# mystery leak in my '66



## Bensjammin66 (May 12, 2009)

So let me start by saying that I have a slow rear main drip and these pics were before I put an inspection cover on my bellhousing. 

Ive replaced the oil filter housing gasket and the plug on it is tight. The oil pan is bop's one piece and doesnt leak. Valve covers do not leak either. Is all this oil from the rear main drip? Flywheel maybe chucking it up top like this before the inspection cover went on? It only happens on a real hard pull, 5000rpm+. Regular street cruising it doesnt happen. Getting very frustrated. :banghead:


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## Bensjammin66 (May 12, 2009)

ill have to post a pic tomorrow. keeps saying invalid page specified. anyways the oil is about 10"x10" on my lower inner fender well and the lower part of the firewall. only happens when i jump on it. what else could it be?!?!

the pics are on my profile page under the album "mains"


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## Bensjammin66 (May 12, 2009)

Ive since installed a new inspection cover to my belhousing. Could all this oil be from the flywheel exposed and the rear main drip?


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## geeteeohguy (Feb 2, 2008)

I've had my share of rear main leaks, and NONE of them looked like that! Not the rear main, most likely. Most likely is the breather vent I'm looking at, the oil filter housing, the oil pressure switch, or possibly the dipstick. Clean it all off with brake cleaner, dust with talc, and take it out for a romp and see where it's coming from. Do you have a baffle in the valve cover to keep oil out of the breather?


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## WhittP (Jun 19, 2013)

Seems like if it was the breather the pattern would be dispersed all over the right side of the firewall and not concentrated in that one spot. It doesn't look like one of the breathers that has the hose port on one side. I bet its the oil pressure sending unit or the fittings its attached to. Possibly the oil filter housing.

We are sure its not transmision fluid right?

Nice looking engine BTW. I like the plug wire routing.


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## chuckha62 (Apr 5, 2010)

I'd be inclined to think oil pressure gauge/adapter. There must be a pin hole there somewhere.


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## Bensjammin66 (May 12, 2009)

It sure looks like its coming from the oil filter housing but the gasket is new. Is there something else on it that can shoot oil all over like that? I know there is a little plug in it but its tight. The oil pressure sending line is back by the distributor and nothing back there is wet... 

I have no baffle in the valve cover, its just a hole with a grommet and the breather shoved in there. I thought about maybe duct taping it closed then going for a drive. That would eliminate the valve cover breather right? Where the dipstick enters the block is not wet either. Not tranny fluid as my tremec 5 speed is a completely sealed case. Its certainly oil


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## Bensjammin66 (May 12, 2009)

So high rpm is when i have 60lbs of oil pressure. If i had to guess id say the fitting on the oil filter housing is stripped or not sealed. I'm gonna take it off tonight and teflon tape it real good if its not a cracked housing or something else obvious. The only place oil can really come from down in that spot has got to be that housing.


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## Bensjammin66 (May 12, 2009)

Oil filter housing adapter checked out fine. Bought some baffled valve cover grommets from Summit last night and installed the inspection shield on the bellhousing. Fingers crossed.. I'll post this weekend after i run it.


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## BearGFR (Aug 25, 2008)

Another thought - it's very possible to over-tighten the oil pressure switch/sending unit when installing it and crack the housing.

Bear


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## PontiacJim (Dec 29, 2012)

Another thought. I have heard of oil pressure, at higher RPM's, passing oil through the gasket seal on the oil filter. Try a different filter? I used to use a Fram and I know I would wipe it dry near the oil seal at the top of the filter after installation and would soon see oil setting on top of the filter. I would wipe it dry again, and would find the oil back on the top again. I figured this was what was happening after reading an article or blog about this. I used to wind my engine tight all the time. I think the AC Delco PF-24 is a recommendation for a Pontiac filter.

I often wonder if the gasket material, and/or thickness, might not be as the original factory type was. I had an issue with a rubber gasket on the front pan of a 360 Mopar I rebuilt. It slipped out -oil all over the place. Told my machinist and he was not surprised at all. Told me it used to happen to him on his rebuilds as well. Said the rubber seals were not the same compound as they used to be and that they will slip out from the pan crush when you tightened the bolts or blow out under pressure. He now uses a gasket adhesive to prevent this. My point being, the rubber material of the gasket on your oil filter may not seal as well under higher pressures as you wind up the RPM's and the oil is spraying out past that seal.


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## Bensjammin66 (May 12, 2009)

Thank you everyone for the ideas and replies! I have discovered under high rpm the crank case pressure is pushing the dipstick out of the tube just about 1/8" and the air turbulance from hauling ass is making the misting oil coming out hit the upper a-arm, frame, firewall and inner fender. Now more importantly, where can I find a quality 455 dipstick that will stay in place? Locking preferaby lol! I shoulda known, the one I use is some cheap mr gasket job from my previous 400 but its marked for a perfect 6 quarts. Any advice on what to use and where to buy is appreciated.


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## ALKYGTO (Mar 29, 2010)

Ben, I've seen people drill a small hole in the handle of the dipstick tube and hook a tension spring into it and attach the other end to a hole below the dipstick handle to keep it in. You could maybe tack weld a washer onto the tube to attach the other end of the spring.

Something like this.....HOW TO: Oil dipstick retainer spring


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## Bensjammin66 (May 12, 2009)

ALKYGTO said:


> Ben, I've seen people drill a small hole in the handle of the dipstick tube and hook a tension spring into it and attach the other end to a hole below the dipstick handle to keep it in. You could maybe tack weld a washer onto the tube to attach the other end of the spring.
> 
> Something like this.....HOW TO: Oil dipstick retainer spring


I like it. That is a great idea and thanks for the reply. Im a part horder so im sure i got an old carb return spring laying around. This will work perfect. Thanks!!


