Gasoline in oil pan

[texasvet54]

Hello All,

I found a message on iboats saying to do a search for "making oil" and I now have a pretty good handle on what has happened to my mercruiser.

Basically, I needed a new carburetor back in November for my 1998 Mercruiser 350cid. So, a local shop ordered and installed a remanufactured one for me to the tune of almost $800 installed. The stalling when putting into gear problem was solved and I thought that all was right with the world. A few weeks later I noticed that my oil looked a little thin so I put new oil in but I left out one quart to see if the level was going to rise. Well, after running the engine through the winter every so often for a total of three hours, my oil is again thin and it is above the full mark on the dipstick. I pumped about a quart out and put it in a clear plastic jar and headed over to the marine shop. They instantly told me that the oil smelled like gas, something that I had suspected, but they were at a loss as to how it could get there. I should add here that both of the guys were young and said that they only worked on outboard and that the owner would be in Monday to take a look at it.

Well, after reading all of the posts about gas in one's oil and looking at the timeline for when my problem started, it looks to me like I got a bum carb. It's either that or the fuel pump, but I'm not looking in that direction yet because the problem started after a new carb was put on. So, I'll be talking to the owner on Monday about getting me a new carb.

My questions to those more experienced in this area than me are, is there any chance that I've damaged any seals or bearings in the engine by running it for a few hours with gas in the oil? The engine never got hot and the oil pressure was always over 30. Also, when I get a new carb on, should I change the oil and run it for maybe half an hour or so and then change the oil again in an effort to wash out any gas?

Any other recommendations would be appreciated.

Thanks,
TexasVet

 

[HT32BSX115]

Re: Gasoline in oil pan

Howdy,


It's fairly unlikely that your carburetor is causing your fuel in oil problem unless it;s literally DUMPING gas in the engine AFTER you shut down. If it was doing it while running, it would literally blow incredible amounts of black smoke......and probably wouldn't run very long and would foul the plugs in short order.


More likely your (engine driven) fuel pump has a leaking diaphragm and is dumping fuel directly into the crankcase...

Although remotely possible.....You probably didn't damage the engine.

[Back in the "old" days up in the arctic and other cold areas, aircraft engines had oil "diluters". It was set-up so the pilot would pull a knob to literally "dump" avgas directly into the crankcase in a running engine immediately before shutdown in freezing weather.

The avgas would effectively be mixed with oil so that it would be diluted for the next morning (cold-soaked) start. After startup, the engine would be warmed up and when warm the pilot would take off normally. After the oil temp got up to "normal" the gasoline would start to evaporate and after a while would be completely gone.....it didn't hurt a thing.....(unless there was a spark!!!)] (they don't do this anymore!!! they just use multi-grade oil or pre-heating)



Just change the oil and get a new fuel pump. ....... then get after the carb problem (if you have one)

You don't need to worry about any residual gas in the oil.......... It will evaporate out.


Regards,


Rick

 

[Bondo]

Re: Gasoline in oil pan

my 1998 Mercruiser 350cid.

Ayuh,... Is the Block a 98, with an Electric fuelpump,..??

 

[texasvet54]

Re: Gasoline in oil pan

Rick,

Thanks for the reply. I'm going to be heading out to the boat this afternoon to take a look at how hard it is to pull the fuel pump. The only thing that concerns me is that it does appear that the problem started after the new carb was put on. One other note though, when I start the boat up, it does spin a few times before ignition and for the first minute or so after startup, i get some pretty white fumes from my exhaust then everything looks fine.

Thanks,
texasvet

 

[texasvet54]

Re: Gasoline in oil pan

Bond-o,

I'll be at the boat this afternoon and looking at the fuel system. Since it's now starting to get into the 70's and 80's, I'm in Texas, I'm going to thoroughly examine the engine and bilge. I'm pretty sure that it is a mechanical fuel pump, but I'll look for sure today. If it's electical, then I'm back at the carb I guess.

It's an 87 boat so I have lots to learn. I have to draw up a wiring diagram since none was provided by the prior owner. Looks like I have a new hobby along with golf.

Thanks,
texasvet

 

[HT32BSX115]

Re: Gasoline in oil pan

Basically, I needed a new carburetor back in November for my 1998 Mercruiser 350cid.

