Idle Questions etc...

[Portland Suburban]

Alright, some basic diesel questions here:

1. Is it bad to idle at at 650 RPM for long periods of time-say all night. If so, can I just have it high idle?

2. Is Delo 400 an OK oil?

3. I have a Turbo 350 tranny. What is an optimum cruising speed with 3.60 axles?

Thanks,
Chris

[twaddle]

On item 1/ DO NOT let a diesel engine idle for long periods of time at low idle (650rpm).

1000-1200 rpm would be more suitable.

Can't help you on the two other items, sorry.

Regards

Jim Twaddle
Biggar, Scotland

[CleviteKid]

I agree with our Scottish correspondent, don't idle your engine for long periods of time at low idle. Is your goal just to keep the engine warm overnight, or to run an inverter at a campsite, or what?

Delo 400 from Chevron is an excellent oil for our engines. Chevron has an extra refining step for the base stock that cleans it up considerably.

"Optimum" cruising speed also has multiple definitions - best fuel economy, low noise, etc. Your engine will be happiest cruising between 1500 and 2000 rpm. It can cruise at higher rpms, but the noise and fuel consumption will increase. My truck really runs nice at about 2300 rpm (85 mph in 4th gear, 700R4, 33" tires, 3.73 axle). At that speed, most of the noise is behind me ;) .

Dr. Lee :cool:

[john8662]

Due to the high valve train load in these engines, I do not recommend extended idle for ANY reason.

I used to religiously go outside on a cold day and start the engine and let it warm up for at least 10 minutes (while I ate frosted flakes) before leaving in the morning.

Bad Bad Bad

It didn't allow the engine to last any longer, as a matter of fact it shortended the engine life considerably.

Upon tear down of that exact engine I found two main problems with the engine that I directly contribute to the extended idle I always subjected it to (it's a diesel, you let it idle right?).

1. Cam bearings were galled and so was the camshaft itself, this led to a large drop in oil pressure, which contributed to me not being able to get lifters to fully pressure up and hold oil pressure to keep the valve train clearance correct.

2. The head valve guides were SHOT, needed a whole set of guides, which I had updated to the Bronze guide version. I suspect the guides were worn more than normal due to idle situation.

During idle, your oil pump in the engine isn't generating it's peak amount of pressure because it isn't being rotated an enough RPM. A lower oil pressure will allow the larger load of the valve train to overcome the oil film low pressure on cam bearings and then allow direct contact of the metal of the camshaft to the bearing surface. This lower oil pressure situation only gets worse as the bearings wear and the clearance increases, causing other problems. When the oil pressure in that circuit drops, then oil going to the lifters drops (think leak in the system) and then the quantity of oil going through the lifters and then to the pushrods in the engine drops, causing lubrication on the top of the engine to be starved, and then bad guides.

Whew.

Don't let em idle.

The ONLY reason to let one idle is after a run, where you have a turbo present on the engine. But a pyrometer installed on the truck would allow you to know when you can safely turn off the engine when the temperature is safe for the turbo.

The wise tale that you're supposed to let diesel engines idle, and that it's good for them is false, especially when applied to light duty diesel engines like our 6.2L.

[twaddle]

Idling a diesel engine can also lead to a very quick failure if the injection system is down in performance ie injector/s not atomising properly.
Due to the engine not reaching operating temperature and the fuel not atomising you can end up with unburnt fuel which can result in piston siezure and engine failure.

Jim Twaddle
Biggar, Scotland

[Portland Suburban]

Hmmm.....I wonder if this is why my oil pump shows 50PSI at idle....hmmm could the previous owner know all these things and make it produce a huge amount of pressure at idle?

Interesting...

[CleviteKid]

The electrical oil pressure gage systems in our trucks are notoriously uncalibrated. If you have not put a good mechanical pressure gage in parallel with your electric gage, you really don't know what the real oil pressure is.

IMHO 50 psi at idle (warm or hot engine) would be almost impossible to achieve, unless you were running straight SAE 60 oil, or a gallon of STP.

Dr. Lee :cool: