90% of engine wear occurs at startup

[moribundman]

Or so I've heard. I don't know how they came up with this figure, but I guess they just wanted to emphasize that starting up a cold engine does cause disproportionally more wear than driving at regular operating temperature. How does one find the best balance between an oil that protects best at startup and at high engine/oil temps? One would have to consider cold start temperature, frequency of cold starts, and the amount of time spent driving the engine hard. How much worse for a motor is a cold start at an ambient temperature of 20˚C versus one at 0˚C, for example? Any thoughts? [ August 01, 2003, 07:55 PM: Message edited by: moribundman ]

 

[pscholte]

M'man, I can't wait to see the discussion on this one...my thinking is a well-packaged (additive quantity, quality and balance in synergistic relationship with base stocks), stay-in-grade 0W30/40/50/60 (depending on the motor and operating conditions) OUGHT to be the best of all worlds...we'll see what "the gang" says.

 

[Patman]

I don't believe it's true that 90% of engine wear occurs at startup, if this were true we'd all see the best UOA results with 0w20, since it has the thinnest viscosity at 40C compared to the rest of the oils. So obviously you are still getting a lot of wear long after that initial cold start. You're definitely getting engine wear once the engine is warmed up and you're accelerating hard or under any kind of load, but the time when the least engine wear is occuring (other than when it's shut off!) is when your engine is fully warmed up and you're at a steady speed on level ground.

 

[moribundman]

quote:

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the time when the least engine wear is occuring (other than when it's shut off!) is when your engine is fully warmed up and you're at a steady speed on level ground

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I think we all can agree on that. What I'm getting at: If you live in Alaska (it's a mild winter, okay? ), and you do a lot of short distance driving, you'll probably get a lot of startup wear. Let's say I live in California (what a coincidence!), and I see barely ever temperatures that approach freezing, and I do the same kind of driving that you do in Alaska. I think it's safe to assume that my engine will suffer less wear, despite you using a thin oil, and me using a thicker oil. Now, do we know if there is a (low) temperature at which engine wear does increase sharply during a cold startup compared to a cold startup at a higher temperature? In other words, is engine wear during a cold start ever a non-issue above certain temperatures, or is always an issue?

 

[pscholte]

Well, if you believe some OEMs that was the selling point for 5W30...they may have included the increased fuel economy aspect, but the explanation I remember was startup wear and the 90% figure (maybe 85%) sounds awfully familiar.

 

[Jay]

My guess is that the severity of wear at startup is proportional to the pumping viscosity of the oil at the temperature in question.

 

[Ken4]

I've heard this saying: "Twice as much engine wear occurs during engine startup" Does it mean 90%, I dont know?

 

[Rexman]

I think the 90% figure is reasonably accurate if you count the actual start-up and then the first few miles until the engine has warmed. Tests show that once out on the highway at a steady speed, the amount of engine wear is virtually nil. There is a lady in Washington who does almost 100% highway miles as a substitute school teacher. Each day she drives to a different small town somewhere in the state to fill in. She currently has about 700,000 miles on her Subaru--engine never rebuilt to the best of my knowledge. My next door neighbor, on the other hand, has a 25 year-old Sunbird he was hoping to get just 100K mi. out of. But he only drove it a few miles around town each day, all stop-and-go city driving. He finally gave up when the car wouldn't run anymore after 80K mi. and now has it stored in a shed. I think everyone agrees that fully warmed-up hwy miles are the key to long life for your engine. If you do mostly brutal stop and go city driving with a lot of cold starts and idling and you can be sure your engine is heading for an early grave. The city driving is the real killer here and that's where you REALLY need everything a good synthetic can give you! It seems to me the first to look for on a UOA is the percentage of hwy versus city driving--without knowing that, how the heck can you make an accurate judgment of how well the oil is really protecting the engine?! Sure, a lot of UOA's look terrific at first glance, but then you see that all they were doing was just driving 60 miles up and down the highway each day to get to work and back. That kind of driving would even make a cheap 69-cent a quart dino from Costco look good!

 

[Ken2]

A journal rides on a wedge of oil that it creates by the fact of it's rotation inside the bearing. There is no metal to metal contact. When starting, there is just residual oil from the last running which contains some boundary lubrication properties. With this in mind, it's easy to see that most wear does indeed occur upon starting. Ken

 

[moribundman]

For how long are cam lobes, camshaft bearings, etc are running "dry" upon startup? The "clinginess" of the used oil should determine how thick a proctective film is left behind after shutting an engine down. How does this oil film compare in terms of thickness to an oil film at operating temperature? How quickly is oil pressure up inside of the bearings? And how does expansion of parts during warmup effect clearances? When an engine is shut down, does the protective oil film literally get squeezed out by the weight of engine parts until metal parts meet? Sorry for my unscientific way of saying all this...

 

[JohnBrowning]

I agree that more wear occurs at start up then any other time but do not belive in dry starts. First we have all of these fine AW additives that have been taken up by the metal. Then we have residual oil films on parts. Synthetics can cling to surfaces as long as a month compared to a few hours for non-synthetic. Gone are the days of washing the cylinders with gas while trying to start the car. Gone are the days of haveing to run at a high RPM until the engine would idle. GOne are the days of haveing to rev the engine on cold start to keep it running. Most vechiles have full oil pressure in less then 15 seconds in the winter time with synthetics. They have possitve oil pressure almost imediatley. I just do not buy all the drama about dry strarts!! It would be different if you had an unprimed pump and oil system and no AW additives!

