Stupid newb question about running a tank dry...

**pcrussell50** · 08-13-2020, 06:10 PM

If you run a tank dry until it the motor dies, could that create a dangerous lean out and burn a piston?

My recreation boat has two tanks and I want to go kind of far, which means I want to run one dry, so I can have plenty of extra in the other tank. But I don't want to be stupid if there is risk of burning a piston as the first one goes dry.

-Peter

**DangerNewb** · 08-13-2020, 07:10 PM

Somebody with better knowledge will chime in but I've always considered running a 2 stroke out of gas as something to avoid especially if running it high rpm and high load like a boat motor runs. Never have run an outboard out of gas but have on mx bikes and various yard tools. None locked up yet.

**FUJIMO** · 08-13-2020, 07:39 PM

...not a problem. you go right ahead and run out of gas wherever your sweet little bippy wants to.

**pcrussell50** · 08-13-2020, 11:06 PM

Originally Posted by FUJIMO

...not a problem. you go right ahead and run out of gas wherever your sweet little bippy wants to.

Well damn. No offense. I know you're a senior poster here, and I read your Merc stuff all the time. But I'm too much of a newb to even know if this is serious.

-Peter

**H2OPERF** · 08-14-2020, 05:10 AM

Not a good idea.. one carb circuits allways gonna run dry first and ur gonna get air as it starts to get low..reason race stuffs uses swirl tanks. Plus You may end up in the water if you are on the pad at wfo..

**FUJIMO** · 08-14-2020, 08:14 AM

...joking pc.

...damn if i always forget to put a smilie face at the end, it comes back in my court.

**JPEROG** · 08-14-2020, 08:27 AM

You have more then likely run a small motor "lawn mower, weed whip, chainsaw" out of fuel and seen it rev up due to being lean as it draws its last little sip. This is not a happy point for the air/fuel ratio that the motor is designed to maintain. --Switch tanks before its dry so you don't hurt the motor and don't have to re-prime it for another start up.

The other thing to consider is that dirt, water and trash fall to the bottom of the tank--is that really what you want to feed your motor on its last desperate breath?

Joe

**pcrussell50** · 08-14-2020, 10:46 AM

Ok guys, got it. It's a 2.0l 150. Usually cruising between 3000-4000 rpm. I will plan on not running a tank dry. Thanks, all.

-Peter

**Jay R.** · 08-14-2020, 08:30 PM

Originally Posted by JPEROG

The other thing to consider is that dirt, water and trash fall to the bottom of the tank--is that really what you want to feed your motor on its last desperate breath?
Joe

'

I hear this a lot but I gotta point out that unless your pickup is some custom deal on a float, you are always picking up off the bottom of the tank, just like a straw in a sippy cup. Still a good idea to keep a tank full to fight condensation, but the first sip and the last sip all come off the bottom of the tank.

**JPEROG** · 08-14-2020, 08:42 PM

Let the tank get down the bottom and everything collects to the point of suction more so then being displaced with a few gallons in the tank. I have seen this first hand with my old diesel "it gets down to the bottom and things don't sound so good". Fill it up, change the filters and back to normal.

Joe

**FUJIMO** · 08-14-2020, 09:06 PM

...joe, thats what the filters for... anyways, the best reason i've heard so far, for not running a tank dry before switching to the next is...you don't have to reprime everything to get restarted. just plain logical. if your at a cruise rpm, the motor will let you know when its "about" to run out. you immediately shut it down & switch over...and away you go. no damage, no noth'n...

**perfmarine1** · 08-15-2020, 10:56 AM

Originally Posted by pcrussell50

If you run a tank dry until it the motor dies, could that create a dangerous lean out and burn a piston?

My recreation boat has two tanks and I want to go kind of far, which means I want to run one dry, so I can have plenty of extra in the other tank. But I don't want to be stupid if there is risk of burning a piston as the first one goes dry.

-Peter

Over a thousand posts so you consider yourself a newbie? Anytime you starve a motor for fuel you risk burning a piston.

**pcrussell50** · 08-15-2020, 11:22 PM

Originally Posted by perfmarine1

Over a thousand posts so you consider yourself a newbie? Anytime you starve a motor for fuel you risk burning a piston.

I didn’t grow up boating. I started from scratch in summer 2008 with my first ever boat. (I did know a thing or two about car engines... EFI anyway), but carbs were new me and I still learn new things even to this day.

-Peter

**FUJIMO** · 08-16-2020, 11:52 AM

...i have relatives in boulder city nevada...neat little town... its got some cool history too.

**rock** · 08-16-2020, 12:40 PM

Originally Posted by pcrussell50

I still learn new things even to this day.

It's cuz you're payin attention. It's a good thing. I am old and have been messing with these things since the late 70's and still stumble into new things all the time.

Rock