Um.....you said the boat is an 87......and the engine is a 98? If it's a 98 it may have an electric fuel pump. If it's a 97, it may be a mechanical engine driven/mounted pump.


So......what it is REALLY?

 

[texasvet54]

Re: Gasoline in oil pan

Well, I just got back from the boat. The verdict is in. It's an electric fuel pump that is mounted on the left side of the engine as you look at the front.

So where does that leave me? The engine seems to run fine, at least when I had the new carb put on and changed the oil. Now, there is no way I'm running the engine until I find this problem.

Here's some more food for thought: I've got a small leak from the aluminum hull that makes the bilge pump run about once a week. I started noticing what seemed like some fuel in the bilge water probably around the time I put the new carb on in November. Today, I got down in the bilge and looked under the engine for the first time and the bottom of the engine, right down to the oil pan, is dry and clean as can be. I'm going to do some more looking around, but now I wonder if I have a leak in my fuel line or connection to the fuel pump to compound my problems.

I've only owned this boat for 5 months now and I'm beginning to think that I have a lot of work in my future.

texasvet

 

[HT32BSX115]

Re: Gasoline in oil pan

Sounds like you have some trouble-shooting to do!

 

[texasvet54]

Re: Gasoline in oil pan

I just came back from the marine shop and they tell me that there is no way that the carb could leak a quart of gasoline into the oil in a few hours of run time unless the engine was running like crap, which it isn't.

Also, I took one plug out and it looked normal and I took the pcv valve out and it works fine.

I'm going to check the compression in each cylinder in the next few days and then report to the shop what I find. I'll be surprised if it is the rings, because the engine only has a few hundred hours or so on it.

If anyone has any ideas, I'd sure like to hear them.

texasvet

 

[Bondo]

Re: Gasoline in oil pan

If anyone has any ideas, I'd sure like to hear them.

Ayuh,... Got any dockside Enemies,..??

With an electric fuel pump,...
There's just No way for it to be coming from the carb...
Even without rings, the plugs would be Black, 'n carbon fouled...

 

[wifisher]

Re: Gasoline in oil pan

You say that the quart of gas got into the crankcase after 3 hours of running through the winter. How many times was the engine run? It sounds to me like the gas is leaking into the crank after shutdown (or before startup). That would explain the white smoke at startup. And the gas in oil with only three hours of running. Is the fuel pump running when it shouldn't be, coupled with an overfilled bowl? I would check the wiring to the fuel pump, the fuel pressure, and the float level. I don't think it is compression related, or you would hear it when running. Maybe start with fresh oil, and run it under load for a few hours and see if it is making oil when being used, or just when sitting and starting/stopping?

 

[texasvet54]

Re: Gasoline in oil pan

Ayuh,... Got any dockside Enemies,..??

With an electric fuel pump,...
There's just No way for it to be coming from the carb...
Even without rings, the plugs would be Black, 'n carbon fouled...

I only pulled one plug and it looked fine. Not like new, but pretty clean.

texasvet

 

[texasvet54]

Re: Gasoline in oil pan

You say that the quart of gas got into the crankcase after 3 hours of running through the winter. How many times was the engine run? It sounds to me like the gas is leaking into the crank after shutdown (or before startup). That would explain the white smoke at startup. And the gas in oil with only three hours of running. Is the fuel pump running when it shouldn't be, coupled with an overfilled bowl? I would check the wiring to the fuel pump, the fuel pressure, and the float level. I don't think it is compression related, or you would hear it when running. Maybe start with fresh oil, and run it under load for a few hours and see if it is making oil when being used, or just when sitting and starting/stopping?

I've been trying to run the engine every week for 10 or 15 minutes. It's an electric fuel pump and if it's running without the ignition turned on, I have a problem, but I'll check it out. As far as an overfilled bowl, that was my first guess, but I haven't gotten that far with my troubleshooting.

I hit the marine shop up with the following theory:

The water temp was in the 39 to 45 range when I ran the engine for 10 to 20 minutes at a time. The block doesn't heat up as quickly as a car does due to the conduction of the temp through the hull and outdrive. This allows the gas to slip by the rings while it is cranking and then when it starts up, the white smoke is a result of the rings not getting up to operating temperature and making a good seal. He didn't seem to agree with my theory.

