Questions Of My Way Into Work ...

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Aug 2, 2002
I can warm up my truck by driving @ 55 mph in 5th gear at 2000 rpms, but it takes a long time to reach equilibrium coolant/oil temps ....

I can warm up my truck by driving @ 55 mph in 4th gear @ 2500 rpms, in which case the oil/coolant will reach an equilibrium temp significantly faster.

Engine wear is a function of "mean" piston speeds along with average rpms. However, conventional P/Zn/S, anti-wear additives typically don't become fully effective until bulk oil temps reach approx 140F/60C.

Given this "Tradespace":

1) Which is the more effective strategy for minimizing engine/transmission wear during the warmup phase, and why?

2) Can the answer to #1 even be determined analytically, or strictly through a controlled experiment?

3) How dependent is the answer to #1 on the design and operating parameters of the engine & transmission? For example, pushrods vs DOHC, high rpm vs low rpm, gas vs diesel ....

4) Is the answer to # 1 completely independent of ambient temps during the warmup phase?

Partial credit will be given, and all the heavy hitters get to play too ...

Note: Automatic transmissions can easily be locked out of overdrive, so these questions have general applicability.
If you're saying that wear is a function of rpms, then you've already answered the question yourself. You will have less wear at 2k rpm (assuming you're not lugging the engine) as the temperature should not have any function on the oil's ability to lubricate.

The reference to boundary lube addatives is only in extreme if you were racing it cold and then asking us if there's more wear than racing it warmed up.
How significant is significant? Do you mean less than 75% as far? Surely wear must be proportional to the distance the parts move and load on them. All the moving parts in the engine will travel 25% more in relation to each other for every mile the truck travels at 2500 than at 2000. Since surely you are running a suitable grade of quality oil for the temperature and a filter that lets plenty of clean oil through, do you have that much more wear before the engine warms up? After all, you didn't replace you last truck because the engine was worn out did you? Which gear is a direct drive? Using it should make for less wear on the transmission. High gear is usually quieter and uses less fuel. Warm engines also use less fuel.

On colder days, you might go with fourth gear just to kick in the heater sooner. Definitely might be a great idea on the days when the defroster struggles to keep up before then. As far as engine wear and fuel usage, I doubt it makes any real difference.
For what it's worth, this is from Shell Canada:
"Q: Does it help to let your car warm up in winter before you start driving? A:During the winter when an engine is cold and the oil is thick, DO NOT rev up the engine immediately after starting it. The best compromise is to wait two or three minutes, then drive slowly for the next five to 10 minutes until the engine reaches the proper operating temperature. This procedure keeps engine revs down and builds up the oil pressure required to allow lubricating oil to move throughout the engine.

One of the main purposes of lubricants is to control friction and subsequent wear by putting an oil film between moving metal parts. Critical lubrication areas are the camshaft and connecting rod bearings, the cylinder walls and pistons. It takes a few minutes for the engine temperature to warm the oil to make this lubricating process work properly."
Ok, bear in mind Im a novice and not a "heavy hitter", but here goes:
First you would have to see which heats up fastest, your oil or your coolant. Whichever is slower, you may want to heat artificially before starting out each day. And your experiment would have to be a controlled test since all auto's are different. Im not sure how engine design would determine heat-up rates, a smaller engine with tighter tolerances would heat up the oil faster (I would think). Block composition would factor in as well (aluminum or iron). I would think if you wanted to minimize wear during warm-up, get a block heater and an oil pan heater or heated dipstick. Novice opinion

[ December 12, 2003, 08:21 PM: Message edited by: Jason8691 ]
1. I believe getting the engine to operating temp. as quickly as possible would be best so the fourth gear warm up would be best.
2. Yes
3. Completely not dependent on engine design etc.
4. Yes completely independent.
Just a Novices opinion.

Engine wear is a function of "mean" piston speeds along with average rpms.

I think that load is also a factor in engine wear, especially when the engine is cold. Therefore, running at 55 in forth gear reduces the amount of load on the engine/transmission, which reduces wear. Whether or not this load/wear reduction is enough to offset the rpm/wear?????? My incilination is yes. JMO

Now, I'm assuming you have less concern over fuel economy during this warm up. The gasoline engine will burn more fuel in 4th gear. I think if it were a diesel you would not see a difference. At least not with the naked eye.

As far as being able to prove any of this. With an oil temp guage, coolant temp guage, outside air temp guage, and a dyno it should be feasible. Oh yea, you will need to tear down your engine for measurements prior and post.
My gut feeling is that achieving operating temp more slowly would indicate more efficiency (less energy going to thermo) and less friction loss from slower rotating parts. Lower revs when cold has got to be better. Ask a hi-rev sport biker, maybe.
My uneducated guess....
1) 5th gear would be better due to the lower rpms until the metals are fully expanded, and oil temps have come up.
2) I would imagine that it would have to be a controlled thing and might not be the same with all engines in all temps across the board.
3) I would imagine that it will vary depending on metals and engine design used (aluminum vs iron block etc) to determine time necessary to achieve normal operating temps.
4) Ambient temps affect how quickly the engine temp I say it is not independent.
Ted, are you being hypothetical here or have you actually determined that your engine reaches operating temperature faster at 2500 rpm in 4th gear? Unless you are driving down hill, the higher exhaust gas and cylinder head temperature attained will driving in 5th gear at 2000 rpm (as the result of increased load on the engine) should balance the increased frictional heating at 2500 rpm in 5th gear.
1)Tooslick, You are better off geting the oil and coolant temp up quickly and in equilibrium faster buy driveing at 2500RPM's. You would want to accelerate slowly up to those RPM's. Wear metal is directly correlated to coolant temp especialy with high sulfur fuels. The critical RPM range to try to stay below dureing cold engine operation ( non-commercial gas engine) is 3000 RPM's until the engine and fluids is at operateing temps.

