Read what JAG said again. Cold engine/hot oil = low wear. So the clearances inside the engine are not the issue but the temperature of the oil iteself. It also bears mentioning that we are not talking the time it takes to get lube flowing during the actual start but the ability of the already-flowing oil, when cold, to lubricate and protect properly. In other words, correct me if I'm wrong, the only real variable that can account for the difference is the chemical properties of the oil at different temperatures. Not even the physical properties of the oil can be included as a variable because different viscosities showed the same amount of wear. Also synthetic vs conventional showed the same amount of wear.
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"Most wear occurs at start-up"
- Thread starter Brian Barnhart
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It all depends upon what is meant by "cold" and "hot" as it relates to engines and oils. Even more specifically, it pertains to the engine being a heat generator and the oil is a heat remover. The theory is hot oil produces less wear because it induces less heat flux across the critical bits.
Originally Posted By: jpr
The theory is hot oil produces less wear because it induces less heat flux across the critical bits.
Who started this theory and why?
The theory is hot oil produces less wear because it induces less heat flux across the critical bits.
Who started this theory and why?
Just tossing it out for discussion - I don't know of any proponents of it other than me, but my hunch is that it is not an orginal idea. I'm just not well enough read to know of a citation.
It does however, seem to connect the dots rather nicely.
* A cold engine produces little wear - it was built that way and everything is nice, round, and in spec
* A hot (operating temperature) engine produces little wear - it was designed to operate at that condition and once it is thermally saturated, everything has expanded as designed
* The period of high wear is in the transistion state between cold and hot - due to differential rates of thermal expansion, parts don't fit quite as well as they do when cold or hot.
* Hot oil helps to maintain this thermal saturation
* Cold oil works to degrade this thermal saturation
It does however, seem to connect the dots rather nicely.
* A cold engine produces little wear - it was built that way and everything is nice, round, and in spec
* A hot (operating temperature) engine produces little wear - it was designed to operate at that condition and once it is thermally saturated, everything has expanded as designed
* The period of high wear is in the transistion state between cold and hot - due to differential rates of thermal expansion, parts don't fit quite as well as they do when cold or hot.
* Hot oil helps to maintain this thermal saturation
* Cold oil works to degrade this thermal saturation
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Machining and blueprinting are done with all parts at the same temp. A good machine shop when resizing a connecting rod will do it in steps so that it doesn't heat up. Boring a block should be done on opposing sides so that heat doesn't start building up.
Just because you set it to the recommended cold clearances doesn't mean that's what it's going to run at. For example you have aluminum forged pistons in an iron block. Piston to cylinder clearance has to be set loose so that by the time everything has expanded (with the aluminum pistons expanding much more) the clearances are correct. My forged JEs in the GN run .004" clearance and have quite a bit of knock for the first minute until the pistons get a little heat in them.
Just because you set it to the recommended cold clearances doesn't mean that's what it's going to run at. For example you have aluminum forged pistons in an iron block. Piston to cylinder clearance has to be set loose so that by the time everything has expanded (with the aluminum pistons expanding much more) the clearances are correct. My forged JEs in the GN run .004" clearance and have quite a bit of knock for the first minute until the pistons get a little heat in them.
jpr, I will keep that in mind. I'm generally opposed to developing theories when we can just learn from the experts in these areas. I dug up a study that touches on this subject but I have not digested it yet...I will later. You all can do the same and see what you think.
http://eprint.iitd.ac.in/dspace/bitstream/2074/1021/1/kumarsys2002.pdf
http://eprint.iitd.ac.in/dspace/bitstream/2074/1021/1/kumarsys2002.pdf
I was wondering lately about all these hybrid cars that shut their engines off at red lights and restart the gas engines after the electric assist is done; doesnt that constitute a lot of startup situations where wear and tear might be very high?
The Prius I believe actually has a thermos chamber where it keeps at least some of the coolant, the idea being to keep it as hot as possible between starts. Apparently it retains quite a bit of its heat after even 24 hours.
But at a typical red light stop the temperature won't go down enough to make a difference. And if it does go below a threshold it will start itself back up.
But at a typical red light stop the temperature won't go down enough to make a difference. And if it does go below a threshold it will start itself back up.
