Why most engine wear occurs during cold start up?

[Wing]

What is phyisical reason for 75%-90% wear engine occurs on cold start up?

I can't find exact reason..

Is that beacuse ?
1) rich fuel mixture on choke, splash oil film from cylinder wall?

2)corrosive wear on cylinder and piston rings?

3)cold oil don't lubricated well?? (but oil when is cold ,it has higher viscosity and higher is better lubricate because it has thicker oil film then hot-low-viscosity oil)

4)engine clearance at cold temperature?

5)It takes time to oil pump make oil pressure in bearings?

Can you answer or better give a links with scientific explanation...

 

[tech99]

I believe it is caused by the oil film on the bores being washed away by the rich mixture required for starting. It is important to reduce choke as soon as the engine will run, however roughly, and to encourage rapid warm up.

 

[Wing]

This is one

I believe it is caused by the oil film on the bores being washed away by the rich mixture required for starting. It is important to reduce choke as soon as the engine will run, however roughly, and to encourage rapid warm up.

This is one of reason but only when choke is ON,first 1-2 minutes.

But why low coolant temperature cause higher wear then hot?
If we use 90C thermostat ,we have lower wear then 60C thermostat...

For 60 Hour engine wear tests:

At 20C coolant temp, cyl wear = .008"

At 68C coolant temp, cyl wear = .001"

At 98C coolant temp, cyl wear = .0003"

 

[tech99]

This is one

This is one of reason but only when choke is ON,first 1-2 minutes.

But why low coolant temperature cause higher wear then hot?
If we use 90C thermostat ,we have lower wear then 60C thermostat...

For 60 Hour engine wear tests:

At 20C coolant temp, cyl wear = .008"

At 68C coolant temp, cyl wear = .001"

At 98C coolant temp, cyl wear = .0003"

View attachment 213531

Low coolant temp allows fuel to condense on the bores, removing the lubricant film

 

[Wing]

Low coolant temp allows fuel to condense on the bores, removing the lubricant film

In cylinder is 800C-1000C ,how condenese can exist in that hight temperature?
And when you drive on 60C thermostat I think there is no condese,but still wear is higher then 90C coolant..

 

[Ranger Mike]

When an internal combustion engine sets overnight the mechanical components will be cooler than when at “ideal” operating temperature.Engine wear is most experienced at cold start due to the lack of oil available to engine components.The dimensional tolerances will be at the non-ideal design limits.

Maximum clearances in all bearing and piston to wall specifications.

The piston will be an oval shape having not expanded to true oval for minimal clearance. Some piston slap will cause some wear on the piston skirts until thermal expansion maximizes.

No lubrication oil will be top side or on the cylinder walls.

This is where the most “wear “ occurs. Metal to metal and no lubrication. Why? The oil pump galleries may be dry with no oil present.

Today 99% of the cars on the road use mechanical oil pumps. This means the pump oil pump cannot deliver oil pressure until it has sucked up the oil from the oil pan sump and has begun pushing the oil through the oil galleries.

From cold start until the engine warms up and the oil fills all the oil galleries and we have a steady oil pressure reading we do not have proper lubrication.It was true that we suffered a lot of cylinder / piston wear about 20 years ago. The cylinder walls used to be honed and finished with many peaks and valleys remaining in the surface profile.

The introduction of Plateau Honing meant the peaks were knocked down on final hone pass so the engine break in time was a lot shorter and we had significantly more valleys to retain oil.Todays computerized fuel monitoring means we do not have excessive fuel splashing on cold cylinders at start up unlike the day of the “choke”.

Your assumption that ”thicker oil” does better lubrication is not true today with the introduction of synthetic oils. Cold start lubrication is best achieved from an oil with good cold flow Properties.


The reason the 98C wear is the least is the engine is functioning properly. At 20C the engine is way too cold and piston rings are permitting too much blow, washing the lubricating oil off the cylinder walls. The piston is not thermally expanding for a tight piston ring seal. When the oil is not heated to proper temperature harmful deposits, moisture, and acid accumulate rapidly, then eat away at the inside of your engine. There is a lot of chemical things happening during the combustion process so you must change engine oil at least every 3 months regardless of the miles driven. You literally have acid and sludge developing in the crankcase.

 

[tech99]

In cylinder is 800C-1000C ,how condenese can exist in that hight temperature?
And when you drive on 60C thermostat I think there is no condese,but still wear is higher then 90C coolant..

