robclark

I posted this post on Sunday and have not figured things out yet. I had a few folks that mentioned the area between the transom and impeller getting clogged with debris. That turns out to be fine also. Any other ideas from anyone as to what else can be checked at this point?

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.

Pwrbt33

iTrader: (2)

For grins Rob, have you checked the flush caps on the back of the boat? If they are loose or off the motor will overheat. Also check the flush hose inside of the boat for having pin holes and or loose clamps at both ends. To check if the flush has any relations with the running hot, take a pair of vice grips and 2 pieces of small plywood and pinch off the flush hose close to the "T" at the bottom. This will eliminate that hose and fittings.

Let us know what you find.

John S.

Thunderstruck

Do you have oil temps? What are they compared to the other motor? Water pressure? Don't worry about responding if you went through this on another post.

Are your suction and discharge hoses on the raw water pump on the correct spots on the water pump? Compare to the other motor.

Thermostat opens when put into hot water on the stove even if its new?

Try running without the thermostat.

Assuming you have checked a bunch of other stuff:

The hose barb on the inside transom assembly that passes the water from the transom to the sea pump suction covers the hole in such a way that water can corrode the hole in the transom assembly. The corrosion products swell, pinches and constricts the hose (this hose comes from the gimbal housing outside the boat) that passes through the opening. This can restrict water flow. There is a plastic fitting that screws into the hose from the transom assembly that I replaced after cleaning out the corrosion products. The corrosion had just about crushed the plastic fitting. This was done with the engines out of the boat but my buddy did it with the motors in the boat.

This problem is hard to diagnose but should occur gradually, starting with high oil temps before the engine starts over heating over several months, usually in older boats.

I don't like the head gasket theory. Too many other symptoms would show up.