Mercury Xri 150 overheat and high water pressure

[dclarke963]

Hey guys I'm new to the boaters world and bought a nitro bass boat with a mercury xri 150 on it. I've been trying to figure out what is causing the overheat alarm to go off. First off I took the boat to a mechanic and have had the water pump and impeller replaced that's including the housing, changed the thermostats, checked all the lines and passages for debris, replaced the gaskets between the power head and mid section and it's still overheating. It's also got 15psi at idle and plus 30 once over 1500 rpm and it's a brand new gauge and lines, I've checked the poppet valve as well and didn't see anything wrong with it but I'm not sure how to tell when it opens. I'm stuck and so is everyone I've talked to I need some help anything will help thank you!!!

 

[wired247]

Have you checked the sensor to see if its really overheating?

High water pressure in and of itself isnt really that much of a problem. My pressure readings are similar to yours but I'm using a low water pickup lower and its the ram effect causing the high pressure . Used to be higher but I drilled the poppet dump port out a bit wider and got terminal pressure under 30 and called it a day.

 

[Dukedog]

Abnormal high pressure in a production V6 Merc/Mariner is usually a "restriction" somewhere. Most of tha time it ends up being tha power head gasket and/or debris of some sort in tha adapter plates. I say this 'cause ya didn't mention tha gasket between tha plates. Also tha wrong gasket there will casue high pressure. Usually tha same effect as if tha poppet is stuck closed. Its sometimes caused by "air" intrusion but usually (but not always) fluctuates with that type of high pressure..........So it could actually be tha gaskets at tha pump. Just not tha usual thing.

That's all I got without being able ta reach out n touch it!

 

[dclarke963]

Ya I've change all the gaskets at the adaptor plate, and all the gaskets at the water pump are new as well, even ran it with the spring out of the poppet valve and didn't see a drop in the pressure, I've also shot both cylinder heads to make sure they were heating up and they were both over 170 when the alarm came on, it only comes on when you get to half throttle then as soon as you come off plane and let it sit for 10 secs the alarm goes off, I've pulled both heads and I'm going to try replacing them and see if that's the cause, when I pull the upper water hose off(the one that goes to the poppet valve) I saw a little bit of exhaust coming out of it before the water caught up and starting coming out any ideas why that is?

 

[dclarke963]

Also when it's at idle and I pull the thermostats the port bank seems to shoot out more water then the starboard side and when it's idling the port side seems to stay cooler then the starboard side until you get up on plane, normal? Also when I pulled the poppet valve right out the water pressure dropped. But with the spring right out it still reads 15psi at idle

 

[dclarke963]

Ok so I got an update, I came home after work and pulled the port side head off all 3 cylinders had water in them, head gaskets had no visable breaks or blow by and I also pulled the exhaust divider to see if the water was getting in through there and there wasn't anything noticeable, anything else that's possibly pushing water into all 3 cylinders? Head and block seem pretty flat as well I checked them.I assume head gasket but it doesn't look all that bad

 

[Dukedog]

Sounds like ya coverin' all tha bases. Can't think of any other way other than a crack or hole etc. Maybe tha gaskets are just being deceiving. Surprised it hasn't "bent" something...........

 

[OperativeK]

Hey guys my brother in law is having this same problem with his motor. We think we found the fix but aren't sure yet. Will let you know but essentially would be blockage. Be sure to check the water flow diagram here : http://www.biggerhammer.net/mercury/...0_blizzard.jpg
Here is the link showing the tubing and T fittings for the top at the heads. I would check the tube at the top for blockage, the one that goes down. Some how we think the T at the top of the cylinder was taken out, would that cause air to trap at the top of the heads? I think so but just wondering if you would agree.

 

[Dukedog]

That dia is for an "early" production ('88 and older) and also High Performance motors. Not yours