Shell 10W60

Ziad:

There is no particular reason to flush the oil by wasting a whole fill of oil. Enough is removed at the drain of the old that the new oil will be the very vast majority of the oil in the engine. If you are concerned by the old oil, just set the subsequent drain and refill to 2000 miles, and after the second change you can be assured that the oil in your engine is as fresh as it is supposed to be.

I follow a 3000 mile between oil changes with the added caveats of A) if there has been more than 1000 miles I will change the oil before I go to a track event, and B) I change the oil after every track event.

Re: gear oil. Since you just bought a 328 you might not be aware that 2nd gear is notorious for being hard to shift into unless the transmission oil is fully up to temperature (which arrives about 20 miles of normal operation). The 308/348/355 are similar in respect to shifting into 2nd gear until the transmission is up to temperature.

Mitch,

Thanks for the quick responce. I have been hearing here and there about the second gear problem when cold. With regard to the trans oil level, do you think that the fact that the level is higher than the bottom of the filler hole could contribute to the shifting difficulty(ie too much oil creating too much resistance or pressure)?

Thanks
Z

"do you think that the fact that the level is higher than the bottom of the filler hole could contribute to the shifting difficulty(ie too much oil creating too much resistance or pressure)?"

No, its in the way the shift linkage is machined into the transmission housing. Until the oil get up to temperature, the oil acts like a shock absorber as the various shafts move into and out of sliding bushings that hold them in their correct positions.

A racers trick to to drill tiny little holes in these sliding bushings so that oil can move out more easily. See "Engineer to win" Carroll Smith (may he rest in peace).

Mitch,

I'm going to sik Dr. Hass on you...

Just Kidding....

For more on oil, go here:

http://theoildrop.server101.com/cgi/ultimatebb.cgi

aehaas

Mitch - as usual, your discussion adds great value to any forum.

I have a contrarian view of start up dynamics. Conventional wisdom suggests that most wear occurs during cold startup. However, anyone who has torn down an engine and rebuilt it over a period of weeks or months will attest that metal surfaces retain a film of oil for months at a time. That said, is the issue with startup viscosity one of getting oil to a journal (main or cam, for example), or is it the characteristics of the thin film of oil already present in the .003 inch clearance of the journal?

I submit that since oil is already there, it is the characterisitcs of this thin film of oil that is important. And while the lubricating characteristics of a film of oil is dependent on temperature, how long do you suppose it takes a .003 inch thick film of oil to heat up when exposed to sliding friction (at the journal-bearing shell interface)?

Your thoughts?

Jim S.

"Conventional wisdom suggests that most wear occurs during cold startup. However, anyone who has torn down an engine and rebuilt it over a period of weeks or months will attest that metal surfaces retain a film of oil for months at a time."

Agreed. The figure goes somewhere between 85% and 95% of all wear happens during the first 20 minutes after starting a car. For 80% of all trips, this is longer than the duration of the trip! Also notice that 'normal' use of automobiles has become restricted to (basically) driving straight down the freeway at constant velocity. Any othere uses (like starting the car and driving in the city) are now termed severe useage.

"That said, is the issue with startup viscosity one of getting oil to a journal (main or cam, for example), or is it the characteristics of the thin film of oil already present in the .003 inch clearance of the journal?"

There are a variety of interesting startup issues.

The journals will have oil on then at startup, and since the pump gets up to pressure in the first couple of seconds the journals will have oil flowing rather quickly. But that oil is highly viscous. Highly viscous oil has a property that if enough pressure is applied, the oil will become 'stiffer' than the (metal in the) bearings and instead of lubricating the space between the journal and the bearing, the oil becomes a solid (instantaneously under the pressure) and actually slides upon the bearings and journals. This is why you don't want heavy loads before the oil gets up to 120dF or so.

Another issue with startup is that the combustion byproducts are acidic and rather hot. This acid attacks the upper cylinder area, the exhaust value seats and the exhaust port itself. As the engine heats, the acids are blow out as vapors. Thin oils will reach the upper cylinder areas before thicker oils will.

"I submit that since oil is already there, it is the characterisitcs of this thin film of oil that is important. And while the lubricating characteristics of a film of oil is dependent on temperature, how long do you suppose it takes a .003 inch thick film of oil to heat up when exposed to sliding friction (at the journal-bearing shell interface)?"

An oil flows through an engine based on its viscocity which is a function of temperature. With an 10W40 oil the startup viscocity is around 100-150 cSt that same oil in a fully warmed up engine will have a viscocity of about 8-10 cSt and will be flowing ~10 times faster at the same pumping pressure*.

Back to your actual question: I suspect the oil leaves the journal significantly hotter than it got pumped in, and its temperature increases from the point of entry to the point of exit rather linearly. But I don't necessarily think that the journals are the main points of wear at startup!

You have sliding friction in the cylinders and valves, and wiping friction on the cam lobes! Valve to guide clearnces are on the order of 0.00025" valve to guide (both sides together = 0.0005"). I suspect capilary action holds a useful oil film.

Sliding friction on the cylinders and rings are a different matter and thick oil will simply get scraped off and not make it up to the upper cylinder areas until it thins enough to get past the rings. Until this happens the upper cylinder area is not protected by the acid reducers in the oil (Base Number of the oil).

The wiping friction on cam lobes is also problematic. Once again, high pressures can cause the oil to go 'solid' and the lubrication properties are not present until the oil thins some.

Mitch

[*] assuming the clearances do not change much during warmup.

Mitch - just as I thought.

Thanks.

Jim S.

Interesting info.

Since I live in the desert I had high oil temp concerns with a 911Sc I used to own and experiemented with different oils and found synthetics such as Mobil 1 actually caused higher oil temps such as Mitch experienced than a good dino oil such as Valvoline Racing 20/50, my assumption is that synthetics just don't dissapate heat as well, they have the appearance of a watery brown soup when hot compared to dino oil. I will say the dino oil would break down at lower temps though and get cloudy.

I used to have a quick lube so heard all the speel from the brands such as Pennzoil or Havoline which are big in that industry, so its hard to tell whats reality or not as each has great facts and info why theirs is best.

An independant oil supplier of 76 brand who was a chemical engineer that specialized in oils was more unbaised and he mentioned a good old quality dino oil is best with quality additives from the manufacturer added in, which their are only a few refinerys in the US and companies such as Pennzoil and others buy direct and add their own additives, so the oil you have in your Valvoline bottle may come from different refinerys and have different quality levels in each. Finding a brand thats most consistent and has the best additives is what is most important, I prefer Valvoline 20/50 Racing.



While I agree much wear occurs at start up it does not compare to a severe oil failure issue due to too thin a viscosity at high rpm, which is where you will have a major malfunction such as a rod through the block or seized camshaft, so I am going old school with a thicker film protection and its higher breakdown temp from a thicker oil and sacrifice some start up wear.
If you could very accurately measure the oil temps throughout the motor you could "tune" your oil to as thin as possible but of course gauges are vague and inaccurate or lagging depending upon where the sensors are and aside from that you could have hot spots anywhere in the engine from worn parts or poor water circulation so you would need the max protection at all times IMO.