Some back ground. I bought my I35 with 56K miles back in January of 09. By the summer time it had about 60K and I started noticing the dreaded pinging on the hotter days. Around my 3rd oil change, I also noticed it was consuming a little oil between changes. Fast forward to the present, it now has 127K and is consuming ~3-5 quarts in 3000 miles between oil changes, and still pings pretty much every day here in southern California.

Note: I have always used Valvoline oil and K&N oil filters and have been really strict about my change intervals.

It was never spewing dark smoke, and I never noticed any significant lack of performance, so I didn't ever really think it was bad rings. Even still, I wanted to back that up with proof, so a couple weeks ago, I finally did a compression test, and the numbers were great, almost like a new engine. The numbers were all really consistent w/in 5-15psi. 2 of them were around 180-185, 3 of them were around 190-195, and the only anomaly was cylinder 6, which hit 210 and was still climbing for some reason when I had my helper stop cranking. I thought that was really weird and have no idea what would cause that, but it wasn't low, so I didn't worry about it too much.

Since the compression test was good (barring the weird high value in #6), based on my countless hours of research, the OC can only be oil leaking past the intake valve seals. This is backed up by the presence of significant amounts of oil in my UIM.

So here's the theory I've pretty much settled on. The oil is leaking by the valve seals (OC), and making it's way into the combustion chamber which is causing the pinging. If it's not pinging the only other thing I have read about that it could possibly be, is the timing chain rattling around. Which I suppose could be possible since it gets much worse when the engine is low on oil. But low oil would also cause the pinging to be worse, right? Since when the oil is low there is more friction and more heat, contributing to the pre-detonation, right?

Anyway, since these problems are both so common in the VQ's, I have to believe that there is a design flaw in the cylinder heads that causes these seals to fail and start allowing oil to get by.

Solution? if it's pinging, and not chain rattle, then I'm thinking about finding the cheapest remanufactured cylinder heads I can with a decent warranty, and swap them out myself.

There are 3 questions I have about all this, that I would really appreciate some experienced peoples feedback on.

1. How difficult is it to swap out the heads? Is it as easy as tearing every thing off, making sure the cams/pistons are in the right position and installing the new heads? Or is there other things that need to be done, and disassembled besides the UIM/LIM, fuel rails, and other little things?

2. What other things are easy and or smart to replace while I have all that torn apart. Already did coils and plugs very recently. I know I should replace the water pump soon at this mileage, but don't think that will be any easier to replace while doing this. Please correct me if I'm wrong. Oh ,I recently replaced my valve cover gaskets, and I have the NWP plenum spacers so I don't need UIM/LIM gaskets either.

3. What could cause the abnormally high compression in #6, and should I be worried?

Any and all thoughts will be appreciated.

 

usually when the valve seals leak, you would get some smoking in the mornings on a cold start, even a long crank to start the engine and rough idle if it is bad enough.

"1. How difficult is it to swap out the heads? Is it as easy as tearing every thing off...:

well, yes just a matter of tearing half the engine apart. the difficulty is in removing the timing chain covers with the limited amount of space you have to work in the engine bay, I drop the motor to do a job like this especially to do the cylinder head by the firewall.

the point is, if you are going to get new heads, you'll need to deck the block to accept the new headgasket. I would not leave the bottom end untouched in a vq35 with 130k miles. If you are going to do the work, do it right the first time so it lasts you a long time. At this point, it might be cost effective to get a reman long block or a low mileage vq35 from a 6th gen. (6th gen long block is a direct swap).

 

Thanks. That's what I needed to know. Time to get rid of this thing for sure. Not worth spending $2-3K on a used long block on a car that would only be worth $5-6k max when it was done.

As far as the smoke in the morning, I've never noticed any, but since it's not rings, and it's not an external leak, then there is nothing else it could possibly be but intake valve seals, right? Especially with all the oil I'm getting in my UIM. Oh, I do have a bit of a rough idle as well.

I'm thinking of getting a G35. If I got one and it had OC issues, I imagine it would be easier to replace the heads with the timing cover being in the front? Can it be done w/o taking the engine out?

Thanks again.

 

yes, the g35 engine head removal is a bit easier since the timing chain covers are in front by the radiators.

 

You're 100% sure it's a direct swap? It will work with my harness/ecu, and it will bolt right up to my trans? I just found a used 08 max motor with 39K for $1800, with a 3 year warranty, now that might be worth doing, if I was sure my trans would hold up.

Thanks again.