Mercruiser 4.3 cracked intake manifold

[LWD]

Last Wednesday I dewinterized my boat, a 2001 Mercruiser 4.3 EFI. It turned into a bad day!

Below are notes I made afterward while it was still fresh in my head....

- I hooked up water.
- The engine started quickly.
- After a couple minutes water started coming out the back of the boat (normally).
- Kept an eye on the gauges, the temperature gauge never rose.
- I felt the water coming out the back, it was very hot.
- The engine started running rough.
- I shut the motor off, I noticed some popping noise from engine.
- Let it sit for about 20 minutes.
- Restarted the engine, it ran rough, gave gas, smoothed out.
- Got rough again, noticed water spurting out of the oil dip stick.
- Shut off immediately.
- Bummed out….

End of Notes

The next day I checked the oil level on the dip stick, it was a milky color and ¾ up the stick...

Today I removed the intake manifold and it's cracked. I've owned this boat for 20 years now, and have always winterized it the same way. I drain the water, poke a wire in the drain hole, and using a plastic tube, vacuum out the hole. I guess some water did not drain.

I visually checked the heads after removing the intake, and from what I can see they look ok. Using a socket and breaker bar, I was able to turn the crank over to bring it to top dead center before removing the distributor. Other than compression, it turned easy enough. I started draining the milky oil today, which is going very slow and may be drained by Thanksgiving. If the temp gauge was working

I would appreciate some opinions -

Basically what am I'm dealing with at this point?
I would have shut it down a lot sooner if the temperature gauge was working. Was the gauge not working because of the cracked head, or was that coincidental?
Should I pull each spark plug and check them?
Could there be more damage than I'm aware of?
Is there any way to speed up draining the milky oil, short of pulling the oil pan, which is next to impossible.
Can I upgrade the manifold for better performance?

Here's a few pictures of the crack. One thing of interest are the scratch marks on the crack, which had to be there since it was new. I doubt it had anything to do with the crack after 20 years though.

Thanks

 

[dubs283]

when you say you pulled the plug and drained the water at winterize do you mean the square head pipe plug at the fwd of the intake?

in any case that is a freeze crack and intake manifold must be replaced

you mention a cracked head? guessing you meant intake, in that case yes the temp gauge would be mostly unresponsive due to lack of pressure in the block from the water leak into the valley

one suggestion to get the milkshake oil out is to clean up and jb weld the crack(s) in the intake, add some mineral spirits to the oil and run the engine to temp. don't run under a load, just enough to get the oil/water mix warm to aid in removing. may take multiple flushes to remove milkshake

once the oil is clean, you can use the repaired intake for testing to ensure no more water contamination is happening, then replace the intake. not sure of any upgrades available

 

[Lou C]

I’m not sure of the reason but the intakes on the Vortec V6s are prone to cracking unless that square plug in the front of the intake is drained in addition to the normal engine drains. This is not the case on the older pre Vortec design in that it just drained when the engine was drained. I’d just get a new or good used intake ASAP and put it back together and get it up & running. Change the oil 3-4x until it stays clear of water. You want that water out ASAP because water in the oil can damage bearings. I had salt water in the oil due to blown head gaskets and was able to save the short block by getting the water out and draining the water after each oil change. I pickled the cyls with fogging oil ( had water in 2 cyls from the bad HGs) and it was fine even months later when I took it apart. No rust inside cam & lifters looked like new.

 

[LWD]

when you say you pulled the plug and drained the water at winterize do you mean the square head pipe plug at the fwd of the intake?

in any case that is a freeze crack and intake manifold must be replaced

you mention a cracked head? guessing you meant intake, in that case yes the temp gauge would be mostly unresponsive due to lack of pressure in the block from the water leak into the valley

one suggestion to get the milkshake oil out is to clean up and jb weld the crack(s) in the intake, add some mineral spirits to the oil and run the engine to temp. don't run under a load, just enough to get the oil/water mix warm to aid in removing. may take multiple flushes to remove milkshake

once the oil is clean, you can use the repaired intake for testing to ensure no more water contamination is happening, then replace the intake. not sure of any upgrades available

The square plug you're asking about, forward on the intake, is the one plug I've never removed, I had no idea about that plug till yesterday while trying to do some research on here. Apparently that lack of knowledge (negligence) on my part is what did me in.

