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525 water pressure problem

Old 04-14-2016, 08:26 PM
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A customer had high water pressure problem with a set of 502 mag mpi's with CMI etops, blew a couple hoses, and had high pressure at idle. I ran some tests and determined it was the tails. For a quick fix i cut the jumper port off the tail, dented in the inner pipe as the clearance can be really tight there on cmi's, then welded the jumper port back on. That completely fixed the one side, the other was still on the high side, ended up putting a new set of cmi's on that side and pressure was down where it should be. in this situation it was showing 5+ psi in neutral at idle, and of you revved it the pressure would jump upwards of 15 psi. What I did to isolate the headers the tails was pick up 6ft of clear 1" water hose. First I ran it right off the Tstat housing and dumped right over board taking the headers and tails out of play completely, only let it run for a few seconds, started it, revved it, shut it down. next I used the clear hose from the header jumper port and dumped over board to just take the tails out of the equation. Those 2 tests showed normal water pressure. Hooked the tails back in and water pressure was high again. Took no time to do
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Old 04-15-2016, 04:54 PM
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Just returned from CMI. Both headers were tested for flow and pressure. I have 22GPM water flow @ 20 lbs pressure on both headers. Pressure test was fine on both headers no leaks/cracks 40LBS pressure. The folks at CMI were extremely helpful and concerned regarding my high water pressure problem. A special Thank You to(sales engineer) David Rank. What a nice person. I was also very impressed with the factory and the CMI employee's I came in contact with during the testing process. What a great team.

I'll post again when I get the heads back on.
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Old 05-26-2016, 09:36 AM
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Has this problem been resolved. I suddenly have high pressure in a motor (carbed hp500). Gauge reads 25psi or over when I get up to 3500 0r 3800 rpms and will keep going up if I accelerate. So for now its lower speeds until its fixed.
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Old 05-26-2016, 09:59 AM
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Old 05-27-2016, 06:24 AM
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If you have the motor apart for a rebuild, take the heat exchanger apart and the oil cooler off and look through them. Sounds like this is the only option you have left. It is pretty simple and you would not believe the rocks, sand, and past impellors that will be stuck in there. A coat hanger and some compressed air is all you will need.
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Old 05-27-2016, 07:04 AM
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Just for the record the maximum water pressure on a 525 is 43 psi according to the Mercury shop manual. I often see over that due to the huge inlet on the Imco lower. I've had the inlet welded up some to keep it down. I know people who regularly run 50 psi on these engines and mine will get that high if trimmed down at speed. I can use my water pressure gauge as a trim gauge. I put in a pressure relief valve and dump but took it off when Allan Brown advised me to. After several mods to the water inlet I've got the pressure where I'm happy with it. I also did not do the header water by-pass elimination because my headers never get hot so I decided it's best to not restrict flow there if I don't need to. The proper water restricters are in the header water ports.
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Old 05-27-2016, 08:11 AM
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I pulled out the power steering cooler. Big chunk of fabric lodged in there so Ill see what happens later on the water. Oil cooler on the back and I'm not sure it can be pulled without pulling the motor. Whats the reason for not using a relief valve?
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Old 05-27-2016, 02:31 PM
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Originally Posted by DoubleThunder
I pulled out the power steering cooler. Big chunk of fabric lodged in there so Ill see what happens later on the water. Oil cooler on the back and I'm not sure it can be pulled without pulling the motor. Whats the reason for not using a relief valve?
Sounds like you found the problem. When Brownie comes on here and gives me advice I take it and run! He said the relief valves can stick open at the worst time and the result can be disastrous. I'll try to find the post.
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Old 05-30-2016, 04:59 PM
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Still doing it. As soon as I hit 4000 rpm the water pressure jumps up quick. The PS cooler is after the oil cooler so maybe there is some of the same stuff in there. It wont be easy pulling the oil cooler though.
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Old 07-02-2016, 07:39 AM
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My water pressure is 15lbs @ 3400 rpms and goes over 20 - 25 lbs @ 5000 rpms. Last year my water pressure on one engine was at 10 lbs and the oil temps were on the higher side of 230 @ 3400 rpms. My oil cooler located at the back of the motor fortunately has removable ends caps. After looking inside there was sand, tiny rocks clogging some of the holes in the cooler. I used a small steel rod first and then back flushed the cooler. This corrected my water pressure and oil temp problem. From my seawater pump water flows to my combo oil/steering cooler first and then to my thermostat housing. My water pressure sensor is just a brass fitting on the right side of the block where water travels up a hose to my dashboard and connects to my Gaffrig gauge. It is a mechanical gauge. After reading all these previous posts
I am a bit confused as most of them said that pieces of the bad impeller clogged the cooler and is causing the excessive water pressure.. The way I see it is if the pieces of impellers, sand, rocks were clogging the oil cooler that would cause a drop in water pressure like a restriction, not an increase unless your water pressure sensor was mounted at the inlet of your oil cooler
My 2 cents
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