Help! Bought a 1993 Four Winns W/ 5.0 OMC Cobra Motor and Drive - Losing power after crusing

[cameron92]

I have it hooked up to the hose that comes off this which leads to the intake on the thermostat.

 

[cameron92]

I have my pressure tester hooked up this way. That line leads to the freshwater intake. My tester has a bladder on it. If I cover my hand over where the hose came off I can hear water bubbling somewhere but no pressure holds.

 

[cameron92]

I figured it out I had it open going back to the drive. Capped it off and now pumped it up. It's holding 15lbs psi

 

[cameron92]

What's the next step if the cooling system is good?

 

[Lpgc]

So the engine coolant circuit is holding pressure?

The other way water can get into oil is if the exhausts are leaking water into the engine via exhaust ports. If there's such as a problem the water can get past piston rings into oil but the water can also cause hydraulic lock of the engine cylinders (which can damage valves, piston rings, pistons, cause cracks, etc), dilute the oil film on cylinder bores (so cause rings to overheat and lose springiness / lack of compression), cause bore and piston scoring, cause excessive valve wear.

My engine didn't seem to have water in the oil but it did have a cracked exhaust allowing water into cylinders and suffered most of the above (but not cracks in the block or heads). I had to buy new exhausts, new valves, have the heads re-seated and skimmed, new pistons and rings, hone the hell out of cylinder bores to remove scratches. At least the crank, bearings and cam were still good but I did also put in new lifters and pushrods. Parts were cheap from RockAuto, did all the work myself except for the head work which I got a machine shop to do.

 

[cameron92]

So the engine coolant circuit is holding pressure?

The other way water can get into oil is if the exhausts are leaking water into the engine via exhaust ports. If there's such as a problem the water can get past piston rings into oil but the water can also cause hydraulic lock of the engine cylinders (which can damage valves, piston rings, pistons, cause cracks, etc), dilute the oil film on cylinder bores (so cause rings to overheat and lose springiness / lack of compression), cause bore and piston scoring, cause excessive valve wear.

My engine didn't seem to have water in the oil but it did have a cracked exhaust allowing water into cylinders and suffered most of the above (but not cracks in the block or heads). I had to buy new exhausts, new valves, have the heads re-seated and skimmed, new pistons and rings, hone the hell out of cylinder bores to remove scratches. At least the crank, bearings and cam were still good but I did also put in new lifters and pushrods. Parts were cheap from RockAuto, did all the work myself except for the head work which I got a machine shop to do.

Yeah it held 15 psi. It's slowly crept down over about 5 to 10 minutes but I think that was the plug I was using to pressurize the system.

I had to leave town for a few days so I put a bunch of WD-40 penetrating fluid in all the cylinders. Going to retest compression when I get home. I guess the next step would be to pressure test or acetone test my manifold likely the one with the low cylinder compression.

Heading up to a cottage on Saturday, was really hoping I could get the boat at least going to enjoy sometime on the water. But that leaves me Thursday night and Friday to get it going.

Would you be ordering any parts right now if you were in my situation or would you just abandon bringing the boat to the cottage.

 

[Lpgc]

If the engine cooling system presssure test crept down over 5 or 10 minutes I'd be doing it again and making sure there were no leaks at the plug... Creaping down is exactly what would happen if there were a small leak.

Yes I would also be testing the manifolds. The worst thing that could happen is you go to the expense and effort of fixing up / rebuilding the engine (if engine problems are confirmed) but re-use manifolds that were leaking water into the engine thus breaking the rebuilt engine again... you'd still need new manifolds but would need to rebuild the engine a 2nd time.

I wouldn't order any engine parts until I knew exactly what was needed, though if the manifolds are strongly suspected I might order and maybe even fit them to see how it runs with them and see if the compression figures come up.

