ckin62

I have had this issue on and off with one of my 'close to stock' Hp500s. It will run a couple times and oil looks great then, MILKSHAKE. I have pressure tested everything several times. I have replaced numerous intake gaskets and intakes. I have made sure the intake bolts were not bottoming out. I have use thread sealer even on blind threaded holes. New oil cooler and pressure tested exhaust. The only thing I have not replaced has been the exhaust due to pressure testing fine. I know that a pinhole can open up at temp and leak, but can that cause a large amount of water to get into the oil? I run the HP t-stats and the oil temp runs about 220 on the gauge. Water pressure is from 0 to 25 max. and oil pressure is 40-60 depending on rpm. I should add that I have changed head gaskets a couple times and made sure the gasket I used have been correct for the block and heads. I have never found anything that I could say, yep that is where the water came from.

PROTOTYPE28

I would bet its the exhaust with a hair-line crack and it swells when it gets hot. Switch the exhaust from one motor to the other and that will tell you if its an exhaust problem or not.

hullofjustis

iTrader: (1)

Did you change the cam on the nearly stock 500's? Are they cmi exhaust or gil exhaust? Gils with the hp 500's had some reversion issues because of tailpipes could be to short or not enough rise. If they are cmi's pressure test them with piping hot water iin them

wannabe

I would bet either a bad head gasket or a cracked head/block. Do a compresion check when warm.

Wannabe

Young Performance

Are you sure that the water pressure is only getting to 25 psi? I had one in the past that would do fine as long as we stayed under 4500 rpm. The reason that it was 4500 rpm was that the boat was going fast enough at that rpm to increase the water pressure enough so that water was creeping past the head gasket. There was the absolute slightest sign on the gasket that water was creeping. It was extremely difficult to spot it. These were Fel Pro head gaskets.

Another similar but related problem could be if either the heads or block are not perfectly flat. You could have a dip, or low spot, in either one, causing improper compression of the head gasket. The only way to tell is to remove the heads and place a machinists straight edge on them and try to insert a .001 feeler gauge under it along it's length. You must use a true machinists straight edge so that it is absolutely flat. Be sure to check it both North to South and East to West.

Good luck with it. Hope you get it figured out. Let me know if I can help in any way.
Eddie

Young Performance

duplicate

ckin62

The gauge shows 25 max and I'm pulling the pressure point off of the raw water pump. I use to run a water t-stat but saw high spikes in water pressure which would push water past the head gasket. Now I just have an orifice. I have pulled the heads and had them pressure tested. I have also checked the deck for flatness. This is a merc 500 block so something could have moved since I did that. The motor is basically stock with m-1 procharger (4psi max) and head studs. I have have questioned the exhaust before and decided to replace the Gil high raise with the Hardin cyclone system.

cruis

Not sure what year has what manifolds but I have a 97 Baja 302 with twin 454 I bought in Florida, it was in salt water but high and dry its whole life rinsed after being ran.
The Riser that bolts on to the manifold and makes the 90's at the top has a longer inner water jacket that rotted away and was letting water back into the
engine. When running it was never a problem, certain times we stopped it was not a problem. Just depended on if the exhaust valve was open
and I believe it let It back onto the piston and run down threw the rings. I was lucky and found it after about the 3rd or 4th trip after trying various things.
Never had a problem after changing the risers (I believe they are called). So far so Good that was about 5 years ago.

ckin62

I ran the motor for about 20 mins and pulled my manifolds off last night. Number 5's exhaust run was very wet. The heads were recently pressure tested, so I'm feeling confident that the manifold has a leak. This is the first time I have found something that seems to be a smoking gun. After I pulled them, I also noticed that the coating on that manifold's exterior is starting to bubble. This was not the case just a couple months back when I pulled the heads. I'm hopeful I found the culprit.

blindriver

Did you pressure check intercooler for the procharger