Rings need pressure to seat, idling does not create enough pressure to seat them properly leading to glazed walls. Pcv systems take a hit from the pressure imbalance between the case and manifold fouling the system up. Timing is usually more retarded at idle combined with low piston speeds giving unburned fuel more time to slip past rings that don't have enough pressure to seal properly, ruining the viscosity or your oil.

AFAIK

 

I agree with everything you've said regarding extended idling and its ill effects. however, to answer the question "why do big trucks idle fast?" with "because idling is bad" is not entirely true. go to any rest/truck stop. 8 out 10 trucks parks are idling at a normal 5-600 rpm idle. given that scenario, a lot less trucks would be making the 500k-1mil mile marker.


you're absolutely right, idling is terrible on an engine. what's funny is the company I work for wants us to shut our trucks off at every stop we have in an effort to save fuel. this ranges from 1 stop to as many as 20 per day. we have trucks with <200k miles on them requiring new starters, turbos, and batteries annually. what they haven't figured out is it requires the same amount of fuel to start the truck as it would to let it idle for 30+ minutes. most of the trucks will burn .2-.3 gal per hour idling normally. .4-.5 at a fast idle. I personally think it's funny. corporate America doing my blue collar job for me.

 

It does not take the same about of fuel to start as idling for 30 min. More like 10 seconds

 

letting a diesel idle at 500-600 rpm from cold is asking for cylinder wash, wetstacking/slobbering. maybe not so much in newer ones. i've done it unknowingly in the past. in new trucks with particulate filters its bad all around as it backs up those filters up pretty quick. for some trucks it's damned if you do, damned if you don't. every maufacturer has their recommendation...

to the original point, i only idle my heep as long as it takes the oil pressure to stabilize before i drive away. even on -30 mornings (yes i use my block heater) it warms up faster, and i don't drive like a red neck until it at least reaches operating temp. i would like to install an oil heater too, but feel it may be overkill as i use a really good synth oil already.

 

If I'm reading correctly, you are saying that you have a lower compression ratio when idling? And every time you start your motor your rings have to reseat? I thought PVC was positive crank case ventilation, its job is to relieve pressure. I also thought that EFI set fuel to air ratio and timing to match rpm. years ago when timing was fixed or you adjusted it with a lever on the column and carbs had jets that didn't adjust at rpm I could understand a motor loading up, but not now. I don't understand your complete statement.

 

He's talking about a large diesel, and pressure inside the combustion chamber. A number of engines need to be worked hard to keep everything happy, not just keeping the rings up to snuff but avoiding crud build up too.

 

ok

 

your rings seat (push harder on the walls) on every combustion down stroke. the extra pressure generated from the combustion actually goes between the ring and piston forcing it out harder against the cylinder wall. idling not so much. less air and fuel = less pressure.

 

Ok, so compression is the area compressed on every stroke, the same amount each time. Pressure is added by fuel and air ignited (making a bomb so to speak) inside that compressed area. The bigger the bomb, (more fuel and air) the more pressure. I think I got it. Some times I'm a little slow, but if you have patience I usually catch back up.

 

Talking about the jeeps, What about the automatic transmission, would putting it in neutral be better for the transmission than leaving it in park, ( Transmission fluid warming up faster)

 

On Chrysler transmissions, yes, they pump fluid in neutral. Your profile says Grand Cherokee so this would be you.

The AW4 and AX- series always pump fluid

 

So, would putting it in neutral make the fluid reach operating temp faster than it would in park? Reason i ask this is because when you checking your transmission fluid, it needs to be in neutral. Thank you by the way.

 

Yes, in Park you get the torque converter beating on fluid but the rest of the system sits still in the cold. In Neutral the transmission's pump is engaged so you'll get this warmed up fluid from the torque converter circulated around the system, you'll also pick up heat from the "cooler" portion that runs through the radiator. Well, assuming there's some heat there. lol

 

Much Thanks!!!!!!!!!