You are correct, I meant to say cracked intake. I've had the words cracked head, cracked head gasket and cracked block going through my head so much lately... unless there's anything else I'm not aware of yet, it seems like I'm in a best case scenario.

Thank you for the suggestion with the mineral oil and clean up.

 

[Lou C]

Here are a couple of the older 4.3 pre-vortec intakes (1995 and earlier), I picked these up as spares because I'm in salt water but my orginal 1988 intake is still good believe it or not, just checked it again when I replace the 'stat. They tend to rust out right under the stat, if the engine is not filled with AF over winter storage.
like I said I don't know what they changed but these never cracked as long as you drained the engine by pulling and probing the block drains and pulling the bottom end of the big hose from the thermostat housing to the front water circulating pump. You were pulling the lower end of that hose correct?

 

[LWD]

I’m not sure of the reason but the intakes on the Vortec V6s are prone to cracking unless that square plug in the front of the intake is drained in addition to the normal engine drains. This is not the case on the older pre Vortec design in that it just drained when the engine was drained. I’d just get a new or good used intake ASAP and put it back together and get it up & running. Change the oil 3-4x until it stays clear of water. You want that water out ASAP because water in the oil can damage bearings. I had salt water in the oil due to blown head gaskets and was able to save the short block by getting the water out and draining the water after each oil change. I pickled the cyls with fogging oil ( had water in 2 cyls from the bad HGs) and it was fine even months later when I took it apart. No rust inside cam & lifters looked like new.

Not removing the plug on the intake has to be what did me in, after 20 years of not doing that, I thought I had it all figured out..

After I got the intake off yesterday, I got to thinking about the water settling to the bottom of the engine (the bearings), and another panic set in.. so I went out right then to drain the milkshake. I'm guessing a little more than a couple gallons of water came out first, then the milkshake started, and slowed to a molasses...

I don't think I got any water in my cylinders, but I'm going to remove each spark plug today and check them, then spray some fogging oil into the cylinders. I'm also going to remove each plug to drain whatever is in there also. Thank you for the suggestions.

 

[Lou C]

What I did, to get the oil/water mix out, was to VERY CAREFULLY warm up the oil pan with a heat gun WHILE MONITORING TEMPS WITH AN IR TEMP GUN (no hotter than 150 degrees or so). This enabled me to do the first oil change (using a vacuum pump, it won't work unless the oil is warm) before actually changing the cyl head gaskets (and heads). After that I got it running and changed the oil 3 times but drained the water out at the same time to keep water from seeping back in. In your case this won't work because that intake is going to leak right away and I don't know if JB weld will seal it. I'd get another intake as soon as you can, get it up and running.....

 

[LWD]

They tend to rust out right under the stat, if the engine is not filled with AF over winter storage.

pulling the bottom end of the big hose from the thermostat housing to the front water circulating pump. You were pulling the lower end of that hose correct?

In the 20 years of owning this boat, I don't remember ever adding antifreeze to it, and yes I noticed the rust in the thermostat housing. It will be part of my de-winterizing routine from now on.

I've never pulled any hoses, except to replace the spark plugs. I've always just removed the plug plastic drain plugs, poked and vacuumed... what I've been doing is obviously not bullet proof, and I'm learning the hard way.

I've probably been very lucky to not have this happen sooner. Needless to say, I need a whole new routine after this...

 

[LWD]

pulling the bottom end of the big hose from the thermostat housing to the front water circulating pump. You were pulling the lower end of that hose correct?

About that bigger hose from the thermostat housing, I did have to install a check valve on that hose about 8 years ago. It's the blue cylinder in the picture, and it added a new water drain to my routine. Instead of the usual 6 drain points, I now have 7, and that drains the bigger hose which leads to the electric fuel pump. I had to install the check valve because hot water was back flowing into my fuel pump and causing vapor lock.

