Jake_T18

Hi everyone,

I've been having a few problems with my '91 RS / 305 TBI (all stock minus a smog pump removal.) 158K

The biggest problem is oil consumption. My engine will drink about 1Qt of oil for every 300-500 miles. This was not the case about 3 months ago, where it was much less; 1Qt for ~1500 miles.

Meanwhile, my car threw a SEL - code 32 (EGR / EGR Solenoid). I took the EGR valve off the car and cleaned it up. It does hold vacuum, and I replaced the solenoid for good measure. While I was taking the EGR valve off, I noticed a pool of oil in the bottom hole on the intake mount for the EGR.

Is it possible my EGR is sucking oil out of the intake and burning it? ie - a blown intake gasket? I've also noticed a bit more drippage of oil in my driveway. It seems to be from the back of the block up near the intake.

I don't believe the intake gasket has been replaced in this car's lifetime. For 158K, would it make sense for the IG to be shot?

Sorry if this doesn't make any sense, I'm fairly new to the mechanic world - my day job is a computer tech :P

LsxMatt

iTrader: (4)

Is the car blowing any blue smoke? If your burning that much oil you should see some blue smoke out the exhaust. Also, if your seeing dripping at the back of the motor, its either your distributor o ring that's leaking oil, or most likely your oil pressure switch. My monte carlo was spewing oil out the oil pressure sender, would leave a quart of oil on the ground wherever it was parked.

Jake_T18

It does blow blue smoke, but not a lot as if it were a smoke screen. Even at higher RPMs. If I let the car sit and idle in drive for about 5 minutes the smoke is definitely noticeable. Oil pressure switch is not leaking.

Night rider327

iTrader: (13)

Would not be intake gaskets. Very uncommon for the engine to suck oil into the intake ports. The oil is in the valley and the bottom of intake port is a good 3.5" higher up.

Most common intake gasket failures will leak coolant into the oil giving you a higher oil level plus the milk shake looking oil, or you'll get an internal vac leak, or you will get fuel leaking into the oil again showing a higher oil level.

Blue smoke out tail pipes could be worn/leaking valve seals and piston rings.

If the engine was burning 1qt every 400 miles you would have a smoke screen behind you.

My guess is the common worn valve seals, plus an oil leak somewhere.

Back of block, up towards intake is a common leak point and will be one of these.
Leaking oil pressure sender unit, like where it screws into the block.
Leaking dizzy gasket/seal
Leaking rear intake end seal between the block's china wall and intake.

FRMULA88

Also check for a clogged/dirty/old PCV valve / PCV line.

An inoperable PCV system will pressurize the crankcase and let oil blow by the piston rings.

There is no valley pan on a SBC (the intake manifold serves that purpose) so oil can be sucked into the combustion chambers from the bottom side
of the intake if the seal is bad / weak. if the crankcase is pressurized this will help force oil into the chamber.

The coolant passages have their own ports into the cylinder heads they may not be affected because the water pressure offsets the crankcase pressure.

lastly if the seal on the china wall is bad you have to remove the intake manifold to repair this, so you have to replace all intake gaskets regardless.

you can't expect anything to run flawlessly after 150K.

FRMULA88

other problem areas for leaks on the SBC are:
the front of the oil pan where it meets the timing cover.
the valve covers
front main seal
rear main seal

Because the engine tilts to the rear a worn out rear main seal will seep oil all the time.

The best thing to do is power wash the engine at a self serve car wash.. this will make it easier to see fresh leaks. Park the car and leave some clean cardboard on the pavement under the engine..

Next day the drips on the cardboard will point you in the right direction.
The rear main is partially shielded by the transmission inspection cover, if cover is dripping oil that is sign.

Replacing the rear main seal with the engine in the car is a PIA. You will have to remove the transmission and drop the oil pan just to gain access, hopefully it is not that, but it is worth checking.

TheExaminer

I have oil around my sender, and it has dropped down onto the oil cooler. I may need to replace that, but what about the distributor O ring? Could it come from all the way up there onto the sender? I don't leak much, just little drips here and there. Is the dist O ring a hard replace? What makes me wonder this is that there is still a little oil ABOVE the sender, though most of it is beneath. Could it spray a little upwards from the sender under 60 psi if there's a small leak?

sofakingdom

iTrader: (1)

I disagree. I've seen quite a few do that.

The bottom of the intake ports is adjacent to the crankcase. Vacuum on one side, oil on the other. The gasket is less that a quarter inch wide across there. It frequently fails there, especially but not limited to, right after a replacement. (gets caught on the intake as it's dropped on, and tears) It also gets sucked in if the intake is mis-machined.

As cheeeeeeeep, eeeeeeeeezy, and quick as it is to change them, wouldn't hurt to do so.

I STRONGY agree with the valve guide seal possibility however. They are the single most common failure in the SBC. When replacing those, doing intake gaskets adds only acoupla minutes to the job. Your description doesn't sound like those however, as they don't generally work great one day and wipe out the next. Usually they're more gradual; one cyl at a time over a long period, steadily getting worse.