How to pressure test cooling system

[seapro17]

Greetings all,

I have a 1985 Mercruiser MCM 260 (sbc 350). This is a really noob question, but I just can't get a clear picture on how (EXACTLY)to go about pressure testing my cooling system.

I have four hoses going to exhaust manifolds (one on top each side, one on bottom each side). I gather I need to plug those up and block them so air doesn't escape. Is that right?

Then how do I exactly pressurize the block? Where does the air go in? One person told me to pull the incoming water line from the drive off of the circulation pump on the motor and rig some sort of adapter and put pressure there. Is that how? So what do folks normally do, make some sort of rubber hose adapter to go from my air compressor hose to that big intake pipe on the water pump? How do people even go about doing that? I just can't picture it. Does it have to be pressurized there? I guess that would make sense, since that's where the water is going in. I'm just wondering if there's an easier way.

Thanks!
Stan

 

[Bondo]

Re: How to pressure test cooling system

Greetings all,

I have a 1985 Mercruiser MCM 260 (sbc 350). This is a really noob question, but I just can't get a clear picture on how (EXACTLY)to go about pressure testing my cooling system.

I have four hoses going to exhaust manifolds (one on top each side, one on bottom each side). I gather I need to plug those up and block them so air doesn't escape. Is that right?

Then how do I exactly pressurize the block? Where does the air go in? One person told me to pull the incoming water line from the drive off of the circulation pump on the motor and rig some sort of adapter and put pressure there. Is that how? So what do folks normally do, make some sort of rubber hose adapter to go from my air compressor hose to that big intake pipe on the water pump? How do people even go about doing that? I just can't picture it. Does it have to be pressurized there? I guess that would make sense, since that's where the water is going in. I'm just wondering if there's an easier way.

Thanks!
Stan

Ayuh,.... Not the Big hose on the Circulatin' pump,...

The 1" line from the impeller pump, at the T-stat housing....

Ya use pipe fittin's, 'n whatever it takes... 15 psi is all ya need....

 

[seapro17]

Re: How to pressure test cooling system

Got it.. and the four lines going to the exhaust manifolds, plug all four, right? Or do the bottom ones need to be plugged? Seems like they don't.

 

[Bondo]

Re: How to pressure test cooling system

Got it.. and the four lines going to the exhaust manifolds, plug all four, right? Or do the bottom ones need to be plugged? Seems like they don't.

Ayuh,... Plug 'em All,... yer Testin' the Motor, not the manifolds...

 

[seapro17]

Re: How to pressure test cooling system

Yeah, I just thought by the diagrams I'm looking at that the lines that go to the bottoms of the exhaust manifolds were on the other side of the thermostat, which would be closed. But I may not be reading it right. I'll plug em all to be sure.

Thanks!
Stan

 

[seapro17]

Re: How to pressure test cooling system

Hi Bond-O,

I did a leak-down test. It was inconclusive. Meaning, my rings are good, or the cheap test I bought isn't worth a damn.

Next I pressurized the cooling system to 20 psi (I drained the block first). I could clearly hear gurgling on the starboard side of the motor. So I pulled the valve cover. The last bolt, all the way to the back of the motor was backed out. Like, almost all the way out. I pressurized again, all of the gurgling was coming up that bolt. A ton of air/oil/water was escaping through it.

I have no explanation as to why that bolt is backed out. I torqued that head in sequence, so there's no way I missed that bolt. Maybe I did, but I just don't know how i could have, because I did a three step torque (20, 40, 65 ft/lb) in sequence. I just don't see how I could have missed it. If I didn't miss it, then somehow it backed out on it's own. I did use a thread sealant on it, maybe that lubricated it? I don't know. I cleaned the threads on those bolts too, so I'd get good torque readings. I'm at a loss as to how that happened.

So now I these questions:

1) That bolt definitely caused the water in the oil. Would that loose bolt cause all of the excessive crankcase pressure as well? I don't see how it would.

2) Can I just re-torque the head, or do I need to replace the head gasket?

And there are 3 other problems that still exist, and have never gone away, even after checking manifolds, testing heads, and replacing ALL gaskets. Those two problems are:
1) steam in the exhaust (through-hull exhaust) (well, okay that doesn't count cuz my head was leaking water through that bolt still)
2) lots of oil mist coming out of crankcase breather tubes (no pvc valve).
3) smoke/vapor in valve covers and coming out the breather tubes.

Thoughts?

Thanks!
Stan

 

[IM Buddy8]

Hi Stan, did you ever get this figured out?

 

[GA_Boater]

Hi Stan, did you ever get this figured out?

Stan has been gone as long as you've been a member.