Anti-Freeze in the Oil ? MCM 170

[NascarNHIS]

Mercruiser MCM 170, 3.7 L, 224 cubic inch inline 4-cylinder. Alpha 1 stern outdrive

I have read this is a classic problem with these motors most often caused by, Cam Seal at water circulator pump and would need the seals and possibly Speedy seal on the crankshaft. My question is I did a 17psi leak test that sometimes holds pressure and occasionally fails/leaks down. I pulled the plugs and they all look good a brow/gray color. I did not find any liquid in the cylinders. I did a compression test and found 150, 140, 90,100 psi. That is what concerned me.

Before I tear down the motor and replace the head gasket can someone tell me the odds of it possibly being that AF is coming from the head gasket or do I have both head gasket and cam seal issues? (I know it could be cracked block or head but I’m trying to stay positive). I am not overly concerned about the exhaust elbow gasket or exhaust manifold or gasket because I will change them if I do the head gasket.

Note. - it is defiantly AF in the oil not fresh water (could possibly be a mix but defiantly has AF in the oil).

Also this may sound silly but I cannot find the weep hole on the starboard side coolant circulator pump. Does anyone have a picture or explication of where on the pump the weep hole is located?

Bottom line is a failed leak down tests and failed compression test indicate a head gasket issue. I may also possibly have cam seal issue or should I still be concerned about exhaust manifold.

Thanks in advance.

 

[Scott Danforth]

is this a new problem on a boat you have had for a while, or a new to you boat with the problem

the 470 suffers from both problems as they are common

as little as a 10 degree over-heat will cause it to spit the head gasket. based on compression, I would assume you have a head gasket issue. use only Mercruiser head gaskets

the speedi sleave is also common (however they also pass pressure testing. however if you turn the motor over while pressure testing, it will leak)

check the water pump weep hole. if someone plugged it (a screw is common), then its been leaking for a while and now its pushing water in the oil.

 

[NascarNHIS]

Thank for your reply. This is a new boat to me. It has sat for two years prior. I flushed the gas tank and rebuilt the carburetor. I ran it on muffs in the driveway quite a few times without issue. I checked the oil before my first test run on the river and it was nice and clear. I monitored the heat gauge both in the driveway and on the river and it came up to 160 but I dont relay know if that is any ware near accurate. I checked the engine and it never "seamed" hot to me, for what that is worth.. On my first run in the river after about 10 min. after a short WOT run I took off the doghouse just to look and noticed milky blow back from the valve cove and idled back to the dock. Engine ran and sounded fine to me.
Can you tell me, looking at the from the front of the engine, is the weep hole at 6 oclock or what is it next too ?

 

[Scott Danforth]

see post #13 for a pic of the location of the weep hole https://forums.iboats.com/forum/eng...aded-merc-3-7-470-engine-problem-water-in-oil

with a new to you boat, especially one that sat for 2 years you did all the other maintenance before going out...... correct? such as pulling the drive , performing an alignment, inspecting the gimbal bearing and u-joints and changed the bellows? you also change the raw water pump?

hold on the alignment, as you may need to pull the front mount to pull your water pump apart.

I would start getting parts vs using the motor.

 

[NascarNHIS]

weep hole diagram is just what i needed. I will pressure test and spin the motor next week. Yes my shift cable bellows is cracked so a new cable , water pump, Bering and bellows kit are on the list. I will do the head gasket first before I work on the back in case it is more than just a gasket.

 

[NascarNHIS]

After looking at the diagram I found where the weep hole should be. Unfortunately a previous owner has plugged the weep hole with some JB-Weld or some similar material, they then painted the area with black paint so it was very hard to find. I now know at least one of the seals was bad and not fixed and I am now certain the second seal has failed.

My trouble shooting also disclosed that it is failing a cylinder compression test. 100, 90, 145, 150 psi. So I assume I have a bad head gasket (or cracked head/block)

I think I will now call the boat officially JUNK. I do not want to do seals and head gasket to find other issues. I will sell it for parts and recover what I can.

Thank for your help, this is just the way the old boat game goes sometimes.