View Full Version : New Engine sucking water...

08-14-2013, 12:09 PM
Well it all started with a little drip.

I've been putting off posting my whoas, because I wasn't sure if my problems were severe or just a hiccup. Turns out, the worst fears are a reality. The only consolation is that I appear to not be alone, as someone who's had catastrophic issues with a brand new motor.

Long story short, I bought the boat with a fresh Merc 350 engine. A new block was purchased and then rebuilt with a new rotating assembly. From what I can see, a lot of the original top end parts were used, but the intake manifold is an automotive Edelbrock Performer RPM. The scary thing there is all of the other automotive parts that may have been used. I can see that the intake manifold gaskets are not stainless, but auto grade, and many of the bolts and other hardware used are also not marine.

I was camping in Lake George for a week, running the boat regularly everyday. It started with a leak in the thermostat housing which dribbled water down the front of the engine. That then got worse and started streaming water down the intake manifold. The oil cap then fell off because it was an ill fitting aftermarket rubber cap. I thought water streamed into the engine through the oil opening. Btw, the guys at Performance Marine in LG are the best, and helped me out as I tried to fix the thermostat housing leak in the water. Once we discovered the milky oil though, we pulled the boat out and called the time of death...

So I thought, let me do a few oil changes to see if it clears up, but after three oil changes I'm still getting water in the oil.

So now what. The engine was built by a captain and boat builder, but not an engine shop. It doesn't have a warrantee on the build. The motor still starts and runs, with no sign of damage other than what the mayo like oil has done to the longevity of my bearings. I suppose my only next course of action is to take off the carb and intake and replace it with the proper merc pieces and gaskets. And I suppose that's my question for the board and all of you long time engine builders out there.

Would you try replacing the auto intake manifold with a marine one, or would you pull the motor and completely go through it for cracks in the block or an incorrect build? There's no telling why water is getting in, only theories and suspicions of auto parts. Suggestions please.

87 Donzi ZB21, 350 Merc, Alpha One

08-14-2013, 12:38 PM

sorry about your problems. I am far from a motor guru and some of more in the know guys will give you more info.

Did the engine builder break in the motor, or was it run for anytime or was it rebuilt and test started for a minute or so ,before you purchased it? The reason i ask is when i broke my motor in I had to re torque the intake manifold bolts after it was run up to temp . my builder said to do this I may have done it twice can't recall it was a while ago. I was told the ford are famous for leaky intake gaskets especially the front and back ones . not sure on chevy
my point was maybe the bolts need to be retorqued

good luck

if you need a mech or a motor guy in the area let me know

08-14-2013, 12:55 PM

Since you already had a leak at the thermostat housing it is also possible that the intake's water crossover passage from the two cylinder heads to that intake are also leaking at the intake's gakets.
If you are Lucky this is possibly your problem.

That Edelbrock aluminum intake manifold's front water crossover passage cold also be corroded-out if it was ever run in salt water very long.

The first thing I would do is to mark the distributor rotor on plug # 1 position & pull the ignition distributor and then remove that intake manifold and see what it's front water passage & two gaskets look like~~~

Lets hope it is nothing more than the intake gaskets or possibly a corroded-out water passage on the aluminum intake manifold itself !

By the way~~
Automotive engine parts are used in marine engines all the time with very few issues .

08-14-2013, 01:07 PM
Are you running in salt or fresh water?

The aluminum intake should be fine in fresh water. I run one in salt, but I flush my motor after every use and my boat is kept in my driveway.

You can flush the water out of the engine with a 50/50 diesel/oil mixture. Flush and drain x 3. But you still need to locate and fix the source of the leak.

Non-marine parts I would be concerned about would be the carburetor, distributor, starter and alternator.

08-14-2013, 02:03 PM
Boat is fresh water only, now. Was run in salt on the old motor. The intake is new and not run in salt.

Mattyboy, You're spot on. Some of the intake bolts were loose! Perhaps they loosened and allowed the gaskets to leak? I thought that was just an oversight of the engine builder. The engine was broken in, running it for 1 hour in the boat on ear muffs.

My only issue with the automotive intake was that I think the rear coolant passages are blocked off in marine applications. I also see that Edelbrock makes marine, so perhaps that's what it is? It very well could just be the intake manifold gaskets. I suppose I'll at least try that before pulling the motor. Btw, the alt, starter, distributor, and carb are all marine from the old engine. I've seen guys use auto parts before, but only race engine builders who know what they're doing for marine use. Ooof, looks like I got a job ahead of me. I just worry about doing all of this to find out the block was cracked or something? Maybe I'll find the intake cracked when I take it off, who knows?

Thanks guys,

08-14-2013, 04:17 PM
That intake should have been installed with a thick bead of RTV High Temp Silicone to seal the intake across the front and back. There should also be a small bead around each water passage. If it was leaking, I would think you would have had a hard time getting it to idle.

I hope it is an easy fix and flush for you!


08-14-2013, 04:19 PM
Also pull the spark plugs to make sure the cylinders are not getting water, don't be overly concerned about the water in the oil for a short period. I was a salt mechanic for many years, had quite few that sat with water it never affected the bearings only the cylinder walls if left untreated. If there is signs of water in the bores shoot some oil in and rotate a few turns, my guess goes along with Matt's that the intake cross over is leaking. Also on a fresh water only engine automotive gaskets do just fine.