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## chuckha62 (Apr 5, 2010)

Bensjammin66 said:


> Thank you everyone for the ideas and replies! I have discovered under high rpm the crank case pressure is pushing the dipstick out of the tube just about 1/8" and the air turbulance from hauling ass is making the misting oil coming out hit the upper a-arm, frame, firewall and inner fender. Now more importantly, where can I find a quality 455 dipstick that will stay in place? Locking preferaby lol! I shoulda known, the one I use is some cheap mr gasket job from my previous 400 but its marked for a perfect 6 quarts. Any advice on what to use and where to buy is appreciated.


Can you use an original or an OEM replacement and mark it according to what you know to be the correct "full" and "add" levels?


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## PontiacJim (Dec 29, 2012)

If it is pushing the dipstick up & out a bit due to excess pressure when you wind it up, then you may want to address this. A spring on the dipstick may work, but you still have a lot of pressure in the crankcase. Bottle up the dipstick, and that pressure may find another way to escape, like a seal or gasket. 

Does your engine have a valve cover breather? Does each valve cover have its own breather? I had a 400 CI that used to push the dipstick up and blow out oil. It was a stock engine. As I recall, I added another breather to the valve cover side where you add oil simply by replacing the solid oil cap with a chrome twist-on type breather of same hole diameter. Problem solved.


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## Bensjammin66 (May 12, 2009)

PontiacJim said:


> If it is pushing the dipstick up & out a bit due to excess pressure when you wind it up, then you may want to address this. A spring on the dipstick may work, but you still have a lot of pressure in the crankcase. Bottle up the dipstick, and that pressure may find another way to escape, like a seal or gasket.
> 
> Does your engine have a valve cover breather? Does each valve cover have its own breather? I had a 400 CI that used to push the dipstick up and blow out oil. It was a stock engine. As I recall, I added another breather to the valve cover side where you add oil simply by replacing the solid oil cap with a chrome twist-on type breather of same hole diameter. Problem solved.


Thanks for the reply Jim. Yes, i do have a chrome push in breather on both sides. I am thinkin one may be a little plugged up with oil so i plan to replace both soon...


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## Bensjammin66 (May 12, 2009)

As Jim said i still have crankcase pressure to deal with but heres what i came up with. There is actually a threaded hole right by the dipstick tube in the block, maybe alternate motor mount locations? Anywho, drilled a small hole in the dip stick and attached a spring to it and a bolt i put in the block. After a few 5500rpm pulls, CLEAN! Still need to address that pressure though...


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## PontiacJim (Dec 29, 2012)

Yay, a success story. Make sure your PVC valve is working. Also, you may want to look into a "header evacuation system". Do a web search. These are kits that will draw vacuum by using your exhaust system when your vacuum drops at the manifold. Might be an option.


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## Bensjammin66 (May 12, 2009)

PontiacJim said:


> Yay, a success story. Make sure your PVC valve is working. Also, you may want to look into a "header evacuation system". Do a web search. These are kits that will draw vacuum by using your exhaust system when your vacuum drops at the manifold. Might be an option.


My brother recommended the same thing. Summer project for sure. Looks to be as easy as holesaw a small hole in the collector and weld in a bung, then run some line up to a ported breather.


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## ALKYGTO (Mar 29, 2010)

Header evac systems aren't very efficient on muffled street cars. These systems are designed for drag cars that see high rpm with unmuffled exhaust. Street cars don't draw enough vacuum through the exhaust to fully utilize this type of system.

I would just recommend a properly functioning PCV system.

I don't have header evac on my car, I just use two valve cover breathers and I don't have any problems with leakage or dipsticks blowing out.


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## PontiacJim (Dec 29, 2012)

AlkyGTO is correct on the evacuation system. This was something I had in mind myself, but further investigation reveals that it indeed is for drag cars/high RPM's. So that idea just came off my list of "add-ons".


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## Bensjammin66 (May 12, 2009)

ALKYGTO said:


> Header evac systems aren't very efficient on muffled street cars. These systems are designed for drag cars that see high rpm with unmuffled exhaust. Street cars don't draw enough vacuum through the exhaust to fully utilize this type of system.
> 
> I would just recommend a properly functioning PCV system.
> 
> I don't have header evac on my car, I just use two valve cover breathers and I don't have any problems with leakage or dipsticks blowing out.


I have a functioning PCV in my valley cover but it works on vacuum. My crankcase is only being pressurized alot at WOT high rpm where there really is no vacuum. I too have a breather in each valve cover but its still happening...


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## geeteeohguy (Feb 2, 2008)

The only thing that will cause excessive crankcase pressure at high rpm is excessive blowby past the piston rings. A cylinder leakdown test is next. If you have more than 10-15% leakdown, you are in need of an engine overhaul.


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## Bensjammin66 (May 12, 2009)

geeteeohguy said:


> The only thing that will cause excessive crankcase pressure at high rpm is excessive blowby past the piston rings. A cylinder leakdown test is next. If you have more than 10-15% leakdown, you are in need of an engine overhaul.


I hear ya on the rings but the motors new and im quite thorough when its assembly time. I dont think it was as much excessive crank case pressure as it was a shotty mr gasket dipstick that doesnt fit the block tube very well. I held my finder over the dip stick hole and revved it to 5k. Very little, if anything at all was pushing back on my finger. I think it was just rattling outa there 3/8", enough to have oil mist out at high rpm


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