idling down b4 shutting off, is it necessary?

Messages
556
Location
Michigan
Ok guys, I usually do this on my turbo jetski when i flush it to cool down the engine after going wot at 6200-6000 rpms. My question is, i have a 2002 civic ex 5spd, and i ususally give it 10-15 secs b4 i drive it away and drive slow for the first three or four miles until it gets warmed up. Now here is my question: When I get to my destination point, do i just shut off my engine, or should i let it idle for about 30 secs b4 i shut it off to cool it down? Btw, im running m1 0w20 with a bosch filter. Thanks, Aaron
 
Messages
508
Location
milwaukee
I do it, but for the most part it is easier to coast into the parking lot, or coast up to and down my driveway. I do idle down my JD tractor. I find that when I stop the deck and idle it down the temp will go up, then drop all in about 30 seconds. I wonder, is there a thermostat in a water cooled riding lawn mower (kawasaki).
 

CJH

Messages
489
Location
Pennsylvania
quote:
Originally posted by HOndaGuy: my question: When I get to my destination point, do i just shut off my engine, or should i let it idle for about 30 secs b4 i shut it off to cool it down? Thanks, Aaron
Good practice for a turbo engine. Oil lays in the hot turbo and cooks if you dont. No reason to do this in a non-turbo - buys you nothing.
 

Jay

Messages
1,607
Location
Idaho Falls, ID
I agree. Idling is always hard duty for an engine, and you should minimize your idling time when you can. You gain nothing by idling your NA Honda before shut-down.
 
Messages
23,591
If the (normally aspirated) engine is hot from driving it hard, I do let it idle for two minutes before I turn it off. All my manuals have advised that. Here is what my Audi manual says: Do not stop the engine immediately after hard driving. Keep engine running for about two minutes to prevent excessive heat build-up.
 
Messages
197
Location
Montreal, Canada
Same for the BMW manual. But if you've driven hard, it helps to try and get a cool down of 3-5 Km, then idle for 60-120 seconds. When i run my cool down, I turn off the A/C since the compressor generates unecessary heat and demands on the engine.
 
Messages
43,651
Location
'Stralia
If you are running hard, the exhaust valves and ports must be ridiculously hot compared to the rest of the oil wetted areas. 10 or 20 seconds of idling seems like a good idea to me after an engine has seen a high load condition. (Hasn't this been one of the toyota sludge theories also ?)
 
Messages
2,230
Location
SE MI
Racing an engine is different from "driving hard". When I was dragracing my 4.6, everything was HOT to the touch. From the plastic oil filler cap to my air intake heat shielding. everything was broiling. When I changed the engine oil, I didn't smell any gas/hydrocarbon smell. It all burned off. It just smelled waxy/fresh oil like. This was Chevron Supreme 5W-30. [ September 18, 2003, 09:09 AM: Message edited by: metroplex ]
 

Patman

Staff member
Messages
21,989
Location
Oakville, Ontario
If you've got a turbo car, idling it after a hard drive will cool down the turbo more than it would if you just shut it right down, however with a normally aspirated car you're just going to end up with higher coolant temps. In my car, if I were to pull into my driveway and idle the car, I'd just end up with my coolant temps creeping up to 230F, since there is no airflow to the rad. When moving, even if I drive the car hard, my coolant temps stay in the 190-200 range. So in my case, if I idled my LT1 Firebird for a couple of minutes before shutting it down, I'd just end up building up more heat. The best thing to do if you've got a turbo car is to simply keep your foot out of the boost for the last two minutes before you shut it down. Then it will be cooled off enough, and you won't need to waste any time or fuel by just sitting there. And those turbo timers are a disaster waiting to happen, IMHO.
 
Messages
6,388
Location
Washington St.
Pat, When you see high coolant temps during an idle after a hard run, the heat was already there. Your water pump is pumping more slowly, so the heat already there causes the temperature rise. The only time I take time for a cooldown is during a fast freeway drive and I pull into a rest area immediately off the highway. For a normal trip to a roadside gas station, etc., the time spent at a stop light, driving 25 even for a block or two, etc., provides adequate cooldown. Ken
 

Patman

Staff member
Messages
21,989
Location
Oakville, Ontario
quote:
When you see high coolant temps during an idle after a hard run, the heat was already there. Your water pump is pumping more slowly, so the heat already there causes the temperature rise.
In the case of my Firebird, because of the design of it's front end, if I'm stopped or moving slowly, the rad is not very efficient at cooling things down, since there isn't any openings in the hose to draw air from. So I definitely am building more heat during an idling period like this. See the pic below of my car, and you'll see, those nostrils in the front are for show, they are blocked off and no air goes through them. So this design is a "bottom breather" design, where the air to the rad comes from underneath and is only truly efficient when you're in motion at higher speeds.  -
 
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