8.2 L inboard overheat & losing antifreeze

[Tn Formula]

Newbie here looking for help,suggestions on an issue I'm having with newly rebuilt engine. 8.2L inboard carb with closed cooling which includes the manifolds. Engine was rebuilt this spring due to a loss of compression in one of the cylinders (opposite side of engine to where AF is migrating into exhaust). Engine runs hot compared to other engine. These are the things that have been checked or replaced so far. Raw water pump completely replaced with CP performance stainless pump; All HE removed and cleaned @ radiator shop (trans,oil,main); Raw water intake hose replaced from thru hull to water pump; strainer removed and cleaned; These items were done with the rebuild. Since installing the engine she's been running warm, producing a lot of steam and losing a bit of antifreeze. I pressure tested the closed cooling system and it will not hold pressure. Removed both exhaust elbows and 3" spacers and saw coolant in outboard manifold which I vacuumed out, removed manifold, pulled plugs and sprayed cylinders with wd40. Remove main HE and used technique of pressurizing coolant side and removing end caps while submerged in tub of water. No bubbles were observed, pressure held as it should. Filled coolant passages of manifold with acetone and let sit for 45 minutes, no leaks were observed. So I'm not loosing AF thru HE or manifold. I'm thinking next step is to put good side of exhaust back together, partially fill with AF and pressure test system to see if anything is observed coming out of cylinder(s). Check gasket mating surfaces of 3" spacer and top of manifold, perhaps they need to be surfaced?? Antifreeze can only get into the manifold from the head, the manifold or the spacer gasket as far as I know. To muddy the waters a bit more, a tech told me to replace the manifold, they can't really be "checked". Boating in fresh water, looking for any insight or suggestions. Probably forgot some important detail but starting to get desperate and don't wanna lose a new engine.

 

[Bt Doctur]

If you see it in a manifold and its not a manifold or gasket issue then suspect a bad head gasket or cracked head

 

[alldodge]

Howdy

Its a 8.2 but what year or serial number?

Note: just info only but the CP Performance is actually a Hardin Marine pump, CP does not make the items

 

[Scott Danforth]

manifold can easily be checked by pressure testing as well as the acetone test

pressure test your motor itself. Im guessing head gasket

 

[Tn Formula]

It is a '95 year model. I did the acetone test on the manifold but the results were negative. I'm thinking I can re assemble the good side of the exhaust and block off the leaking side at the HE, then refill with AF and do the pressure test again. By using the tester that connects to the HE cap, this pressurizes the whole system right? Any reason why this wouldn't work?? It seems to me that its got to be a spacer gasket issue or head/head gasket issue just as you guys have said. I was a little confused when a tech told me to replace the manifold as they can't really be tested but according to posts I've read on the forum that isn't the case at all.

Something else as far as the head itself is concerned, when the engine was taken to the machine shop and checked over they told me the heads pressure checked fine but a valve job was needed (which I had them to do). By "pressure checking" does this mean the fuel/combustion portion of the head was checked or the coolant side of the head?

As a secondary method of checking the exhaust manifold by utilizing pressure, would it be prudent to figure out a way to do that (and any suggestions on exactly how?) or would that be a complete waste of time since it passed the acetone test?

 

[alldodge]

I would suggest keep the anti freeze out of the block, install the manifolds and pressurize with air to 15 psi using the HE cap as you said. Air will make it thru a crack easier then air.

The machine shop should be able to pressure test the head but depends on what setup they use to do it, and how well. They would only pressure test the water jacket. If they have the equipment they could magnaflux it which would show up any cracks, but head needs to be disassembled.

 

[Tn Formula]

I think I'll contact the machine shop and see if they can give me more info. I didn't really want to reassemble until I can pressurize the system without the manifold in place, its off so why not check it now and maybe not waste a couple of gaskets??

 

[Tn Formula]

Status update: I've disconnected and plugged all antifreeze hoses going to and from both exhaust manifolds. Then pressurized the rest of the system and it holds 15lbs steady for 20 minutes so I feel pretty good about heads,head gaskets. I've ordered a manifold to replace the one that had antifreeze in it and I'm going to have the spacers and elbows surfaced at the machine shop. The suspect manifold held up fine in the acetone test but after block sanding the upper gasket surface I noticed there were some spots that didn't sand out. This was the only area that I couldn't really check so I decided to replace it. I plan to install everything but the elbows and pressure check again before final assembly.