Mercury 25hp EFI Sucked Up Debris, Overheat Alarm

[ztrain727]

Hello,

I have a 2008 Mercury 25hp EFI with ~300 hrs (motor sat unused until 2015). It's a freshwater motor.

Recently, while parked in a cove with lots of fine wood debris, I did my best to splash fresh water on the intakes before starting, but while sitting it must have already gotten jam packed with the stuff.

Long story short, was able to start the motor, but tell tale was peeing weak, ran for a while at low RPMs, eventually tried to throttle up due to sunset and an incoming storm, a few minutes later overheat alarm sounds, so I shut it down and paddle home, very long night.

When I pulled the impeller, two blades were torn. Replaced, launched boat, still weak tell tale. I pulled the thermostat and this is what I found (see photo - that is the thermostat under there!) I ordered a new thermostat because I damaged the seal removing it, probably time anyway.

I was able to stick a pipe in the thermostat hole, plan is to flush it with the muffs, try to get remaining debris to flush out that hole.

My questions are:

1. Do these motors also have a poppet valve?
2. Does all water pass through the thermostat or is there bypass? In other words, should I be concerned of clogged coolant passages in the block as well, or would the thermostat have caught the bulk of the debris?

I would love to not have to pull the head, but I don't want to make any reckless decisions. I don't feel the motor sustained severe damage, it wasn't super hot, so I want to play it safe from here...

Thank you all very much for your help!

 

[saltchuckmatt]

Hello,

I have a 2008 Mercury 25hp EFI with ~300 hrs (motor sat unused until 2015). It's a freshwater motor.

Recently, while parked in a cove with lots of fine wood debris, I did my best to splash fresh water on the intakes before starting, but while sitting it must have already gotten jam packed with the stuff.

Long story short, was able to start the motor, but tell tale was peeing weak, ran for a while at low RPMs, eventually tried to throttle up due to sunset and an incoming storm, a few minutes later overheat alarm sounds, so I shut it down and paddle home, very long night.

When I pulled the impeller, two blades were torn. Replaced, launched boat, still weak tell tale. I pulled the thermostat and this is what I found (see photo - that is the thermostat under there!) I ordered a new thermostat because I damaged the seal removing it, probably time anyway.

I was able to stick a pipe in the thermostat hole, plan is to flush it with the muffs, try to get remaining debris to flush out that hole.

My questions are:

1. Do these motors also have a poppet valve?
2. Does all water pass through the thermostat or is there bypass? In other words, should I be concerned of clogged coolant passages in the block as well, or would the thermostat have caught the bulk of the debris?

I would love to not have to pull the head, but I don't want to make any reckless decisions. I don't feel the motor sustained severe damage, it wasn't super hot, so I want to play it safe from here...

Thank you all very much for your help!

That's crazy. Not good and yes there is some small passageways that it goes through before the thermo opens. Also, in your case the thermo probably opened putting debris in other areas like your head.

Couldn't tell from your explanation but did you back flush it through your t-stat hole?

You could try backflushing as best as you can.....new t-stat and then run your motor checking your heads with a IR gun.

If it gets hot you will know what you must do.

 

[ztrain727]

You could try backflushing as best as you can.....new t-stat and then run your motor checking your heads with a IR gun.

Yes, just getting things setup to backflush through the thermostat hole. I think I will 'forward' flush first for 10-20 seconds to avoid pushing debris back down in the impeller, then back flush. Wish there was a way to back flush the powerhead on these motors...

The IR gun is a great suggestion. There's lost of stuff on the head, would measuring the exhaust manifold do the trick? I'd be looking for discrepancies between the 3 cylinders, indicated a block somewhere. I trust the overheat horn if all 3 were equally clogged.

Fingers crossed most of the debris that made it through the little bypass flushed right through.

Thank you very much!

 

[saltchuckmatt]

Yes, just getting things setup to backflush through the thermostat hole. I think I will 'forward' flush first for 10-20 seconds to avoid pushing debris back down in the impeller, then back flush. Wish there was a way to back flush the powerhead on these motors...

The IR gun is a great suggestion. There's lost of stuff on the head, would measuring the exhaust manifold do the trick? I'd be looking for discrepancies between the 3 cylinders, indicated a block somewhere. I trust the overheat horn if all 3 were equally clogged.

Fingers crossed most of the debris that made it through the little bypass flushed right through.

Thank you very much!

I would pull the gearcase again and flush down....you can also pull the tell tale fitting off the block and run it for a second or two to see if it's stopped up there.

You can shoot the ir gun all over, nothing should be over 145 or so and much less at idle.

 

[ztrain727]

I would pull the gearcase again and flush down....you can also pull the tell tale fitting off the block and run it for a second or two to see if it's stopped up there.

You can shoot the ir gun all over, nothing should be over 145 or so and much less at idle.

Yeah, I planned to pull the gearcase anyway to make sure the new impeller didn't sustain any damage from back pressure.

The tell tale on this motor comes off the fuel cooler. I did pull it off there, seems like good water pressure, but it did eject a bit of debris. The cooling system on this motor seems surprisingly complicated, hoses going all over, none of which are shown in the service manual cooling diagram. That worries me because even if the block is getting water, there could be other components that are not.

Thanks for the tip, 145 is what I'll look for. Does that go even for the exhaust manifold?

 

[saltchuckmatt]

Yeah, I planned to pull the gearcase anyway to make sure the new impeller didn't sustain any damage from back pressure.

The tell tale on this motor comes off the fuel cooler. I did pull it off there, seems like good water pressure, but it did eject a bit of debris. The cooling system on this motor seems surprisingly complicated, hoses going all over, none of which are shown in the service manual cooling diagram. That worries me because even if the block is getting water, there could be other components that are not.

Thanks for the tip, 145 is what I'll look for. Does that go even for the exhaust manifold?

Yes everywhere really. If it's at home probably cooler. Overheat is probably even higher but not familiar with that motor.

I think you will get it flushed but that's just a guess. Good luck.

 

[ztrain727]

Just an update, I was able to stick a 1" PVC pipe perfectly in the thermostat hole to backflush the motor. I also then ran it with no thermostat to flush a lot of water through the block. I also pulled the fuel cooler hoses and some more debris came out.

So far, running great again. Looks like no need to pull the heads. The tell tale is pissing stronger than ever!

I'm going to keep tools on the boat for impeller and thermostat repair on the water if this ever happens again. Once you've done it once, it's an easy job and potential life saver.

Thanks so much for the help!

 

[saltchuckmatt]

Just an update, I was able to stick a 1" PVC pipe perfectly in the thermostat hole to backflush the motor. I also then ran it with no thermostat to flush a lot of water through the block. I also pulled the fuel cooler hoses and some more debris came out.

So far, running great again. Looks like no need to pull the heads. The tell tale is pissing stronger than ever!

I'm going to keep tools on the boat for impeller and thermostat repair on the water if this ever happens again. Once you've done it once, it's an easy job and potential life saver.

Thanks so much for the help!

Good to hear you were successful and thanks for letting us know!