350srs

Hey All,

Long time lurker here, just wanted to ask an opinion from those in the know.

I have a 2004 350z that has been using obscene amounts of oil, yet from a cold start is NOT blowing any kind of blue or white smoke.

The only time I see smoke is after leaving it for around 2 or 3 hours... It will leave a haze of light blue smoke for not more than 10 seconds or so, then run and smell clean from there on.

It's using around 1qt of oil in less than 200 miles, but I don't see any blue smoke when taking off from a traffic stop, cold start or or deceleration/engine braking.

The car had been driven with a failed/blocked cat for around 1500 miles, so I guess from other threads this has caused the rings to fail?

What I don't understand is why:

1) The car cold-starts without smoke from cold, when the cats are cold, shouldn't burnt oil be visible in this condition?

2) Why other engines from other makes/models don't fail when a cat fails.

3) How the engine can still run seemingly smooth and fine while using so much oil!


I pulled a couple of easy to reach spark plugs, and as suspected, they are slightly wet with oily carbon goodness..

Does all this mean piston rings, or could this just be valve stem seals? Seems unlikely.

If it's true about the ceramic pre-cat damaging the engine internals.... How damaged would you expect the pistons and bores to be? Would a hone and new rings suffice, or would you expect to see severe bore wear?

Such a shame, as it still runs so smooth and quiet.

350srs

By the way, I have already fitted a catch-can inline with the PCV and intake manifold... and it's not catching all that much oil.. maybe a teaspoon in a few hundred miles or so.

Also, there are no oil leaks in the spark plug tubes, or anywhere else around the engine.

Cheers

tcode

iTrader: (7)

Cats were failing and clogged because of excessive oil contamination. And eventually will again.

You don't see a bluish smoke because having cats, they do a their job cold or warm. Put a test pipes instead of cats and you will have a lots of smoke from tail pipes.

Your engine needs rebuild to stop oil consumption. In 90% cases on these motors, bad or worn oil control rings are cause.

VenomGT9

iTrader: (1)

Piston rings and valve covers would be my next step

dkmura

iTrader: (64)

OP doesn't mention how many miles are on his Z, but it's a fair bet there are many. If he wants a more definitive diagnosis, a leakdown and compression test will offer more insight.

Esteban350z

I used the right stuff (black rtv) for my spark plug tube seals and it's worked great for over 60k miles.

350srs

Thanks all... I think I will commence teardown very soon. The car has 112,000 miles on it. I agree a leak down test would be a good idea, but given that the spark plug electrodes are so wet with oily carbon - I know for a fact oil is entering the combustion chamber in bulk.

Also given that it's using so much oil, I guess this can only really be oil consumption due to the bottom end (rings) or top end (guides/valve stem seals) - or both.

I don't see valve covers as an issue, as there are no leaks into the spark plug tubes... but I will replace the valve covers and gaskets as preventative maintenance anyway.

I guess what I am most concerned about with (aside from oil consumption itself) is the story many people have told about the pre-cat ceramic substrate breaking down and getting sucked back into the engine when the engine varies cam timing overlap as a kind of substitute EGR system.

Suppose I will see the condition of the cats when removed, but using a stock cat seems risky if this is what can happen.. but I am unsure if the cat failure has caused the engine to fail or if the engine failure has caused the cats to fail.

Thanks again all.

Joe clan

Cat's failed because they got clogged with oil. There should be no damage to the motor, just worn rings. It is best to get the valves seals, new springs and so on redone or replaced if you rebuild. Buying a honing block that goes on a drill bit and hone before replacing pistons with the new rings. It might need to be bored over if there is a lot of wear on the cylinders. If it is running smooth but burns oil, than should have no cylinder damage.

Surfer90291

How much would it be to rebuild like you wrote? I think I'll have to start considering it.

sportbiketed

iTrader: (11)

My money is on bad valve stem seals

Joe clan

All said and done, if no damage , you might be able to do it for 1300$ -1900$ depending how much of the work you do yourself. This would be all parts and services included. Rings, gasket set, special tools, and cost from a machine shop to do the headwork. It has been a few years since I have had to do any headwork so my guess is 700$ or so if you bring them the heads and all they do is press in guides and seats. I would call a shop and ask, see what they say.

Now this is with you doing all the work, and shop just putting new guides and seat. This may get higher if you have to do timing chain and so on. Look up top end rebuild kits. But like I said above, it has been a while since I have gotten headwork done and not sure how much the rebuild kits are and what you might need to be replaced. The head work would be the bulk of the price.

Hope this helps. Anyone else got a better idea on cost or has had to to a top end rebuild or headwork on these cars??

Joe clan

This price goes up to almost double if not more , if you have to bore out the cylinders and then get bigger pistons.

Joe clan

http://www.enginepartsonly.com/2006-nissan-350z-1/ here is a link to give you an idea on parts cost.

Surfer90291

Gotcha, very interesting info. Would it be easier to just source a low mile VQ35DE to swap?

Joe clan

Not sure, I would want to rebuild. Never know what you are getting from another used motor. May turn out to be a good but I wouldn't want to take the risk. If you are capable and knowledgeable to do a rebuild yourself, then that would be my choice. If not, you are going to have to pay someone to do the swap and that will cost more. Plus you know that the motor will not leak or burn oil and last you for many miles once you rebuild. Used motor it's a gamble. That's just my opinion.

Surfer90291

Thanks for the tips, yeah buying a used engine is a gamble and I'd love to see if I can rebuild it myself. If I were to build it myself I'd see if I could venutre in squeezing more hp out. The biggest draw back of that is the car won't be drivable for a long time.
I understand the mechanics of the engine and I'm relatively familiar with it, I just haven't done anything more complicated than bolt on mods (cat back, plenum spacer, catch can etc)

dkmura

iTrader: (64)

Another option is to purchase a rebuilt VQ and have the shop reassemble and install it. Despite understanding the "mechanics of the engine", there's a LOT more involved to building a performance engine. If all your wrenching experience consists of installing bolt-on parts, you're nowhere near to being ready and able to rebuild a VQ properly.