Hello. I went to look at a used Cat304c last night. It is about 10 years old and has over 4000 hours. The machine was generally nice however I had two concerns. First when I attempted to test for blow by I remove the oil cap and I noticed a noticeable amount of air being pushed out of the oil fill hole. There was no smoke but oil was splashing out. My old kubota never did this and it raised significant concern in my mind for blow by especially given the hours. Should I stay away or are my concerns misplaced? second, when the machine was running, the thumb would slowly droop down, yet it would function regularly. Regardless, it didn’t look right and would need to be fixed as a thumb is a big reason I want an excavator in The first place. Does this sound like a big problem that will be costly to fix? Any feedback that you can provide would be much appreciated.
The oil splash is normal. Vapor and smoke smell is what you are looking for when removing removing the fill cap while the engine is running. How the engine starts when cold is another symptom of low compression. A drifting cylinder is most commonly caused by leaky packing. Did you look the thumb cylinder barrel over for dents?
Thanks John. Oil could be splashing from rockers? I didn’t notice and vapor or smoke coming from hole. Air and pressure were coming out of the hole. That was much different vs my old kubota and was noticeably more than my trackloader, although, my loader has much lower hours vs that Cat304. I was there for a cold start. It was slow to turn over and appeared that the battery was weak but it did fire up without any real issue. No strange smoke or anything upon start up. I didn’t look for the dents over the thumb cylinder in particular. Nothing seems out of place and there were not any leaks. I just want to ensure I make the right decision by passing on this or if I am getting worried for nothing.
Does this machine have a turbo charger?
It does not. Naturally aspirated.
Then it should have had a vacuum at the oil fill.
Pardon my ignorance, but does that mean that it is normal for the air and pressure to be exiting the oil filler whole when it is running?
Engines that don't have turbo chargers usually have some kind of positive crankcase ventilation system just like a car. You shouldn't be getting much if any vapor when you remove the cap. There are moving parts inside the engine and you will get some air movement. Was the filler cap all plugged up with oil? Was there oil spillage all around the cap? Removing the cap while the engine is running is not a great test for the condition of the engine. We used to do that type of test in the past on small body Cat skid steers, 216 for example, that had a specific engine installed. I also used to check crankcase pressures with a manometer. Emissions regulations routed the crankcase breathers into the air induction systems which made checking crankcase pressures a thing of the past.
Welcome to HEF, rjv140 !
Thanks. I don’t believe there was a great deal of build up around the cap and there wasn’t spillage around it
this is what broken rings looks like.
Thanks. It didn’t look like that.