2)Controlled experiment best bet.

3) You will see more benifit to adherence to this type of protocal with some designs over others. Materials and loading play bigger role. The protocal is valid with diesels but the RPM rules would differ due to much narrower and lower power band and more extensive loading. The location of the cam has no bearing in this situation.

3b) Transmission if automatic are not as effected by cold as the engine. The fluid is much thiner so cold flow is not an issue. The fluid is not exposed to acid forming byproducts. THe loading is inline and torrsional with very little shock loading.

If it is a manualy trans then cold stiff fluids combined with sudden loading and to rapid of acceleration could leave gears and bearing running dry until fluid warms up. This is why most manual trans. use an oil pump to pump the fluid out to the parts. This is also why so many now use speciality fluids that have viscosity charteristics much more like a synthetic 5W30 or 5W40 motor oil.

4) Yes and No!! In a labratory setting ambient temps do not matter as the temp of the fluids and engine can be controlled. Under real world conditions the ambient temp is the driveing force. THe ambient temps are what drive the oil and coolant temp downs. The ambient temps are also effecting thermal effeciency of the engine. THe computer is going to select a fuel table based on temp wich will also effect this study.
1) Definitely 2500rpm. The oil pressures are higher. Also the oil spends less time in the phase where only its viscocity protects the engine parts.

2) Controlled. Since when can any experiment be done properly w/o controls? Analytically poses alot more variability.

3) Definitely. It will vary from engine to engine, just like how long it takes for each person in the worl to get outta bed each morning

4) Dependant on ambient temps to some extent. If its very hot, then either method will be faily similar. If it is very cold, then perhaps a mix of 2000rpm and then 2500rpm should be used.

The coolant temps increase much faster @ 2500 rpms in the Tacoma - even in cold weather - and testing in my Audi 100, with it's factory equipped, "VDO" oil temp/oil pressure guages, indicates that locking out overdrive warms up the oil perhaps 25% faster. The effect in both vehicles is quite dramatic ....However, I suspect the total # of engine rpms until the engine is warmed up doesn't vary much if I use 4th or 5th gears and drive at the same speed during the warmup phase.

So considering those factors, which way would you go?

What I really want know is how much low oil temps affect the ability of ZDDP to control valvetrain wear under mixed mode, lubrication conditions??? Keep in mind that even a 0w-30 synthetic is about five times as thick @ 40C than it is @ 100C ....So will you even get into boundary lubrication at all when the oil is so thick??? It's just not clear to me at all....

The situation may in fact work out rather nicely ...By the time the oil has heated up to 60C and thinned out, to where you can get metal to metal contact, the ZDDP has become fully active and you are just fine?

OK, I see where you are going now. I thought maybe you were just messing with people's heads.

Empirical evidence trumps theoretical musing, so I believe you re the faster warmup at 2500 rpm.

This is a complex issue because the answer depends on the specific components involved. The goal is to minimize boundary lubrication conditions until both a)the oil reaches a temperature that allow optimal flow viscosity to reach the parts and b)the oil reaches a temperature that allows activation of the EP additives. Remember that raising the pressure on a fluid film has the same effect as increasing the temperature as far as film thickness goes because temperature is a function of pressure. So high rpm and/or high load both cause local heating of the lubricant film at the gear, bearing, ring/piston/cylinder and valve train interfaces. Since the bulk flow of lubricant to the parts is low during warm up, you get to a mixed hydrodynamic/boundary lubrication condition at lower load and rpms than when the oil from the sump is at the optimal temperature and viscosity. So what I am suggesting here is that viscosity limited flow into the parts rather than EP activation temperature is the factor responsible for increase wear during warm up. The local temperature of the lubricant at the wear points reaches the activation temperature very rapidly.

So an ideal warm up procedure would be whatever gets you to the optimal lube temperature fastest while minimizing load on the interacting parts. For the transmission, that would mean maximum mechanical advantage (lower gears) at moderate rpm. The same would hold for connecting rod and main bearings, wrist pins, etc. However, for parts such as camshafts and lifters, the "load" is simply a function of rpm. So overall, moderate rpm without lugging the engine would be the best strategy. Hmmmm, that's what the owner's manual says, right?

My answers for your quiz:

1. 2500 rpm in 4th gear

2. Lube analysis should be able to provide useful info if you were to religiously drive for one full oil change interval under each condition. I would predict lower bearing metals at 2500 rpm but marginally higher valve train component wear indicators at the higher rpm.

3. Engine design will of course be a factor. The overall thermal mass of the engine will have a greater effect on low temperature wear than the specific design. But in general, the moderate rpm low load warmup should be best for any engine.

4) The initial cold startup viscosity and the time to optimal temperature are both functions of the ambient temperature. So any DIFFERENCE in wear observed between the 2500 and 2000 rpm warmup procedures should diminish at higher ambient temperatures.

So there's my $0.02.

Originally posted by JohnBrowning:
This is also why so many [manual transmissions] now use speciality fluids that have viscosity charteristics much more like a synthetic 5W30 or 5W40 motor oil.

Good point. My '95 F150 manual tranny uses automatic transmission fluid.
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