What inside an engine causes high oil pressure?

I have an old 350 block, 882 heads, 10:1 dometop pistons. It's been running fine for 4 years now. But this week, I accellerated a tad hard (not that it's the first time), and I blew oil out, burning it as I sped down the highway.

It appears to be coming from the front of engine, since I had oil all over the front (water pump, front of block, rear of balancer, lower rad hose, etc.) - so I'm guessing I blew out the front seal.

After I let off the gas (back to mild accelleration), it stopped. And didn't smoke any more the last 10 miles of my trip home. Seems to be a very small drip at the bottom of the timing chain cover (takes 4 hours to leak a quarter size spot in driveway).

I checked oil, added a quart (I just did an oil change the day before this happened with same oil I've been using for last 4 years).

Today, I drove it again, watching the oil pressure. At 70mph, it seems to vary... I'll run 70mph, and pressure will be 40. Then I hit a light, and have to stop. Next run, at 70 mph, pressure will be 60 - 65. Sometimes lower, sometimes higher. Entering the highway, I gunned it to get out into traffic again - but not nearly as hard as the other day. I noticed pressure went to 65, and it smoked again, until I eased up - then pressure dropped to 40, and stayed there the rest of my 20 miles home - even when I gunned it again. Right before I arrived home, I noticed the pressure climbing back towards 65 again, but I didn't gun it anymore (2 blocks from house). I drove a total of 100 miles today, but it took 80 miles of "normal driving" (with test accelerations along the way) before a harder accelleration would make it leak.

So - it appears that .... something is happening internally that builds oil pressure after a given time, and at a point (close to 65psi), it has to release, and thus releases out the front seal.

So - what's causing it to build like that?

I know I need a new seal, but I'm concerned that it'll just blow again, and thus looking for a cause before I bother with seal replacements.

Tight bearing clearances (not just the mains & rods; also the cam, dist housing, lifter bores, lifter metering, etc.)

Oil pressure NEVER comes out the front seal. EVER. There's no path available to make it do that.

Check this bolt hole. It needs a bolt in it.



That bolt goes RIGHT DIRECTLY INTO the fuel pump drive rod passage. You can look in there and see the rod. Or, put a bolt there, and disable your FP.

Oil pressure can leak out the REAR main, because there's a path available at that point (between the cap & the block), but not the front.

OK - I'll check that in the morning. I'm running the intank electric pump with a Mallory regulator for the carb.

But - if that bolt was missing, wouldn't it leak always?

Got a dicky oil gauge or sender? Try another, see if it behaves the same.

My pressure on 3.1 V6 sits around 80 all the time (even when hot) at anything above about 15 mph. It drops to about 40 at idle. Is 80 too high? What's normal? Is the V6 different to the V8?

When that bolt is missing, it usually leaks very much only at high RPM and/or high load (from the inevitable blowby)

Don't over-think it and outsmart yourself with paralysis by analysis; just LOOK; it's easy to fix, and "free"

Gotcha - and yes, I have a tendency to do that at times - thanks!

OK - got 2 bolts inserted in both holes (I know you circled the upper one, but I figured I'd cover my bases). Put RTV on them to help seal it up, will allow it to dry overnight and test it tomorrow - thanks again Sofakingdom!

Isn't it great when it turns out to be something easy and FREE?

Hell yeah!

Made several WOT runs today, no issues at all, so that cleared it up.

And, after thinking about it - I've seen you post this to many folks over the years about that hole - why I couldn't remember that myself I don't know {maybe old age, grey hair, 5 kids, 2nd wife, commuting 100+ miles a day to a job better suited to a 20 year old, etc., etc. ?}. But thanks again!

Thank you all for this thread. What a relief...

Can you recall what size and length bolt is needed?

3/8"-16 (std thread), ½" or ¾" long.

Glad you found it useful; that's what forums should be about.