Originally Posted by ByByBMW

The way I read all this information, the viscosity of a 0W-30 oil at 75°F will be, lets say 40 for the sake of argument. A 0W-40 oil will ALSO have a viscosity of 40 at 75°F. True?

If this is true, then why would one prefer a 0W-30 weight oil over a 0W-40 weight oil since at operating temps of 200°F the viscosity of a 40 weight oil will be higher than a 30 weight oil?

Originally Posted by CGZO6

Perfect sense, but how do you measure it?

Originally Posted by Smokin04

A magnetic based dial indicator set up with the tip centered over the valve tip on the portion of the rocker facing towards the rear of the engine.

Originally Posted by CGZO6

So it's fore/aft play at the tip of the rocker. Caused by excessive play at the rocker arm pivot?

Originally Posted by Smokin04

My friend...please read all 10 lessons in the University. It will make sense. A straight 40W does NOT have the same viscosity as a 0W-40 at 75*. I KNOW THAT!!!!!! I can't begin to type all of those lessons man. He breaks oil down at a PhD level.

Originally Posted by Unreal

Agreed that oil temp probably plays a huge roll. They take FOREVER to heat up to proper oil temp. For 95% of the people I bet a great mod would be to do like base vettes and just have no oil cooler. Run the bypass part. You only need an oil cooler if you are beating on it at the track. For those people they can keep one and uncover it when at the racetrack.

Another option is a air/water like the later z06/zr1. Dewitts has a nice setup. My oil temps comp up much faster with the dewitts oil cooler.

Originally Posted by CGZO6

So it's fore/aft play at the tip of the rocker. Caused by excessive play at the rocker arm pivot?

Originally Posted by Smkn 07

Originally Posted by Smokin04 View Post

A magnetic based dial indicator set up with the tip centered over the valve tip on the portion of the rocker facing towards the rear of the engine.



Or is it side to side play of the rocker on its pivot? 0.300" sounds absolutely huge in either case. Are you sure those rockers still have the bearings intact?

Originally Posted by ByByBMW

I'm not talking about straight weights, and neither are you. We are both talking about multi weight oils yet everyone keeps going back to single weight oils and that is NOT what I am asking about.

My question still stands. Basically it is, why a 0W-30 over a 0W-40? (And please notice that I picked up on your mistaken post earlier where you typed 0W-20 and meant 0W-30)

Originally Posted by birdflu

I've always understood the oil boiling out the water/contaminates thing, but I don't think the oil weight and temps play much of a part here.

I cant remember a car that had an oil temp gauge that ever reached 200 degrees in normal driving. That always made me wonder if the oil was getting hot enough. My oil cooled 964 was never near 200 unless I was stuck in traffic. At highway speeds it was always well under 200 degrees.

As far as flow/protection once the oil reaches 100 degrees, it flows as well as it does at 200. The oil pressure in my Z06 is always high when cold, and as the oil warms it drops, as it should. Once the temps get to 100, the pressure levels out. 5K rpm or idle with the oil at 100 degrees, gives the same oil pressure with the oil at 180 degrees. Get near 5K rpm with the oil under 100 degrees and the oil pressure needle is easily pegged. I use Amsoil 0-30 if that matters.

I've seen many Blackstone Analysis reports here and none have ever reported anything contaminating the oil, which could be caused by the oil running too cold. Ive seen contaminated oil before when its changed, and no here has ever said their oil was milky or odd looking during an oil change.

I still think this is all well intended guess work among the collective in this forum. The only source with a large enough sample, and data to actually back up any hypothesis is GM, and they aren't sharing what they know.

Originally Posted by Smokin04

I have discovered what I determined to be (in my opinion) the notorious valve issue. It is caused by 3 things. One of the three is more dominant than the other two. They're listed by order of severity.

