At the end of last season I replaced the original CMI headers on my 2004 Mercury 525's with the new CMI's and installed water pressure gauges at the same time. I hooked the gauges up to the same place that the smartcraft sensor is on the oil cooler and I am concerned with the readings that I am getting. At idle they are both about 8 psi and that is also what the engine scanner says as well. When I get up round 4000 rpms I am reading 40+ psi on both engines. I did not have gauges before so I am not sure if this is correct or not. Seems high even for a closed cooling system.

I also noticed that the restrictors on my tailpipes are .389 for the starboard side and .406 for the port side of the engine and the newer versions have .406 for both sides. The new headers do not have the up/bypass tube to the tailpipe so that inlet is plugged. I have been hesitant to take the boat much above 4000 rpms until I can determine if there is a problem or not.

Any thoughts?

i see 5psi at idle,,,and 25-30 at speed,,,,merc recommends getting rig of the lower by-pass,,,and go with the bigger restrictor in all tailpipes,,,40 seems high,,,but the retro-fit might bring it down some

Water pressure is dependent on the drives you're running to a large degree. I have IMCO's with the water pickups at the very front of the cones and was making 50+ PSI at 80 MPH(which causes all sorts of issues). 40 PSI is too much as well. I would install relief valves set at 20-25 PSI to dump pressure before you start blowing hoses and creating geisers in your engine compartment.

Yeah...I forgot to list that I have XR drives with low water pick-ups in the nose. I would have to imagine that the 525/XR combo must be pretty popular which makes me wonder if others are having the same problem.

I got rid of the lower bypass and plugged the lower inlet on the tailpipe but I did not change the restrictors. When I checked the parts list for the older models like mine it listed .389 and .406 and the newer models w/out the bypass had the .406 for both sides. I guess i am gonna try replacing the .389 with a .406 and see if that helps.

you can just drill out the smaller one to match the others

Thats probably what I am gonna do considering they want $35 each for a piece of copper with a hole in it.

It takes nothing more that a 13/32" ( .406") drill bit in the tailstock of a lathe and the stock .389" restrictor in the 3 jaw chuck head. I bought the .406 restrictor and my friend just laughed at me. We later opened up the .389" restrictor in about 2 minutes on his lathe. Don't waste your money.

They appear to be some grade of stainless steel, not copper.

PS: They are really proud of that brass plug threaded for blue plastic drain plug, too! $$$$

The drives (XR,XZ and HP) with only the LWP always seemed to have high water pressure issues. The drives with the DWP seem to have better balance of water pressure. I see about 30 psi at 76 mph on my DWP XR drive, 19" X dimension. Our previous 35 Lightning twin step with LWP XZ drives pegged the water pressure gauges (35 or 40 psi - don't remember exactly, anymore) at ~ 70 mph and the boat would run 86 mph WOT, so I know the pressure was "up there somewhere".

The 525 likes water pressure. The factory service manual puts the max at 43 PSI so you are OK. I run about the same. I regularly see 40 PSI. Stop worrying; Go boating!

I did briefly install a relief valve and dump but this engine needs more than 25 PSI and if the valve should stick...well it's one more thing that can go wrong. I took mine off. BTW, I run 83-85 MPH.

Also I have not done the header mod because my headers are always cool or slightly warm to the touch.

I also have an XR upper/Imco lower.

Thanx Guys...I just picked up the restrictors from the machine shop. I took the old lower ones to the same machine shop that did all of my engine work and had him open them both up to .406 so I will replace them this week.

I had a good stretch of not having any problems with the boat until last year when I broke a valve and hurt the port engine. Ended up loosing the entire summer getting everything back together so I guess now I am extra sensitive to everything. I didn't have the water pressure gauges before so I never really knew what it was doing before. I would guess it was the same and I never had any problems.

So I am gonna take your advice thirdchildhood and go boating...ALL WEEKEND

Thanx again for the help