Looking for some ideas on where the oil is going?

I have around 14,000 miles on a rebuilt 350. After a 600 mile trip it consumed 2 quarts of oil. A few weeks ago I ran back and forth to Carlisle and used easily three quarts after 750 miles.

The car does not smoke, and I just replaced the PCV valve along with new valve cover gaskets (pass. side was wet before the change). The oil pressure line was a bit loose and was tightened just before this trip. There is only a small drip or two on the garage floor, no puddle.
So, where the heck is the oil going???

TIA,

WB

 

Do you have the original style exhaust. I had a pickup truck that did the same thing. The heat riser below the passenger side exhaust manifold was installed incorrectly and was never opening all the way. It was open enough to not choke the engine, but was always sending exhaust through the intake manifold passage. This was cooking the oil, when I pulled the intake it was ll there baked into a lump. Since it was around the heated passage I backtracked and found the stuck riser. If you have headers none of this will apply to you.

 

Most common cause of excessive oil consumption without seeing any sign of it being burnt is the intake manifold gaskets needing replaced. The engine will suck the oil in small amounts past the gaskets.

 

The simplest possibility is that your valve covers do not have [and or adequate] splash guards below the PCV valve. Oil splash just gets sucked up and burned by the fuel charge a little bit at a time. If you have stock valve covers, this is not likely to be your problem; if you have aftermarket covers, it is worth checking out.

P.S. You can simply remove the PVC valve while the engine is running to see if oil comes out of the hole, or not.

 

Pettes73, Yes the car does have the original style exhaust with the heat riser. There is a possibility that it could be getting hung. I'll try to it it open and run the car. Thanks for the help!

I hope this isn't the trouble. They are not that old and I hope the gaskets would last longer then that. I will replace them if these easier attempts don't work out. Whats the easiest way to check them, without taking off the heads?

Will do, that's a possibility too! The valve covers are the aluminum ribbed style L46 or LT1 style I would say. They should be steel painted ones.
Thanks!

 

....are you running full synthetic oil?

....is there a lot crankcase blowby when you pop the PCV?

 

You say that the car doesn't smoke.
Did you check it at idle, at WOT and at high manifold vacuum conditions ( when you release suddenly the throttle pedal at high RPM for instance ) ?
I would be surprised that you don't see any blue smoke in any of the above conditions and your engine eats 1 quart each 300 miles...
Any visible oil leak anywhere ? Timing cover, oil filter, oil pan & plug, oil pressure gauge fitting, rocker arm covers, rear or front main seal ?
How many miles / years on the valve stem seals, valve guides and piston rings ?

 

Heads don't need to come off to replace intake manifold gaskets.

What type of piston rings were installed during the rebuild? Who did the gapping and what was the results? If the rings are too loose then you will certainly be using oil that way. It would be most prevalent with high RPM but low load conditions.

Something else I just thought of, when the engine was rebuilt was it bored and honed with new pistons/rings or just honed and used standard bore pistons? This would make for a loose setup and could cause excessive oil consumption.

What is your normal cruise RPM?

Your engine sounds a lot like some of the early LS1/6 engines that would consume large quantities of oil. The PVC system can eat some, but the weak oil rings were the main factor. How do the spark plugs look?

Sorry bud, but if it isn't leaking out of the block then it is going out the exhaust no two ways about it. It must be one or the other. The external leaks are much easier to figure out then the internal type.

 

But first, he has to admit that his engine is smoking or has an oil leak somewhere...
That's what I was trying to introduce in my post #7

 

If the oil is ingested at the carb (via PCV system, etc.), that oil will be diluted into the fuel charge and you may not see any significant level of smoking. That's why he should check to see if his valve cover baffles are working or are totally missing. Oil blowing by rings will not be diluted in the cylinder and will smoke.

 

I didn't know that the way the oil could enter in the combustion chamber could make any visible difference at the tailpipe...
Which doesn't mean that you are wrong....
Maybe the oil enters in the combustion chamber at different times in the combustion process according to whether it comes from ( valve stems, rings or diluted with the fuel ) and so burns differently ?
Is that what you mean ?

 

If the PCV valve gets 'raw' oil up to it [not deflected by baffles], the hose going to the carb plate is under vacuum and will suck it in. If it enters below the carb venturi, the point of highest airflow, it will mix with the fuel/air vapor and get burned as a mixture...instead of as oil droplets coming from the rings. Lots of folks have had the same problem...but I don't recall any of them indicating that they had a 'smoking' issue...just an oil consumption problem. Is pulling the PCV valve out of the valve cover [with engine running] that difficult to do? If no oil splashes out of the hole, the oil is not entering the engine by that route.

 

You should be doing a leak down test before replacing anything.

 

OK, I put the car up on stands tonight and found an oil soaked under body. It's an external leak, I have no idea why there's not a puddle on the floor. It appears that the oil leak starts at the back of the motor. I'm guessing rear main seal? What's the procedure........?

WB

 

Rear main seal is not too bad. At least you found the leak and it's easier than the piston rings...
I would say it's a 4 hours job, more or less...
You will have to drain oil, remove the oil pan, probably will have to buy a new oil pan gasket ( FelPro one piece is great ) then remove the oil pump (the shaft will fall ), then the rear main cap and seal ( two halves ).
The lower part of the seal will fall with the cap, the upper part has to be pushed or pulled without scratching the crankshaft.

More informations, pictures and instruction sheet here :

http://forums.corvetteforum.com/c3-t...-qestions.html

Good luck !

 

I will tell of my new engine some 12 years ago....'89 roller truck block, fresh build TRW .030 over pistons...Old castings iron heads 993 as I recall....anyway the intake had to be machines some 20 mils of the top of each intake flange to alter that angle to agree with the heads....heads may have been angle milled enough by p/owner, to allow oil in the bottom edge...the passages were uniformly wet....but in MY case it was visible on startup and on high rpm backdown revving in the garage... I could never see anything in any mirror on a road test....

so I still had a slight consumption problem, not nearly as bad but irritating....I found the PCV rubber vac line had oil film in it....

I played with the valve covers and all sorts of setups, having TPI on it, I went after the throttle body also....just oily passages no matter where I looked....it always sucked oil through the PVC, never did cure the problem even with the Edelbrock heads.....sold them, and went to the #113 factory aluminum heads on there now....same difference,

then for completely unrelated reasons, I went to a LT1 style intake, it has the PVC on the top driver's side center up high in a lifter valley pan area with plenty of large baffling instead of a multi plated small thing in the valve covers.....that cured the problem.....I found that the engine quit burning oil entirely then....

 

Check the simple stuff first: valve cover leaking at the rear of the block; valley seal leak at rear (under intake manifold); oil pressure line broken or split; no gasket under the distributor; oil pan gasket at rear of engine. Hope that the rear main is not the cause [PITA].