Here's another document to read. http://www.ornl.gov/~webworks/cppr/y2001/rpt/112793.pdf
Originally Posted By: JAG
jpr, I will keep that in mind. I'm generally opposed to developing theories when we can just learn from the experts in these areas. I dug up a study that touches on this subject but I have not digested it yet...I will later. You all can do the same and see what you think.
http://eprint.iitd.ac.in/dspace/bitstream/2074/1021/1/kumarsys2002.pdf
At first that made my pants really perky, but then I figured out they were talking about running in and steady state wear in terms of indvidual component lifetime rather than engine operation the moment was gone. It's still an interesting paper, but appears to be more applicable to engine break-in phenomenon rather than general operation.
I'm with you on the general opposition to random theories. This one is really nothing more than an attempt to tie together information from TallPaul, Gary Allan, and the SAE paper Bluemax1 referenced (but which I have not read myself). I'm also quite certain this does not represent any original thinking in the field of engine lubrication research. Hopefully some of the aforementioned gentlemen can provide some further illumination on the subject.
EDIT - there is this gem in the paper -
Quote:
Temperature was found to be the second most significant
parameter for steady-state wear rate. The wear rate decreased
with temperature. This is considered to be due to
the reaction films formed.
jpr, I will keep that in mind. I'm generally opposed to developing theories when we can just learn from the experts in these areas. I dug up a study that touches on this subject but I have not digested it yet...I will later. You all can do the same and see what you think.
http://eprint.iitd.ac.in/dspace/bitstream/2074/1021/1/kumarsys2002.pdf
At first that made my pants really perky, but then I figured out they were talking about running in and steady state wear in terms of indvidual component lifetime rather than engine operation the moment was gone. It's still an interesting paper, but appears to be more applicable to engine break-in phenomenon rather than general operation.
I'm with you on the general opposition to random theories. This one is really nothing more than an attempt to tie together information from TallPaul, Gary Allan, and the SAE paper Bluemax1 referenced (but which I have not read myself). I'm also quite certain this does not represent any original thinking in the field of engine lubrication research. Hopefully some of the aforementioned gentlemen can provide some further illumination on the subject.
EDIT - there is this gem in the paper -
Quote:
Temperature was found to be the second most significant
parameter for steady-state wear rate. The wear rate decreased
with temperature. This is considered to be due to
the reaction films formed.
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Upon reflection, I think the "take away" from the gem quoted above, along with other information in this thread, is that temperature has affects oil and oil additives in complicated ways beyond just viscosity. However, I think this is a supplementary effect rather than a primary one. IIRC, the gist of the SAE paper was that the main dependence was temperature - neither the weight nor the type of oil (dino, synthetic) had a profound influence.
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If this has any merit to it...all that anyone need do is install sump heaters and the majors can send the AW R&D labs on a permanent lay off.
..or so I'd reason..
..or so I'd reason..
Brian Barnhart
Thread starter
Your reasoning doesn't work for the millions of cars parked without easy access to recepticles.
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Is that the only modality that one could use to achieve that outcome? I believe that some hybrids don't have a plug in receptacle at all ..yet have a coolant thermos. Do you mean to say that our automotive icons can't figure a way to do this too with oil?
There are some low wattage oil pan heaters that can be wired to your battery and set on a timer, so it will pre-heat the oil somewhat off your car's charging system. I wouldn't really want to do that on a 40 below day though. There are also Webasto heaters.
http://www.webastoshowroom.com/BlueHeat/index.html
Those, I believe, are a catalytic heater that draws fuel from your tank and a small amount of battery juice to operate a circulator pump to heat and circulate coolant through your engine, gradually bringing it up to temperature. If they could put a second pump on it that was self contained with something like tri-ethylene glycol, and put a heat sink on the other end to epoxy to your oil pan, you could get hot oil in a hot engine with minimal wear and fuel consumption to bring it to that point before you are even outside to start it.
Lots of additional hardware, and you would have to save a lot of wear and a lot of fuel by doing it to claw back your initial investment. It's better for those of us who have cars that idle a lot to warm up, or use a command start system to warm up our cars before we get outside.
http://www.webastoshowroom.com/BlueHeat/index.html
Those, I believe, are a catalytic heater that draws fuel from your tank and a small amount of battery juice to operate a circulator pump to heat and circulate coolant through your engine, gradually bringing it up to temperature. If they could put a second pump on it that was self contained with something like tri-ethylene glycol, and put a heat sink on the other end to epoxy to your oil pan, you could get hot oil in a hot engine with minimal wear and fuel consumption to bring it to that point before you are even outside to start it.
