Mercruiser 8.1 Hydrolock?

Tacoma290

Active Member
Oct 5, 2006
497
Tacoma, WA
Boat Info
340 Sundancer 2007
Engines
Twin 8.1 V-drives
Need help on how to protect the block.
Came back from a day trip on Sunday. Engines ran solid. Shut them down. Came back the next day to flush with these:
Fig%200456%20Flush%20Pro.jpg

While the flush was going, the port engine would not start. Stopped the flush. Smartcraft said Port MAP input Hi. Thought the sensor was bad and that battery was the issue and used the emergency start (in hindsight perhaps not the best move), but the port engine would not turn over. Called it a night.
Now I am thinking hydrolock, and that the pressure of the water during flush may have overwhelmed an exhaust gasket, or the gasket failed when the engine was shut down. And that the MAP sensor was correct. Will pull plugs and check oil today. Have read to add Marvel mystery oil to the 'wet' cyclinder(s) assuming that there is water in there to prevent rust.
Questions: How would this oil be added to the cylinder since it is in a bottle? Is there some other spray in oil to be used?
 
You could be hydro locked!
You need to pull all the plugs immediately. Crank the engine over to expel water out of the cylinders.
 
That ^^ and change the oil, go run it hard, and change the oil at least 1 more time.
 
Forcing water under pressure into the raw water intake line can fill the exhaust system to the point that it backs up into the engine through the exhaust valve.
The exhaust “pulse” or pressure of a running engine is necessary to force the water up and out of the water lift muffler.
 
If I remember correctly it is recommended that the flushing be stopped within 15 seconds of the engine shutdown. From the Merc Manual for inboards:

upload_2020-2-11_12-48-57.png


-Kevin
 
Pull the plugs and drain the cylinders
restart the motor , you must run it TO NORMAL TEMP for about an hour or so.
For long term storage, hook up a remote tank with a gallon of gas, 1 pint of 2 stroke oil, 3/4 pint of Sta-Bil . Run till it smokes
 
[QUOTE/]
Have read to add Marvel mystery oil to the 'wet' cyclinder(s) assuming that there is water in there to prevent rust.
Questions: How would this oil be added to the cylinder since it is in a bottle? Is there some other spray in oil to be used?[/QUOTE]
Use an old fashion oil can if you have one, a turkey baster or a gearlube pump (the ones that screw onto a bottle). You can also use a spray can of fogging oil - even wd40 - at this point the urgency is to get the water out and something in the cylinders to prevent rust from setting in. Then change the oil and get the engine running.

Almost certain that running the flush water without the engine running filled the lift mufflers and backed water up through the exhaust.
 
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Update: pulled the plugs. Water in three holes. Sprayed the holes with WD 40 first then all holes with fogging oil. Drained water from the exhaust runners where they connect to the muffler. Trying to use a breaker bar to turn the crankshaft over with the plugs out The only thing that moves is the nut on the pulley by a small amount. Bar is maybe 24 inches. Bigger bar? Anything else I should look at?
 
With the plugs out that should spin easily with a 24” breaker bar.

I wouldn’t use any more torque until I knew how big the crankshaft bolt is. Don’t risk breaking it!

I’d wait for Someone with more 8.1 experience will chime in.
 
Did you drain / change the oil ?
 
Update: pulled the plugs. Water in three holes. Sprayed the holes with WD 40 first then all holes with fogging oil. Drained water from the exhaust runners where they connect to the muffler. Trying to use a breaker bar to turn the crankshaft over with the plugs out The only thing that moves is the nut on the pulley by a small amount. Bar is maybe 24 inches. Bigger bar? Anything else I should look at?

With the plugs out, will it not turn over with the starter?
 
With the plugs out, will it not turn over with the starter?
I’ll try that next, but worried about the starter. Will switch the starter from the other engine. But I feel like I need to clear all the water from the exhaust. If flushing filled the exhaust side with water, is it possible I need to do more on that side before toasting a starter?
 
That doesn't sound good. How long did the engine sit with water in the cylinders? Without the plugs in it should spin easily with they key/starter or a breaker bar. So, either things rusted up in those 3 cylinders or something broke when you tried to start the hydrolocked engine. Fill the cylinders with MMO or PB Blaster, let it sit overnight and give it another try. If the starter won't turn it, use the breaker bar to rock it. If none of that works, unfortunately I think something big broke.

Don't worry about water in the mufflers at this point, with the plugs out you can't hurt anything - ie the engine can't be hydrolocked with the plugs out. If the engine will start, it will blow the water out of the mufflers.
 
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Your not going to toast your starter with the plugs out.
You need to get that engine running asap. It's only been a couple of days, not going to freeze up from rust that quick
 
I'm still troubled that I can't turn the engine on a breaker bar by standing on it with the plugs out. I agree with Scottlaw that rust should not have taken over in 2 days (flush was on Monday). Could be something inside that failed. My mechanic suggested another possibility that perhaps the starter is stuck in the engaged position. I'll pull the starter, move the old one over, and meet with one of his techs.
 
Let's hope that is the problem. Agree rust couldn't set in that quick. Even if something big bent or broke, I don't think it would completely log up the engine, seems would move, might even start just make a bunch of noise.
 
I'm still troubled that I can't turn the engine on a breaker bar by standing on it with the plugs out. I agree with Scottlaw that rust should not have taken over in 2 days (flush was on Monday). Could be something inside that failed. My mechanic suggested another possibility that perhaps the starter is stuck in the engaged position. I'll pull the starter, move the old one over, and meet with one of his techs.

I'm not sure you are going to be able to pull the starter. You may have to tap the starter housing to jog the drive into retracting. Since you probably also won't be able to get near it with a hammer, you can use a metal rod/bar to contact the starter housing and then hit the free end with a hammer (went through a winter semester with an old chevy with a bad Bendix drive).
 

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