Leaking Intake Manifold Gasket on 4.3L?
 

I started up my boat in the spring and it started up fine. I have a 2005 4.3L Mercruiser. I put it in the water and boated for about 5-10 minutes and then it stalled. I opened up the hood and saw that there was milky oil coming out of the valve cover vents. I took the boat out of the water, drained the milky oil, ran new oil through it twice and then replaced the oil and the oil filter. I took the boat into a boat shop and they removed the intake manifold, saw a crack underneath and replaced it. I thought that I had the self draining manifold but there is a pipe plug in it which I failed to remove. The rest of the engine was inspected and is okay. I started the boat and that's when I noticed it running rough and a small amount of steam coming out of the one valve cover vent. The boat ran perfectly before it stalled in the water. I'm thinking that the gasket on the new intake manifold gasket is leaking on the starboard side. I have partial hydrolocking occuring on only the one side. I think that a little bit of water is being drawn into the number 2 cylinder causing the partial hydrolocking. If I connect the water, and turn it over with the plugs in, partial hydrolocking occurs after turning over 2-3 times. If I connect the water and take out the #2 cylinder plug, no hydrolocking occurs. If I disconnect the water with all the plugs in and turn it over, no hydrolocking occurs. I had no hydrolocking prior to the intake being replaced and now I do. I’ve taken out the plugs three times and turned over the engine to check for water, and no water comes out and the plugs are not wet. The spark plugs are all normal - no steam cleaning. I’ve tested the compression and it’s 120 psi in all six cylinders. The oil is still clear – not milky. Do you think a improperly sealed intake manifold gasket could be the problem? Your suggestions would be appreciated.

Now I don't know what to think. The hydrolock is gone completely now. Guy I think you were right. I noticed a spark by the battery when I was turning it over. One of the battery cables was slightly loose. I guess there was no hydrolock. The engine fires right up but there is still something wrong. There is still a little bit of steam rising from the valve cover vents and it's still not running quite right. There is still no water in the oil or the cylinders.

I put it in the water today and it ran fine at low speeds but when I tried to speed up, it was like there was no power. It was if it was being held back. I have no idea.

I would say you need a leakdown test or at least compression test to see if the head gaskets are OK. The no power could be too many things to start guessing.

For water in the cylinders, I always check the exhaust manifolds first, and exhaust flappers if so equiped.

When you replaced the intake manifold did you set the timing properly?

I checked the oil and it was fine. The level didn't change and no water in it. I recall the shop that replaced the manifold saying that they were having a difficult time setting the timing. Could something electrical be causing the lack of power? I bought the boat in 2005 brand new and the condensor went on the boat after one year. I seem to recall last year a couple of times when it seemed that the boat was lacking power.

i think you are right. I don't think the timing is correct. Is it possible that they could have put back the distributor incorrectly when the intake manifold was replaced or is there only one way for it to go in?

If it's running improperly they could have swapped a few plug wires so first check the firing order.

Second, if the timing is off it could be one of the reasons for your loss in power. If the timing is advanced too far you'll have a hard time starting the engine and it will almost sound as if it's hydrolocked and the idle will be rough. If it's too far retarded the idle will be very low you'll have absolutely no power.

To set the timing on the 4.3L EFI you have to put the ECM into service mode. You can do this with the scan tool and also by grounding two terminals in the datalink connector but unfortunately I don't remember which ones. Possibly A and B but don't quote me because you can fry the computer....

I have a 4.3L carburated. Does the ECM still need to be put into service mode?

Steam rising from valve cover vent on 4.3L Merc
 

I took the boat back today and had the timing set properly. It still has a knock in it at higher rpms. The spark plugs are all still normal, compression is still 120 psi in each cylinder and there is still no water in the oil. It has steam coming out of the valve cover vent on starboard side only. Does anyone know what could cause that?

When the steam comes out is it in a "puffing" manner or a steady stream of steam?

If it's puffing you have engine problems such as a blown head gasket or a holed piston... If it's just steam you can be having some blow-by.

It's really hard to know exactly what's going on unless hearing it for myself.