clogan

Among the schools of thought regarding the valve drop issue is one that centers on engine/combustion chamber temperature. I am not nearly smart enough to understand all I have read about this, but have one simple question that you more experienced types perhaps can help me with. After having my heads replaced with WCCH "stage 2", milled heads, and getting a new tune, I notice that my engine oil temperatures are much lower than prior to the R&R. It has been over a month now, and in various kinds of driving, I have not yet seen the indicated oil temperature exceed 150 degrees. Prior to the work, temps would routinely reach 170 or perhaps more...I don't really remember.

What I am wondering is this: is there a correlation between exhaust gas temperature and engine oil temperature? And if so, is 150 degree max oil temperature less than what would be expected if factory stock?

Jawnathin

I do believe there is a link between SS valves and OEM Sodium Valves when it comes to oil temp, though I'm not sure if its to the degree that you're seeing. I will find out for myself once I get my car back.

Anyway, my theory goes like this.

The valve, no matter what type, will make contact with oil under the valve covers. Sodium Valves transfers more heat more rapidly than the SS valves do. Hotter valves = hotter oil temps.

However, I'd be surprised if it was significant enough to warm up 9+QTs of oil to the degree you're mentioning.

How was weather and driving conditions between the two configurations? If all you're doing is highway when its 50F out, your oil will stay very chilly.

Bill Dearborn

Valve temperature probably has more to do with how much power the engine is producing during any specific time period. If you are just loafing around driving down the highway in 6th gear at 70 mph the temps will be a lot lower than if you are at wide open throttle in 4th gear at 150+ mph. In the highway scenario the engine is probably producing 30 or 40 HP while in the track scenario it is producing closer to its rated 505 HP. The exhaust valve is going to get a lot hotter in the full power scenario and is going to transfer a lot more heat through the guide to the engine oil.

Bill

clogan

My driving has always fallen into the "loafing around town" category. Both prior to, and since, the head replacement. I bought the car new in 2006, and have accumulated 40,000 miles. The car has seen WOT maybe 5 times total. I mean, considering speed limits, traffic congestion, PoPo, poor road conditions, it is a rare occaision that my engine ever sees anything north of 4,000 rpms.

Perhaps it's just the combination of cool weather here in s/e TN, loafing around town, and the new tune. Perhaps I will see 170+ degree oil temps again when the 110 degree days of May, June, July and August get here. But I distinctly recall 170 degrees back in December and early January, before getting the new heads with SS valves. Perhaps the new tune activates engine cooling earlier/longer than was previously the case.

Anyhow, my engine now seems like it's considerably cooler than before.

Unless it's just my imagination.

But it probably doesn't mean anything anyhow.

Mark2009

This old military paper on sodium valves in aircraft engines indicates that the air/fuel ratio (which they are calling fuel/air ratio... divide it into 1 to get A/FR) has a greater effect on valve temp that a 159% increase in power (say, 100 HP to 259 HP). Unfortunately they are using a term -- Indicated Mean Effective Pressure -- that I cannot readily convert to HP.

This takes us back to earlier discussions that the exhaust valve may be getting overheated by closed loop stoichiometric operation (14.7:1 AFR). Loafing around at low RPM under load. Or not.

X25

The fact that this dropped valve issue happens to even those who take it very easy on the valve-train makes me believe that it is not necessarily a heat-issue, but rather a geometrical and/or material issue.

KLJ

Whoever did your tune should be able to answer this question regarding oil temperatures. What did they say?

If someone is modifying the tune they need to have answers for this. As was pointed out, it may be something as simple as a fan being activated at a lower temperature.

clogan

You are correct...they indeed said the tune causes the fans to come on earlier. I am inferring that this in turn means my valves will not get as hot as before, as evidenced by the lower oil temps I am seeing. A further inference would say that lower temps are an additional layer of protection against valve drop, perhaps. New valves, new guides, new springs, lower temperatures...all combine to hopefully counteract GM's lack of quality control.

Bill Dearborn

That is an old document. They haven't been called NACA since the late 50s. I think the summary says in addition to the effect of fuel air ratio the valve temp increases with increased power as well. Increased power means more heat is being produced during each combustion cycle and there are a lot more of them per minute. I forget how much of an engine's energy is wasted through the exhaust but it is more than the less than 30% that ends up being converted to mechanical power. When you change the engine output by an order of magnitude going from a loafing drive down the highway to a full power, high rpm situation for 20 to 30 minutes the valve is going to get damned hot just like the engine does.

Bill