The bore is not itself at such a high temperature, but more like 150C. Higher temperatures also promote the flow of oil to the compression ring where most wear (and also power losses) occur. You might like to look at the following paper:-
http://www.sciencedirect.com/science/article/pii/S0306261917301022

 

[Wing]

The reason the 98C wear is the least is the engine is functioning properly. At 20C the engine is way too cold and piston rings are permitting too much blow, washing the lubricating oil off the cylinder walls. The piston is not thermally expanding for a tight piston ring seal.

Ok so "blow by" is main reason for engine wear which operate on lower coolant temperature(lower thermostat openning).

 

[Ranger Mike]

Oil does three things
1. lubricates directly and by splash oiling. Splash oiling is how the cylinder walls are lubricated. You have pressurized oil squirting out of the connecting rod bearings slashing oil in all directions and even on the cylinder walls. Too much oil and you swamp the bottom piston oil control ring (scraper) too little oil means you will shortly own a boat anchor.
2.Oil cools - your 1200 degree F combustion chamber is cooled by water. The bottom of the piston is cooled by oil. So are the cylinder walls.

3. Oil cleans the inside of the engine. If the engine runs too cold it forms sludge in the oil galleries. I have had to spoon out oil sludge on many a cold running engine over the years. It is like axle grease but dirtier. One side effect of a cold running engine is carbon build up in the intake manifold. Can plug the manifold runners.
So to clean the engine the oil must be properly heated to burn off the toxic after product of combustion.
Engine heat cleans the oil and maintains oils lubricating properties. Cold running engine robs these and adds in the acid and junk..no lubrication..hence...big time wear

 

[Ranger Mike]

Blow byMost modern engines use alloy pistons with control thermal expansion designed into the piston. By this I mean a piston is to manufacture it so the piston is slightly elliptic rather than round. The diameter of most pistons (forged as well as cast) measures anywhere from .010″ to .035″ shorter across the wrist pin axis than the diameter perpendicular to the pin (the “major” axis). This compensates for the greater mass in the wrist pin area which causes the piston to swell sideways as it heats up. This allows the piston to fill the hole as it heats up for a tighter all-round seal.
Piston growth is also influenced by the temperature differential between the top and bottom of the piston. The top can be 300° F. or more hotter than the bottom. Since the top runs hotter and swells more than the bottom, growth can be controlled by making the skirt profile taper in towards the top. The typical piston is widest at the bottom of the skirt and narrowest at the top (which is why it is so important to always measure a piston at the location specified by the piston manufacturer, which may be either perpendicular to the pin at the pin centerline, one inch up from the bottom of the skirt or at the top of the skirt).Piston rings control the heat transfer from the top of the piston to the cylinder wall. Todays piston rings have end gaps so the ring may be slipped over the piston into the ring groove. As good as they are these rings will still permit blow by even at operating temperature. The very action of the ring moving in the piston ring groove will permit combustion gases slipping past the rings and into the crankcase poisoning the oil in the oil pan.Before the emission fad hit we used to have a vent tube from the crank case to the outside air to take care of the pressure difference the engine created during piston motion. It was capped by a breather cap that had a screen element. You could smell the oil when you let off the throttle at high rpm. You could see the milky white deposits on the dip stick after a few thousand miles.Detroit added in a PCV device that was Positive Crankcase Ventilation. Instead of emitting these crankcase fumes into the atmosphere and killing off polar bears (hahaha) it plumbed the fumes into the intake manifold. This small PCV valve was a one way valve that permitted intake vacuum to suck the fumes out of the valve cover and into intake manifold and eventually engine combustion chamber so these fumes were burned off. When this valve become plugged, or when the engine was started and not brought up to proper temperature for a long enough period of time we have white globulation collecting on the inside of the oil filler cap. This happens all the time with older people driving to the market ( very short trips) and in cold climates. The moisture in the crank case combines with the blow by combustion fumes and build up to this white milky goooo. Mom and Pop have not driven the car enough in cold weather to burn off the toxic fumes and moisture condensation that occur in the crank case. Now we have non-lubricating oil and white goopy stuff blocking oi gallery passages and now we have even more wear from lack of lubrication.Bottom line – you are going to have moisture present in the crankcase. You are going to have blow by fumes in the crankcase. You must operate the engine at high temperatures over at least a 30 minute period to eliminate these.

Your dip stick is your best friend to see what is going on inside your engine.

