Just noticed a loud hissing sound while accelerating. I checked under the hood, at idle, theres no sound, pump the gas and it sounds like air blowing out of the engine somewhere. Also I can see a light haze of blue smoke coming from somewhere around the passenger side rear of the engine (even at idle). This smoke smells like burnt oil and very pungent.

Doesn't seem to be using any more oil than usual (1/2 qt every few months)....
Checked the coolant level, doesn't seen to have dropped any...

This just started yesterday, the car is driven easily, never raced and has had a fairly good maintenance history. There is no knocking or obvious pings at any engine speed. (It does have a lifter that clicks when its cold but its done that for years). It also has the usual puff of valve seal smoke when I start it up.

Its a '89 T/A, 305 TPI, all stock and original engine, 700R4.
And, hold on to yer socks, the odometer quit at 230,000 miles, 4 years ago. I figure its up to ~270,000 miles now.

This is my daily driver......
Any ideas?

Thanks
Rick

 

Blowby? Huh?! The engine doesn't even have 300,000 miles on it and you think the rings are worn? What, are you GOOFY? (305s don't last forever, just damn near it...)

Yes, unfortunately, it may be time to do a compression or leakage test. Your description sounds like excessive crankcase pressure from blowby. Just to be sure, inspect the PCV system closely and make sure all the hoses are clear. Are you getting some oil back into the air cleaner, too? If so, that's another indication of blowby at the rings.

My hat is off to you for your apparently good maintenance and care regimen. That's a lotta miles before something has to be torn down. I hope I'm wrong about what I suspect the compression test will reveal, but I rather doubt it. I think you've recovered your investment many times over, and the car doesn't owe you any more. A little DOHC four-banger would be on its sixth or seventh replacement head at that mileage. The old SBC V-8 is a very durable design, as you have proved. You may have just found how durable. If you get it before it's too late, you might be able to save it with boring and new pistons, if you are so inclined.

 

I do have minor blowback, found a few drops of oil in the vent hose (from the pass side valve cover to the throttle body, what is that anyway). My PCV is clean, but a small puddle of oil where the PCV hose connects under the TPI Plenum. For the miles, not bad. And, given that I didn't notice any power loss, the blowback is minor and I can live with that...for now.

As for the hissing/breathing noise coming from the pass side of the engine.......the Donut between the manifold and exhaust pipe.
Thats gotta be it. Just had my exhaust redone (4 or 5 months ago) so I suspect that could have stressed that donut to break.

Am I thinking right here? Looks like its gonna be a bear to fix that sucker.

Spoke with a friend who knows a guy (don't they all) who's ASE cert and works at the local volvo place....says he loves working on GM motors. Could be the guy to help me with my blowback problem. Will talk to him to see if he'd be willing to rebuild mine. Since the motor will be out, are there any headers I can put on that will still be emissions legal?

RB

 

There are several headers that are emissions legal. Edelbrock TES for one (that's not an endorsement, just an observation). Any header with the air injection fittings should be emissions legal, but verify the C.A.R.B. certification for use on your vehicle.

Your leaking exhaust flange gasket may explain the sound, but the oil smoke is a different problem. If the exhaust gasket is in good condition, another possible source of the sound may be the air injection system. A failed diverter valve or restricted silencer (muffler) on the diverter could generate the "hissing" sound under some conditions.

A few drops of oil at the PCV breather is not bad at all for that kind of mileage, but the oil that is going through the breather is getting burned somewhere, thus the smoke. Probably just aas much is going through the PCV valve and getting burned as well. Still, ½ quart between changes is not bad for a high mileage engine.

As for getting the exhaust loose, if it has recently been replaced, the fasteners shouldn't be too badly fused in place or rusted. A generaous application of penetrating oil a few days n advance, and a little added penetrant every day or more will allow it plenty of time to do its thing, making your job easier. As for the amount of space available there, no one can help you with that. It's a tight area. Remember to disconnect the battery before working there, since the starter is very close to the 'Y' pipe and manifold outlet.

 

but verify the C.A.R.B.
Ya lost me there, whats the C.A.R.B.?

Your leaking exhaust flange gasket may explain the sound, but the oil smoke is a different problem. If the exhaust gasket is in good condition, another possible source of the sound may be the air injection system. A failed diverter valve or restricted silencer (muffler) on the diverter could generate the "hissing" sound under some conditions.

I'm almost absolute about the flange gasket. Have dealt with it in other cars and it's beginning to show some carbon deposit around that area, I just dread fixing it.

Regarding the air injection system and diverter valve, correct me if I'm running into left field here, are you refering to the aluminum tubes connecting to the exhaust manifold? (I did check those and they seem clean and tight, no carbon showing there. I have seen those deteriorate and fall clean off before)

A few drops of oil at the PCV breather is not bad at all for that kind of mileage, but the oil that is going through the breather is getting burned somewhere, thus the smoke. Probably just as much is going through the PCV valve and getting burned as well. Still, ½ quart between changes is not bad for a high mileage engine.

Copy that. With the blowback, thats how I initially found the exhaust flange leak, a little smoke helps when finding these things.....LOL

As for getting the exhaust loose, if it has recently been replaced, the fasteners shouldn't be too badly fused in place or rusted. A generaous application of penetrating oil a few days n advance, and a little added penetrant every day or more will allow it plenty of time to do its thing, making your job easier. As for the amount of space available there, no one can help you with that. It's a tight area. Remember to disconnect the battery before working there, since the starter is very close to the 'Y' pipe and manifold

It was replaced, but from the Cat back....so I've got my work cut out for me. Might as well do plugs/wires while I have my bleeding knuckles under there.

Theres actually a story with the exhaust/plug bit.....
When I changed the plugs last time, I broke my exhaust at the CAT. I discovered that if I jack up the motor slightly, I get easy access to the passenger side plugs from under the car (especially the one near the firewall) Been doing that for years. Except this time when I was done, and lowering the motor back down I heard a faint snap behind the cat. Knew it was the exhaust so I grabbed the pipe and shook it a little and it fell right to the ground. Both bolts had snapped off behind the cat.
Gave it the old 'alabama' treatment (clothes hanger) and drove it that way for a week til my wife cried foul (prolly the neighbors too). Didn't have the cash for a complete install so I just had back end done.

Maybe this is a really stupid thought, but if I took the passenger fender off, would that give me easy access to the manifold?

 

no not really becuase if i remeber correctly when you take the fender off you still have the inner fender setting there and no way to get it off..atleast that is how mine is so anyway

 

Looked the fender idea over and it's not an option.
But...
See my new post (Air injector thingy), its not the exhaust donut afterall.......