Onan Oil Mystery Water

[gr8legs]

Greetings all,

We have an Onan 12.5 KW 4-cylinder natural gas power plant as our standby power source.

It usually lives under a rainproof cover and has been trouble free for years. We are having the house painted and I removed the generator cover so the painters could more easily paint the siding behind the generator.

It rained quite a bit whilst the gennie was not covered. When I fired it up for its monthly test it started right up, sounded fine and then died after about 10 seconds.

Checking the oil dipstick the crankcase seemed to be overflowing with a whitish oil/water emulsion. Ugh.

So, nothing ventured, nothing gained. Trying to salvage the unit I drained the oil and the crankcase had a couple of gallons of water along with the oil. Double ugh.

I replaced the filter, poured in enoiugh oil to get onto the dipstick and cranked her over. Eventually, after a lot of wheezing and other unpleasantness she started running and eventually sounded pretty normal. I figure the residual water that was in there after draining will be diluting and contaminating the oil so I will run it for a while to get all the water suspended and then drain and refill with fresh oil again - along with another filter change.

So, now to my question: How did all that water get into the crankcase? There's no obvious open filler neck. PCV valve or other place for rain to infiltrate into the crankcase.

I'd like to avoid such unpleasantness in the future but so far I'm stumped as to the water source. Any ideas?

Thanks in advance,

Stu

 

[matthewsx]

Most likely through the air cleaner or exhaust. You should be ok with the oil changes and make sure to put a tarp over it if you need to leave the cover off again. I wouldn’t try to change anything in there since airflow is pretty important and should be designed for that.

One thing the standby generator salespeople don’t really tell you is about the need to check oil if the unit is running for more than a day or two. The four cylinder models should be better but I’ve had v-twins burn up from running too long without a rest. If you have a long outage you should be prepared to at least check, and probably change the oil every few days. Especially if your unit is out of warranty. Also shut it down for a few hours during the day if you can.

Cheers,

John - Former standby generator tech.

 

[mksj]

Like the Onan and Kohler generators. I am also thinking that it was probably the exhaust manifold, I put in a few generators and had the end of the exhaust facing down. If it has a flapper cover check that it is closing. Just to be safe, pop the radiator cap and make sure their is no oil in the coolant water, a failed gasket can dump a lot of the coolant into the motor oil.

 

[gr8legs]

Especially if your unit is out of warranty.

Thanks for that, I'm happy it is running again.

Warranty??? The previous owners probably ran it out of warranty 30 years ago

Thanks again

Stu

 

[gr8legs]

Just to be safe, pop the radiator cap and make sure their is no oil in the coolant water,

Definitely no oil in the radiator coolant ~ the unit is air cooled

Thanks!

 

[Tozguy]

A couple of gallons of water in the crankcase is a lot of water. It is hard to imagine that much water getting in there accidentally. How well do you know the painters?

 

[Downunder Bob]

Could it have got in through the exhaust pipe? do you have a picture of the unit?

 

[Latinrascalrg1]

A couple of gallons of water Inside any motor world have hydro locked that engine up tight enough to break major parts!

 

[john.k]

Provided you can get the motor hot,the water will all evaporate from the oil. Ive seen cars where the oil looked like milk from short runs in cold weather.There is a trick to draining water,just unscrew the sump plug enough for water to drip out,then leave it for a few hours,when oil starts to drip,tighten it up again.Water wont hurt the motor if its not left for weeks.

 

[Cadillac]

Definitely no oil in the radiator coolant ~ the unit is air cooled

Thanks!

That narrows it down. A air cooled engine can only get water in the crankcase acouple ways.
One is through the carb. Water gets into the carb fills the carb and intake. If the intake valve isn’t closed the water will flow into the cylinder and eventually the water will seep past the rings and mix with the oil.
Quicker way would be the exhaust. Water goes in the muffler ,in the cylinder washes out the rings and goes into the crankcase.
Being a 4cyl the chance of having a valve always open is great so that’s most likely how it happened. Yes running a air cooled for hours and hours could produce some moisture in the cases but filling the engine would not happen. I would run the engine through some heat cycles to try and evaporate any moisture in the cases and do a oil change again. Then get some flappers or covers for the exhaust so it won’t effect the engine when running.