Something I meant to mention earlier, you said there was a bang.. If the bang wasn't transmission related it could be a backfire from the engine. It might backfire if the mixture gets extremely lean or if the igntion system fires a plug on a cylinder's compression stroke, the latter could possibly tie-in with the tacho suddenly reading higher than actual rpm.

If/while you've got the manifolds off it might be worth trying to look at the bores using a bore-scope through the spark plug holes, any scuffs on the bores (maybe from water diluting the oil film) might mean you'll need to pull the engine to rebuild it with a rebore or at least a hone anyway.

I think there's still a lot of diagnostic work to be done before you'll know what's causing the problems but water in oil, low compression readings, the tacho suddenly reading high with drop of power, the smell of rubber burning and the bang give you/us a lot to think about.

 

[cameron92]

If the engine cooling system presssure test crept down over 5 or 10 minutes I'd be doing it again and making sure there were no leaks at the plug... Creaping down is exactly what would happen if there were a small leak.

Yes I would also be testing the manifolds. The worst thing that could happen is you go to the expense and effort of fixing up / rebuilding the engine (if engine problems are confirmed) but re-use manifolds that were leaking water into the engine thus breaking the rebuilt engine again... you'd still need new manifolds but would need to rebuild the engine a 2nd time.

I wouldn't order any engine parts until I knew exactly what was needed, though if the manifolds are strongly suspected I might order and maybe even fit them to see how it runs with them and see if the compression figures come up.

Something I meant to mention earlier, you said there was a bang.. If the bang wasn't transmission related it could be a backfire from the engine. It might backfire if the mixture gets extremely lean or if the igntion system fires a plug on a cylinder's compression stroke, the latter could possibly tie-in with the tacho suddenly reading higher than actual rpm.

If/while you've got the manifolds off it might be worth trying to look at the bores using a bore-scope through the spark plug holes, any scuffs on the bores (maybe from water diluting the oil film) might mean you'll need to pull the engine to rebuild it with a rebore or at least a hone anyway.

I think there's still a lot of diagnostic work to be done before you'll know what's causing the problems but water in oil, low compression readings, the tacho suddenly reading high with drop of power, the smell of rubber burning and the bang give you/us a lot to think about.

Add in a dry power steering pump as well lol. Looks like I'll be learning how to rebuild an engine potentially. There's a first for everything I guess.

I guess I'll tell my wife very well unfortunately be no boat for this cottage trip . Unless I can figure out the issue and patch it up in a day lol.

 

[Lou C]

I'm in agreement with Lpgc here, I would make sure that your results from the air pressure test are consistent, and even though we didn't see evidence of water in your manifolds or exhaust ports, it's still a good idea to test them. So, the only parts I'd order are the gaskets for the manifold to head joint and the manifold to elbow joint because when you do put it back together those have to be replaced anyway.
Better to take the time now to get it right vs trying to get it done fast and winding up being frustrated.
And, with the rubber burning smell and "bang" you also may have some other work to do....don't lose hope, you will get there but the time it takes is hard to predict. For the outdrive and shifting issues, see if you can find a good local shop that will still work on Cobras, there are none really around here except my local boatyard guy who has known me like 25 years.
I would not be putting this boat in the water till I knew it was right.
BTW my top end engine overhaul took me months, just making sure that I was doing each step correctly, consulting with mechanics and machine shop guys.
Went from this:

to this:

 

[Lou C]

also there is an excellent list of informational articles right on this site:

MUST HAVE Technical Information for DIYers.

MUST HAVE Technical Information for DIYers. (< An @ Work Safe Search Version Of ^^^) If you have NEVER posted in this forum before, please click on How to ask a question link first. 1. How to Ask a Question .... Please Read This Before Posting A Question... 2. Miscellaneous Mercruiser...

forums.iboats.com

 

[cameron92]

How long should I let the pressure test go for? And what's an acceptable loss

I also ordered a smoke tester, figured it'd be good to try that as well. How would I operate that? Same way as the cooling pressure system?

 

[Scott Danforth]

the water jacket should hold 15psi forever