high water pressure

jrocksho

Seaman Apprentice
Joined
May 15, 2007
Messages
39
1990 Mercury XR4 150hp. I replaced upper housing assy., t-stats, poppet assy., and I still have 28-30psi at 5000-5500rpm's. What else could cause this? Before the changes, I was at about 25psi wot, now I'm almost pegging the gauge. Please help me if this is even a problem, I've never seen pressure this high on any Mercury I've owned or worked on. There's no overheating, but I'm scared I'm running too cold unless I idle. Thanks.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: high water pressure

Might suspect your gauge. Pump is centrifugal, not gear and at high rpm's on some engines that have the water inlets up front on the lower unit, the blades fold back and the ram effect does the work.

HTH,

Mark
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: high water pressure

Check your poppet as that only thing that would keep block pressure high,also where is you water pressure gauge plumbed in?
 

jrocksho

Seaman Apprentice
Joined
May 15, 2007
Messages
39
Re: high water pressure

i replaced poppet diaphram and washer, but i'll inspect it all again. gauge plumbs in at top of block, between the heads just under the stator. this all began with just a simple water pump replacement, pressure has been high since. thanks. i will check my poppet again as soon as i get more gaskets. i know the poppet is for high rpm's, why would i still get high pressure at idle? im seeing between 7-10psi while idling. after a minute, it goes down to about 3psi, but if i run then stop again, its back at 7-10psi. i went out yesterday, temp gauge is still pegged on cold while running, normal temps while idling, no overheating.
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: high water pressure

I suspect the differences you are seeing in idle pressures are with stats opening and closing, off idle increased flow the stats may be cooling and closing, slightly raising the pressure again.

Is this a 'salted' motor?

Can an accumulation of salt in the cooling passages raise the water pressure yet not yet be so thick as to cause cooling problems, yet?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: high water pressure

gauge plumbs in at top of block, between the heads just under the stator.
Your feed from poppet goes there, where does line off poppet housing go??
 

jrocksho

Seaman Apprentice
Joined
May 15, 2007
Messages
39
Re: high water pressure

charlie, it has seen a little salt water, but not much..i thought of that too actually but all this happened suddenly after i replaced my water pump housing assy.
 

jrocksho

Seaman Apprentice
Joined
May 15, 2007
Messages
39
Re: high water pressure

faztbullet, no. i have no lines coming off my poppet housing at all.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: high water pressure

Ta Da!!! its not a 1990 model as that is the old style cooling system . The new style has the poppet valve cover that uses 4 bolts to hold it on and has water tube from top of block to poppet cover. If this is a old style system or powerhead the pressure will be high and the gauge may be off a tad but 20-25+ psi at WOT is normally for this style cooling.
 

aussieflash

Lieutenant Junior Grade
Joined
Feb 5, 2011
Messages
1,004
Re: high water pressure

Post your serial #, im guessing you got same cooling as my 88 V6.
 

jrocksho

Seaman Apprentice
Joined
May 15, 2007
Messages
39
Re: high water pressure

serial# 0c110157..at wot im at almost 30psi, i was getting 25psi wot with the last two water pumps, but now im at 25psi at 4500rpm or so..i just never seen it this high before.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: high water pressure

Its going to be high with the old style poppet set up. That serial number must be on the midsection as thats not the year of your cooling system.
 
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