Why idle before shut off?

[Gary Fowler]

I gotta pose one other thing for the group to consider. Wouldnt the coolant still have some flow due to natural convection with hot fluid rising and cooler fluid being sucked in from the bottom of the radiator as long as the thermostat was opened, I think you would get a bit of circulation. Maybe not much but enough so that the radiator would disipate some engine heat after shut down.

 

[RoyJackson]

I gotta pose one other thing for the group to consider. Wouldn't the coolant still have some flow due to natural convection with hot fluid rising and cooler fluid being sucked in from the bottom of the radiator as long as the thermostat was opened, I think you would get a bit of circulation. Maybe not much but enough so that the radiator would dissipate some engine heat after shut down.

Maybe some movement...but would it be enough? Well, I'm not going to experiment with an engine that costs $3000-$4000 to rebuild. Not to save 10 cents worth of fuel...

To the guys who shut down immediately...I read an article (review) of the new Porsche Cayenne (sp??) which shuts down almost every time you stop (fuel economy and air pollution reasons). I wonder how they handle "heat sink"? (my guess is an electric pump keeping the coolant flow going...but that's just a guess).

 

[ModMech]

If you shut down a HOT engine, the thermostat will remain open until the coolant cools to below the "start-to-open" temp. This will *allow* some convective flow thru the radiator but because hot air/water rises the flow will be very limited.

MANY vehicles are shipped with full or semi-synthetic oil from the factory, the Corvette is on long-time example with many other high end vehicles as well. The Ford GTs, Lightnings, Cobras ALL get full or semi-synthetic oil at the plant. Saying the use of synthetics will harm the engine is 100% false, period.

One of the biggest factors in CHT is EGT, when you lean out a gas engine EGTs go up and fast. When you land an airplane with a carb, it is LEAN because the air is much more dense at ground level than at 5,000 ft. Add to that the fact that airflow is greatly reduced at 50 mph compared to 120 mph and it is easy to understand increased CHT/EGT after landing.

The main point is, if the engine is HOT it will not hurt anything to idle a little before shut-down, but if it is cold then you are doing more harm than good!

 

[ray66v]

Synthetic oil was not shipped in My Chevy Truck and I dont know where anyone picked that up. My owners manual doesnt tell me what kind of oil they put in for break in oil, just what to use when I change it and I dont believe yours does either. Every motor supplier I have ever heard of tell you not to use synthetic during a break in period. You actually want the parts to wear in together and all my operation manuals tell me not to put additives in the oil or use sythethic during break-in period.

No, I did not say that GM puts synthetic oil in everything. If your trying to hold down prices, that would not be a smart move.

I was making the point that GM is selling brand new cars, with synthetic oil in the engine. So are other manufacturers.

It's 2010 now. The additives in mineral oil toady make it so good, the lubricity test results on mineral oil, and synthetic oil are almost identical, so the parts are not going to "wear in" any different.

When an engine is designed to "wear in" a special breaking oil is specified, and supplied, for that purpose, I believe Deere has some equipment that still uses a breaking oil.

The only difference between synthetic oil, and mineral oil today is the synthetic oil holds up better in extreme temperatures, and can last longer as a result.

So, you can use synthetic in new equipment.

I have no doubt however, some will never accept that fact.

The following is a partial list of cars that are, or were, shipped with synthetic oil from the factory. If you don't agree with any of them, take it up with Mobil oil, it's from their web site:

> Acura RDX
> Aston Martin
> All Bentley Vehicles
> All Cadillac Vehicles
> Chevrolet Corvette C6 and Z06
> Chevrolet TrailBlazer SS
> Chrysler 300C SRT-8
> Cobalt SS S/C Coupe
> Dodge Caliber SRT-4, Charger SRT-8, and Magnum SRT-8
> Jeep Cherokee SRT-8
> Mercedes-Benz AMG Vehicles
> Mercedes SLR
> Mitsubishi Evolution
> Pontiac Solstice GXP
> All Porsche Vehicles
> Saturn Ion Red Line and Saturn Sky Red Line
> Viper SRT-10

The thinking that you cannot use synthetic oil in a new engine goes back to the very early days of synthetic oil many decades ago.

