engine idle on returning to port

beernutz

beernutz

Member
Aug 16, 2009
427
Mobile, AL
Boat Info
2000 190 Signature BR
Engines
5.0L EFI 240 hp Mercruiser
My owner's manual has a section in the back on what to do when performing various boating operations including returning to port. One item in that section caught my eye because I have never done it and I don't believe I've ever seen other boaters do it.
The line said:

Returning to Port
Engine
Tachometer.................Idle the engine for five (5) minutes to cool down
Ignition key.................Turn to OFF position when engine is cooled down

Does anyone else follow this suggested practice?
 
Very good question. Technically, this should be followed if you are running at high end RPM's especially. Keep in mind, when you are running in a no-wake zone on your way back to port, that is considered idling, or close enough. Operating at no-wake speeds does the job, no problem. Not sure about your location, but if your port is not in a no-wake area, then it would probably be a good idea to let it idle for a few minutes at the dock.

Mainly, this should not be an issue. For the last few minutes of any outing of ours, we have to run in a shallow bay, that is a no-wake zone, so I only go 3-5mph. This does the job.
 
5 minutes seems like a long time. But letting the engine idle for a while after a hard run isn't a bad thing. The temp always spikes (goes up) after shut down so that would allow the block temp to come back down a bit before shut down. Also helps avoiding run on. Just what I noticed on my engine.

Bushway 9172 and I posted at the same time.
 
Last edited:
How would you not do this for 5 minutes? I've never seen anyone go to a slip or ramp at more than idle speed. It takes us 5 minutes to tie the boat up. When it's tied up, the keys are turned off.
 
Operation manuals are writen for the masses. There are some that would operate an engine wot full load for hours, bring the throttle abruptly to low idle and instantly shut down. Under these conditions there are internal engine parts far hotter the even the water temperature. Uneven internal cooling begines resulting distortion and stress risers. One very good example of this is cold piston slap from out of round piston pin bores.

You always want to let you engine warm up some before loading it and definatly not hammer on it til she's up to operating temp. Some Cat off road haul trucks that have a programable idle shut down timer. ...Ron
 
sbw1 said:
How would you not do this for 5 minutes? I've never seen anyone go to a slip or ramp at more than idle speed. It takes us 5 minutes to tie the boat up. When it's tied up, the keys are turned off.
Click to expand...

sbw1 I understand what you mean. You have very a nice boat. Its takes a little bit more time to dock and tie up your boat than a small one like mine. Our house is on a main channel and the waves get big in the summer. I pull off the channel and into our slip in about a minute or less. If you were pulling skiers and shutting off the engine often, you wouldn't idle for 5 minutes each time. When I get fuel I do idle in the channel out of harms way. Then pull in and tie up one side in a minute or less before killing the engine.
 
Yes, once I'm backed in my slip I leave the boat idle while I secure my lines, shore-power and get the fenders in place. counting the fairway idle it's well over 5 minutes. I also run the blower for that time as well.
 
on a similar note, my owners manual says to run the bilge blower for 2 minutes before starting the engines. sometimes i remember and run the blower for 30 seconds, other times i forget. is that a serious safety issue?
 
Letting the engine "idle and cool down" for 5 minutes is a "carry-over" from engines with turbo chargers. Turbo chargers are driven by the exhaust and spin as fast as the exhaust is coming out of the head, ie. the more RPM and exhaust flow the faster the turbo spins. Most turbo chargers are also cooled by the engine oil or coolant. With a turbo charger you could come in with a turbo "spooled up" and shutting down immediately would allow the turbo to continue spinning without any oil or coolant pressure causing the oil/components to burn and cause damage. With an engine without a turbo this becomes less important as the whole engine stabilizes temperature much quicker. The turbo really is the "weak link" with fast shutdowns. If you have a non-turbo charged engine I would think that 2 minutes would be more than enough idle time prior to shutdown. I always secure the lines prior to shutting off the engines-no turbo's. I'm guessing that this takes at least a minute, with another minute of idle time prior to that while I'm pulling into the slip. If you've got turbos I'd recommend at least a few minutes of idle time once you've got the engines at low idle.

To oversimplify this.....which most manuals do....if your engine is turbo charged.....allow 5 minutes of idle time to allow the turbo to reach minimum RPM and for oil temp to stabilize prior to shutting down.
 
according to kindredspirit it only applies if you have a turbo diesel....:huh: but if I've heard it once I've heard it a hundred times..... "really baby, can't we shut off the motor yet?"
 
You must log in or register to reply here.

Forum statistics

Threads
113,182
Messages
1,428,076
Members
61,089
Latest member
KDKING
Back
Top