Engine Warm-Up Discussion.

Status
Not open for further replies.
Joined
Dec 12, 2002
Messages
43,887
Location
'Stralia
Thought I might modify a few Stribeck curves to demonstrate what happens to engines when running cold, with cold oil.

For reference, hydrodynamic lubrication is where a lubricant, the load, and the relative motion produce sufficient separation forces to keep the parts away from each other...it's the definition of zero wear, and when established, parts, and their asperities cannot touch.

The mixed regime is high friction, very high wear, with no fully developed hydrodynamic lubrication...the development of Anti Wear additives produces the lower line, where tribofilms protect surfaces and reduce wear, by making glassy layers of substrate, and additive components...a wee bit of parent metal is consumed, but overall wear is reduced to the point that your cams last (virtually forever)

Here's a standard curve, with an Anti Wear additive line imposed...it's representative of a running, fully warmed engine through it's load profile.

Stribeck%20Shannow.jpg


Points of notice...

Bearings are hydrodynamic. Low speeds, high loads are to the left of the range, high speeds, light loads are to the right...more to the right, more parts separation, but more friction and oil induced drag. Manufacturers are moving more to the left, into mixed lubrication, as evidence by what they are saying, what they are requesting for GF6 certification, and moving towards thinner lubricants at operating temperatures.

Cams and followers...completely the opposite, generally at operating temperature operate in mixed regimes, and are demonstrated to have very very long life, testimony to the additives and the tribofilms.

Pistons and rings. Hydrodynamic and EHD...the ends of the strokes are mixed, the middle hydrodynamic due to surface speeds. More load moves the curve left, more speed moves it right, and more viscosity moves it right.

Next pic has numerical overlays of where the ranges would be with cold oil after start-up at 0C. Given that the Stribeck curve posted is not representative of an actual design, I've taken the liberty of Using M1 5W30 ESP at operating temp (100C) as the baseline, and DEMONSTRATING where the curve goes at other temps.
Shannow%20Stribeck%200C.jpg


at 0C, the 5W30 is 52 times the viscosity of the lubricant at 100C, and what it does, is move EVERYTHING to the right...massively...can't fit it on the scale (would require logarithmic scale)

Bearings become more hydrodynamic, but as hydrodynamic is zero contact, can't be any less wear than zero.

Camshafts are pushed to the right, into EHD, and well into full hydrodynamic for part of the range.

Pistons and rings again are moved into EHD, and full hydrodynamic.

Clearly, there's a huge increase in friction, but it's not at the expense of wear, parts not touching aren't wearing.

It's the bit in the middle, the warm-up that's the problem. The oil is thinning with temperature and the anti wear additives haven't kicked in as yet.

This is the point of the Sequence IVA wear test. The engine (Nissan KA24E) is operated between an idle speed and 1500RPM, with the oil temperature controlled to 49-59C. There is plenty of oil volume, just at the wrong temperature. The choice of temperature and engine speed ensures that the situation is the "perfect storm" for camshaft wear, in mixed mode, but the Anti-Wear additives not functional...it still takes 100 hours to do the test...

What does the Stribeck Curve look like at that operating point ?

Shannow%20Stribeck%2055C.jpg


Cam and followers are clearly back into the mixed range, and with AW additives not replacing the tribofilms at the rate that they are removed...

Bearings (still not wearing, they are hydrodynamic).

Pistons and rings, still have a lot more hydrodynamic than at full temperature, but again, the additives aren't as strong.
 
That middle warm up section where the oil thins BUT additives haven't kicked in is worrisome in so far as these things can be. I'm assuming a PAO would rely less on additives and more on the base oil to get through this period unscathed? I'm unfamiliar with M1 ESP chemistry...

Thanks for posting.
 
Last edited:
Thanks for taking the time and posting this. It is very interesting. The transition period from cold to operating temp is where a lot of things are happening to the engine.
 
Originally Posted By: wemay
I'm unfamiliar with M1 ESP chemistry.

Thanks for posting.


wemay, don't concern yourself at all with the M1 ESP chemistry.

