robclark

Hi all. This board has been a tremendous help to me in the past and I hope someone can guide me here also. I have a 42 Sonic with twin 500 EFI's. The motor heats up to 200 degrees plus quite quickly at idle or under load. The motors have always run at 150 on the dash temp guage. I have changed the sea water pump/impeller, thermostat with the correct 140 degree setting, and circulating pump. The water flow appears good through the whole system and my mechanic assures me that there is normal and sufficient flow. I have checked the oil cooler for a blockage also and it is clear. My mechanic says the only thing he can think of is a head gasket leaking and causing exhaust gas to head up the water and is suggesting pulling the heads. One side of the motor was running about 8 degrees higher yesterday when measured with a hand held temp guage but it was the side of the motor where the water passes through last. The motors are 100% stock with about 290 hours on them and have never given me any problems at all. Any ideas or suggestions would be greatly appreciated. Thanks.

Additional info - The boat has only been used about 30 hours in salt water and not at all in salt over the past 2 years. The first 20 hours were in salt and then just a few times since. It does have the original stainless exhaust that the motors come with from Mercury Marine. I appreciate the responses so far and please keep them coming. I really want to get up and running again and want to avoid any unnecessary work. There is no water in the oil at all. The mechanic said that sometimes the head gasket will not fail in an area where there would be water in the oil and that sometimes it would fail in an area where the exhaust would interact with the cooling water flowing through the heads. Sounds logical to me but I am no mechanic.

Vinny P

I wouldnt be too quick to pull the heads off just yet. A cracked head gasket doesnt heat up the water. It does suck water into the cylinders. It will wash out the plug in that cylinder and turn your oil to chocolate milk. Hows is the oil? Any signs of water? Pull all the plugs to see what is going on. If 1 or more are washed out, then you found the problem. Are the headers original? Being that you are from VA, I assume you run the boat in salt water. The headers can and do rot from the inside and slow down water flow. That will make it run hot.

Longrange4u

Not to ask the stupid question... but your Impeller is good... what about your water pump?

88Fountain

iTrader: (1)

I had a similar problem with my boat once. There is a hose that goes through the transom that has sea water pulled through to cool your engine. This hose is held in place with beveled plastic rings that screw into the hose. Sometimes, these plastic rings collapse and collect debris. In the bilge, looking at the transom, there is a small cover, looks like a small thermostat housing, that has a hose connected to it which goes to your sea water pump. Remove this housing and inspect the hose/plastic ring under this cover for blockage. The other end of this hose can be checked after removing the outdrive. Do the one in the boat first, as it's easier. My boat seemed to have adequate water flow, but it wasn't. I was told that salt water use causes these plastic rings to break down.

robclark

thanks for the ideas so far, please keep them coming

LakeRacer

This is exactly what happened to my engine. I was ready to pull the heads too but my mechanic wanted to check this last option. Thank goodness.

robclark

I will have the mechanic check things out further. Thanks to anyone who read this and if you have any additional suggestions please post them.