Mercruiser 4.3 V6 issue

B

bdreger

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Feb 19, 2002
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7573
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mercruiser 4.3 L. gen2 issue
engine was running ok then started to lose power . upon restarting it hydro locked . removed all spark plugs and observed excessive amount of water coming out of three cylinders on the right side when cranking . no water coming out of left side. engine oil on dipstick is milky white.
removed riser and manifold but water issue still exist. removed intake manifold and cylinder head to check head gasket which looks ok sludgy milkshake oil everywhere .
did a water test on the intake manifold but didn't see any leaks but when i water test the cylinder head it looked like water was leaking internally so i purchased a new / refurbished one.
after installing new cylinder head and gaskets, the engine runs ,no water in cylinder s , but very low compression on all 3 cylinders less than 90 lbs . also there is a large amount of fumes / blow-by gas , emitting from the valve cover pcv ports ( both sides ) and the oil fiil neck if the cap is off .
even after 2 oil changes the oil is still milky . interesting that i put in 4 quarts but the pump out through the dip stick only delivers 3 quarts

i torqued the head bolts to 75lbs , the service manual says to use a torque angle guage which i tried but couldn't get it to work ,so i just went with the standard torque wrench.
must be a leak somewhere in the head ) or block , i don't know .
 
I didn't, but will do it next time. Also wondering if I should tighten the head bolts to 80 lbs
 
do not over torque the head bolts, 80 ft lbs is way too high!
1) what year Merc is this? If its between 96-99 or so does it have the one piece manifolds? If so they are a known failure point because of the lost foam casting technique that allowed some of the wall thickness to be too thin and it can crack or rust through easily. First thing you check if you get water in cyls is the exhaust system, there are conversion kits to get rid of the one piece manifolds. I had the one piece units on my OMC 4.3 V6 and while I never had trouble with them I have heard of people who did. I converted mine over in 2017 when I did a top end overhaul (reman cyl heads).
2) When you replaced the cyl head, did you measure it for flatness (less than .003") and also measure the block deck surface (less than .003")? The most important thing about that job is clean, clean, make sure the mating surfaces are immaculately clean and you also must clean out the threads for the cyl head bolts in the block because they get crud in the threads and then your torque readings are not accurate (they will be less than what the torque wrench indicated). I spent hrs cleaning the block deck surface and cleaning out the cyl head bolt holes with a thread chaser, carb cleaner and compressed air.
3) did you replace the head bolts if required? are the torque to yield (one time use only)? My old ones were not, they can be reused but they were so rusted that I replaced them with a new set of ARP head bolts and Fel/Pro marine head gaskets. So far so good!
4) did the engine overheat before hydrolocking? If so you can warp cyl heads, crack them in the valve seat area and blow head gaskets. When I had to fix mine it had overheated in 2013, ran fine the next 2 seasons, then blew the head gaskets at the end of the '16 season. I took it apart, had the cyl heads checked and wound up replacing them with reman heads, new gaskets etc.
5) are the exhaust flappers in place at the top of the Y pipe, if they melted due to an overheat, they can allow water up the exhaust and also block the exhaust and cause performance problems....
 
Hi , thanks for the advice. It's a newer engine , probably 2006 , also called gen+ I think. The water entering the cylinders cleared up after replacing the head. I used new bolts on the head , don't think they are tty . I didn't check flatness because the head is new and the engine had good compression prior to the work . Checked it about a month ago . The engine did not overheat . I cleaned the block surface as good as I could with cleaners , solvent , light wirebrush.
 
mine overheated bad back in 2013. Ran fine for the rest of that season and 2 more summers. Eventually blew the HGs about 3 years later. Heads were cracked in exhaust seat are of center cyls. Surprisingly the block deck surface was fine. Cast iron closed deck construction is far superior in tolerating overheats vs outboards.
So I'm guessing you don't have the one piece manifolds, which is good. Then to further evaluate you need to do a cyl leak down test. That will tell you where the compression loss is happening, valves or rings/cyls. If its the latter I'd start thinking about a reman long block.
 
Thanks for the response. My gut feeling is the head is not sealing properly to the block I don't suspect valves because they are new with the head . The rings are unlikely because all 3 cylinder are low compression and the compression was fine a few weeks before. What are the odds that all 3 go bad at once ? I'm also concerned about the excessive blow-by gas emiting from the pcv ports which vent into the engine carberater. It has a smoky , exhaust smell , rich unburnt fuel odor , . It maybe coming from the head gasket seal , somehow the exhaust / or intake strokes are bleeding into the crankcase
I plan on following the advice here, wet compression test , pressure test , clean and check surface for straightness. I'm wondering if I can use a gasket sealer on the head gasket?
 
I would do a cyl leak down test, that is the most comprehensive test because it tells you where the compression loss is from. Question: does this 4.3 have an adjustable valve train like the older models (mine does). If it does and the hydraulic lifter preload is set too tight the valves will not close all the way and low compression will result.
What brand of head gasket did you use? I had good luck with Fel/Pro
Did you clean out the cyl bolt threads in the block? They get crudded up from raw water cooling and if not really clean they may not allow accurate torque readings.

Good cyl head install results depends on very clean sealing surfaces, flat & level to less than .003", good head bolts and clean bolt holes in the block. It literally took me hours to clean the sealing surfaces and bolt holes and had to do some more than once. Then I threaded all the bolts in by hand first to make sure they would thread in all the way, I found one that was still not clean enough!

As far as sealer on the head gasket see what the manufacturer of the gasket says, I know Fel Pro says not to. The only sealer I used when I did mine was just a bit of Permatex Aviation on the water ports for the intake gasket and also the head bolts require sealer on the threads. The permatex helps seal the intake water port as they sometimes get a little pitted from corrosion, on the intake manifold. On the older pre-vortec engines without the locater holes for the gasket in the cyl head it also helps hold the gaskets in place as you lower the intake into place. The Vortec style intake gaskets have pins that fit into holes in the cyl heads to hold it still.

This is not really a hard job but there are things that can affect the installation for sure. Fel Pro has a lot of good info on their website.
 
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