ran without the hose like an idiot merc 850

[bugelingkayaker]

dear god i just screwed up with my 1973 merc 850. i was working on fine tuning some stuff with it in my driveway and running it on the hose. in between short runs, killing the engine, tweaking things and starting it up again, i was turning the hose off after killing the engine (trying to save a little water) and then turning the hose back on to run it again. well apparently going back and forth like this was stupid because i forgot to turn it back on one time and proceeded to run the engine for about 1-2 minutes before i realized what i had just done. freaking out i turned the water on and then started the engine hoping to cool it down. in retrospect that may have been about the worst possible thing i could have done (thermal shock).
so anyways here i am now about 15 minutes later kicking myself and doing a damage assessment. ran a compression test on all 4 cylinders and by some miracle compression is still good (140 on all cylinders). I tried to start it again after the compression test and it wont start. i'm praying that i might have simply flooded it with fuel during the compression check and i'm gonna let it sit for an hour before i try starting it up again.
anyways clearly im a bit panicked here. this was a project boat that i got back in october, when it wasn't running, have spent 100's of hours working on only to screw up right when it was nearly ready.
so what are your thoughts? since compression is still good, does that mean i might have miraculously dodged a bullet here and not damaged the head? i'll obviously be taking a look at the impeller and replacing that, but is it possible that MAYBE because i had just been running it on the house minutes previously that there was still enough water inside to have prevented any serious damage? is there anything besides your cylinders, pistons, rings, and your water pump assembly that can get damaged by running dry?
thanks for any info, words of encouragement, or condolences.

 

[QBhoy]

I’d say you might be lucky and get away with just an impeller change.
I’d also say that your compression tester gauge is reading a little high perhaps. May be wrong, but that’s likely a hell of a high reading for a 2 stroke of any kind.

 

[bugelingkayaker]

I’d say you might be lucky and get away with just an impeller change.
I’d also say that your compression tester gauge is reading a little high perhaps. May be wrong, but that’s likely a hell of a high reading for a 2 stroke of any kind.

thanks for the response. the first compression tester i got was from harbor freight and only read 80 psi on each cylinder. returned that one after i used another compression tester and got a much higher reading this one was a supposedly nicer one i got from advanced auto. any way to check accuracy besides just getting a bunch of them and doing a side by side?

also big update, i just tried to start the motor again and i did get it to start (after triple checking the hose was running this time). ran it for about 5-10 seconds and then killed it. weak stream out the pee hole so im assuming that impellers probably ruined.

 

[QBhoy]

thanks for the response. the first compression tester i got was from harbor freight and only read 80 psi on each cylinder. returned that one after i used another compression tester and got a much higher reading this one was a supposedly nicer one i got from advanced auto. any way to check accuracy besides just getting a bunch of them and doing a side by side?

also big update, i just tried to start the motor again and i did get it to start (after triple checking the hose was running this time). ran it for about 5-10 seconds and then killed it. weak stream out the pee hole so im assuming that impellers probably ruined.

Yeah. Most likely. Change the impeller and I’m almost certain you are all good !

 

[flyingscott]

Your compression is fine. You probably did no damage if you only ran it.for a short time.

 

[racerone]

Perhaps the fuel / air going through the motor did enuff cooling.

 

[jimmbo]

There wouldn't have been much water in the engine as they drain out quickly when shut off. You may have warped the Water Jacket cover on what would be the Cylinder Head, Keep an eye for water leaking out around the Spark Plugs the next few times you use it.

In the mid 70s a 5 1/2 Evinrude we had got so hot the Paint on the Head and Block turned Brown. Never tested the Compression, just replaced the Impeller. That engine ran for another 15 yrs before we sold it,

 

[mav6759]

You are good, I run mine for about 30 sec to a min. But never over that without water.. I see my mechanic do it all the time..not for very long, but he says 30 sec to a min. Won't hurt anything.

 

[racerone]

Running an impeller dry will ruin them in 30 seconds !!----That fact is well documented.---------Perhaps the mechanic has put grease on a new impeller , so that is a different story.

 

[harringtondav]

I'll throw in my vote for engine being OK. Not much power, fuel, heat from idling two minutes. I'll also caution about your impeller. If you have a bucket, water trough, etc big enough to submerge the motor above well the water pump (well above the lower unit joint) use it before you restart the motor. A water pee will tell you the story on the impeller.

Or just change the impeller and lay that question to rest.