Grey motor oil

[jcupo6]

I have a 1973 Mercruiser 140 hp 3.0L motor. We just took her out this weekend for the first time. While we were out we checked the oil and noticed that was grey. We ran the boat for about 4 hours before we noticed the oil. The motor ran and sounded great, better than I anticipated actually. We had changed the oil before we went out, and it was the same grey color. The boat sat for a while before I bought it so we figured that was the reason for the color. When we change the oil we took note of the exact level on the dipstick. The new oil has turned the back to that grey color, but the oil level is exactly the same. If there was an water leak somewhere wouldn't the oil level rise, even just a little bit? Any advice would be greatly appreciated.

 

[jtybt]

Re: Grey motor oil

I think contaminated oil is a dead giveaway NOT to buy the boat.

Also, I would rather see old oil in a boat I plan to purchase. New oil... may be trying to hide something.

 

[jcupo6]

Re: Grey motor oil

I think contaminated oil is a dead giveaway NOT to buy the boat.

Also, I would rather see old oil in a boat I plan to purchase. New oil... may be trying to hide something.

Thank you for the input, but I already purchased the boat. I only paid $600 for the boat motor and trailer. I am trying to find out what is causing the contaminated oil, not considering whether to buy it or not.

 

[Bart Sr.]

Re: Grey motor oil

I have a 1973 Mercruiser 140 hp 3.0L motor. We just took her out this weekend for the first time. While we were out we checked the oil and noticed that was grey. We ran the boat for about 4 hours before we noticed the oil. We had changed the oil before we went out, and it was the same grey color. The boat sat for a while before I bought it so we figured that was the reason for the color.

Do you know how long it sat before you bought it???

Best scenario:
This was covered recently and someone said that sitting through temperature variances could build up condensation in the oil pan.Several changes were required to get all of the water out.

Worst scenario:
You have a small coolant leak internally.

Good Luck.

 

[jcupo6]

Re: Grey motor oil

Do you know how long it sat before you bought it???

Best scenario:
This was covered recently and someone said that sitting through temperature variances could build up condensation in the oil pan.Several changes were required to get all of the water out.

Worst scenario:
You have a small coolant leak internally.

Good Luck.

Thanks! I will keep my fingers crossed for option number 1 and change the oil a few times. I believe it sat for 2-3 years and I was told that it was winterized, but obviously I can't prove that. Not sure if that is long enough to build up enough condensation to turn the oil that color. I am going to stick with the theory that if there is a leak my oil level would rise, just because it gives me some hope that this issue is not too serious....

 

[jcupo6]

Re: Grey motor oil

Okay, so here is an update of things we have done in order. We changed the oil again. Bought a new themostat and installed it because the previous owner removed it. Took the boat out again and noticed more water than ever. Took the boat home and did a compression test - 1-150, 2-170, 3-150, 4-120. Great, right... So we took the head off. Gasket looked okay. No cracks, a bit of water in 4. Cleaned everything out and it looked pretty good actually. We did notice that the bolts on the head were rather easy to remove. Put a new gasket on and tightened everything up with a torque wrench. Redid the compression test and got 1-130, 2-130, 3-130, 4-120. Motor ran and sounded solid, but it always had. Unfortunately the oil quickly turned back to the grey color.

So here are my thoughts. Let me know what you think, I need all the help I can get!
1. The head gasket seemed okay, but the bolts did not seem tight enough. Maybe the previous owner changed the head gasket and didn't use a torque wrench when putting the head back on. Could that have been the source of the water, and now it's just a matter of multiple oil changes to clean the milky oil out?

2. I am concerned about the thermostat. Like I said, when we put one in it seemed like there was more water than ever and the motor ran hot. It ran in the red for about a minute before cooling back down. Could there be a leak in the cooling system leaking into the oil? How would I check that?

 

[Maclin]

Re: Grey motor oil

Does the oil level rise at all?

Do you get a lot of blow-by out of the valve cover vent?

 

[myoldboat2]

Re: Grey motor oil

The motor shouldn't run hot before the thermostat opens. Remove the thermostat and check it in a pan of water on the stove with one of those candy thermometers in the water. My 1974 Merc 140 uses a 140 degF thermostat, I suppose yours does, too. If the thermostat checks OK you might have an intermittent blockage in your raw water cooling circuit. If you have a Late Model I sterndrive like I do, you might check the water pocket in the upper unit. That's where I had pieces of old impellers. The really bad part is you never know when the blockage will block, and I don't have an overheat warning.

