Onan CK-S Engine Oil

[desighitter]

I recently got an old Onan/Miller welder. What kind of oil should I use in this old brute?

Mod. # CK-S/259M, Ser. # 55B518817

What I drained out looked almost like automatic transmission oil????

[Keith Kessler]

Hi,

According to the factory engine manual in normal operation, 30F to 90F, SAE 30 Detergent oil. In otherwords, your normal run of the mill modern single viscosity "30" oil would be fine. If the suff that you drained from the engine looks thin, watch carefully after the oil change for an increase in oil level with a likely decrease in oil pressure. Oil pressure must be monitored at running temperature. This applies to CK-S engines with a mechanical fuel pump. If the diaphram is old and leaking, it is thinning your oil with petrol. Watch for this in any old engine with antique rubber parts.

Hope this helps.

Keith Kessler

[desighitter]

Sure enough. After trying to start it, the problem seems to be an old worn out fuel pump. The gas was probably leaking through the diaphram. Any ideas on how I can fix it. Know of anywhere I can get a replacement fuel pump?

[Keith Kessler]

Hi,

It might not be a bad idea to put a gravity feed tank going directly to the carb to verify the unit is all there and working. Be careful and make sure that you don't have leaks. Engine fires are not fun.

www.perr.com is one place to get parts. They seem ok but I have no idea how they stack up with the rest of the dealers. They have been helpful for me so far. I hate to say it but you could also search ebay to see what turns up for CCK parts.

Good Luck,

Keith Kessler

[Billy J Shafer]

Keith is correct about the oil and the fuel pump.The pump was the first place I always looked at when I had gas in the oil.When it leaked the fuel dumped into the oil.I think the pumps are still in the system,you can also try ebay or Bruce may have one.Alot of welders I know would change to a electric pump,then they did not have to worry about being on a job and the pump leaking fuel into the oil.If you do this be sure and get a low pressure pump.Four pounds is the max you can use.

[Gunny]

Yup. Go with an electric if you can.