LT1 oil consumption

[Craig 94 TA GT]

Is there a reason for oil consumption besides blow-by? I noticed that my "new" engine is using over a quart of oil every 2,000 miles. It could be close to a quart and a half, but I haven't gauged the exact amount.

The motor has about 18k on it, since the build. I was told to use a higher weight oil, due to the better bearings, so I'm using Mobil 1 15w-50. It does have a couple very minor leaks (not sure where, but it appears to be minimal). I also notice that there is a fair amount of an oil coating inside the intake manifold. The stock LT1, prior to the build, didn't consume 1 drop of oil.

So is it common for a "performance" LT1 build to consume this much oil? Or does it sound like I have a problem? Thanks in advance.

[Trash man]

although u can consume a 1qt of oil every 1000 miles by us standards, in my book u shouldnt consume any, fix the leaks and see if u can find out why you have oil in ur intake manifold, maybe its a bad pcv vavle

[Injuneer]

Good advice. The PVC system is not handling the blowby. Either the valve is not working, or the blowby is excessive.

Worn valve seals/guides will also increase oil consumption, but that wouldn't put oil into the intake manifold.

[Al 96 Ram Air T/A]

To add to what Injuneer said, you are still using the PCV system right? I see it far too often where people disconnect the system and install an old style breather. Even on tricked out LT1 engines, the stock PCV system is more than adequate, and in most cases, beneficial to leave intact.

The oil is going somewhere...if not on the ground, it's going out the tailpipe. Burning that much oil should produce white smoke in the exhaust. Have you checked your plugs recently? They're probably coated by now.

[Craig 94 TA GT]

Thanks guys.

The PCV system is stock, but it uses an aftermarket type PCV filter on the valve cover. I'm not sure what kind it is, I'll have to ask Steve (Z ya later) because he bought it for me. I thought it functioned more or less stock, but I could be wrong. There is a bit more oil behind the throttle body though, where the PCV hose goes into it. Is the PCV valve inside the black box on the passenger's side valve cover?
[EDIT] Found out what it is - it's a Fram PCV filter (or valve?) that sits on the valve cover.

The heads are full ports directly from AI, and the used K-line full bronze liners with new Manley Stainless Pro-Flo Valves so I don't know if it's possible for that to be leaking within this many miles?

The plugs look pretty dry though. I just regapped them a few weeks ago, and they appear a bit "orangy" on the ceramic or porcelain, with just a little oil on the rim. I can post up pics later today.

I asked the engine builder about this and his response was that he's not a fan of synthetic oil in built engines. I did notice that while breaking in, I used conventional Castrol 20w50 and I don't recall it using much, if any at all. He suggests I use Kendall 10w40.

[Al 96 Ram Air T/A]

Sounds like the PCV system is original...just make sure the ball-valve is working on the valve itself (pull it from the valve cover, place finger over end...you should hear the ball moving)

I re-read your original post...you're consuming/losing a quart/quart and a half every 2,000 miles?? That's a lot. If you were burning it, you would see smoke...at the very least, you'd smell it. But, if your plugs are dry like you said, I'm starting to think you're leaking out somewhere.

What puzzles me is, if you were leaking, why can't you see it? If it's leaking out while your driving, odds are it will contact the exhaust somewhere and you'd smell it. Very puzzling to say the least.

By your estimates, you're going through 3 qts. every 5,000 miles. That's huge!

[Craig 94 TA GT]

Here are some pictures. I guess the plug had a little more oil than I thought, but still nothing I would have thought twice over.

The intake picture was out of focus, but you can see how much oil is in the intake manifold - is that anywhere near normal?

And yes, it does burn between 1 and 1.5 quarts every 2k! I can't believe it either - I was over a quart low and noticed that I have ~2300 since my last oil change. I'm so not used to this because I would never see anything burned with the stock motor.

And I agree, if it was leaking that much, I should see it on the ground. I don't notice anything except for a thin layer coating on the oil pan and oil filter. Maybe a little on the torque converter shield. But I had way more than that leaking on the old motor - it would be coated really well before. Yet, it wasn't enough to change the oil level?