I recently cleaned a lot of gunk out of my oil pan, without removing the pan. Folks on here have said that with modern oils no gunk should accumulate, but I have no idea what oil the prior owners ran. Anyway, here is what I did. This first step you can skip if you'd rather--I warmed the engine, then put 1/3 can of Seafoam into the oil, ran the engine for 5 minutes and then drained the oil through the oil pan drain hole. (Previously was sucking old oil out the dipstick tube and that never got the gunk out.) A fair amount of gunk came out. Using something like Seafoam scares me (so don't use it if you're not sure), so I then did my best to wash all of it out, along with any remaining gunk. I had gone to Wallyworld and bought 2.5 gallons of SuperTech 10W-30 oil (less than 10 bucks for a 5 quart jug). I refilled with this oil,, ran for 5 minutes, drained. Did that twice more. Then let the oil pan drain overnight. Changed the filter, filled with Mercruiser 25W-40 and test ran it. My original symptom was that the oil pressure was coming up very slowly on start and wasn't going high enough. Figured it was a clogged up oil pump screen. Fixed--good oil pressure now. Anyway, this is something you can do in just a few hours for something like 35 bucks including filter. Then take her out and see if you still get milkshake oil. I even gave all that drain oil to my buddy who has an oil burner to heat his shop in the winter. Good luck, hope you find it. Must admit, I am jealous of a $600 boat, I/O and trailer! How cool is that.

 

[bigskiohio]

Re: Grey motor oil

so what did you figure out?

 

[jcupo6]

Re: Grey motor oil

so what did you figure out?

Well, we ran the motor for a few minutes after we changed the head gasket and the oil still seemed to change rather quickly. It seemed to fast to be from leftover water so we kept searching.... We removed the exhaust manifold and found some interesting problems. It was obvious from rust and corrosion that water was entering cylinder #4 from the exhaust manifold. We filled up the water chamber and could see water leaking which mean the manifold is cracked. We ordered and new one and should have it on tomorrow. With the exhaust manifold off we noticed there was an open tube which looked a bit odd to us. We did some research and found that there should be a flapper valve on the top of the tube. I read that without this valve the motor can run hot, which answers another of my questions. So, hopefully I have all the answers I need and can have the boat in the water worry free this weekend. It has been very frustrating over the last few weeks, and I would like to thank everyone on here who has helped out.

 

[Maclin]

Re: Grey motor oil

Regarding the flapper valve in the exhaust tube, those will melt if there is not enough raw water flow from the cooling system, which is the result of an overheat and not the cause. But if the flapper did melt away in a previous incident then it made it's way on thru the exhaust and could be clogging the exhaust which can put extra strain on the engine.

Also with no flapper valve and engine off the exhaust system is subjected to backwash that can make its way thru that tube and into the riser and exhaust manifold, then on into any open exhaust valves. That could be a source of water in the cylinders.

 

[BAproject]

Re: Grey motor oil

A cracked intake would definitely cause water to leak into the crankcase, or improperly torqued head, or a number of other things. Here's the problem though, if the level of the oil is the same when it is grey as when you first put it in then you must be burning oil or you have an oil leak.

There should be displacement if new water is leaking into the system.

Your compression checks out so I am a bit boggled as to what's going on.

-BAproject

 

[Peter1950]

Re: Grey motor oil

Any time I buy an old car (have had over 20), or boat, I always change the oil right away but I run it with a conservative use of motor flush first. You can take clean looking oil to black muck in 3 minutes. If the can says 5 minutes at idle I run it 3 minutes. Drain it letting it take its time, change the filter. I've NEVER had trouble with this and getting out all that muck just has to be good.
Once you sort the water leak, I suggest you do what I just said. Water makes a horrible lubricant in an engine.

 

[jcupo6]

Re: Grey motor oil

Here is an update...
We replaced the exhaust manifold and the flapper valve and changed the oil. We ran the motor for about 5-7 minutes. The oil did change back to the same color fairly quickly, but there is probably still a ton of water in the system from before. We are hoping a few more oil changes will do the trick. I know for a fact that the exhaust manifold was cracked, so hopefully the water issue is fixed. If there is still a leak somewhere, I really don't know where to go from here. I guess the only other thing would be a cracked block? My buddy is fairly confident that we have fixed the issue, but I seem to be a little more hesitant. I guess after all of the issues we have run into it is hard for me to be confident...