I used it's data sheet for viscosities and VI purely for comparison purposes.
 
So from a practical standpoint, is warming up a car 5-10 minutes on a cold winter day the worst you could do for an engine? I see people in the dead of winter just get in their cars, turn the key, and just take off. I have always warmed up my vehicles before taking off, usually with a remote starter. Am I doing more harm than they are?!?
 
SwedishRider,
I firmly believe that you should start the vehicle, wait for oil pressure, put on seatbelt, and move off at a sensible, traffic conscious pace.

I don't have any experience at -10C for more than a single day or so however.
 
One of my cars don't let me go above 35 miles per hour before the engine warms up. The transmission does not shift unless/until the coolant temp reaches a predetermined temperature.
 
Originally Posted By: Shannow
SwedishRider,
I firmly believe that you should start the vehicle, wait for oil pressure, put on seatbelt, and move off at a sensible, traffic conscious pace.

I don't have any experience at -10C for more than a single day or so however.


Thanks Shannow. Here, weather during the winter has been routinely under 14F (-10C) for days on end. I have remote starters in my vehicles and can warm them up so they aren't freezing cold when I get in. I just set the heater to high the night before and let the engine warm for 10ish minutes the following morning.

Works well so that I don't freeze upon entry, but I've always thought warming a car up was a good thing in that kind of cold...
 
Generally speaking,you start off in constricted streets that gradually open up into highways. So just taking off takes care of the warm up.
 
Originally Posted By: Shannow
SwedishRider,
I firmly believe that you should start the vehicle, wait for oil pressure, put on seatbelt, and move off at a sensible, traffic conscious pace.

I don't have any experience at -10C for more than a single day or so however.


Agreed.
However, when the ambient temeprature is somewhere south of 0F, letting the car ldle for a bit to at least get some heater output is a good idea unless you can hold your breathe for a few minutes while driving off.
I write this because merely breathing can produce enough condensation that you end up with frost on the inside of the windows.
Also, it is sometimes virtually impossible to remove the ice from the outside of the windows unless you warm the car for a while and allow a film of water to develop between the ice and the glass, at which point you can just slide the ice off pretty easily.
Yeah, warming the engine with gentle driving is probably optimal and is my usual practice, but there are times when it simply isn't practical or even possible.
 
Thanks Shannow...really nice post...will also help me make my case for moving to Florida from Ohio (today it's 20f)in order to reduce wear on our engines
grin.gif
 
The trick is to find AW additives which don't need high pressure and high temperature to work.

ZDDP works well at high temperatures. High viscosity itself protects cold. That middle region is served by moly, poly-esters, boron, etc.

Trying to prevent the picture below from happening:
toppistionbearing-300x283.jpg
 
Originally Posted By: Shannow


It's the bit in the middle, the warm-up that's the problem. The oil is thinning with temperature and the anti wear additives haven't kicked in as yet.



The AWs that are temperature related surfactants won't work at low temperatures, BUT, what about the solid lubricants, as MoS2 and graphite. The would shime in there reducing the wear at warm up.
 
Originally Posted By: Pontual

The AWs that are temperature related surfactants won't work at low temperatures, BUT, what about the solid lubricants, as MoS2 and graphite. The would shime in there reducing the wear at warm up.


Nobody uses graphite anymore AFAIK. ArcoGraphite bit the dust in the 1980's. Ceratec might help.
 
Originally Posted By: Shannow
SwedishRider,
I firmly believe that you should start the vehicle, wait for oil pressure, put on seatbelt, and move off at a sensible, traffic conscious pace.

I don't have any experience at -10C for more than a single day or so however.


I agree. Wasteful and not beneficial for the vehicle. That said, the vehicle is a tool and many don't mind sacrificing wear for comfort.

Personally I think that a block heater is the smarter/cleaner/better means of working through this "issue".
 
Originally Posted By: fredfactory
High viscosity itself protects cold.


Assuming you get flow... Which isn't guaranteed using sufficiently heavy lubes in low temps. And that other issues, like hydraulic tensioning of the timing chain.
 
Status
Not open for further replies.
Back
Top