Lots of additional hardware, and you would have to save a lot of wear and a lot of fuel by doing it to claw back your initial investment. It's better for those of us who have cars that idle a lot to warm up, or use a command start system to warm up our cars before we get outside.
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Well, I imagine that the benefits of the coolant bottle method for the hybrids probably doesn't pay for itself after R&D and added complexity are indexed into the mix too. The point, more or less, that I was making is that you've reduced startup wear to ONE challenge.
If you've read the quotes from Dr. Haas' posts on Schneider on cylinder/ring wear, the wear tapers off as you approach 20 minutes of operation. He interprets it as a visc slide side effect, I interpret it as a component thermal saturation progression side effect.
This would suggest that neither disposition has merit.
If you've read the quotes from Dr. Haas' posts on Schneider on cylinder/ring wear, the wear tapers off as you approach 20 minutes of operation. He interprets it as a visc slide side effect, I interpret it as a component thermal saturation progression side effect.
This would suggest that neither disposition has merit.
Originally Posted By: [email protected]
I was wondering lately about all these hybrid cars that shut their engines off at red lights and restart the gas engines after the electric assist is done; doesnt that constitute a lot of startup situations where wear and tear might be very high?
I have a 2007 Prius outfitted with a ScanGauge 2 so that I can monitor RPM and Coolant Temp. Not only does the Prius shut down at stoplights, it also will shutdown at speeds up to 41mph when possible to conserve fuel. It will only do this after the engine is sufficiently warm (> 164°F coolant temp).
As mentioned earlier, the Prius has a "thermos bottle" that it uses on cold start up to preheat the cylinder head. This is actually a feature to reduce cold start emissions; part of the AT-PZEV emission system. I have been watching coolant temp at cold start up with the ScanGauge - at approx 50°F ambient, at "boot up" (engine not running) the coolent temp will climb to approx 140°F, then as the engine starts will drop to approx 95 - 100°F as the coolant begins to circulate. It takes approx 5 min of low - moderate speed driving for the temp to reach 164°F which allows full hybrid operation. Normal operating temp is 188°F.
The other difference compared to other vehicles is that the Prius does not have a conventional starter to crank the engine. Instead, it uses MG1 (motor/generator 1) to spin the engine up to 980 rpm without applying fuel or spark. The oil pump is crankshaft driven, so oil pressure is present before fuel and spark are enabled. Starts are very smooth; it can be difficult to tell if the engine is running or not without the ScanGuage to monitor rpm.
The highest mileage privately owned Prius was a 2002 which had 349k when it was totalled by another driver pulling out in front of it. The 2002 did not have the "thermos" but all Prius have the same starting system. 2004+ models have the "thermos". There are other Prius with +200k , but many of these are taxicabs because the average driver hasn't had time to put that many miles on yet.
I was wondering lately about all these hybrid cars that shut their engines off at red lights and restart the gas engines after the electric assist is done; doesnt that constitute a lot of startup situations where wear and tear might be very high?
I have a 2007 Prius outfitted with a ScanGauge 2 so that I can monitor RPM and Coolant Temp. Not only does the Prius shut down at stoplights, it also will shutdown at speeds up to 41mph when possible to conserve fuel. It will only do this after the engine is sufficiently warm (> 164°F coolant temp).
As mentioned earlier, the Prius has a "thermos bottle" that it uses on cold start up to preheat the cylinder head. This is actually a feature to reduce cold start emissions; part of the AT-PZEV emission system. I have been watching coolant temp at cold start up with the ScanGauge - at approx 50°F ambient, at "boot up" (engine not running) the coolent temp will climb to approx 140°F, then as the engine starts will drop to approx 95 - 100°F as the coolant begins to circulate. It takes approx 5 min of low - moderate speed driving for the temp to reach 164°F which allows full hybrid operation. Normal operating temp is 188°F.
The other difference compared to other vehicles is that the Prius does not have a conventional starter to crank the engine. Instead, it uses MG1 (motor/generator 1) to spin the engine up to 980 rpm without applying fuel or spark. The oil pump is crankshaft driven, so oil pressure is present before fuel and spark are enabled. Starts are very smooth; it can be difficult to tell if the engine is running or not without the ScanGuage to monitor rpm.
