Shamblin

PS- Kumacho touched on this earlier, saying in essence that oil breakdown (reg. dino oil) is rarely if ever seen in daily drivers or even all but the most severe racing applications (therefore syn's are overkill, basically). However, I for one would enjoy seeing more info. on the topic of thermal/viscosity breakdown, both to round out this discussion, and to satisfy my curiosity.

Kumacho

Maximum Useful Range of All Proof Synthetic Motor Oil - 600 degrees.
Maximum Useful Range of Diester Synthetic Motor Oils - 500 degrees.
Maximum Useful Range of Polyolefins (these are a plasticizers added to some base dino oils) - 450 degrees.
Maximum Useful Range Premium Petroleum Motor Oils - 400 degrees.

Now average engine temperatures. (note: the maximum numbers are taken from racing applications on normal octane fuel i.e. Not racing fuels)

Upper Cylinder walls ---------- 300 - 500
Exhaust Valve ------------------ 1200 - 1500
Piston Crown ------------------- 700 - 800
Hydraulic Valve Lifter ---------- 250 - 300
Crankcase ----------------------- 200 - 300
Top Ring ------------------------- 300 - 650
Exhaust Gases ----------------- 500 - 1000
Combustion Chamber -------- 3000 - 5000
Coolant Jacket ----------------- 165 - 230
Connecting Rod Bearings ---- 200 - 375
Main Bearings ------------------ 200 - 350

So what happens when oil is heated above it's Maximum Useful range? The oil begins to evaporate. This results in oil consumption so you will easily be able to tell if it is happening...

Under normal circumstances and yes even in racing applications there are only six areas where dino oil will begin to evaporate. Those being:

Upper cylinder walls - This is the area where the oil rings and even the upper piston ring does not touch. No lubrication is needed in this area.

Combustion Chamber - Again this is an area where no lubrication is needed and none is delivered here.

Exhaust gases - See combustion Chamber...

Exhaust Valves - The only portion of the exhaust valve that requires lubrication is the mid to upper portion of the valve, where it moves through the valve guides. This area of the valve is quite a bit cooler than the face and seat of the valve. And no oils are capable of withstanding the temperature of the unlubricated seat of a valve.

Top ring - The top ring of the piston is only there to create compression. To do this it does not even have to make a complete seal. Rings are designed to move in and out of the piston. The ring that most often causes scuffing on cylinder walls is also known as a scraper ring and is the middle ring in the piston. It's located directly between the oil ring and the top -or- compression ring and serves two purposes. 1) It scrapes carbon and burnt oil from the cylinder wall and 2) It assists the top ring, somewhat in making compression. However, it is very rare for any ring to cause scuffing in the cylinder and this comes most often from the piston skirt.

Piston Crown - Top of the piston and does not come in contact with any other engine component. No lubrication needed.

I've somewhat simplified some of the descriptions of what certain components do. I was really getting too in depth when I originally typed this out and felt I needed to make it a bit easier on the eyes of the reader.

Shamblin

Kumacho to the rescue . . . again! I notice that dino "evaporates" when it's max. temps. are exceeded, which still leaves me wondering . . . does it just evaporate and that's it, or does it leave a cooked-down sludge type of residue behind (like in those pesky TV commercials)?

Second, I've heard that one of the reasons that Nissan may recommend dino and not syn is that some motors are designed to burn a little oil on purpose (cooling and/or lubrication in hard-to-reach places?). If this is true, then the fact that some areas such as the Top Ring exceed oil's max temp's would be o.k. even so, and in addition this would also mean that syn's could be interfering with a vital process that the engine was designed for, no?

Kumacho

The amount of oil that does get "cooked" is very small. It is only the oil that actually hits the top of the cylinder and is only a slight film over a very small area. What determines wether or not an oil leave sludge is it's ash content. However, the ash content in most Dino oils (not all mind you) is so low that this small amount of "cooked" oil does not create any real quantities of sludge.

In your second question/statement, you are absolutely correct. Some manufacturers do build their engines so that a small amount of oil does cook at the top ring. Several V8's are designed to burn oil as well, the LS1 is notorious for burning oil in the upper portion of the cylinder.

Shamblin

Thanks, doc . . . I'm feeling better already! (for changing out the new Amsoil syn back to good 'ol dino)

Interesting to note that when I changed out the trans oil that came in it (dino) and put Amsoil syn in, it seemed to shift noticeably smoother (except for trying to put it in 1st while still rolling). But, when I put dino back in the other day, it seemed to keep shifting as smooth or smoother, plus no more problem w/ 1st while rolling. While there may be too many variables clouding the issue to know for certain, still it makes me wonder about what I heard recently: Many auto manufacturers buy fluids in bulk that don't have all the additives like the same thing bought at your local Kmart. If this is true, it might explain this situation.