XJriot

So Jeep Cherokee == (heavy?) equipment and a turbo diesel.

I had no idea that the I6 resembled them so closely that a valid comparison could be made.

wcshale

Yep, they all are internal combustion engines.
I started to add my wifes blender in there but we don't operate it when its cold. LOL

XJriot

A blender motor is probably closer to an XJ motor than a diesel is lol.

aren't diesels supposed to idle at a higher RPM if they're sitting for a while? Pretty sure semis have a switch or something that increases their idle RPMs? Idling at a normal RPM doesn't let all your fuel burn off and can contaminate your oil.

s346k

most newer big trucks will idle themselves up if it's cold enough. in the summer they will not. they have a fast idle setting, but I only use it to get heat in the cab quicker, idc bout the environment lol

edit: the piston slap in gm lsx engines was caused by the short piston skirts. despite the constant cold start up knocking they still make 200k+ mi regularly.

wcshale

The blender has more HP than some of my diesels.
Probably right on the fuel, we worry about hot turbo's frying the oil and gumming them up if shut down to quick after working them.
We kind hijacked here, I tend to ramble off......

black label

I'm not an engine builder nor am I a machinist but aren't the tolerances greater on a production engine than what would by specified by the blueprints for the engine?

Wouldn't what you are saying about the expansion/contraction of metal be less significant on a mass produced engine than it would be to one which had been rebuilt to blueprint specs?

salad

No. I suggest you look up how engine oil actually works. Synthetics are naturally able to flow better when cold than conventional mineral oils. Your statement reads that dino juice freezes and synthetics never change viscosity, both of which are incorrect.

The typical 5w30 synthetic has a viscosity of 11 centistokes at 100 degrees Celsius and around 60 centistokes at 40 degrees Celsius. Engines are built around the best performance at operating temperature. I can assure you that cold oil is a lot thicker than hot oil, regardless of type. You may think "well if it's so thick, the buffering should be enormous". It is, but the issue is that once it's been squeezed out of the bearings, the rest of the oil is so thick that it does not flow quickly enough to replenish it at an acceptable rate for applying any sort of meaningful load. To do so will result in excessive bearing wear. The oil is still really cold, too cold to provide adequate lubrication. This is why cold weather pumpability and pressure relief bypass valves in the oil filter are so important, and why I strongly advocate the use of an accurate oil pressure gauge in these engines.

Lol. Well if it doesn't get cold down there you have nothing to worry about. However I'm not sure if your first part was serious... the composition, age, and original design specs decide everything about how you should treat an engine.

The 4.0L has a lot more in common with a diesel than it does a brand new car. Know the caveats and treat it with respect and they'll last forever.

Yes, there are three big reasons for this.

The first is that in high compression/high torque engines engine wear as a result of improper lubrication is even more pronounced. It is very important to let the oil warm up. These guys reach 1,000,000 miles easily. See a pattern?

The second is to build up air pressure. Generally if a truck has been sitting long enough the air leaks down over the course of a few hours, an you ain't moving until you hit 120PSI in both tanks.

The third is because humans are squishy flesh bags that get cold easily lol

s346k

not trying to start a war here, but I disagree with the first 2 items. here is why:


1) the engines last so long for a plethora of reasons, I believe a few key items include: inline design. simple physics. having no angular load on the rod bearings greatly reduces wear, regardless of oil temp. take our beloved 4 liters for example. low rpm. wear items, simply stated, will last longest when used the least. use of the engine between shut off and start up. 99% of "normal" engine damage occurs at/shortly after startup. continuously removing that cycle from the life of the engine obviously will aid in its survival. the engines are governed very well with regard to coolant and oil temp. the cooling systems on big trucks are huge. the trucks I drive see the same coolant temp (+/- 10*) whether the ambient temp is 100* or 0*. just my opinion(s), take with a grain of salt (and some tequila if that's your thing).


2) entirely false. first of all it only takes 45 psi +/- to release the brakes. trucks sit days without losing air pressure, the engines certainly don't fast idle in an effort to build it at startup. I've only noticed the recent "certified idle" trucks to fast idle on their own. I believe this to be related to emissions, stemming back to the fact they have huge cooling systems and without fast idle the egt doesn't get hot enough to burn clean. none of the older trucks I've driven, regardless of make, would do this on their own. all trucks have a fast idle setting, only the new ones do it by themselves (my experience). I believe the old(er) ones to have this function for adequately recharging the batteries, keeping climate control (a/c and heat, ie sleeper cab trucks) in check, and for the same reason the new ones do it, but it was up to the driver to take action.


3) I agree with 100% haha.

salad

Sure, you're the trucker not me lol. I'm not disagreeing with you at all as those are valid additional points. I also don't see as how you're disagreeing with me, either. I'm going on mostly what I've read about Detroits, if you don't let the oil warm up you're gonna be rebuilding them annually lol.

Not sure I'm with you there. The spec is pretty lose, at least up here, as long as you don't really lose more than 6 PSI per minute you're good to go. A lot of older trucks around here will dump pressure after a couple of days.

Getting the EGTs up to heat the DPF is a good one of course, as well there are a lot of accessories that need hot oil to work right and being compression ignition there are other reasons too, but I didn't start on that because they're not relevant in this context lol. Drivers have been letting their trucks idle before moving for a lot longer than emissions control gear has been a concern though. Hop into a 90s FLD120 and your "idle up" is the cruise control lol

JackJare9455

man.. good reading.. lots of informative stuff... but honestly.. when its stupid bitter cold.. you might want to have an oil similar to 5w40 in your case.. let it idle for about 5 minutes.. walk around.. check your tires and lights.. by that time your engine should be plenty warm to soft foot it around untill you reach operating temps..

if my reading was correct on the aw4... the fluid does not circulate in park.. only in neutral.. you could even drop her down into neutral for a minute or two to let the fluid start to heat up... just suggestions

its really totally up to the operator on how they start up and warm up their jeeps.. i dont let it sit for 30 minutes.. but i always give her a minute or a normal day to get everything flowing.. .02

hankthetank

Idle up is for increased oil pressure. Ever hear of "that truck idled to death"?

salad

Nope that's the stupid Chrysler transmissions. (And a big reason they fail.) The AW4 pumps fluid in all settings so you're good to go!

Are you talking the kind where EGR causes soot build up or ancient two-strokes that build up goopy slime if they aren't run hot enough?

wcshale

If oil pressure drops at idle to a point that would hurt an engine, then you have other issues.

s346k

i disagree. if the new trucks have OP that low they turn themselves off

hankthetank

extended idling is hard on any motor. it is considered severe duty in almost any owners manual.