v6 150 mercury ob

TFALZO

Cadet
Joined
Jul 1, 2008
Messages
10
I installed a water pressure gauge in my v6 because I have had a alarm on overheating issue. Upon testing on land w/ears on the pressure never exceeds 6 psi even though i brought rpms to 3000 . I figured it should be at least 10-15 psi. I originally tapped into the hose between cylinder heads but then installed at base just past 90 degree fitting. I also installed a new waterpump impeller housing and seals. The boat will run to 1500 rpms without the alarm on, the minute I throttle past temp rises alarm goes on. After waiting only 20-40 seconds start back up alarm off.Thank you for any help you can offer.
 

tysonnathan

Petty Officer 1st Class
Joined
Jun 2, 2008
Messages
246
Re: v6 150 mercury ob

Im pretty sure merc specs for that motor is at least 15psi at WOT. it will be significantly lower than that at 3000 rpms. Check it running wide open and see what you get. I dont think merc gives any other recommended ranges than WOT so a pressure reading at 3000 tells you nothing. was the old impeller or housing damaged? do you have any debris in the lines or water jacket? is it peeing good?
 

TFALZO

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Joined
Jul 1, 2008
Messages
10
Re: v6 150 mercury ob

The impeller looked new, housing unscored yes there is a good stream out pee hole. There is no water coming out exhaust.
 

hkeiner

Lieutenant Junior Grade
Joined
Oct 17, 2006
Messages
1,055
Re: v6 150 mercury ob

The below thumbnails contains some troubleshooting information. You would have to run it out on the water at various RPMs to get all the readings needed to fully evaluate if the water pressure is OK. Also, the following link describes how to properly connect a pressure gauge to a 150hp V6.

I hope this helps.

http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49
 

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TFALZO

Cadet
Joined
Jul 1, 2008
Messages
10
Re: v6 150 mercury ob

The installation instructions said to cut bypass hose 2-3 inches from 90 degree fitting at top of engine. I do not have a 90 degree fitting other than at the base {across from tell tale outlet} I tried tapping in there and saw no pressure difference. The problem I have with actually running it in water is within 100 feet from dock throttling up to 3000 rpms the temp gauge {I have both installed in dash} rises as fast as tach/speedo. I am afraid it is going to wreck motor heating up and cooling so much. I also pressured up water tube with stats out and heard the air coming out of outlets. Is there any other way of flushing coolant passages? I really appreciate eveyones help. Tom
 

gss036

Commander
Joined
Jan 18, 2003
Messages
2,914
Re: v6 150 mercury ob

On top of the block, just behind the fly wheel you probably have a pipe threaded plug in the block that comes off at 90 degrees, there should be a hose feeding the poppet valve from there. That is where they say to tap into the hose. The hoses from the thermostat will not work for water pressure.
Water pressure at WOT should be 12psi.
Maybe you should take a look at your poppet valve.
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: v6 150 mercury ob

On top of the block, just behind the fly wheel you probably have a pipe threaded plug in the block that comes off at 90 degrees, there should be a hose feeding the poppet valve from there. That is where they say to tap into the hose. The hoses from the thermostat will not work for water pressure.
Water pressure at WOT should be 12psi.
Maybe you should take a look at your poppet valve.

On some engines there is a plug in the hole. Remove it and install a hose barb.

I'm willing to bet when you get the pressure gauge installed right, you'll find pressure too high. (Just a bet) That would indicate plugged passages, probably in the exhaust plate below the engine block.

hope it helps
John
 
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