Warm up time?

[StoneHeartFarm]

<font color=blue> only exhibit the optimal... </font color=blue>

I read a 4x4 mag that basically said oil gets ropey at low temps. So, when you start the engine, it splashes around and hangs on the inside of the block and crankcase. Until the engine warms up and thins the oil it will not flow down into the sump real fast and your engine can wind up oil starved since there's not enough in the sump to supply the pump. Which is why they make 5W-30 oil. Is that basically correct?

SHF

 

[r0GuE]

Ok ok...
You got me, but they have really warm areas too.

Rogue

 

[BruceW]

Thanks for the advice on engine warm up with an especial thanks for the lessons in geography and climates around the world.

bruce

 

[StoneHeartFarm]

Okay, so we digress. You gotta admit it's cool, though. Kinda like sittin on the front porch and yakkin with the guys.

But I still want to know if anyone else thinks this stiff oil not running into the sump is the real reason behind long warm ups.

SHF

 

[Hawgee]

Ya, I can remember Dad talk'n bought the early days when they drained the radiator at night too. Even if you pour in a new warm gulp of morning oil, the cast metals and steel against softer bearing surfaces are not ready yet. The only thing that would get me out of bed any qwicker would be a house fire.
Fire! That would be one time not to worry bout warm'n up. /w3tcompact/icons/laugh.gif

Thanks to Muhammad for the edit feature.
News Flash. Just saw GW's speech on global warming on MSNBC cable. To listen to him, I guess there is a fire. This means no warm up and no idle'n. Your operators manual will be rewritten. /w3tcompact/icons/laugh.gif I don't see the Federal Gov. replacing engines that have worn out with less than 1000's of hours.

"What is a weed? A plant whose virtues have not yet been discovered."
Ralph Waldo Emerson (1803-1882)<P ID="edit"><FONT SIZE=-1>Edited by Hawgee on 06/11/01 11:36 AM (server time).</FONT></P>

 

[FarmerBob]

Thanks a bunch kubmech. I've got my 50-hour coming up in a couple of weeks and I'll have my dealer check it out then. Doesn't seem to be causing any problems during normal operation.

FarmerBob

 

[skent]

Stationed at the Small Boat Station in NY Harbor in the 70's. Most of the boats (30 and 40 footers) had twin diesels. Some were Cat engines, some were Detroit Diesel, Duty boat and standby boat had to have preheaters on and a seaman made rounds every half hour and logged the engine temps. The 41 footer had a V4 Cat engine for the fire pump - it had it's own heater too. Usually the heaters were sized to keep engine temp in the mid 130's. (seems to me they were around 1500 watts each) Ran the heaters even in summer. When you gotta go. . . you gotta go! I guess it kept the engines in one piece.

Steve

 

[RPM]

SHF said <font color=blue>But I still want to know if anyone else thinks this stiff oil not running into the sump is the real reason behind long warm ups.</font color=blue>

Stiff is probably not the right word - but viscous is. Here's my stab.

I doubt that the problem is oil not returning to the sump. There's typically ample oil in the system (with special exception for Rogue's BX /w3tcompact/icons/crazy.gif!) to not have to worry about this.

I believe that the warm-up has more to do with tolerances between components in the engine - and how the oil lubricates between those moving parts. Ideally, you should wait until the oil has warmed up sufficiently that it reaches its ideal viscosity and flows easily in between these components. You then have a nice lubricated film that minimizes wear. This is why synthetics are good - they are close to their desired viscosity even at low temperatures (they also don't lose too much viscosity at high temperatures - unlike dino juice oils).

These tolerances change as the components heat up, so it's also good to wait for this change to happen before loading the engine. Cast iron, steel, aluminum etc. all have different coefficients of thermal expansion - i.e. expand and contract at different rates - so this problem is accentuated if you have components machined from different materials.

What happens if you load an engine while cold? Well, that applied load will tend to force these components against one another (e.g. no shaft is perfectly balanced rotationally). These components with tight tolerances (e.g. crankshaft with other rotating/reciprocating components etc) will tend to press against one another harder. If the lubricating oil film is insufficient you will get excess wear.

You are almost always bound to have some oil film left from the last time the engine was running. What you need though is a flow of lubricant. To get that to the critical tight spots you need the oil to be the right viscosity.

Of course, on the other end of the spectrum - for a worn engine with slack tolerances you want to use a heavier oil to 'fill the gap'.

Hope this makes sense - I'm no tribologist so I'm not convinced I'm right.

 

[StoneHeartFarm]

Makes sense. Pistons are aluminum. Rings are steel or some exotic stuff. Cylinders cast iron? All three are going to expand and contract at diffrent rates. I would suspect the engineers have it worked out so that the COLD engine may even have a little slop in that ring/piston/cylinder combination so that a HOT engine will have tight fitting parts. I think the amount of oil film left on parts though would depend on the length of time the engine has set.

SHF

 

[RPM]

With regard to the amount of oil left coating surfaces after the engine is turned off ...

At a microscopic level, the machined surfaces are still somewhat rough. The oil can therefore cling to these surfaces - although it will be in small quantities. Over time (weeks, months) that thin film will evaporate if it is a fairly open surface - such as the cylinder walls. That's why you can still get rust inside an engine if left unattended for a long time resulting in all kinds of other problems.

A couple of comments ...

First, do you remember the commercials where there are two engines running side by side - one has an oil additive (can't remember the brand) and the other doesn't. The oil is drained from both systems and the engines are left running. The engine without the oil additive seizes quickly. Point of the commercial is that the additive adheres to the internal surfaces of the engine and improves lubrication - I can't vouch for these products, but this illustrates the problem quite well.

Second, a more controversial subject is 'cool down' for an engine. If you've been operating under load for a long period of time you should allow the engine to return to its normal operating temperature before turning it off. Why? For a start, the normal (not synthetic) oil viscosity drops off at high temperature. This makes it 'runnier'. If you turn the engine off at high temp then you will lose some of that beneficial film of oil that is left behind in the critical areas where there are moving parts and tight tolerances. The problem is compounded because the retained heat in the engine will serve to drive off the remaining oil film by vaporization.

There are also other factors such as thermal stresses invoked because of uneven cooling - oil acts as a coolant as well as a lubricant (never mind the rest of the cooling system being turned off!). Added together, not allowing your engine to return to normal operating temperature causes as harsh a wear environment as not warming it up correctly.

This is the cause of many of the problems with engines when someone runs it hard, turns it off and then wonders why the engine has seized.