 

[Lou C]

Yep you need to:
pull the block drains, poke the holes make sure it drains
pull the lower end of the big hose that connects the stat housing with the front circulating pump, this drains a lot of water, in fact when I change the stat (I do this each year because in salt water they get sticky) it will actually drain that water passage in the intake manifold on the old style pre vortec 4.3.
pull exhaust manifold drains, poke holes
also disconnect water hose from transom mount to thermostat housing, point it down in the bilge to drain, then put drive all the way down. Now hold the hose up, and fill it with -100 Marine AF till it comes out the water intakes. This will push water out of that hose, any coolers in line with it and the water passages in the outdrive.
this is what I've always done on my 4.3 OMC Cobra and nothing has ever frozen, even down to zero or a little below.
I do fill the engine and manifolds with AF, (after completely drainng) but I use the best stuff, either -100 or I mix up a 50/50 mix of Sierra brand no tox AF. The -50 or -60 in my opinion is OK for plastic water pipes but not cast iron engines, it gets hard at 5-10* above zero, not good enough for me to relax all winter.

 

[Lou C]

About that bigger hose from the thermostat housing, I did have to install a check valve on that hose about 8 years ago. It's the blue cylinder in the picture, and it added a new water drain to my routine. Instead of the usual 6 drain points, I now have 7, and that drains the bigger hose which leads to the electric fuel pump. I had to install the check valve because hot water was back flowing into my fuel pump and causing vapor lock.

View attachment 341836

that looks like your raw water intake hose, I'm referring to the one on the other side that connects the stat housing wiht the front circ pump. The drain you have on there is not low enough to fully drain that hose but better than not taking it off. I would still disconnect that hose at the bottom.....
Yes its all a pain. This is why I say, these I/Os should ALL have closed cooling from the factory, they would be easier to winterize, last longer and run at proper temps for which they were designed. I HATE raw water cooling for inboards with a passion, and when I repower this boat it will for sure get closed cooling.

 

[Scott06]

Not removing the plug on the intake has to be what did me in, after 20 years of not doing that, I thought I had it all figured out..

After I got the intake off yesterday, I got to thinking about the water settling to the bottom of the engine (the bearings), and another panic set in.. so I went out right then to drain the milkshake. I'm guessing a little more than a couple gallons of water came out first, then the milkshake started, and slowed to a molasses...

I don't think I got any water in my cylinders, but I'm going to remove each spark plug today and check them, then spray some fogging oil into the cylinders. I'm also going to remove each plug to drain whatever is in there also. Thank you for the suggestions.

Try putting kerosene in the oil, take the spark plugs out and turn the engine on the starter. I think this is your best bet for getting the molasses out. You will need to do several times and also after you get it running again chacnge the oil and filter multiple times until it goes clear. You can run the engine at fast idle with 3 qts in in to save some oil.

 

[LWD]

I started draining my milkshake on Monday, so far I haven't tried using kerosene, or even turning it over. I'm guessing about 2-3 gallons of water came out before the oil started. In the side view picture below, the bottom layer is water, and it finally has a steady, but small, stream coming out.

As far as the bearings go, how much of a concern is it that this motor was running a little faster than idle speed with water spurting out of the dip stick? I shut the motor off pretty quick, and it didn't build up enough pressure to blow the dip stick out.

 

[Lou C]

It’s impossible to say but what I did when I did mine was I removed the rocker arms & pushrods (label positions with a sharpie & stuck pushrods in a piece of cardboard marked so all parts went back together). Then one by one I pulled out each roller lifter to inspect the cam lobes. The lifters and cam lobes basically looked like new so I rolled the dice and installed reman heads. In my case as far as I could determine the bearings were ok because my oil pressure readings were the same as before and no knocking under load etc. I didn’t have as much water in the oil as you have there though, but it was salt water (took about a week with the boat on the mooring to figure out was wrong).
Now I know many will say the marine oil standard is BS, but I used the Merc 25/40 marine oil for several years before this happened. And you can see in the pix there was really no rust on any of the internal engine parts, only on the combustion chambers of some of the cyls. And it was salt water.
What was happening with my engine was that after the engine was shut off, a bit of water was seeping into both of the front cyls, more on #2 than on #1 which was just a trace of water. When I pulled off the heads you could see where the HGS were blown and how the water got in. This was all from an overheat back in 2013, the engne ran fine from then till 2016 where I started having reluctance starting which was really water in #2 and #1 cyls. If I ran it and checked for water right after, there would be no water but if it sat overnight, there was a small amount, more in #2 than in #1 but not enough to hydrolock. When the heads were checked out they both had cracks in the center cyls exhaust valve seats so because of that and 15+ years of raw water cooling in salt water I replaced them with a pair of reman cyl heads ($550 for the pair, plus $120 for Fel/Pro gaskets and $100 for ARP cyl head bolts.

