gas in oil?

[texasvet54]

I have a 250 HP Mercruiser with under 300 hours on it and I just drained and replaced my engine oil. Instead of the 5 qts. that I installed last year, i have 7 or 8 quarts of something that is obviously not entirely oil. This happened last year when I replaced the oil for the first time. I took last years old oil to the local Mercury shop and I was told that it was definitely not water in the oil.

The old oil is light black in color and has a hint of a smell of gasoline in it. Last year I let it set for a few weeks after removal and I noticed no separation whatsoever. I might add that I only have 12 hours of engine run time between now and last year's oil change as the engine is on my houseboat that mostly sits in the slip.

I have a raw water system and I have noticed that my engine never gets very hot while running. I have worked on cars for many years and I was wondering if maybe I have a cylinder that is not firing and the gas is flowing past the rings and dripping into my crankcase?

Any thoughts?

 

[GA_Boater]

Re: gas in oil?

A bad mechanical fuel pump diaphragm can cause that problem and gasify the oil much faster than a dead cylinder.

BTW - PM a Mod and ask them to move this thread out of the outboard section to the MerCruiser section.

 

[Don S]

Re: gas in oil?

If you are concerned about a cylinder being bad, do a compression test.
Since you say it runs cool, that could be part of your problem. Does it have a thermostat in the engine? It should have. You should be running around 160? to 175? under load.
'
'It would also help if you posted some engine information. Serial number would be best. Is the engine carbed, fuel injected? year?

 

[texasvet54]

Re: gas in oil?

A bad mechanical fuel pump diaphragm can cause that problem and gasify the oil much faster than a dead cylinder.

BTW - PM a Mod and ask them to move this thread out of the outboard section to the MerCruiser section.

Thanks GA Boater. I'll be at the boat this evening. Now that you mention it, I did have an old Chevy station wagon that had a bad diaphragm that caused the pump to be low on fuel pressure.

texasvet

PS Sorry to all if I posted in the wrong forum.

 

[texasvet54]

Re: gas in oil?

If you are concerned about a cylinder being bad, do a compression test.
Since you say it runs cool, that could be part of your problem. Does it have a thermostat in the engine? It should have. You should be running around 160? to 175? under load.
'
'It would also help if you posted some engine information. Serial number would be best. Is the engine carbed, fuel injected? year?

Thanks Don S,

I'll try to get my son to help me with a compression test this weekend. I'll have to hunt around for my guage, it's been a while since I've been a shade tree mechanic, but I know I have one somewhere.

Also, the engine is carb'd and I had the Mercury shop put a rebuilt carb on the engine when I bought it as the old carb was shot. Is there any way that the float could be set wrong and that be my problem. BTW, the rebuild came from Mercury, supposedly.

And, yes it has a temp gauge. I checked the sending unit per the service manual and it had the correct resistances. Also, if I take the wire off the temp sending unit and short it, my meter on my console pegs indicating that my signal is making it to the gauge on the console.

texasvet

 

[Don S]

Re: gas in oil?

I didn't ask about the temp gauge, I asked about the thermostat. That is the part that controls the engines temp and allows it to warm up.'

I have tried using 3 different rebuilt carbs from Merc, and none of them were worth anything and the engines actually ran worse. I don't know which back yard shop does their rebuilding, but they don't have a clue. Missing parts, bent parts, you name it. The first one was a Quadrajet. Flooded really bad with it. Pulled it apart, no float. Not a defective float, there wasn't one in it.

You have yet to give a year or any model ID for your engine, nothing more than 250hp, and that sure doesn't tell us much Which is why I asked for a serial number. Year of the boat may not be the year of the engine.

I also forgot to add the service bulletin for the compression test.

View attachment 97-25 Compression Test.pdf

 

[Volphin]

Re: gas in oil?

The first one was a Quadrajet. Flooded really bad with it. Pulled it apart, no float. Not a defective float, there wasn't one in it.
View attachment 145233

This is unreal! :facepalm: Also agree with Don on serial number. It is key info we need.

V

 

[texasvet54]

Re: gas in oil?

Thanks guys,

I'll get the s/n this evening when I go out there.

I put new oil in the engine the other night and ran it for no more than 10 seconds. Here's a picture of the new oil that I pulled out this morning through the dipstick. I was expecting it to look quite a bit lighter. Also, I think that it has a hint of gas smell in it.

Also, I have an electric fuel pump mounted on the engine so a easy fix of replacing a bad mechanical fuel pump is now out.

texasvet

 

[Don S]

Re: gas in oil?

10 seconds shouldn't be enough to get gas in the oil again. It might take a couple changes of oil and filter to get it back to normal.

Since you have an electric fuel pump, might want to check the fuel pressure too. Is this an OEM pump installation? It doesn't run with the key on and engine not running does it?

 

[texasvet54]

Re: gas in oil?

10 seconds shouldn't be enough to get gas in the oil again. It might take a couple changes of oil and filter to get it back to normal.

Since you have an electric fuel pump, might want to check the fuel pressure too. Is this an OEM pump installation? It doesn't run with the key on and engine not running does it?

Hello Don,

I went by the Mercury guys this afternoon and showed them the old oil that I removed and the new oil that had 10 seconds on it. They agreed that it sure smells like gas in it and that it is definitely not water. They also suggested checking the pressure from the electric fuel pump, which I don't have the gauges for, and checking my compression. As a last resort, if the compression checks good, I'll remove the carb and let them take a look at it.

One thing that I agreed with them on is that if the carb has a problem, why is the engine starting so quickly, running smoothly and never flooding?

Also, my engine s/n is 0L060433

texasvet

 

[texasvet54]

Re: gas in oil?

I didn't ask about the temp gauge, I asked about the thermostat. That is the part that controls the engines temp and allows it to warm up.'

I have tried using 3 different rebuilt carbs from Merc, and none of them were worth anything and the engines actually ran worse. I don't know which back yard shop does their rebuilding, but they don't have a clue. Missing parts, bent parts, you name it. The first one was a Quadrajet. Flooded really bad with it. Pulled it apart, no float. Not a defective float, there wasn't one in it.

You have yet to give a year or any model ID for your engine, nothing more than 250hp, and that sure doesn't tell us much Which is why I asked for a serial number. Year of the boat may not be the year of the engine.

I also forgot to add the service bulletin for the compression test.

View attachment 145233

Don,

Thanks for the service bulletin. The Merc shop told me to just remove the wire that goes from the coil to the distributor cap, not to ground it. I told them that I had blown up a solid state ignition module on an old Ford by doing that and they said that removing the coil wire wouldn't do that.

As far as the temp, I did replace the thermostat with a new one and I checked the temperature sending unit as I stated earlier.

Thanks,
texasvet

 

[Don S]

Re: gas in oil?

You want to go to ground with the coil wire, with it just removed, you can damage things and crack coil towers. That's why the manuals even recommend you ground the coil wire. Just pull your kill switch lanyard, does the same thing, kills spark to all the plug wires.