Pat McPherson
08-14-2013, 08:12 PM
You likely have a leak at the intake as other have suggested. The different materials expand at different rates and the bolts will loosen. I don't know that there is much of a difference between auto and marine intake gaskets. Using RTV around the water passages on the heads is a vary good idea; I've put it on both sides of intake gaskets when assembling. The only difference with an Edelbrock auto vs marine is anodizing. A Merc / GM Alum intake has a brass insert cast in at the thermo. Good Luck...

08-14-2013, 08:42 PM

at this point I would gamble get the torque procedure for an alum intake on the sbc do that, then do the flush Patrick mentioned run it in the lake and check it out.

I don't want to be a Debbie downer but i hope the guy who built the motor wasn't in charge of doing the torque on more crucial areas.

my guess is the motor never really came to temp on the hose and when you used the boat in lake george under load it came to temp and as mentioned the intake expanded and the bolts loosened up.

once you get the leak fixed and you have flushed as much water out as possible any left over milk will be burnt off once you take a good run

08-15-2013, 03:10 PM
Fix the leak, change the oil a bunch, and enjoy. Maybe you will only get 2000 hours out of it instead of 3..

08-15-2013, 03:55 PM
I agree that the prime suspect is the intake manifold water passages. It's amazing how much torque you lose on the bolts after a good heat cycle, particularly aluminum parts bolted to cast iron heads. I have started bringing the torque wrench with me on the boat during a test run with new parts.

Automotive gasket material isn't an issue; to be honest I have yet to find an aftermarket intake gasket nearly as good as the one supplied by GM. That's why those suckers cost $35. RTV front/back and around the water passages is a good method, and I use a little gasket adhesive to glue the intake gasket to the heads, along with sealing the intake bolts that go into a water passage.

If it's not the intake it might possibly be the exhaust riser gaskets, but that's unlikely as the normal failure mode for that is to hydrolock your motor when you try to start it with a cylinder or two full of water. It's still good policy to retorque the risers after an hour or two of run time as they can loosen up appreciably.

Pulling the plugs and fogging the cylinders with Marvel Mystery Oil pickles the motor while you swap parts and will help deter corrosion. Last thing you want is your rings rusting to the cylinder walls, because the motor will be coming out for sure at that point. I'd do that, get the parts reinstalled, and change the oil 2-3 times with the cheapest stuff I could find at Walmart once it's running.

Bottom line, I think you caught it in time to avoid catastrophe but you've got some work to do.

08-19-2013, 10:54 AM
Thanks guys. I just hope it's not something more severe like a cracked block? I can't imagine that, on a brand new block that was never in freezing conditions. The boat was in a heated garage all Winter which never dropped below 40.

I think duckhunter hits it on the head, "Bottom line, I think you caught it in time to avoid catastrophe but you've got some work to do."

Work indeed. The oil changes have been done with the cheapest oil possible (cam 2) but she's still getting water. I think I'll pull the intake and try to reseal it. What sucks the most is I think my season is over. That kills me as I was looking forward to having such a good time this year.


08-19-2013, 11:08 AM

still a month and a half to 2 months of season left plenty of time to get her done. :) hang in there.

08-19-2013, 11:17 AM
shouldn't take more than 2.5-3 hours to accomplish...

08-19-2013, 03:28 PM
Pulling the intake isn't too bad. Mercruiser makes it pretty much plug and play with the wiring harness. I like to take a bunch of pictures of wire routing & connections and especially of distributor body / rotor position for reference. Helps a lot during reinstallation.

The hardest part can sometimes be all of the ankle biters that can pop up and drive the need for parts that you didn't anticipate. Gaskets in particular. For example, I had to pop off the port side exhaust riser to get clearance to loosen the valve cover in order to get the intake off. I was planning on pulling everything anyway, but it could have been a pain if I didn't have a new exhaust gasket ready to go.

Also, depending on your carb and fuel line configuration you might need a large crush washer for the line to carb body connection. That should be available at a local auto parts store but you never know. Reusing the old one is a good recipe for a gas leak.

The best intake gaskets I have seen are the GM hard plastic style with rubber o-rings around all of the ports. They still need the RTV front and rear and I like it around the water passages as well. Edelbrock makes some nice thick intake gaskets too.

Good luck, this is a straightforward Saturday project if you have all of your tools, parts, and beer ready to go. Plenty of time left in the season, and wouldn't it feel better to have the boat sorted out vs. worrying about it all winter?

08-20-2013, 10:11 AM
"...wouldn't it feel better to have the boat sorted out vs. worrying about it all winter?"

YES, yes it would. And that's the thing, having all of the parts and then a hand to run for tools is also nice. Is it just me or is the worst part of working on a boat the getting in and out of it? Climb in, forget a tool, climb back out. LOL My pop usually comes over and just sits there, running for an occasional tool every now and then.

So the oil in it now is sorta ok, but clearly getting water. It's the third change since the problem began. I'll get some good gaskets and high temp RTV for the manifold. I then might locktite the bolts to keep them from loosening. It shouldn't be too hard to do, but I'm hoping I won't have to remove a riser. I also have a few more issue, such as my main harness plug is getting bad and I might have to replace that. The distributor is a bit of a concern but I take pics as I'm working too, so I can remember where things go.

We might have a little season left after all. Thanks for all of the tips, guys.