Re: Agreed. Its alwasy good to allow some oil circulation at idle to distribute heat

I will be driving a new to me 2010 base Boxster from Arizona to Minnesota next week. This is my first Porsche. I have the owner's manual for a 2009 Boxster in pdf form which I downloaded from Porsche years ago. I'd like to know anything which is missing or poorly covered in the manual that might be helpful. I have one specific question right now. According to the manual "Do not stop engine immediately after hard or extended driving. Keep engine running at increased idle for about two minutes to prevent excessive heat build-up before turning off engine." If I am cruising at 75 mph on a 90 degree day with the air conditioner running, can I check the oil temperature with the on-board computer to see if it's safe to turn off the engine after pulling in to a rest stop? The car is manual transmission with only 14500 miles on it, and it must have been driven fairly gently because it has the original tires (Boxster S wheels) with about half the tread left.

a while after a spirited run is good advice and advice I have followed for years with my Boxster and my 996. (And cars/vehicles before these.)

When I pull off the freeway after running at speed I give the engine some cool down time as I make my way to say a gas station. But if the station is right off the exit at the pump I'll let the car sit a while and let the engine idle. I try to face the car into the wind to help the cooling. Not that the radiator fans need any help but the moving air helps carry engine and drivetrain heat away from the car.

I would nto worry.

That said i agree with marc's sentiment below. If the motor really is hot, let it cool down. Especially useful in turbo cars.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

the level highway at highway speeds.

To give you some idea.... with my VW TDi that's 40hp out of a max of 90hp or 46% of its output.

For the GTO with its 400hp engine that was 10% of its output.

The Boxster with 220hp (approx) that's about 18% of its output.

With the 996 and its 420hp that works out to around 10%.

While 40hp doesn't seem like much load it does generate considerable heat. And the heat is uneven, concentrated.

No need to get all wound up about it but if one pulls off the freeway even after driving at a steady highway (legal) speed a bit of a cool down at idle is a good thing.
Often times when I leave the freeway by the time I reach home or work I've driven a minute or two at low speed and the engine has spent some time idling at a light or two that for the Boxster I might give it 15 seconds (if that much) idle time. (I also enjoy listening to the Boxster engine idle and note its smoothness and quietness even after all these miles... amazing engine!)

For the 996 I give the engine a longer idle time. Also, I observe the oil pressure gage and if I wait long enough I can see the oil pressure drop a bit. Not much but a noticeable amount. This arises from the oil picking up the heat from the hotter areas of the engine. Remember the oil is in contact with the hottest areas of the engine, not the coolant.

These engines are still to a good degree oil cooled.

my point is that highway cruising does not really qualify as "hard use" or whatever the manual said.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I just checked the weather for Phoenix, and the high tomorrow is expected to be 99 degrees. To be safe, I am going to define cruising under those conditions as "hard or extended driving." Most driving tips in the manual are common sense, such as letting the car reach normal operating temperature before hard driving. This is one I haven't seen before.

I am really excited right now because I'm picking the car up tomorrow. The Autotrader ad is still up and here it is:

[www.autotrader.com]

I consider the car quite a find, and thought I'd give some details for anyone interested. The car was under lease by a retired CEO who gets a new Boxster every three years. It's his wife's car. I'm sure that by buying the car at the end of lease and immediately selling it to me, a substantial profit is being realized. The residual value of the car is, I'm sure, a lot less than the 38K I was able to negotiate as my purchase price. I'll post with a picture after I get the car home to Minneapolis.

to the gas station is short -- sometimes the gas station is just a few hundred feet from the freeway exit -- the radiator fans come on which signals the coolant temp is up to 212F. Now the day is mild or I would have had the A/C on and thus the fans would have been already on.

While this kind of driving/usage is not hard or spirited in the usual sense it does still result in a significant heat load the engine has to shed, will shed and the radiator fans coming on is a clear sign of this.

Obviously if the engine is shut off right away the heat can't be removed by oil and coolant. It is my opinion that the majority of this heat load should be shed with the engine idling which will cut down on the hot parts "cooking" the oil at various locations.

For instance the exhaust valve stems. When the engine stops some exhaust valves will be open, off their seat. The exhaust valves are very hot. The heat leaves by radiating and from conductivity. This latter method means the heat flows up the stem from the valve head and then through the very thin layer of oil that exists between the stem and guide. This heat "cooks" the oil to some extent and breaks it down and can in extreme cases result in some solids forming which are abrasive. What is left of this overheated oil provides poor startup lubrication upon the next engine start.

This is one reason why in the case of my 996 Turbo the engine is supposed to be idled some -- the owners manual calls out two minutes -- after a run. If the engine is shut down right away the heat in the turbine wheel (the part spun by the exhaust gases) heats the shaft and its plain bearings and the oil in these bearings and upon the next engine start this cooked oil provides poor start up lubrication. Premature wear results.

Anyhow, your car sounds very nice. And it reads like you are going to pick it up in AZ and drive it home to Minneapolis. That will be a nice drive.

Quote

...can I check the oil temperature with the on-board computer to see if it's safe to turn off the engine after pulling in to a rest stop?

Oil *pressure* can be checked using the on-the-dashboard display (left stalk). You can check the engine temp with the right-hand dial that shows that temp.

Driving a new-to-me '09S in Aqua Blue Metallic. It does .5 past light speed. I made the Kessel run in less than 12-parsecs.
Motto: If you have your top up, that storm outside had better have a name!
Motto 2: Having the top up on a convertible is an oxymoron. Don't be a (oxy)moron.

Enjoy the road trip back home and be sure to capture and document the beautiful USA scenery (and your new Porsche, lol) with lots of photos!

Regards, -rick