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

[cameron92]

Starboard Front to Back
110
109
115
120
Port Front to Back
110
85
105
105

Blown head gasket? How would I check for that without a leak down tester. I don't have a tester or air.

Already this far in I'm thinking of just pulling the heads

 

[Lou C]

Before you do that, do the air pressure of the cooling system test, very important!
A blown head gasket can be tricky, they can leak between cyls, between a cyl and the edge of the block or between a water passage and the cylinder. Mine was the last case, I got water leaking into 2 cyls after the engine was shut off for a day or so. Just for a few hrs, no water. Compression test results are were close to normal for the V-6 (160-170). So each blown HG situation can be a little different.
If you're going to be doing this work, it is well worth it to get the right equipment for doing a leak down test, but the air pressure test is even more important and once you pull the heads, you lose the chance to get that information.
Looking at your comp test results they are all low, the lowest at 85 psi could be simply a stuck intake or exhaust valve, or a rusty valve seat. However, compression tests on a cold engine aren't really that accurate, so I wouldn't take that as the last word here.
Do the air pressure test, do a leak down test, see what you get.

 

[cameron92]

Before you do that, do the air pressure of the cooling system test, very important!
A blown head gasket can be tricky, they can leak between cyls, between a cyl and the edge of the block or between a water passage and the cylinder. Mine was the last case, I got water leaking into 2 cyls after the engine was shut off for a day or so. Just for a few hrs, no water. Compression test results are were close to normal for the V-6 (160-170). So each blown HG situation can be a little different.
If you're going to be doing this work, it is well worth it to get the right equipment for doing a leak down test, but the air pressure test is even more important and once you pull the heads, you lose the chance to get that information.

Excuse my ignorance, what will that test tell me and how do I go about doing it?

 

[cameron92]

Is it somehti

Before you do that, do the air pressure of the cooling system test, very important!
A blown head gasket can be tricky, they can leak between cyls, between a cyl and the edge of the block or between a water passage and the cylinder. Mine was the last case, I got water leaking into 2 cyls after the engine was shut off for a day or so. Just for a few hrs, no water. Compression test results are were close to normal for the V-6 (160-170). So each blown HG situation can be a little different.
If you're going to be doing this work, it is well worth it to get the right equipment for doing a leak down test, but the air pressure test is even more important and once you pull the heads, you lose the chance to get that information.
Looking at your comp test results they are all low, the lowest at 85 psi could be simply a stuck intake or exhaust valve, or a rusty valve seat. However, compression tests on a cold engine aren't really that accurate, so I wouldn't take that as the last word here.
Do the air pressure test, do a leak down test, see what you get.

Is it something like this?

 

[Lou C]

You basically have to disconnect the hoses for the exhaust manifolds at the manifolds and use a 3/4" adapter to connect those hoses together with the other ends still connected to the thermostat housing. Then disconnect the raw water inlet hose at the 'stat housing and make up an adapter that will allow you to pressurize the cooling passages.

 

[cameron92]

You basically have to disconnect the hoses for the exhaust manifolds at the manifolds and use a 3/4" adapter to connect those hoses together with the other ends still connected to the thermostat housing. Then disconnect the raw water inlet hose at the 'stat housing and make up an adapter that will allow you to pressurize the cooling passages.

Do I need to put the manifolds back on?

 

[cameron92]

Sorry for all the questions. I'm going to pick up a cooling system tester now. Once I get it hooked up, am I listening for where the leak is coming from?

 

[cameron92]

Sorry for all the questions. I'm going to pick up a cooling system tester now. Once I get it hooked up, am I listening for where the leak is coming from? And how much psi should I be putting in?

 

[Bondo]

Starboard Front to Back
110
109
115
120
Port Front to Back
110
85
105
105

Ayuh,...... With numbers like that, you have a rebuildable core, not a viable runner,........
A new/ rebuilt motor will be 'bout 150 psi across the board,....

 

[Lou C]

Do I need to put the manifolds back on?

Not necessary they are out of the loop. We are checking the cooling passages in the block, cylinder heard and intake manifold.

 

[Lou C]

Sorry for all the questions. I'm going to pick up a cooling system tester now. Once I get it hooked up, am I listening for where the leak is coming from? And how much psi should I be putting in?

The exhaust ports of the cylinder heads, and also remove the oil fill cap, and listen there.
after doing the pressure test (12-15 psi) if it fails, I'd probably also try to hook up a smoke machine, like you use for checking out exhaust leaks and evap system leaks, it can make the leak a lot more obvious. I used one to fix 2 evap system leaks on my old Jeeps and also for an O2 sensor code, that is affected by exhaust leaks.

 

[cameron92]

The exhaust ports of the cylinder heads, and also remove the oil fill cap, and listen there.
after doing the pressure test (12-15 psi) if it fails, I'd probably also try to hook up a smoke machine, like you use for checking out exhaust leaks and evap system leaks, it can make the leak a lot more obvious. I used one to fix 2 evap system leaks on my old Jeeps and also for an O2 sensor code, that is affected by exhaust leaks.

Thanks for all the help!

Just got it will report back with results.

What's the best case scenario?

 

[cameron92]

Ayuh,...... With numbers like that, you have a rebuildable core, not a viable runner,........
A new/ rebuilt motor will be 'bout 150 psi across the board,....

It actually ran and idles very well until about 3000rpm then it would die out after about 5 mins

 

[cameron92]

I've never been this deep into a motor. But I don't want to be completely out of 5 grand so I'm willing to try. Seller actually sent me back 1,000 because he felt bad.

 

[cameron92]

You basically have to disconnect the hoses for the exhaust manifolds at the manifolds and use a 3/4" adapter to connect those hoses together with the other ends still connected to the thermostat housing. Then disconnect the raw water inlet hose at the 'stat housing and make up an adapter that will allow you to pressurize the cooling passages.

And I would be pressurizing into the thermostat housing correct?

 

[Lou C]

Yep via the raw water intake nipple.