Mercruiser 170, 1985 year. Oil pressure dropped to 0

[glennj3]

Very odd thing, for the first time in years my boat is fixed and running great. Went out 2 times ago, hit a log, very hard but driving relatively slow. Struck several times before I could get out of this shallow area.
While driving to a sandbar where other boaters were hanging out I noticed my oil pressure was at like near 0 ! Engine sounded like normal. After turning engine off, later when ready to leave I noticed the ignition switch did not turn on anything under the dash (lights, instruments, fuel gauge etc.) the engine would do nothing. After getting home the first thing I did was look under the dash, found a large red wire with an in line fuse, it was burned. Replaced it and everything fixed!
So I went out again last week, no problems except after running a while I saw at idle the engine oil pressure was again near 0. I have a second gauge direct to the engine, it was showing the same pressure like about 5 lbs. Again the engine sounded normal. Oil pressure goes up at higher RPM but not at 40 like it used to be.
It seems to be taking on some water in the engine compartment also with oil leaking and floating on top of that water. Not a lot but enough.
The outdrive looks good, the prop does not look like it hit anything.
Sure would like to know what to look for?
Thanks for any assistance.

 

[Bt Doctur]

check the oil level and condition for fuel contamination

 

[glennj3]

I have a new oil water separator and seperate fuel filter. The oil level measures near full so it is not losing enough for me to measure with the stick.

 

[alldodge]

1985 170
have a second gauge direct to the engine, it was showing the same pressure like about 5 lbs.

If your second gauge is mechanical you should be good.

What weight oil are you using?

If you using straight 40W or multi 10W40 something, then just go boat and don't worry about. I think your motor is just getting tired. Manual usually list 4 psi minimum at idle

 

[glennj3]

Wow, seriously? My main concern that made me concerned is the sudden change in pressure.
at this age I guess I’ll drive it until it dies permanently, just too often doing repairs!

 

[glennj3]

I don’t get the connection?

 

[alldodge]

Your looking at gauges, and the issue can also be in the gauges. Even mechanical gauges can be off a bit. If both gauges were on the motor and both changed lower at the same time, then there may be more of a concern. If both were not on at the same time and one added to check the other, then it may not be so much un my opinion.

If they were both on and both changed, maybe the oil pump got a small chuck of something which scored it in one spot, maybe something happened in the bypass valve. I'm just guessing.

 

[TurtleTamer]

I have a new oil water separator and seperate fuel filter. The oil level measures near full so it is not losing enough for me to measure with the stick.

I believe he was talking about fuel dilution in the engine oil. Running excessively rich, bad rings, lugging, etc can cause fuel to get past the rings and into the oil. This will dilute it, lowering viscosity and therefore dropping pressure. In essence, the lubrication system could be fine, but is not producing pressure because of the low viscosity. If your level is staying constant, it's probably not the issue. To check for fuel in the oil, just smell the oil on the dipstick. It'll smell like fuel if it's there.