Have 2500 miles on my 81 rebuild now...have fixed the valve cover oil leak (finally)...but am still using a quart of oil every 200 - 250 miles!!

There is no blue clouds behind me or anything..

What/where do I look??????

Thanks,
LannyL81

 

Have someone follow you. It's hard to see blue smoke while driving, unless it's really bad...

 

my recently built 570 hp 406ci engine consumes a good quantity of oil as well, specially since, after a running in period, i went from fully mineral 40 grade to fully sintetic 0/30 grade, i have no fumes whatsoever, no malfunctions and the car goes like a rocket

 

Look at the underside of the body. A leak will flow oil towards the back while driving, coating the whole underside of the car. You may or may not see a puddle when parked, and may not know that you are leaking, verses burning. You may have to wipe the underside off in order to tell if the oil is fresh or not.

 

Fresh build w/excessive oil use ...
Look for intake manifold-to-head leak [sucks oil from lifter valley into port(s)] ... also, an upside down 2'nd ring will pump oil ... it does happen.

 

Misaligned intake gasket is always a good one to look for. I have 20K on my 406ci and it doesn't use any oil at all, I don't put any in between oil changes every 5,000K. A properly built and broke in motor should not burn/use any oil or very little

 

I had the same problem on my 81 rebuild. Went through 3 qts of oil in less than the first tank full of gas. I had no idea, no smoke out the exhaust and any type of indication until I started loosing oil pressure and checked the oil level. It was the intake gasket. Replaced it and haven't used a drop of oil in over a year. I would check that first before anything else.

YBnormal...drive a vette

 

For misaligned intake gasket, pull all the plugs and look for one that is fouled ( dark and wet )

 

When I did my rebuild, I had the block zero deck (actually came out to be +0.006) and the 76cc GM 882 heads were milled down to 74cc...all of this resulted in using shorter push rods and I had to have the stock intake milled down 0.010" (I think) to get a good seal.

So I leaking intake gasket is the first thing I am going to do. I will pull the plugs (again) and check them. Last time I did this they were all a bit black on one side only...so I could be leaking all the way around..which would also explain why I have think the engine is lacking in performance from what it should be.

Sure glad the weather has cooled off now so its not 110 in the garage anymore. Thanks for the info....time for me to get busy.

Later,
LannyL81

 

do you have breathers on the valve covers?

Check for oil leaking out of there.

 

one side has the PCV valve, the other side has the tube going to the air cleaner. Both are clean...well, not oil soaked or anything like that.

I was going to pull the intake this past weekend, but ended up putting a B&M short throw shifter in my 96 LT4 instead. May be next weekend I will tackle the intake.

LannyL81

 

I checked the intake gasket for leaks by using a propane torch set to a very low flow (unlite) and passed it over the head to intake area several times on each side with the engine running...listening to the engine idle and expecting a slight increase when the propane was sucked into the intake.

Never heard any increase..nada...nothing.

The engine used about 1/2 quart today in about 70 miles of combined highway and traffic driving.

What is going on here??????
Is the propane check not good enough to tell me that there is an intake gasket leak?

jackson: you suggested an upside down 2nd ring....would a compressions check find this or am I looking at taking this engine apart?

I will pull the plugs again and replace the intake gasket and try that before taking the engine apart. But is there something else I can do to find out why it is using so much oil???

Question: Again this is on an L81 stock rebuilt engine, except that I used a set of GM 882 heads instead of the stock 624 heads as they were cracked. Anyone know if the metal heat riser part that goes into the intake could be causing this oil consumption? I believe I put it on correctly, followed the instructions on the gasket set box, but just happened to think about it when looking at another set of gaskets. Do both sides get this piece, one side..????


Thanks

 

That's your problem right there, a good machinist will make sure everything lines up, all the others won't really give a crap and try and blame it on you somehow.

Take the intake off and see if you can tell how far off the angles are and you might want to try and seal the intake off with a bead of silicone all the way around the intake gasket on both sides, especially the bottom where the oil from the valley could be getting in.

 

You were looking for a vacuum leak? But you are sucking oil.

Passing the propane over the top is not going to find the suspected internal leak that could be sucking in the oil.

Oil crusted plugs on one side sounds like you are sucking it in. Milled heads make it much more likely. Pull the intake manifold and see what the gasket looks like. It sounds like it is not sealing well enough to prevent the oil from getting sucked in.

-Mark.

 

MAN!!! That's a lot of oil consumption!!!
My car has bad valve guide seals and after 500-600 miles, I see a very slight burnt oil film on the back of the car....do you notice this? I go thru a quart every 500-600 miles...And also, have you put down a tarp under the engine to see if it is leaking? That much oil has got to be showing someplace, I wonder if it is a rear main seal...also, I agree, have a friend follow you and see if he see's blue smoke when you get on the throttle....good luck

 

How did the plugs look? Any oil fouled? If so which ones. I am willing to bet it's an intake manifold gasket. After 2500 miles on a rebuild you should check the torque on the manifold/s. It's cheap just to install a new intake manifold gasket and see if that fixes it.

 

Mark..... ....you are so right.....what was I thinking

With having to mill the intake to get a good seal at the top, I am sure I do not have a seal along the bottom of the intake.....

I will take the intake off and put down a nice thin bead of RTV around the intake ports between the intake and the gasket.

Thanks everyone for clearing my head....sometimes it does take a to get the mind working again.