So, I'm going to change the oil and filter in the next few days and run the engine for a couple of hours and see what the oil looks like then.

One thing I will say abou the shop I'm using for my maintenance. They are always pleasant and always willing to answer a question from this shade-tree mechanic.

texasvet

 

[texasvet54]

Re: Gasoline in oil pan

Here's the latest. I got down on my back in the bilge and replaced the oil filter and I pulled the plug on the oil pan instead of pumping it out from above. I then added 5 quarts of new oil and ran it as follows:

RPM Oil Pressure Minutes Ran

1,000 27 5
1,500 29 5
2,000 37 10
2,500 40 10
3,000 40 2

So, I ran it for 32 minutes and at no time did it produce any white smoke. I might add that it was 83 degrees today. The engine seemed to run smooth as can be. The only thing I noticed was that when coming down from 3,000 rpm, it sat around 2,000 rpm for about 30 seconds before it dropped down to 1,000 rpm.

Also, i checked the dipstick 20 minutes after I shut her down and the oli was still at full and looked pretty clean. I'll be out there tomorrow to run it again and see what happens.

One other thing. I still can't get the temperature gauge to move off 0. I question why the temperature sending unit is mounted in the thermostat housing where it will continue to read the lake water temperature which is currently just above 60 degees. Wouldn't it be better if the unit was mounted down in the block since I have an open cooling system?

texasvet

 

[Bondo]

Re: Gasoline in oil pan

One other thing. I still can't get the temperature gauge to move off 0. I question why the temperature sending unit is mounted in the thermostat housing where it will continue to read the lake water temperature which is currently just above 60 degees. Wouldn't it be better if the unit was mounted down in the block since I have an open cooling system?

Ayuh,... It's in the T-stat housing because the hottest water in the motor, is Just under the T-stat...
The raw water only sees the very front/ top area of that housing...

 

[fastimz]

Re: Gasoline in oil pan

My .02 cent. I am in the belief that the carb is leaking down after you shut the engine off. Does it take a few extra turns to get it started teh next time you use it? If so its refilling the bowl on the carb before it will fire up. After it runs for a while and you shut it down, try to restart it after about 15-20 minutes. If the carb is leaking down then it will be really hard to start because the engine will be flooded.

 

[texasvet54]

Re: Gasoline in oil pan

Ayuh,... It's in the T-stat housing because the hottest water in the motor, is Just under the T-stat...
The raw water only sees the very front/ top area of that housing...

Well, the block is pretty warm, yet my temp guage doesn't move. I take the wire off the temp sending unit and ground it and the meter pegs. So, my wire to the guage and the guage are good. I took the temp sending unit out and put it in hot water and the measured resisitance is within tolerance according to my service manual. So, when is my guage going to start reading any engine temp?

texasvet

 

[texasvet54]

Re: Gasoline in oil pan

My .02 cent. I am in the belief that the carb is leaking down after you shut the engine off. Does it take a few extra turns to get it started teh next time you use it? If so its refilling the bowl on the carb before it will fire up. After it runs for a while and you shut it down, try to restart it after about 15-20 minutes. If the carb is leaking down then it will be really hard to start because the engine will be flooded.

When I started it yesterday, it started right up. I'm going to run it again this afternoon and I'll try what you suggested.

Thanks,
texasvet

 

[texasvet54]

Re: Gasoline in oil pan

When I started it yesterday, it started right up. I'm going to run it again this afternoon and I'll try what you suggested.

Thanks,
texasvet

Well, I ran the engine today for 20 minutes and so far so good. No increase in volume above the "add" line on the dipstick. I waited about 15 minutes and it started right up. I'm still at a loss about the gas in the oil, but maybe my theory of running it for short increments when it was in the teens and twenties was the issue.

texasvet

 

[texasvet54]

Re: Gasoline in oil pan

Ran the engine again today and everything looks good. I'm going with my theory that when I ran the engine for short times throughout the winter, I had some gas pass by the rings. Maybe not, but I'm sure glad that everything looks good at this point.

texasvet