 

[Wing]

When an internal combustion engine sets overnight the mechanical components will be cooler than when at “ideal” operating temperature.Engine wear is most experienced at cold start due to the lack of oil available to engine components.The dimensional tolerances will be at the non-ideal design limits.

Maximum clearances in all bearing and piston to wall specifications.

The piston will be an oval shape having not expanded to true oval for minimal clearance. Some piston slap will cause some wear on the piston skirts until thermal expansion maximizes.

No lubrication oil will be top side or on the cylinder walls.

This is where the most “wear “ occurs. Metal to metal and no lubrication. Why? The oil pump galleries may be dry with no oil present.

Today 99% of the cars on the road use mechanical oil pumps. This means the pump oil pump cannot deliver oil pressure until it has sucked up the oil from the oil pan sump and has begun pushing the oil through the oil galleries.

From cold start until the engine warms up and the oil fills all the oil galleries and we have a steady oil pressure reading we do not have proper lubrication.It was true that we suffered a lot of cylinder / piston wear about 20 years ago. The cylinder walls used to be honed and finished with many peaks and valleys remaining in the surface profile.

The introduction of Plateau Honing meant the peaks were knocked down on final hone pass so the engine break in time was a lot shorter and we had significantly more valleys to retain oil.Todays computerized fuel monitoring means we do not have excessive fuel splashing on cold cylinders at start up unlike the day of the “choke”.

Your assumption that ”thicker oil” does better lubrication is not true today with the introduction of synthetic oils. Cold start lubrication is best achieved from an oil with good cold flow Properties.


The reason the 98C wear is the least is the engine is functioning properly. At 20C the engine is way too cold and piston rings are permitting too much blow, washing the lubricating oil off the cylinder walls. The piston is not thermally expanding for a tight piston ring seal. When the oil is not heated to proper temperature harmful deposits, moisture, and acid accumulate rapidly, then eat away at the inside of your engine. There is a lot of chemical things happening during the combustion process so you must change engine oil at least every 3 months regardless of the miles driven. You literally have acid and sludge developing in the crankcase.

Engine has 4 types of wear:
Adhesive,abrasive,fatigue and corrosive wear.

What do you mean what is percentage of each wear type ,so what type of wear has most affect on total engine wear?

 

[Ranger Mike]

abrasive is most destructive as aluminum piston rubs on iron cylinder,
adhesive is frictional as in bearing contact until oil pump gets up to pressure -very few rod and crankshaft bearing failures these days,

corrosive can be as bad as fatigue failure but if the engine is properly serviced , this is minimal .
Usually the corrosive failure is caused by poor maintenance of cooling system. Not changing anti freeze at proper interval and blowing head gaskets.
fatigue failure - breaking parts like connecting rods is hardly ever the case now a days unless you got lead foot.

 

[Wing]

abrasive is most destructive as aluminum piston rubs on iron cylinder,
adhesive is frictional as in bearing contact until oil pump gets up to pressure -very few rod and crankshaft bearing failures these days,

corrosive can be as bad as fatigue failure but if the engine is properly serviced , this is minimal .
Usually the corrosive failure is caused by poor maintenance of cooling system. Not changing anti freeze at proper interval and blowing head gaskets.
fatigue failure - breaking parts like connecting rods is hardly ever the case now a days unless you got lead foot.

So engine wear is 3 times more when engine operate on 68C coolant temperature instead 98C !
0.001" : 0.0003" =3.333
You think that most reason for this big difference in wear is blow-by, because piston ring is not close the gap enough?

For 60 Hour engine wear tests:
At 20C coolant temp, cyl wear = .008"
At 68C coolant temp, cyl wear = .001"
At 98C coolant temp, cyl wear = .0003"

 

[Ranger Mike]

Ok , we will try this one more time.

An engine operating at the proper 98 ° C will have wear but it will be the minimum you can expect.

An engine operating at 20 ° C will cause sludge, destroy the oils ability to lubricate and cause much more piston to cylinder wall wear.

I believe I have explained in great detail the reasons.

 

[Wing]

Ok , we will try this one more time.

An engine operating at the proper 98 ° C will have wear but it will be the minimum you can expect.

An engine operating at 20 ° C will cause sludge, destroy the oils ability to lubricate and cause much more piston to cylinder wall wear.

I believe I have explained in great detail the reasons.

I also read somewhere that zinc start protect engine parts(boundry lubrication) on higher temperatures,this is one more reasone for less engine wear on operating tem..