Does the study/data that indicates “most wear occurs at start-up”, also indicate that the lighter weight oils reduce start-up wear? Or is that just a frequently made assumption?

If the oil is so cold that it takes along time to get drawn into the pump etc. like a thick milkshake as compared to water. There will be more wear than a thinner oil .Also more involved is the increased wear during the warm up .The clearances are different the pistons are oval when cold the seal is not as good so the oil is washed off the cyl walls somewhat the heat activated additives etc .

Hi,
this is a complex issue so I'll only touch these two cold start aspects which are often forgotten in this regard

a) A more viscous lubricant than needed will trigger the lubrication system's by-pass valve at quite low revs so vital flow throughout is reduced. In some Euro engines this can be as high as 150psi or more. Even some high viscosity synthetics can still trigger the system's by-pass at 90C or so and at only mid range revs

There is always a good case for using the lighest of any Manufacturer recommended viscosities (of course depending on ambient and intended use)

b) A more viscous lubricant than needed will also trigger the filtration system's media by-pass valve directing largely unfiltered lubricant around the system. This can remain for quite long periods of time - depending on the filter's design and the media used of course. There is always a good case for using an OEM filter!

As an example, the ex racing era Porsche Engineers that now look after the Porsche Museum's collection always warm the lubricant's temperature to 80C before applying revs above around 1200 and and significant load

most wear occurs at start-up, oh so true.
I love the chevy truck like a 1995 where one
can open the oil cap and look inside and see the
oil flowing when cold or when hot.
it is simply amazing how slow cold petrified conventional
oil flows compared to when it is hot 20 minutes later.
I like the die hard oil changers that always think it is a good idea to wait a few minutes before driving away, like they think it makes a difference
some do it simply cause the engine refuses to go due to friction

I tend to think this is true only on a cold motor that has been sitting over night. Once the motor has been run and brought up to temp it should be good for the rest of the day. Unless it's freezing out.

Here's more interesting info to mull over:

The SAE paper that did testing on cold starts vs. hot starts and resultant wear had some interesting results too.

As it turns out, cold oil (room temp IIRC) causes more initial wear till it warms up to operating temps. They had uoa results from cold engine cold oil, cold engine hot oil, hot engine hot oil, and hot engine cold oil (draining the oil after 20 minutes (?) of startup running.

The hot engine hot oil and cold engine hot oil tests showed the lowest wear levels and the cold oil (hot or cold engine) showed significantly higher wear.


Max

Very interesting. How long does it take the oil to cool down after a 15 to 20 minute drive,thus, resulting in a second cold start?

Not debating the cited tests, but. Had the top cut out of a set of valve covers as to adjust rockers in a running engine. Was running straight 50w race oil at the time. Stone cold engine and oil, partner would fire it off and oil was up in the valve train RIGHT NOW, and I mean all over the place. To see it kind makes any "slow to flow" theorys hard to believe.

I'd guess the wear reduction hot vs cold, has more to do with the viscosity being more "correct" for the design clearances etc, than it does any pumpability issues? and hot vs cold is more a viscosity issue than it is actual temp of the oil.

Reminds me of the other day. It was a very cold morning here and I too was curious about oil flow. I took off the oil filler cap (you can see one of the cam shafts perfectly) and had the car started. As soon as it fired up,the cam shaft was intensely and immediately saturated in an oil bath. Even on the coldest days I`ve never experienced any engine noise at all.

On another note,I read a post on one of the Z forums where a guy was asking a thick vs thin oil question. He wanted to know if a thick oil protected engines better when you re-started a hot engine (wondered if thicker oils stayed on all the upper engine parts providing a thicker more protective oil film vs a thin oil mostly draining off and back down into the oil pan). He said he got upper valve train clatter with a thin oil upon hot engine re-start whereas he didn`t get any noise at all with a thicker oil.

What do the BITOG experts think?

Was explained to me by an ex Castrol chemist.

Broadly

Cold oil, the parts won't touch, as they can't get to each other. As the oil warms, it lose viscosity, and the adds haven't kicked in, wear is high. Oil and parts are warm, additives functioning, wear is low.

With a functioning ADBV, and a positive displacement oil pump, the oil will start running out the holes as soon as the engine turns.

I think we are using strange terms. "freezing", "immediately", "coldest" and so on. Humans or water do not have the same baseline of hot and cold, time and so on as oil and mechanical parts.
1. When starting cold, how long exactly/how many mm of unlubed movement did the engine surfaces actually move? If unlubed, the oil will not possibly reach all surfaces in an engine "immediately" as in 0 sec. It will however always get there quicker with a thin oil, hot or not.
2. Unlubed is a key here. If there is oil on a surface, how long will it stay in sufficient amounts? Long enough for new oil to be pumped there?
3. You may freeze at a windy -5 C, but almost no oil have bad pumpability at that temp and the "freezing storms" and so on does not affect oil. Bad pumpability appears much lower, like -30C or lower.

Like in science class: If it was 0 degrees yesterday and it's twice as cold today, how cold is it?

It's time for my invention, which is yet to be developed, but consists of making the oil sump like a propane hot water heater, much like the ones found in motorhomes. A thermostat would control the temperature. A small LP tank would fuel it, or you could go LP all the way, for both the heater and the engine's fuel, which will add the bonus of clean running oil. The heater not only keeps the oil at an optimal temperature (can run lower temp when parked a long time and hit a boost button for a quick warming before startup (or on a timer), but also the exhaust from the LP heater is directed to warm the entire engine bay and perhaps shoot back over the tranny on it's way out.

Now, once we get rid of cold start wear, the manufacturers can make thinner bearings, since most wear is eliminated and they don't want the vehicle to last too long or it will hurt sales.

Of course, even with winter start up wear here in Michigan, our engines outlast the bodies, so the average Joe just doesn't care that start up wear is the major wear factor. It won't affect him anyway.

As for me, well I plug in an oil pan heating pad in winter.

It looks like my question has been answered. Everyone seems to be saying thinner oil flows better, or that the additional flow of thinner oil might reduce start-up wear. Since nobody referenced any study/data that indicates that the lighter weight oils reduce start-up wear, it’s obvious that it’s just a frequently made assumption/opinion.

I’m not suggesting that it’s good to run straight 30W or 20W50 in northern winters. But I am suggesting that it’s possible that “more wear occurs at start-up” because the parts are cold, and using another weight oil, within reason, has little affect on start-up wear.

Some have argued that a thicker oil (within reason) will leave more of an oil film in the engine parts after shut down (and associated drain down) than will a thinner oil, and so while the thinner oil will move up into the engine somewhat faster on cold start, the thicker oil is to a degree already there. But in the big picture, it really doesn't matter. If you use a 10wXX above zero and a 5wXX to -15F, and I suppose synthetic or 0wXX below that, you should see the rest of the car go in the dumps before the engine wears out. There may be exceptions such as a poorly designed engine, though.

I bet that was in Florida.