1) Operating oil temps and weight. First we should be using a 0W-20 because 90% of engine wear happens on start-up. You want oil that thickens the least possible amount when cooling, but still offers protection (proper viscosity) in the needed pressure/temp range. Also, a lot of people don't realize that oil should be at least 10% (in general terms) hotter than the coolant to protect properly. When oil doesn't get above 212*(considered “normal operating temp”) it's not hot enough to boil away the water which it collects when not running, thus, it's considered contaminated or not protecting properly at a minimum. Problem is exacerbated further in the ZO6 because not only does oil not reach 10% hotter, it doesn't even reach 200* in most street applications. This can be why we're seeing failures of stock (unmodded or lightly modded) street cars. It's well documented that oil needs to reach 200+ to even work properly (or achieve operating temp). The track guys (environment where the ZO6 was designed to survive in) often see (average) normal oil temps of 250-260 with coolant in the 220 range. This is the "sweet spot" for proper engine protection and function as designed by GM. But when those track cars operate on the street as well...that's where their excessive engine wear is coming to fruition...much like the rest of us. This has to do with the materials being utilized (IE Sodium filled valves…more on that later).

2) Poor exhaust rocker arm side loading. Now I actually measured the deflection on my car when the rockers were swapped for Yella Terra's. How does .382 grab you? (This was the extreme case, as there was typically between .250 - .300 on the others) That’s almost half an inch of deflection. This was measured on 4 separate exhaust valve with my dial indicator. It was so extreme; you could see it with the naked eye. Notably, there was virtually zero deflection on the intake side. This deflection will have the effect of unwanted pre-load or “side load” with every opening of the valve. It makes sense to me that the severity of the deflection would vary from engine to engine. This can be why some valves fail at 5K miles and why some last longer. Combine this with oil not being able to protect the way it should...the proverbial plot thickens. Some might say this is more severe than the oil temp…and you could argue a case to that point. I think that these are both serious issues, but this issue would be less of an issue if the oil could protect properly.

3) Sodium-filled valves. Now this is where it gets tricky. Sodium valves work VERY well. Once they reach 206* the sodium liquefies and begins transferring heat to the heads through the guides. Normally, this is a good thing. In our case however, the sodium actually cools to a point that it keeps oil temps at bay (hindering the oil temps reaching normal operating temp). On the track this is a non-issue and where the valve was intended for use (also why GM used them IMO). Yes the "weight issue" can be brought up here, but not really because GM could've used titanium (or hollow stainless) if they were worried about weight vs. heat transfer. So GM using the sodiums makes the problem worse for the street guys. Ideally, you could have a solid (or hollow stemmed) valve head for the street, and the sodium equipped for the track days. Obviously, guys aren’t going to swap heads every time they want to run, so GM elected to go for the big guns and protect the track guys. Fair enough. I don’t think GM counted on the oil temps being so low. But one can only speculate on GM’s decision for using this valve at the corporate level. All we can do is protect our investments with research and appropriate counter-measures.

Combine these 3 issues, oil not protecting with horrible pre-load, and thin walled sodium-filled valves, you have found a recipe for failure. The sodium chamber can develop frictional "hot-spots" from the excessive side load that will eventually fatigue just below the sodium chamber (its thinnest/most sensitive point) and eventually break causing the head of the valve to break off. This excessive wear occurs with every mile but really only has to occur once or twice to start the proverbial "snowball" rolling down-hill. This wear is occurring at the factory level, and only gets worse as the miles add. Once started...there is no repair unless you replace the guides (or heads) such as GM is doing. Without regulating the oil temps, and fixing the rocker pre-load...you could change heads a dozen times and the problem will likely still occur. Even in my case, with proper oil temp control, and corrected geometry, the damage is done and I too will need new guides/heads.

