1983 Mercury 115 water in 3 and 5

[Gotdunes]

Original post 9/26/2003 I have an 1983 Mercury 115 inline six on a '94 18' Spectrum Sport 19P prop. She runs great on the trailer, but will only do about 10 mph in the water. Compression is 120 on all 6 cylinders. I am getting spark on all cylinders. New primer bulb and the fuel pump works fine. I need some suggestions as to what to try next. The boat ran great all year until about a month ago.<br />Update:<br />I finally took the boat to the mechanic. All the electronics checked out fine. They found a small amount of water in 3 and 5. What could cause this? besides a cracked block. The motor appears to run fine until you put a load on it. According to the dyno it was putting out 35% of the power it should. The compression is still 120 on all cylinders.<br /><br />Thank you,<br />Steve<br />

 

[jimmbo]

Re: 1983 Mercury 115 water in 3 and 5

Since this engine doesn't have a head gasket it can't be that. The inner exhaust cover or the gaskets might be leaking and allowing water in through the exhaust ports. A cracked cylinder, while possible is unlikely. Pull the plugs and using a small light take a good look at the cylinder walls for scoring. You say the electrical system checked out fine, did they test while it was good and warm?

 

[Gotdunes]

Re: 1983 Mercury 115 water in 3 and 5

Jimmbo

 

[Gotdunes]

Re: 1983 Mercury 115 water in 3 and 5

Jimmbo, Thanks for the reply. Would a leak in the exhaust cover cause the loss of power? I am not sure if the motor was warmed up when they checked the electronics. The mechanic told me the fuel and ignition systems checked out.

 

[jimmbo]

Re: 1983 Mercury 115 water in 3 and 5

water in sufficent quanities will interfere with the combustion process, that said, Water is also one of the products of combustion.

 

[Chris1956]

Re: 1983 Mercury 115 water in 3 and 5

GotDunes, Water in the cylinders will put out the fire, causing not only 1/3 power loss, due to the not firing of the two cylinders, the balance of the motor needs to carry the two dead cylinders. This may be the sole cause of your power issue. I recommend you remove the powerhead and remove the port side exhaust cover. You may get lucky and not break any bolts and find a hole in the exhaust baffle. If not the baffle, the inner water jacket cover is the next likely cause for the water infiltration. I recommend you heat the bolt heads and apply gentle impact from a hand or air impact wrench. I only broke 6 bolts on the inner water jacket cover, (and none on the outer cover). I was also able to remove the broken parts of two of these six. Good luck!

 

[Gotdunes]

Re: 1983 Mercury 115 water in 3 and 5

I will tackle the motor this weekend. Thanks for all the help!!