OMC 5.8 Cobra with water in the oil

OK, this boat is not going to get the best of me.

I bought a 1991 23' Caravelle with a 351W 5.8 Cobra. The top end of the engine came in a box. The heads, intake, carb exhaust manifolds etc. The short block was still in the boat covered with a tarp for about 4 years.

The Port side exhaust manifold is cracked and been repaired with JB Weld (previous owner). I have reassembled the motor and got it running (thanks mostly to this site). Now when getting the timing done and ready to change the oil to take to the river. I have a very light mixture of oil and water, not necessarily milkshake consistancy but enough to notice.

Cracked block? (Did not see any visible cracks when putting back together)
Engine sitting for that long and rain in it?
Cracked manifold?

any suggestions would be great.
Thanks,
Brian

Re: OMC 5.8 Cobra with water in the oil

First time for everything said:

OK, this boat is not going to get the best of me.

I bought a 1991 23' Caravelle with a 351W 5.8 Cobra. The top end of the engine came in a box. The heads, intake, carb exhaust manifolds etc. The short block was still in the boat covered with a tarp for about 4 years.

The Port side exhaust manifold is cracked and been repaired with JB Weld (previous owner). I have reassembled the motor and got it running (thanks mostly to this site). Now when getting the timing done and ready to change the oil to take to the river. I have a very light mixture of oil and water, not necessarily milkshake consistancy but enough to notice.

Cracked block? (Did not see any visible cracks when putting back together)
Engine sitting for that long and rain in it?
Cracked manifold?

any suggestions would be great.
Thanks,
Brian

Click to expand...

Howdy,


Well, you could have a cracked block. (Pretty likely if the manifolds were cracked.)

You'll have to pressure check it to be sure. That will require isolating the block from the exhaust manifolds (disconnect the cooling water hoses to them)

Plug all the hoses with any sort of suitable plumbing fittings. Use an air compresser, a valve and a 0-30 (or so) PSI gage.

Apply air to pump the block up to about 15-20 psi and turn off the valve (turn off the compressor so you can hear too............the gage is on the pressure side when the valve is OFF)

If the pressure drops, you have a leak.

If the block is cracked, that's the leak.....then you must replace the block. If the manifolds are cracked, you should replace them too. You cannot see internal cracks and if they leak into the engine it will damage the engine beyond repair eventually.

Hope you didn't pay a lot for the boat!

Good luck,


Rick

Re: OMC 5.8 Cobra with water in the oil

Rick,

Thank you, by chance is there a diagram or anything that shows where to attach the fittings and pressure gauge?

Thanks again,
Brian

And luckily no only paid $1000 for the boat.

Re: OMC 5.8 Cobra with water in the oil

Thank you, by chance is there a diagram or anything that shows where to attach the fittings and pressure gauge?

Click to expand...

Not really.

All you're doing is closing up all cooling water entry and exit points.

It really doesn't matter what you use as long as they'll handle 20 psi or so and not leak......same for the valve and gage. it also doesn't matter where you pump in the air.

You're just closing all the "holes" and pressuring it up. There's the thermostat housing (with 2 or 3 hose connections on it) , The (engine driven) water pump, and whatever hose connections it has (big and small). The exhaust manifolds and risers can be disconnected from their hose connections.

There should be no other connections to the engine to close off.....but if there is, you'll find them because you'll hear the air rushing out of them!!

Re: OMC 5.8 Cobra with water in the oil

PM sent.