Luke

1992 4.9L excess oil consumption

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Hey guys, I bought a 92 DeVille a while back for $800 that I'm using as a daily driver. It was more of just a project as I also have a 1980 Seville Limo, 92 Allante, 98 DTS, and 09 STS-V.  The DeVille has 151k miles now. After complete tune up, new injectors, and various minor repairs, it runs excellent and has probably better power than other 4.9's I've owned. No drivability issues at all. I'm pretty sure it has an intake gasket leak. MPG is lower than it should be. It was leaking oil which I tracked down to the intake manifold near the distributor. I tightened the intake bolts on that end and the leak stopped. I changed the oil at that time and have not seen any more leaks.  That was only 300 miles ago and it has already lost one quart. My question is, can a bad intake gasket cause oil consumption? Is it leaking oil into the combustion chambers internally? None of my previous 4.9's ever burned any oil. With the power it has, I can't imagine the problem is valve guides or rings. I don't really want to put the time and effort into doing intake gaskets unless I think it will fix oil consumption. Anyone have any input?

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I had a leak on my 91 Seville in the oil cooler lines, they run from the top of the engine on the driver side to the radiator.  There are O-rings in there that dry out, crack and leak.  If they are disturbed at all, they need replacing.  Check those lines carefully.  I had the tranny rebuilt and they disturbed the lines and they leaked badly.

I do not think that the intake manifold has oil running through it, you might be seeing oil from the cooler lines.

Valve seals will cause the engine to smoke out the exhaust after the engine has sat overnight.  Start it in the morning and let it idle, see if it smokes out of the exhaust.

Check the PCV valve for proper function.

Do not use synthetic oil

Use a high mileage 10W30.


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Mike, I replaced both oil cooler lines when I bought it because one of them leaked. When it started leaking quite a bit, I looked closely and could see oil bubbling from under the intake manifold under the distributor towards to front of the car. A little forward of the oil filter adapter. Tightening the three manifold bolts on that end stopped that leak. I think just oil splashing under the intake manifold was bubbling out. 

The problem doesn't appear to be valve seals nor rings. The car never smokes from the exhaust at all. Not on cold start nor ever while running. That's why I'm at such a loss. If there were bad valve seals or rings, not only would it smoke from the exhaust, it would affect power. This is my fourth 4.9 and it has more power than the previous three. It will roast the tires and pulls hard up to full throttle shifts. 

So, I just can't figure out where the oil is going!

Oh, and I did use high mileage 10w30 when I changed it 300 miles ago. 

Edited by Luke

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Did you replace the oil seals behind the oil filter adapter?

I have a 91 FSM, Ill look later for sources of oil leaks


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I didn't. But I never removed the oil filter adapter. And, after tightening the bolts, it isn't leaking any oil anymore. 

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  Make sure the 1 rear oxygen sensor is working it might be lazy. As for other fuel mileage items go with the basics, tire pressure, winter fuel will give you 2-3 mpg less. 

    Do you see any oil leaks at all or blue exhaust? Could the intake manifold bolts be loose under the valve cover? It's possible but that would create a vacuum leak and a higher than normal idle. Maybe hook a vacuum gauge up and see make sure the reading is 18-21 " at idle warm. The oil cooler lines do leak on these motors along with the oil filter adapter housing. The adapter housing is held down by 2 15mm bolts. Just loosen the one under the distributor and remove the other taller bolt. You will find 2 big fat seals in the oil filter housing i'm sure dealer only. 

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