I'll take a look at the PCV - the metal area that it's enclosed in is beat up - I had to work it to get the Comp Cams RRs to fit. It's not pretty, but I had done that with the old motor, so I'm not sure if something may have went bad since then.

So I assume a bad PCV causes a high pressure build up in the crank case? Would this then force blowby because of the pressure built up?

[FTA1995]

If there is a filter of any kind on the lower end on the vent hose to the pass side valve cover, it could allow oil to build via capillary action, slowly getting pulled in little streams into the back of the TB. Maybe try it without that filter, you'll probably see results.

[Injuneer]

You asked if the PCV valve was in a box on the passenger side valve cover.

The PCV valve is on the driver's side, middle of the intake manifold.

[FTA1995]

Honestly, if you don't have any visible leaks or any visible signs or smells of burning oil......

Do you have any extension of the oil system like a cooler, bypasses of any type, is there anything that could *possibly* be in question? It's got to be going somewhere... What about getting an exhaust gas analyzation? I'm pretty sure the can tell you what and how much of what is in your exhaust gases.

[Joe 1320]

If the PCV checks out, I would do a leakdown and compression test. Something about the recommendation of "thicker oil due to better bearings" makes me nervous. Was this motor built for an extended rpm range?

[Injuneer]

Have a leak-down test done. Faulty rings allow blowby, which overloads the PCV system, and causes oil to end up in the intake manifold. At the same time, when the piston on the intake stroke, the faulty rings allow oil to be sucked up into the combustion chamber, increasing oil consumption. And don't overlook the worn valve guides or worn seals. If it isn't leaking, its being burned.

Oil in the combustion process increases the chances of detonation (knock). By the time the oil reaches the exhaust, its just another hydrocarbon that has been converted to water, CO2 or CO in the combustion process.

[Craig 94 TA GT]

Thanks Fred, Joe and FTA (don't know your name!)

I purchased a new PCV valve over the weekend but didn't have time to install it. I'll put it in as soon as I can.

I was afraid that I was going to need a compression and leak down test. I'll do that if the PCV valve checks out. I agree that value guides is a possibility now because the builder didn't put in the correct length pushrods (but insisted that they're still proper length). The block was decked, using Felpro 0.039 gaskets, and heads were milled. I ended up measuring them to need 7.050 length. He had 7.2 in there and said they were fine. I ended up changing them myself after about 300-500 miles. It could have been a little more, but I think it was no more than 500 miles. I really took it easy then though, never trying to surpassing 2000 RPM (but still passing it once in a while). The contact patch on the valve was towards the bottom 1/3rd. The new 7.05 is almost directly in the middle. I think it's possible that the guides were prematurely worn there too.

Oh and oil in the combustion causing knock...not good for me. The tuner completely tuned our KR because I was getting KR all over but the motor was new (and supposed to be healthy), exhaust is loud, valve covers stock and not composite.

Also, it was supposed to be built for a high RPM range - the builder said he put in "race bearings" and ARP studs throughout. Rev limiter is set at 6651 and shift points are 6300, but the shift completes at 6400. I never take it that high though, unless I'm at the track or dyno - and I had it dyno tuned twice and took it for 7 runs at the track in March. So basically about 8 total dynos, 7 quarter mile runs.

[FTA1995]

You should be picking up a lot of false knock with that motor, but did you guys determine if it was false knock, real knock, or a combination of the two? A compression test should give you a clue IF there is any problems involving rings and the seating of valves. Name is Alex by the way

[Craig 94 TA GT]

I finally replaced the PCV valve - the old one was clogged. It took some pretty violent shaking to get it to rattle. Just some mild shaking, and no noise. I hope the new one helps with the consumption. I put another 800 miles and lost at least 1/2 quart again. And I think I did notice smoke under heavy throttle sometimes - but only sometimes.

I did pick up a lot of false knock with this motor - before and after the new engine (exact same intake and PCV, which looked original so it prob had 145k). I don't know for sure if any of it was real knock, but I just assumed it was always false.