The highest mileage privately owned Prius was a 2002 which had 349k when it was totalled by another driver pulling out in front of it. The 2002 did not have the "thermos" but all Prius have the same starting system. 2004+ models have the "thermos". There are other Prius with +200k , but many of these are taxicabs because the average driver hasn't had time to put that many miles on yet.
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Originally Posted By: Gary Allan
If this has any merit to it...all that anyone need do is install sump heaters and the majors can send the AW R&D labs on a permanent lay off.
..or so I'd reason..
I don't think that really follows...
The data from the Schnieder paper on the relative wear rates can be looked at two ways - the start-up wear is very high and/or the steady wear is very low.
I'd guess the low steady state wear is directly related to the success of the AW R&D guys. But steady state is always a simpler case than the transitional ones and would suspect a lot of effort is put forth trying to make a better band aid for it.
If this has any merit to it...all that anyone need do is install sump heaters and the majors can send the AW R&D labs on a permanent lay off.
..or so I'd reason..
I don't think that really follows...
The data from the Schnieder paper on the relative wear rates can be looked at two ways - the start-up wear is very high and/or the steady wear is very low.
I'd guess the low steady state wear is directly related to the success of the AW R&D guys. But steady state is always a simpler case than the transitional ones and would suspect a lot of effort is put forth trying to make a better band aid for it.
I read as much of this thread as I could. I dunno what happened with oilgal. I thought she was cool and as informed as most posters here. I think she was trying too hard, getting ahead of herself, and was frustrated. I apologize on behalf of the Forum IF there was anything said impolite.
My 2c on the visc and thickness thing...
Specs should be reversed. Say a 30-5w, 30-10w. See? The IMPORTANT part is that they are both 30s as far as the engine is concerned....at op temp, +100c. the fact they pas a w test is secondary. Easier to see how a 30 weight THICKENS less if it's a 5w at colder temps.
I have a dumb rule that I made up (I like dumb rules).
10w oil above +10f
5w oil above +5f
If you see +0f, maybe a 0w oil is indicated.
Again, I'll say...
THE FORUM DEFINATELY NEEDS SOME GOOD VISC GRAPHS OF TYPICAL OILS AT REAL TEMPS.
-10f to +200f
All the graphs I have seen suck. It needs to be a log chart without the various lines overlapping. So many brains here, can someone produce them? Typical dino oils compared and maybe a synth vs dino chart.
My 2c on the visc and thickness thing...
Specs should be reversed. Say a 30-5w, 30-10w. See? The IMPORTANT part is that they are both 30s as far as the engine is concerned....at op temp, +100c. the fact they pas a w test is secondary. Easier to see how a 30 weight THICKENS less if it's a 5w at colder temps.
I have a dumb rule that I made up (I like dumb rules).
10w oil above +10f
5w oil above +5f
If you see +0f, maybe a 0w oil is indicated.
Again, I'll say...
THE FORUM DEFINATELY NEEDS SOME GOOD VISC GRAPHS OF TYPICAL OILS AT REAL TEMPS.
-10f to +200f
All the graphs I have seen suck. It needs to be a log chart without the various lines overlapping. So many brains here, can someone produce them? Typical dino oils compared and maybe a synth vs dino chart.
I tried to edit, but the forum locked up...for the tenth time today.
The whole using a number value for the w rating is confusing. A long time ago, the w rating MEANT the multi visc oil was "like" a strait 10 weight oil ~would~ be at freezing. That system is long gone, except in old tymer's heads and the sorry souls who listen to them like they know something.
Now, I leave my car run if it is still cold. After it's warm, I'll shut down if I stop for more than 30 sec to a minute. Once it's warm, it cranks easy and start wear is NOTHING. Also, I think 2 cycle oil in gas can help start up wear. I put a double dose in when temps go down to single digits.
The whole using a number value for the w rating is confusing. A long time ago, the w rating MEANT the multi visc oil was "like" a strait 10 weight oil ~would~ be at freezing. That system is long gone, except in old tymer's heads and the sorry souls who listen to them like they know something.
Now, I leave my car run if it is still cold. After it's warm, I'll shut down if I stop for more than 30 sec to a minute. Once it's warm, it cranks easy and start wear is NOTHING. Also, I think 2 cycle oil in gas can help start up wear. I put a double dose in when temps go down to single digits.
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