Idling isn't good because the engine is running hot with little airflow other than the radiator fan kicking on occasionally to stop the engine from overheating. it is also not running at peak efficiency as it has to run richer to keep it idling which can cause oil dilution.
Also the oil isn't flowing as fast and may not cool and lubricate the parts as well as when running above 1K RPM.
With modern fuel injection technology its much less of an issue compared to earlier fuel injection and carbeuration, but it does cause slightly more deposits in most engines. (some more than others)
If it can be avoided, this is best, but sometimes it can't...
I used to be in sales and sit in the company car idling for hours every week typing on my computer ...even during 90 degree days in the summer with the air cond. on constantly.
Never a problem even with 5,000 mile oil changes.
It used to be the issue with gas getting into the oil in carb engines...poor oil cooling etc...
We sit in our trucks for hours on end filling out reports and powering all the accessories.
We get many miles out of our engines with no concerns. I will say that since Fuel injection the engines seem to be easier on oil when idling.
In our Toyota's the water temp stays within 5 degrees no matter what I'm doing. 4x4, sitting, responding or driving around.
They seem to have a pretty good control on the temps.
When we had Fords the temps were all over the place. But the last model year we had them was 1999-2001. Never had a Dodge even though we had them.
Now with all that said, the most I idle my own vehicles is a max of a couple of minutes. I just don't want the by products getting in my oil.
Take care, Bill
So if idling with ac on, with fan going would that help keep temps down?
No because the engine is under excess load. I have monitored my coolant temperature with my Scan gauge both with the A/C on and off and it runs about 10 degrees hotter with the A/C running in traffic.
Depends on the fan settings. Most GMs will idle darn near at 230, since the fans turn on slow speed at 220ish, high speed 230ish.
Click the A/C on and the fans instantly go on high and stay on and the coolant temp will drop to around 200.
My cooling fan has 3 speeds and is the only fan I have. It is on slow when sitting in traffic up to medium, and then goes to fast when the A/C compressor kicks in/out.
My engine in summer heat usually sits around 195oF WT on the scan gauge and with the A/C running it's 205-212 oF
I have an 05 F-150 4x4 V8 as a company vehicle. It has 140k on the clock and runs perfectly.
It has thousands of hours of idle hours on it. There are days once I arrive to the job site, it will idle for 10+ hours, then a long drive home. It has done this since the day it was given to me with 5 miles on the odometer.
Oil changes are every 5k, and haven't had the first engine-related failure or oil leak. Everything else has fell apart, except the motor... =)
The old pushrod V8's (and v6's too I guess) would eat cams if idled too much. The cams were lubed from oil thrown off the rods and at an idle not much oil got thrown.
There were many roller pushrod V8's, the SBF went roller in the Mustang in 1985.....
Oil is pressure-fed to the lifters, which regulate oil flow to the top-end. Oil coming down the lifter bores lubricates the camshaft lobes, the camshaft bearings are pressure-fed.