In the mean time, this myth is still spread, so it continues to be considered true.

 

[ray66v]

Is it a case of cooling the turbos or allowing oil to flow through the turbo bearings?

Many believe the oil in the bearings of the turbo will cook, if the cool down period is not utilized.

Some aircraft manuals apparently were published with this procedure in them.

As I said, this was debunked.

The turbo is never gets any cooler than it is on touch down.

Like the synthetic oil in new engines myth, many refuse to accept that it as incorrect, and still use a 5 minute clock after landing, before shut down. :confused3:

 

[RoyJackson]

Many believe the oil in the bearings of the turbo will cook, if the cool down period is not utilized.

Some aircraft manuals apparently were published with this procedure in them.

As I said, this was debunked.

The turbo is never gets any cooler than it is on touch down.

Like the synthetic oil in new engines myth, many refuse to accept that it as incorrect, and still use a 5 minute clock after landing, before shut down. :confused3:

Well, at this point, all we have is your post. Why not provide a link to a reputable study backing up your assertions?

 

[Transit]

I gotta pose one other thing for the group to consider. Wouldnt the coolant still have some flow due to natural convection with hot fluid rising and cooler fluid being sucked in from the bottom of the radiator as long as the thermostat was opened, I think you would get a bit of circulation. Maybe not much but enough so that the radiator would disipate some engine heat after shut down.

You are only looking at the water-engine coolant. Oil is also a coolant and only cools when circulating removing heat deep within the engine.

 

[TripleR]

I simply cannot draw a conclusion that what is good/bad for an airplane is good/bad for my turbo tractor, so I will continue to follow the manual printed by the people who designed and built it and follow a cool down procedure.

I AM NOT saying anyone is wrong, I am just uncomfortable drawing such a correlation absent apples to apples comparison.

 

[ray66v]

Well, at this point, all we have is your post. Why not provide a link to a reputable study backing up your assertions?

I was unable to find the article on line, or I would have done so.

I did not think anyone would be interested enough in flying, to spend a lot of time looking for it.

I am going to the airport today, I will see if anyone has it. It was several years ago, so it is not going to be on the top of anyone's pile.

There was considerable discussion about it in our club at the time. So, if you check in your inner circle, you probably can find people who are aware of it.

I will post a link if I can.

 

[whodat526]

However, the coolant flows stops once the engine is shut down and the thermostat had been open since the engine got to operating temperature.
So, you still have the heat sink situation.
As far as my road vehicle, I don't run the engine hard except when merging on to a highway. Even then, I shift (manual transmission) 1000-2000 RPM below redline. So, it doesn't really get that hot...and ambient (outside) temperature doesn't affect the operating temperature of an engine too much.

At this point, I'd say the guys who shut down immediately will continue to do so..and the guys who idle for a few minutes will also continue to do so. Furthur posts (n this thread) will likely be reiterations of earlier posts.
Not too much use continung...

1000-2000 rpm below red line in a car is 1-2000 rpm above what most tractors will even rev. up to they don't go but to the most is 2800 to 3000 most modern days cars will do 6000-7000 so how haven't u been running it hard as to the tractor and coolant does stop flow when it shuts down the thermostat still opens and closes it has nothing to do with the tractor running and u need to stick a thremo temp. reader to your tractor after running it mowing for a hour then to your car motor after running it down the interstate and 70 for a hour and tell me which gets hotter i know which will get hotter and if everything is to specs on the head and is running at normal temp which means not running it with the thermostat stuck or low on water it will not warp nothing i have ran many many when i say many i mean many tractors in my life and have never warp a head unless the tractor ran hot and blowed the head gaskett which in turned made the bolts not hold to spec thats the only way u will warp a head or block