Merc 525's

[Shanghied Again]

Do a pressure check on your headers if they are stock CMI. We have seen a lot of failures within the years. There is a cure when we get the headers repaired we install drains on the rear lower rail of the headers with fittings and hoses that run out the transom of the boat. This allows the water to drain out of the headers and prevents corrosion from water laying in the headers. The drains will drain all the time but will not do any harm when operating. No loss of water pressure in the block or cooling system.

 

[Geronimo36]

Although it's just a safety patch, I agree with Shanghied.

It may not stop you from dropping a valve from having cold water spraying on your exhaust valves from a crack in a weld while it's running but definitely a good thing to do and gives some peice of mind so you don't hydrolock an engine, rusted valves or have piston rings sieze from water draining back into a cylinder while you're at work making money to pay for this habit we call boating!

 

[95south]

this go around, I dont this it was from the headers leaking. I will have them install the drains before we take the boat south, but I think the problem goes way past just the headers

 

[MOBILEMERCMAN]

I hope you get it worked out so you can enjoy your boat.

 

[Geronimo36]

Definitely sounds like more investigation is needed 95south and like I said before, I'm glad to hear it's not the headers for a change!

In addition to pressure checking the headers, also be sure they check the tailpipes, especially near the ends of the clamping flanges. The CMI's are known for having leaks near those spots also. The fact that water is getting into the cylinders you still need to pay attention to the exhaust because those engines are fresh water cooled and you would have anti-freeze in the engine if it wasn't the exhaust.

You may test the header and find zero leaks only to have a leak on the tailpipe. The tailpipes are harder to test than the header but just something to look out for!

Another suggestion, have a competent marine guy either make the tailpipes dry or 3/4 dry like I did to my CMI's when I had them... In our area (NJ) John Trione is the man and I can put you in touch with him. Lessen the risk so to speak!

 

[Big Time]

Another suggestion, have a competent marine guy either make the tailpipes dry or 3/4 dry like I did to my CMI's when I had them... In our area (NJ) John Trione is the man and I can put you in touch with him. Lessen the risk so to speak!

I even thought about doing that but was concerned about the noise level.

 

[Bradz]

It is interesting that these few problems seem to happen in salt water. I have been running CMI headers on many boats for years with not one issue in fresh water. I have even had the 525EFI engines. No issues. A race boat with dry tailpipes still has water (salt) running through the headers and tailpipes. The dry pipe exits out a bung and the wet exits at the end of the tail pipe. No difference other than some slight back pressure wet and a lot of noise. The exit of the water make no difference to the header.

 

[MOBILEMERCMAN]

It can be so frustrating. The tail pipe mod is a good way to go. Again I like to look up the pipe immediately after you shut it down while on trailer. The collector area and out 12 or 18 inches should be dry. It is hard to test tailpieces I find looking is easier than trying to pressure test. If there is a bend try to borrow some ones inspection probe. I suspect everything has been checked on the engine. A miss from bad wire, plug or injector can draw water back because of the dead pulse in the pipe.

 

[outriggers]

I just replaced a set of 525 headers. The new set had a different fitting on one side. After some phone calls I was told that there is a Mercury mod to route all of the water through the headers and plug and remove the (bottom)bypass hoses to the tailpipes. If you still have bottom bypass hoses you might want to look into this some more. Doug

 

[MOBILEMERCMAN]

Doug , Did they reference a bulletin number?

 

[Geronimo36]

I just replaced a set of 525 headers. The new set had a different fitting on one side. After some phone calls I was told that there is a Mercury mod to route all of the water through the headers and plug and remove the (bottom)bypass hoses to the tailpipes. If you still have bottom bypass hoses you might want to look into this some more. Doug

Since water tends to take the path of least resistance that makes perfect sense to me!!!

I often wondered why they did that to begin with, I thought it was unessary and could starve the header of water on the high spots and bends.

It is interesting that these few problems seem to happen in salt water. I have been running CMI headers on many boats for years with not one issue in fresh water. I have even had the 525EFI engines. No issues. A race boat with dry tailpipes still has water (salt) running through the headers and tailpipes. The dry pipe exits out a bung and the wet exits at the end of the tail pipe. No difference other than some slight back pressure wet and a lot of noise. The exit of the water make no difference to the header.

Believe me, it's not just a "few".....

Someone had suggested the internal flappers going bad and causing reversion while the engine was running. If you have dry pipes you eliminate the flapper and the possibility for reversion, epecially with a big cam.

Yes, water still runs thru the header and a leak will still cause a problem...

I've seen problems in fresh and salt water boats, it's not isolated... Salt a little worse cause the salt crystalizes near the weld's and cracks them, especially by the collector which usually drains out when you shut the engine down so the mosture evaporates and you're left with salt to expand and mess up your mojo!

 

[Indy]

It is interesting that these few problems seem to happen in salt water. I have been running CMI headers on many boats for years with not one issue in fresh water. I have even had the 525EFI engines. No issues. A race boat with dry tailpipes still has water (salt) running through the headers and tailpipes. The dry pipe exits out a bung and the wet exits at the end of the tail pipe. No difference other than some slight back pressure wet and a lot of noise. The exit of the water make no difference to the header.

I've known three 535 boats, they all had the problem, big bucks repairs too.

 

[outriggers]

My 525 only had 49 hours on it, cyls 7&8 but I bought it that way. One side had a pin hole in a collecter but this boat also had exahuast diverters. A No-No as per Mercury Racing. Donnie at Offshore Performance has been a big help. I put the repaired headers back on after JC Perf totally rebuilt it. I ran it once on the hose and couldn't sleep at night thinking of trashing Jeff's work and my money. So new CMI's, ouch. I see if I kind find more info. I was told it was for more cooling. Doug