96 Yamaha 50hp 4 stroke - "milky" oil

[pplkook]

All

For all intents and purposes, my 96 Yamaha 50hp 4 stroke runs fine, doesn't overheat, etc. The problem I am seeing is when I change the oil, it comes out looking like a chocolate milkshake. After the oil change, it takes a while (4 trips or so) for this to redevelop.

Any ideas? I am thinking water is getting in the oil somehow, but it can't be much volume. I am going to do a compression and leakdown test this weekend.

Thanks in advance

Jack

 

[Ober51]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

From what I've read around here it sounds as if your lower unit seals need to be replaced. Again, I don't know crap, but after reading these type problems over and over, that's what it seems like.

 

[pplkook]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

Thanks for the reply ober. I did some searching around for an hour or so, and didn't run across that as a potential cause. Thinking of a cracked block/head or a head gasket vs. changing the lower unit seal, I will take the later. I am still scratching my head "how" the lower unit seal would allow water intrusion into the powerhead though.

Anyway, any more thoughts and/or suggestions are appreciated

Thanks

Jack

 

[pplkook]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

bump for some love?

 

[Silvertip]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

A lower unit problem will not put water in the crankcase. Leaky head gaskets, cracked head, and cracked block will allow intrusion. Restricted exhaust perhaps could allow this to happen.

 

[pplkook]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

Silvertip

I thought it was too good to be true. I am going to do a leakdown test this weekend. Hopefully it is only a head gasket and not a cracked head and/or block.

The only good new is that I have a donor motor, so if I need to do some rebuilding I can pull parts from it.

Once I get the results from the tests, I will post.

Thanks

Jack

 

[mdunn]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

Not trying to hi-jack your thread just sharing my experience and bumping it back to the top
I?ve seen this twice now in my 2002 F115 that only has 300 hours. Once about a year ago and the second time just recently. It runs great and a leak down test shows minimal leakage. 3% or less.
I usually don?t idle around much with the 115 as I have a 8 hp I use for trolling but the two times I have seen my oil go milky happens to be when I have idled it for quite a while. Coincidence? I don?t know.
After the 1st time I changed the oil and put a new t?stat in and didn?t see a problem until just a few weeks ago after doing routine maintenance including a new timing belt, t?stat and oil change.
I took it out for a test run and did idle around quite a bit although I ran it above 4000 for the last half hour.
My wot is 5900 rpm?s.
Can there be a leak between the cooling system and crank case that a leak down test doesn?t show?

I?m thinking of raising my motor up one hole and seeing if that makes a difference as I think it does sit pretty low in the water at idle.
I?m interested to see what your leak down test showed.

 

[mdunn]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

Hello Jack.
Any resolution to your water intrusion problem?
How did your leak down test go?

 

[pplkook]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

Sorry - just did the compression test this weekend, with the equipment we had we couldn't do a leakdown test - any good instructions on holding the engine at TDC in gear? Car is easy, but the prop kept wanted to turn over, so accuracy was impossible.

Anyway compression was 185-195 across all 4, but that doesn't mean much.

Idling? Yes actually, 3 of the last 4 trips I trolled all day at the lake, and two trips in the ocean where the motor idled or ran at near WOT all day. My readline is roughly 5500.

 

[Arny]

Re: 96 Yamaha 50hp 4 stroke - "milky" oil

would have changed the gasket between powerhead and rigg first of all.Also check your thermostate.