My mechanic warned me of the possiblility that the bearings could be bad, but I gambled and it worked out, I think each case is different, how much water was in the oil, fresh or salt and for how long. I figured if worst came to worst I could just remove the reman heads and get a reman short block and put it all together but that turne out to be unecessary.

good luck with yours, get a new or used good manifold ASAP and get it up and running, change the oil as many times as it takes. On mine I changed the oil 3x and drained all the water out, after each change, then pickled the engine with foggin oil till spring when I took it apart. Even then the bearings were OK.

 

[nola mike]

I’m not sure of the reason but the intakes on the Vortec V6s are prone to cracking unless that square plug in the front of the intake is drained in addition to the normal engine drains.

I don't think this is the case. I've drained the block at least 6 times now. Removed the plug maybe 3-4 times, got zero water out. If you pull the t-stat hose, I can't imagine that enough water can accumulate in that large section to crack. Even without pulling the hose that area must be the first thing in the engine to drain when you pull any of the other plugs. Also, none of the merc manuals mention pulling that plug.

 

[Lou C]

That's kinda what I thought but I found years back an OMC service bulletin from a year or so after the Vortecs came out that said that these were prone to cracking unless the plug is removed. The only way I can see that is if the big hose between the t stat housing and the circ pump is not disconnected at the bottom end. Yet there is a plug there for a reason and the pre-vortecs definitely do not have the plug.

 

[LWD]

I've never pulled the plug on front of the intake, but obviously I'm going to have to change my winterizing procedure.

My latest theory on why this happened, is I jack up the front of the boat as far as it can safely go, for the winter. I do that to help the bilge drain after draining the motor, I don't want water standing in the bilge and freezing there. But by doing that, it may have made the water collect in a water pocket about midway back in the intake and it didn't drain. In the picture, the thermostat is on the right hand side, and there is an fuel port (or whatever it's called), on the left of where it cracked. My boat may not be perfectly level side to side either, which may have prevented it from draining, I need to check that out.

 

[nola mike]

That's kinda what I thought but I found years back an OMC service bulletin from a year or so after the Vortecs came out that said that these were prone to cracking unless the plug is removed. The only way I can see that is if the big hose between the t stat housing and the circ pump is not disconnected at the bottom end. Yet there is a plug there for a reason and the pre-vortecs definitely do not have the plug. View attachment 342017

Yeah, dunno the reason, but it isn't a standard drain plug, and it's horizontal, and there's a lot of room in there for water to expand. Would be odd for omc to have a TSB and not merc if the manifold and potential issues are the same. Maybe @achris knows of one?

 

[LWD]

Today I pulled all the spark plugs, they all looked good.

I drained all the water from the motor, it all looked good. At no time did any water escape from the motor into the boat, it's all internal. Although I did have a small drip for a day around the harmonic balancer, but that must have swelled and sealed. (hopefully not a future problem).

I took pics of the heads and intake valley, zoomed in and don’t see any cracks.

At this point I think I'm going to get a new intake and put it all back together and get 'er going, keeping fingers crossed.

 

[Lou C]

be careful with the intake gasket and make sure you use the correct torque specs, there were some mistakes in manuals on this because the pre vortec took like 30-35 ft lbs but the vortecs are much lower like 10 or 15, you have to check, or else you'll be back where you started (water in the oil!)