Intermittent rattle at highway speed - wtf? [w/VIDEO] UPDATE!

[Grand Moff Joseph]

UPDATE!!

 

Mechanic took the car for a long drive today and was able to reproduce the problems. While monitoring the oil gauge during and immediately after the rattling fit, the oil gauge was seen to be barely over zero at idle, and just over 1/4 under load.

 

SO... Brian's initial bet on oil starvation seems to be the culprit. The resulting rattle is coming from the lifters, which are running out of oil on extended hard runs. (your instincts prove correct again, detective!) Ergo, the plan is to replace the oil pump assembly with a high-flow pump that can pick up extra oil capacity if needed. Of course, along with that comes a new oil pan gasket and a freshly cleaned oil pan.

 

While he's at it, my mechanic will also inspect the bearings, which are supposedly very easy to look at with the oil pump stuff out of the way. We figure it's worth it to check them while we're in there - if they're out of spec, no sense in fixing more stuff when the bearings are on their way out.

[AWeb80]

Good to hear Joe.

 

do the 3.1's come w/a crank Scraper? Should put one in if not...you're right there

[Grand Moff Joseph]

Good to hear Joe.

 

do the 3.1's come w/a crank Scraper? Should put one in if not...you're right there

 

I'll be sure to mention that to him today. Out of sheer ignorance, what does that part do, and iss it prone to failure?

[AWeb80]

it scrapes the oil off the crank for less parasitic power loss.

[Grand Moff Joseph]

it scrapes the oil off the crank for less parasitic power loss.

 

Ah, I get it. Thanks again for the advice Adam, I appreciate it.

[Pontiac6KSTEAWD]

Glad we caught it early befor any real damage was done...

 

I am starting to get good at this phone diagnosis.. LOL!@

[1990lumina]

Hope it doesn't cost you too much. IIRC you have to at least lower the subframe to get the oil pan off.

[Pontiac6KSTEAWD]

Had me thinking about it again. This low oil pressure problem occurred after you had the oil change done. Faulty oil filter?

[Crazy K]

Had me thinking about it again. This low oil pressure problem occurred after you had the oil change done. Faulty oil filter?

x2!!!!

 

what brand did you put in???

[Grand Moff Joseph]

Don't know what brand it was, though I'm sure it was not Delco. Been getting my oil changed at the same place for a while with no issues, though you never know.

 

That said, I talked with Brian on the phone today about this same idea. I was thinking about mentioning this to my mechanic anyway, but they started work on the car last Friday. Also, I figure at this point in the car's life, going the whole nine yards only helps the car in the long run.

[Grand Moff Joseph]

One other random thought: According to my big GM service manual (and a few others on here), it looks like the engine subframe has to be lowered to get the oil pan out cleanly.

 

Assuming that is correct, are there any bushings/bolts/whatever that would likely need/desirable to change?

[White93z34]

you could change all the cradle bushings if you were so inclined, parts numbers are in the P/N thread.

 

I've had a bunk oil filter cause oil starvation issues before, never again ACDELCO filters

[AWeb80]

WIX or go home

[Grand Moff Joseph]

UPDATE:

 

Car should come back tomorrow, after a lengthy trip to surgery. Highlights:

 

**Oil pump replaced with high flow pump for extra capacity. Of course, this also nets a new oil pan gasket, always a good thing.

 

**Main bearings and connecting rods were checked for adherence to spec. All connecting rods were EXACTLY to spec. All bearings were within tolerance except for one, which was only off by 2 thousandths of an inch (.0029 vs. spec of .0027). Verified with machine shop, is not out enough to warrant replacement/serious concern

 

**Inspection of oil pan and crankshaft area show ZERO gunk, varnish or excessive wear. Other than being greasy (natch), the oil pan was spotless. :woot:

 

**Inspected subframe mounts - all found to be in very good condition - no need to replace at this time

 

**Lower engine mount and transmission mount found to be "passable" but worn. These will be replaced.

 

**Will be switching to 10w-40 oil to help lubrication

[AWeb80]

cool.

 

It's good to hear the bottom end is all clean. I know when I pulled the valve covers on the GP, they were new looking.

 

Let us know how every thing goes

[Grand Moff Joseph]

FINAL UPDATE: The Lumina Rides Again!

 

I was sent out of town for most of the last week on a last minute business trip, so I did not get a chance to pick up the car before I left. This allowed my mechanic to take the car for a looonngg test drive - a "shakedown run" you might call it for the new oil pump.

 

He took the car on a 2 hour drive, using both extended highway speeds and street driving, and allowing it to idle in gear for over 30 minutes. Result: Not one peep or rattle from the engine at all! :woot:

 

Observed oil pressures, post repairs

Cold start/idle: pegged at 80

Cold at speed: hover near 70ish

Hot at speed: 50-60

Hot at idle: 20-25

 

ALSO, we both noticed that replacing the bottom motor mounts quieted A LOT of extra vibrations. So this may be one way to partially silence those FFP dogbones so many of us have.

 

Finally, a big thanks to all for their advice and help, especially Brian!