Overheat and a thump 470

[gimmieaclue]

Took the boat out to the bay yesterday, ran for about an hour doing 25 at about 3000 rpm then the engine lost power and died. I pulled the engine cover to find the coolant boiling over but the temp only said 180 (usually about 160).
Figured I just overheated because its a Mercruiser 470 with the 3 inch heat exchanger and I've heard stories. Now when I turn the key all I get is a single loud thump sound and for some reason the steering wheel kicks pretty hard even though I have it out of gear (don't know what to think about that).
The last few times I've taken it out I've had to top off the coolant but other than that I've had no problems with it (not counting yesterdays hefty tow bill). If it was just overheating I would know what things to look for but the other issues have me confused.
I'm a fairly handy guy and would like to fix it myself if possible just not sure what should I be looking into.
Thanks for any type of info you can give me.

 

[Rocky_Road]

Re: Overheat and a thump 470

Did it just lose power and stall? Or did it come to an abrupt (and loud) halt....

My 470 hydro locked under power (and was bogging down just before) due to the head gasket being blown.

 

[gimmieaclue]

Re: Overheat and a thump 470

It lost power for a few seconds, I throttled down a little and it died no noise at all. There's no water in the oil which I thought was how you checked for a blown head gasket (am I wrong?).

 

[Rocky_Road]

Re: Overheat and a thump 470

It lost power for a few seconds, I throttled down a little and it died no noise at all. There's no water in the oil which I thought was how you checked for a blown head gasket (am I wrong?).

The only surefire way to check your head gasket is with a compression check.

If this were mine, I would pull the plugs and spin the engine to see if any water (coolant) exits any of the plug holes. The next step would be the compression check.

Everything will hinge on those results.

Happy boating!

 

[gimmieaclue]

Re: Overheat and a thump 470

Hey, thanks for your help. I was pulling the plugs as you were typing your last message (didn't even think of it till I read it in your first response). Cylinders were dry as a bone, plugs looked good, double checked no water in oil and that the batteries were fully charged. Gonna be hard to get compression numbers with it not turning over lol, did do that about 4 months ago when I changed the plugs and they were all around 170. Guess I'll do some more reading

 

[fmalott]

Re: Overheat and a thump 470

my manual for 470 says thermostat should open at 155 F - 162 F and should open completly at 182 F

 

[stonyloam]

Re: Overheat and a thump 470

Now when I turn the key all I get is a single loud thump sound and for some reason the steering wheel kicks pretty hard even though I have it out of gear (don't know what to think about that).

I can't think of anything in the engine that would do that. My guess is that you lost a universal joint in the outdrive, and the water stopped pumping and the engine overheated. I think you need to pull the outdrive to see what is going on.

 

[Rocky_Road]

Re: Overheat and a thump 470

Took the boat out to the bay yesterday, ran for about an hour doing 25 at about 3000 rpm then the engine lost power and died. I pulled the engine cover to find the coolant boiling over but the temp only said 180 (usually about 160).
Figured I just overheated because its a Mercruiser 470 with the 3 inch heat exchanger and I've heard stories. Now when I turn the key all I get is a single loud thump sound and for some reason the steering wheel kicks pretty hard even though I have it out of gear (don't know what to think about that).
The last few times I've taken it out I've had to top off the coolant but other than that I've had no problems with it (not counting yesterdays hefty tow bill). If it was just overheating I would know what things to look for but the other issues have me confused.
I'm a fairly handy guy and would like to fix it myself if possible just not sure what should I be looking into.
Thanks for any type of info you can give me.

I wouldn't consider 180 as being hot enough to do any harm (assuming that your gauge is accurate). My 470 reached 210 when it blew the head gasket. I created my own problem by ignoring the small leak in my heat exchanger that was 'eating' my coolant....

I am at a loss for your engine lockup...have you tried to rotate it with the plugs out, and a breaker bar on the crankshaft end bolt?

 

[gimmieaclue]

Re: Overheat and a thump 470

I didn't think 180 was enough to cause a problem either as I've read a lot of people engines run that hot anyways.
I haven't tried turning it over with a bar but I did hit the key with the plugs out and all I got was the engine and steering wheel kicking hard to one side and the thump (don't think I'm gonna do that anymore for fear of making things worse).

Checking the outdrive makes sense, I did have it apart a few months ago checking everything out(u joint looked good with a fitting so I greased it up).

 

[Eric 3.7LX Alpha 1]

Re: Overheat and a thump 470

Yeah if you can't turn her over with plugs out the next step is pull the drive.

It's either inside or outside.

Good Luck.

 

[gimmieaclue]

Re: Overheat and a thump 470

I pulled the drive this morning and it turns out that water got in and the gears in the upper gearcase are hammered.....from what I can tell it might be cheaper to by a new (used) outdrive, still have to look into it more.

Very curious as to how the water got in there. Guess I'll read up on that.

Thanks for the help