 

[NThomas]

This is something that i have often wondered about since i drive 1 mile to work and 1 mile back. (The odo. reads exactly 1 mile) I have been using Mobil 1 10-30 /w 15-50 (mixed 50/50) and changing every 3000 miles. I dont know if this is to soon to change, but considering the driving habits i figured not. I have not done a UOA, but would like to do one to see what the results are.

 

[Leo]

I asked my Medicial Chem lecturer today about Esters 'clinging' to metal. He said that the electromagnetic attraction between esters and metals would probably be insignificant; Van De Waals forces would be stronger, which any molecule exhibits. So by his opinion, esters providing better startup protection is bullocks!

 

[Shannow]

Spent an interesting dinner with a former castrol chemist one day (moved to a newly established refinery near Wagga). His statement was that the boundary lubrication results in high wear before pressure is built. Once oil is flowing, the very thick oil provides perfect hydrodynamic lubrication. As the oil passes through "warm", the oil wedge shrinks with viscoscity, and the additive pack hasn't kicked in with the E.P additives etc. That's where he stated a lot of wear occurs also, as most drivers are fairly throttle happy once they get moving.

 

[BOBISTHEOILGUY]

Several points I want to make quickly. I agree with Leo's statement about clinging. Oil, like many other liquids are held together by ionic tension. Viscosity of the oil will determine the amount of time the oil will "cling" than the "magnetic attraction" some people feel the esters have. Gravity will over come this so called attraction over time. Take the petroleum base stock of lucas's additive, it's not synth but it will cling extremly over any motor oil. It's base stock is much thicker. All motor oils are designed to flow. To say a synth will cling is incorrect. The only clinging that is happening is where the aw/ep's have been bonded due to the heat/friction to the surface. Point here is, I can take a motor oil, stick it on the timken race, rotate it, then pull it out, and see if it has any protection. No, it will lock right up. Take that same motor oil, run it, create some heat/friction with the two surfaces, and the barrier additives will plate up. drain it, clean it off, and restart with no oil, and it will provide momentary protection. This is due to the barrier additives. I do not agree that start up wear being that much. When is the highest wear. When an engine is completley warmed up driving in traffic. What most are forgetting is LOAD. At a start up, cold or warm, you have no load on the engine until you put it in gear to move. Starting an engine has no load thus do demand to shear the oil film. At stop and go traffic, the wedge of oil is minimal and as someone commented, it's when you have a heavy foot from light to light that's when you create wear. The amount of scuffing due to load/shear of the wedge oil is dramitic. You'll see many "little old lady's" drive their car local, start it, put it in gear, do the in town driving only and it never wears out, but take same car,with the same amount of startups, put a young person, they do jackrabbit starts from each light, and see the difference. The little old lady does easy starts off at lights, the other, putting heavy load and demand on the engine at start while the wedge between the parts is a mixed film at best. So, imo, stop and go traffic with a heavy foot is where most wear is created, not startup.

 

[nortones2]

Bob: given that taxi's (usually diesel over here) seem to get the most miles out of their engine, I deduce that they must all be driven by old ladies.

 

[Whimsey]

Having driven in the UK for over 20 years I can definitely say the little old lady drivers in the UK are much more aggressive than any taxi driver I ever encountered. Well, except maybe for the ones in Liverpool! Whimsey

 

[alexiskai]

The trick is, are they aggressive or just oblivious? I've had brain-dead moments at the wheel that to others probably looked like I had a death wish.

 

[Virtuoso]

quote:

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Originally posted by JohnBrowning: Then we have residual oil films on parts. Synthetics can cling to surfaces as long as a month compared to a few hours for non-synthetic.

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When I took my valve covers off to do the valve adjustment on my SHO, my cams & shims (and everything else) were still coated with a very liberal amount of Castrol GTX. The engine had not been run in 36 hours.

 

[moribundman]

quote:

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I do not agree that start up wear being that much. When is the highest wear. When an engine is completley warmed up driving in traffic. What most are forgetting is LOAD. At a start up, cold or warm, you have no load on the engine until you put it in gear to move. Starting an engine has no load thus do demand to shear the oil film.

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I'm not sure when wear is the highest, but according what I have over and over heard, an engine shows generally more wear at idle (especially when cold) than when under load. Idling and revving an engine without putting load on it is especially bad for the camshaft bearings and cam lobes? I'm sure engine temperature is very important. For example, don't some new BMW cars electronically limit the RPM to about 3000 until the engine has reached operating temperature?

quote:

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When I took my valve covers off to do the valve adjustment on my SHO, my cams & shims (and everything else) were still coated with a very liberal amount of Castrol GTX. The engine had not been run in 36 hours.

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When I recently pulled a valve cover I was astonished by how little oil was on the cam lobes. They felt barely oily. The car had been sitting for maybe 12 hours, and the oil was M1 0W-40. [ August 02, 2003, 01:50 PM: Message edited by: moribundman ]