[Verdoro 68]

My new build has been running great, but I've been trying to diagnose an oil leak that seems to occur at higher RPMs. I figured the rear main was toast, but looking at where it's splattered I'm not so sure.

I put some UV dye in the oil and it looks like the leak is concentrated on the passenger side on the filter area. There is oil down the passenger side rear of the pan, but it doesn't look like it's originating from the rear seal area and the flex plate doesn't have the oil flung out from the center. There is oil built up on the passenger side corner of the pan, but a bulk fo the mess It looks like it's coming off the filter or sending unit. No indication of leaks from the valve cover or distributor and it doesn't leak when it's sitting.

Has anyone seen an oil leak from the filter or sending unit under high pressure before? My gauge hits 80psi above 2500 and idles around 45psi. It doesn't appear to leak - or is way less severe - cruising around town below 2500.

[hurryinhoosier62]

It IS possible that the filter housing has porosity in it. That COULD explain oil seepage at high rpm only.

[Gach]

It could very well be oil filter gasket seal, spraying as oil pressure goes up at high rpms. Had it happen to me. Possible?

[Verdoro 68]

Originally Posted by hurryinhoosier62

It IS possible that the filter housing has porosity in it. That COULD explain oil seepage at high rpm only.

The filter housing is new, but that doesn’t mean it’s ok. I’m not seeing any oil on the housing itself though. Looks like it’s mostly on the filter and sending unit.

Originally Posted by Gach

It could very well be oil filter gasket seal, spraying as oil pressure goes up at high rpms. Had it happen to me. Possible?

This is what I’m thinking, but I wasn’t sure of the likelihood. I wonder if a fix could be as simple as tightening up the oil filter some more? It’s hand tight right now.

The pattern on the oil pan is throwing me off. It could be spraying against the pan, collecting and dripping down. There is a tiny bit of oil on the starter, but nothing substantial.

[Gach]

You can try tightening it more, my guess though is the seal is compromised. I would at least take filter off, and look at it, although sometimes its hard to tell, just by looking at the rubber seal.

[sdbob]

Just thinking. Do you have a spare oil filter housing? Make a block off plate to seal block side,screw on filter you are using and pressurize it with air slowly checking for leaks.

[steve25]

Since you know youroilpressure is good and senders have been known to leak, remove the sender and install a 1/8" pipe plug and see if the leak is still present.

[PDC]

I traced an oil leak in the exact same location under my 455 and discovered that the oil filter housing had a very small crack straight up and down the center of the housing between the opening and the lower bolt hole. Thanks to several coats of Pontiac blue paint on the block and oil filter housing, it was extremely difficult to diagnose. Found it when I pulled housing off to replace the housing gasket. Got a new oil filter housing from Butler and all was well.

[HWYSTR455]

I once found out that the bolts I used on the filter housing were a CH too long, and you couldn't tighten them enough, they would bottom out.

Same condition, only at higher RPM would it leak.


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[HWYSTR455]

Helped a friend one time with a similar problem, and found an oil FILTER gasket, the round rubber on top of the filter, was stuck to the filter housing from a previous filter. Popped that off and done.



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[HWYSTR455]

I always go tighter than 'hand tight', give it like a half a turn with the filter wrench.


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[mgarblik]

Pontiac engines are so very hard to seal, your UV dye shows us that! I recently had a leak very much like yours on my fresh engine. It ran for hours on the dyno including 43 power pulls, not a drop of oil leaked. Put it in the car, damn thing leaked much like yours, splash on right rear, higher RPMs. Just couldn't find it. Was sure it was a rear main. Turned out to be the lower rear valve cover bolt on the right side. For reasons unknown, the damn thing just wouldn't seal. Ended up having to put one of those Moroso bolt spreaders on in just that one location. Now 1000 miles later, not a drop of oil leaking. To test, I would put brake clean on a rag and clean the heck out of the underside of the Right valve cover flange. Then drive it and run your hand under that flange after it is parked. It should be dry. If that is not the leak, a smoke machine is much better than UV dye to really pinpoint a leak. The dye runs everywhere as you can see and makes it difficult to find the source. If you fill the engine with smoke through the valve cover, wherever it comes out is the leak, simple as that. Almost every repair shop that works on 1996 and newer cars has a smoke machine. Possibly you can beg, borrow or rent one and in 10 minutes, you will find the leak. Good luck with it. Let us know what you find.

[sdbob]

I had same leak years ago on my street 421. Heard about those 'corvair' valve cover spreader brackets still use them today with thick cork gaskets.

[Verdoro 68]

Thanks for the suggestions.

Just want to double check that I’m not fooling myself - it doesn’t look like it’s coming from the rear main, right?

I’m not seeing any oil above the filter or on the housing. Behind the passenger valve cover feels dry and it looks clean with the UV. I’ll give it another look.

I remember testing the length of the bolts for the housing when I built the engine so those should be ok. The block to housing mating surface looks dry.

I think the source is either the filter or the sending unit. I’ve noticed there are certain times where the gauge very slightly fluctuates. It’s usually after I get off the freeway and come back to idle. That may be when it leaking.

I checked the tightness of the filter last night and it’s on there pretty good. I got maybe another 1/4 turn out if with a wrench. Last time I changed the oil the gasket stuck to the housing (same filter brand). I’ll try a new sending unit and maybe a different brand of filter to see if that helps. I like the idea of plugging the sending unit port, I may try that.

My last housing had a crack like PDC mentions. Doesn’t take much for these things to leak and make a big mess.

[HWYSTR455]

Good way to know if it's coming from the filter or filter housing is it puddles up on top of the filter. Yes, a valve cover can do that too, but to me a valve cover leak is obvious. Just run your finger around the lip of the cover and if it's wet, you know.

Does not look like a rear main leak to me.

Doesn't appear to be a timing cover leak either, sometimes it blows/rolls along the pan rail to the rear corner of the pan.



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[Verdoro 68]

I pulled the filter to start with an easy suspect. Since it's been sitting for a day, the oil had drained back and the filter came off clean.

There's a bulge and some waves in the gasket and oil towards the outside edge where the UV highlighted a ton of oil dripping down the filter. The gasket itself came off pretty easy because there was oil under it so this may be a culprit. Thinking back - there was a little evidence of a leak on the back side of the pan before my last oil change. It looked like someone randomly squirted oil on it. The leak got much worse after the last change, which may lend itself to the filter seal being a problem, but I also did more freeway driving.

[dataway]

You probably know this and didn't do it ... but if you put a filter on a dry housing without lubing the sealing gasket/ring and tighten it a bit too much it will wrap up that seal and tear it away from the filter sometimes.

Only reason I mention this is that in those last photos parts of the filter seal look pretty dry.

[HWYSTR455]

Yeah I think you found the culprit.

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[Verdoro 68]

Originally Posted by dataway

You probably know this and didn't do it ... but if you put a filter on a dry housing without lubing the sealing gasket/ring and tighten it a bit too much it will wrap up that seal and tear it away from the filter sometimes.

Only reason I mention this is that in those last photos parts of the filter seal look pretty dry.

Yeah, It does look dry. I always lube the gasket, but maybe I haven't been lubing it enough. I usually dip my finger in oil and give the seal a pass.

[hurryinhoosier62]

Originally Posted by Verdoro 68

Yeah, It does look dry. I always lube the gasket, but maybe I haven't been lubing it enough. I usually dip my finger in oil and give the seal a pass.

If in doubt, try Dow-Corning Compound #4. We used it on oil filters and assembling the shock struts in aircraft landing gears since it is designed to cause the seal/ o-ring to swell slightly. I’ve never had an oil filter leak since I started using it.