression head can increase oil leaking. You could consider fixing the leaks too. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

06-06-2025, 06:56 AM	#4
Bob Bidonde Senior Member Join Date: May 2010 Location: Long Island, NY Posts: 4,113	Re: HC head increasing oil leak? Ditto nKaminar! Do a compression test. The cylinders should hold 90 to 95 PSIG. __________________ Bob Bidonde

06-06-2025, 09:07 AM	#5
johnneilson Senior Member Join Date: Jun 2010 Location: 34.22 N 118.36 W Posts: 1,181	Re: HC head increasing oil leak? The real test is leak down This will help diagnose where the leakage is originating The other question is are you driving it harder and exposing a weakness? J __________________ As Carroll Smith wrote; All Failures are Human in Origin.

06-06-2025, 09:09 AM	#6
Richard Knight Senior Member Join Date: Mar 2021 Posts: 243	Re: HC head increasing oil leak? Sponsored Links (Register now to hide all advertisements) Clearly combustion gas getting into crankcase, blowby. If it is a rebuilt engine with not a lot of miles it may be that the rings are not fully seated.

06-06-2025, 10:39 AM	#8
johnneilson Senior Member Join Date: Jun 2010 Location: 34.22 N 118.36 W Posts: 1,181	Re: HC head increasing oil leak? More than likely the driver is advancing ignition too far J __________________ As Carroll Smith wrote; All Failures are Human in Origin.