First post. Thanks in advance for reading and/or responding. I'm trying to understand the blowby breather system in a Hyundai R55-7 mini ex with a Yanmar 4TNV94L engine. Any help is appreciated. The engine service manual, which applies to numerous TNV engines, shows a breather tube that apparently is designed to reduce crankcase pressure by recirculating blowby gas back into the combustion chamber via a breather diaphragm. The diagram in the manual, which I've attached, shows how it should look in a Yanmar 3/4TNV84 engine. No diagram is provided for the 4TNV94L. However, the parts catalog shows a plug where the breather tube would deliver the blowby gas to the diaphragm. This diagram is also attached. And the plugged breather tube is consistent with my engine. Photo attached. I have looked for another breather tube that either circulates the blowby gas or releases it to the atmosphere but haven't been able to find one. So my question is, how is crankcase pressure relieved in the 4TNV94L if the re-circulation system that some TNV engines apparently have is not used? The reason I'm looking into this is because I'm getting blowby gas spitting out oil droplets from the lower oil fill cap if removed during operation when the upper oil fill cap is screwed on and the dipstick is in. A little oil also comes out of the dipstick if removed during operation when both fill caps are on. But if the top fill cap is removed and lower fill cap is on and the dipstick is in, some blowby gas comes out of the upper oil fill hole but no oil, and this seems to relieve enough pressure that if the lower fill cap and/or dipstick are also removed, no oil comes out. This is a 2005 machine with about 2500 hours and apparently pretty well maintained before I recently bought it. Starts great, no apparent power loss, a little white smoke comes from the exhaust when started cold but goes away within a few minutes. I have changed the oil and the level is correct. Any thoughts? Thanks!
Welcome to HEF dwilly ! Just guessing:
@mg2361 : Thanks for your input. You are exactly correct. Yanmar called me and talked through the blowby recirculation system on this engine. Pretty great service that I wasn't expecting. Yanmar confirmed that the formation you pointed to does, in fact, route the compression gases internally (in lieu of the breather tubes earlier designs use) after oil is filtered out of the gas by the baffle shown at part #53 on the Bonnet schematic I attached above. He also confirmed that spitting oil from the lower oil fill is expected due to the nearby gears, and that a better indication of blowby problems would be oil spitting from the upper oil fill or gas exceeding about 5 psi coming from the upper oil fill. With the ultimate indicator coming from a compression test, of course.
I had a customer leave his oil fill cap off the gear on a similar Isuzu and it painted a stripe on the wall 5 feet away.