Overheat, hydrolock & starter

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08-05-2020, 10:25 PM
filschoppin

Overheat, hydrolock & starter

Hi all, happy Supra owner new to the forum. My boat is a 97 Comp with a 351 H.O. PCM according to the tag on the motor. History is unknown, I traded it for a bike. It looks almost new, sounds amazing and crazy fast. Since I've had it I only changed the oil and repaired minor things here and there, has run extremely well until yesterday. Moving down the lake at a good pace I noticed temp climbing fast. Dropped to idle and things started smoking. I turned the motor off and scanned for options. I just happened to be near a closed ramp where I was taking my littles to swim. Jumped out and swam boat to the dock. Called a friend who took me to my truck and I was able to convince the guards to let me in to collect my boat. It was not cooling fast but while waiting for her I decided to see if it would start. It had a sluggish crank, then just a click.
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Back in my garage today and tried to start it. Just click. Bypassed the solenoid, just click. Pulled the spark plugs and found water in two cylinders. I was able to turn motor over by hand and tried to use the starter to push water out. No go. Pulled starter and bench tested- it's toast. Back to original problem, for some reason I pulled the hose off of the top of the impeller housing expecting to find fragments of rubber. Looked good from the top, I turned the motor over but did not see the impeller move at all. Belt was turning pulley, but not impeller. Removed it and opened it- to my surprise it looks new (PO said he had it and the water pump replaced last season. I can see a new gasket on thermostat so I assume so). I'm puzzled and looking for advice on where to start. Obviously will drop oil and am confident if the rings are not melted or bearings trashed I can get it running again but I'm new to impellers and don't know what to think about it not spinning but after I took it apart and put it together I can see it spin. I looked at the oil cooler and it did not have anything blocking it so I'm confused as to why it overheated and where I should start assessing for damage. Any pro's mind sharing some advice? Thanks.
08-06-2020, 06:34 AM
michael hunter

First when you shut down the engine when overheated it probably pulled water into the cylinders and hydro locked the engine. When you tried to start it you killed the starter. Hopefully the rods are stronger than the starter and didn't bend. First try pulling all the spark plugs and turning it over with the new starter. Change the oil and see if it will run briefly. Take raw water pump apart remove the impeller and check the shaft . If all looks good install a new impeller and do a in water test.
08-06-2020, 10:49 AM
tretter7

For the impeller not spinning, I have heard of them spinning on their splined bushing (though it's never happened to me). Once you have some indication that the engine is okay, I would replace the impeller and go from there.
08-08-2020, 01:28 PM
filschoppin

Quote:

Originally Posted by michael hunter

First when you shut down the engine when overheated it probably pulled water into the cylinders and hydro locked the engine. When you tried to start it you killed the starter. Hopefully the rods are stronger than the starter and didn't bend. First try pulling all the spark plugs and turning it over with the new starter. Change the oil and see if it will run briefly. Take raw water pump apart remove the impeller and check the shaft . If all looks good install a new impeller and do a in water test.

So far I think you have it exactly right. After bench testing starter, it's clearly burnt. Pulled plugs, turned motor by hand and got water out. Got new starter, turned over and pushed the rest of water out while performing compression test. 6 cylinders at 130+/- 5, 2 at 100 +/- 5. Cheap gauge so only use it to look for consistency rather than exact pressure. Not adjacent and concerning for sure but I recall a little dieseling when hot so for all I know, it's not a new issue. The impeller was not at all torn up and there was no blockage in lines up to it. My best guess is that it spun off spline. It looks like it may have, unless I damaged it pulling it but know it didn't spin with pulley at first. New impeller pushed water up to the ceiling with the slightest motor turn so I felt good enough to test. Fired right up, heart was happy. Noticed water at the intake at bottom of boat, so either tore it up pulling it or may have also been an issue. It's time for a water test. Fingers crossed, nice diagnosis thanks.