1987 Mercury Mariner 150 V6 Overheating and high water pressure

[Bubba Walker]

Hello,
I have a 1987 Mercury Mariner 150. Father in law passed down to me about 2 years ago. It was overheating and has high water pressure, (15 psi at idle and higher rpms well past 30 psi). Does not over heat at idle. I have installed new complete water pump, have pulled powerhead and replaced all gaskets to include new rubber for water tube, removed heads and checked them. removed the cylinder cover and checked them. removed the divider plate and checked. also replaced poppet components as well. It is still over heating. Also have removed poppet spring and ran it. i have a temp gauge on the port head and buzzer on starboard head. With the poppet spring removed at running speeds the port head reads 160 degrees but the starboard alarm goes off. Have not hit with a temp gun to see what the temp is yet.
Any ideas?? I am stumped at this point.
Also is this motor a 2.5 or a 3.0?
Thanks in advance.

 

[bb572ci]

Are there thermostats in it ? I would swap the sender with the other side see if it follows the sender when swaped

 

[Bubba Walker]

Yes it also has new thermostats too. Sorry I forgot to put that in there. OK I will try that. I am going out Sunday morning.

 

[bb572ci]

15 to 30 is not unherd of if the water pressuer is still hi and it still gets hot pull the thermostats out a stuck one will create hi psi I've seen them bad out of the box

 

[Bubba Walker]

I have taken them out and ran it. Water pressure goes down but it still gets hot.

 

[Dukedog]

You have pretty much covered everything. I would start over by double checkin' tha water pump parts, mainly gaskets.......If you pulled tha power head, heads, cyl. covers, adapter plates, divider plates, how did ya know which gaskets ta buy? Reason I asked is there are a coupla of 'em that "look" like they will work but actually won't............

Unless its an XR4 its gonna be a 2.0 motor.............Something you need ta know for parts.......

 

[Bubba Walker]

I actually had help from a local mechanic. After he helped me with all of it and it still overheated he was just as stumped as I was lol. Starting to think I have a Crack or something.

 

[Dukedog]

Could be but odds are against that. A crack will leave some kinda tale-tail/ won't really produce high pressures.......ie: water, steam where its not supposed ta be. power loss. What type water pump "kit" did ya use? OEM or after market?

Did ya run it with tha poppet completely removed?

 

[Bubba Walker]

I used an OEM pump kit.
It was a quicksilver pump kit.
I have not ran it with the poppet completely removed. Was told not to by the local boat mechanic.

 

[Dukedog]

You can for a short period just for"testin'. With it removed tha idle pressure should drop noticeably..........If it doesn't it might be an indication of adapter plates and/or gasket problem. Did you replace tha "staked" fiber bushing and tha rubber grommet when you replaced tha poppet parts?

 

[sam am I]

LOL @ Duke, yer killing me here w now ok testing w a poppet removal............You need to stop napping on the keyboard Duke!!

But you're spot on as usual!

Either the poppet is still stuck closed/not working properly or issue is down with adapter plate draining issue, concur w Duke......My money is on his poppet is fine(sounds like he worked it over pretty well) and his outflow is plugged, he's got'um a mouse right here I bet.....





hence extra high pressure and only overheating at high speed............

As Duke mentioned, after removing poppet, pressure should drop to norms, but also, it should run cool/norm temps at high speed as well, but only if a bad poppet!! and no mice!!!

However, after removing it, and the pressure stays high'ish and still overheats, ya got a mouse!!!

Lil perplexed thou on the port cooler (160F?) than the star(recall, it takes 240F to set off the buzzer), that's huge!!!.......still scratching my head there. Both cylinder's lower water jackets ports have to combine and flow out poppet, that sounds more like a star. stat. is hanging up ......or a second mouse :facepalm:

 

[Dukedog]

Lil perplexed thou on the port cooler (160F?) than the star(recall, it takes 240F to set off the buzzer), that's huge!!!.......still scratching my head there. :

That needs ta be checked with a gun ta get tha temp its goin' off at. Most probably average 210 ta 220. I've seen some at 190.......One side runnin' cooler/hotter than tha other is not uncommon either........Most head/metal reading temp gauges should be used as a "reference" or "norm" and not a TRUE temp.....jmo