The debate about stainless valves versus sodium-filled valves truly comes down to preference. There are literally thousands if not tens of thousands of successful cases of stainless valves being used in intake and exhaust locations. Stainless valves in performance applications is hardly a news flash and their reputation as reliable valves in performance applications can NOT be debated. But, this is also why I say it’s a matter of preference. Sure, sodium-filled valves can be lighter; but they’re generally utilized for their better heat transferring capability in dedicated racing engines. They were not designed with 200K miles in mind. Also worth noting; with continuously developing tech in metal alloys you’d be surprised at how insignificant the weight variance between the two really is. As a general rule, you want the valve train as rigid and light as possible. Personally, I agree. But, not at the sacrifice of longevity. Even if you control oil temps and side load, a sodium-filled valve is still weaker structurally, than a solid stainless valve. So I will vocalize my opinion and say that based on the track record of the sodiums, a solid valve is the better choice on a street motor.

Valve guide material choices also are a preference in my opinion. I personally have run manganese bronze guides in a street car for well north of 100K miles. This was a street/strip application…about 90% street, 10% track. Is bronze a “better” choice than powdered metal? Personally, I think the difference is negligible on either street or track applications. All have their merits and preferred applications, but I doubt any recordable/measurable difference exists between the guide materials in a street application.

The “fix.” Based on information publicly available, compilation of data from this board, and other conducted research…I believe that fixing the oil temp issue is the FIRST step in the “fix.” Blocking off your oil cooler with something that denies airflow will allow your oil to reach “normal operating temp” and protect properly. Once that is accomplished, address the rocker geometry issue. Either run an aftermarket setup, or find a way to make sure your rockers have NO deflection or side-load. A centered wipe pattern is NOT enough. You have to ensure there is no deflection and proper geometry. This ensures that you’re not chewing up your freshly installed valve guides. Is this possible to do with stock rockers? I honestly don’t know. I know I have not tried because it was easier (on the wallet too) to just go with aftermarket shaft style. Starting over with fresh (read: unworn) guides is necessary. You can use whatever guides you choose. You can replace them in the stock castings, or use aftermarket heads. But if you haven’t addressed the oil temp issue, your new heads/guides may already be being worn. Once these issues are addressed, you can elect to re-use the stock valves, or replace them with stainless variants. Personally, if it’s longevity you’re after, I would choose the solid stainless valves. After you have addressed these issues, in my opinion you’re no longer in danger of engine damage caused by exhaust valve failure.

Sorry this was long winded, but this is my input to the string of failures. There are many inputs from numerous people out there as to their interpretations of what the cause and “fix” is for these engines. This thread is not intended to de-bunk or disagree with any previously listed hypotheses from other members. These are just my thoughts based on independent research I have conducted for the purpose of self-enlightenment. I am an analyst by profession, and a mechanic by passion. I am only trying to help the community for which I have developed a fondness. I think the ZO6 is a supercar, and I absolutely love mine. I know I’m not alone in this passion, and these are sensitive times for us…especially when money gets involved. If you feel what I listed is not an accurate portrayal of the real issue; I encourage you help the community and your own interests by conducting your own data collection and research efforts, and post for the community to see. Hopefully, this has helped someone.

Originally Posted by kenw

OP Thank you very much for you thoughts on this issue, they make a lot of sense.

I have always wondered about the time it takes for the oil to warm up.

What venders sell covers for the oil cooler?

Originally Posted by dcamick

Great post!

What are the consequences of covering, thermally, the entire oil cooler?

Originally Posted by smokin04

[...] i did not measure the "tip-weight" of the yt's. This really is irrelevant to valve train function in the operating conditions we deal with. It has the equivalent affect as say...a mouse fart in a tornado.

Originally Posted by MarkC

Smokin, thanks for taking the time to share your thoughts and opinions on this problem. They make sense to me. I always want to run my car with the oil reservoir full. I am going to pull the oil level down to the min and see if that helps with the heat issue.

Originally Posted by Mark200X

Originally Posted by ZIE06Bernie

Anyone know what the oil temps are like on a ZR1 by comparison.

Seemingly they suffer a lot less valve hassles than the Z06 so I think comparison is valid IF you make the case for oil temperature being a major problem.