Onan 4KY Consuming Oil After Change, Breather Tube/Crankcase

[jayhorowitz]

In an effort to get more hands-on in my generator maintenance I inadvertently caused some trouble. Last week I changed my generator oil myself for the first time. I suspect that I didn't allow all of the old oil to drain fully and therefore inadvertently overfilled when adding 1.6 quarts to the system.

When I ran the generator for a few minutes after changing the oil everything seemed fine although the oil level was unexpectedly low. I added more oil, ran it again, low again. In my tunnel-vision of filling oil (and having no prior experience working with my generator) I missed what should have been obvious: the oil was going somewhere, the crankcase breather tube was no longer connected at the air filter compartment and the preheater hose was detached behind the fan. My grasp of generator mechanics is tenuous, but my hunch is that high crankcase pressure led to oil being blown through the breather tube at high enough pressure to disconnect it, and that the disconnected tube knocked the preheater hose loose. (There is no oil leaking from the dipstick seal or the drain plug bolt.)

I put the preheater tube back in its spot and spent a while reconnecting the breather tube to the air filter box, and ran the generator for a couple of hours last night. The generator still consumes a large amount of oil when running and it looks like there are some leaks around the crankcase and crankcase breather tube. Separately, and perhaps related, my choke housing isn't assembled properly. I don't know if it's been like that all along or if it got knocked loose. Photos are included.

Could my problem be that the breather tube and mesh filter are clogged from the initial debacle? If so, is that something I can check and clean? Is it dangerous / bad to use my generator in the meantime, just keeping the oil between "Min" and "Full" (two hours of running it yesterday dropped the oil level from near-full to near-min).

Here are photos, some before reconnecting, some after. I wiped down the top of the crankcase a bit.

http://imgur.com/a/BlDA4

Learning by doing sometimes hurts...

*Onan Model: 4KY FA26100J

[427435]

64thunderbolt wrote:
Well I suppose Valvoline mislabeled the qt I have in my gen box. It clearly says "30 wt"

In the oil business, "wt" is the abbreviation for "Weight" and "w" is the abbreviation for "winter" rating.

[64thunderbolt]

Well I suppose Valvoline mislabeled the qt I have in my gen box. It clearly says "30 wt"

[427435]

64thunderbolt wrote:

427435 wrote:
(there is no such thing as 30w oil)

REALLY ???

Really.

[427435]

If an Onan 4000 generator, the correct way to check the oil level is with the plug/dipstick screwed in.


http://www.cumminsonan.com/www/pdf/manuals/981-0159D.pdf

[64thunderbolt]

427435 wrote:
(there is no such thing as 30w oil)

REALLY ???

[427435]

Checking the tightness of hardware is always a good idea.

Correcting the chock linkage so the chock fully opens also should be done. As it is probably an automatic chock, it needs to be checked when running and warmed up.

A dipstick or checking process that results in too high an oil level will lead to oil consumption. Every engine (including small engines with a combined fill plug and dipstick) that I've ever dealt with requires the plug/dipstick to be screwed fully in to check oil level. If you are filling the oil level to the full mark with the plug just resting on the opening, the oil level is being set too high and could well be your problem.

How have you been determining the oil level?



A 30 weight oil (there is no such thing as 30w oil) will be thinner at operating temperature (and burn more easily) than a 10w-40 oil. Stay with the 10w-40 oil.

If you end up replacing the breather valve, you might as well buy a valve cover gasket as well. Before accessing the breather valve, be sure dirt/grunge is cleaned off the area so it doesn't get into the engine.

[j-d]

I really don't have much to add. Yes, there is not an Oil Filter or and Oil Pump. 4KY is splash lubricated like a B&S mower engine. Like other small engines, it has a breather box with a reed valve in it. Cleaning that would be a good place to start.

[Handbasket]

More of a general comment than based on what I've read here, be darn sure you're checking the oil correctly. All 3 of my 2800's (the only Onan I'm really familiar with) have required checking the level with the dipstick plug unscrewed and sitting on the edge of the hole. This makes a significant difference in getting the oil level correct. I actually wrote the correct method on mine in silver Sharpie. Check your manual. Be sure to allow enough drain-back time.

I agree with changing back to dino, and using a straight 30W if you don't have an unusual climate. I've always used Castrol in air cooled engines, from lawn mowers to VW Bugs.

The oil has to be going somewhere. If you were burning that much oil, I'd really expect smoke and the spark plug to foul pretty quickly. Assuming that it's sitting level, a leak should show up as at least wetness on the bottom of the pan very quickly. Almost has to be the crankcase vent system, and I'm not familiar with yours.

Best of luck with it.

Jim

[Kpackpackkelley]

Before you pull the valve cover to check the reed valve snug all the head bolts down do not over tighten. Also check the bolts that hold the air housing on they get loose and start pulling air through the gasket to the carb.
If it's leaking oil down around the pan you'll have to pull the gen from the TT to get to the bolts to tighten them or install a new gasket. I would check every thing I could get to before I pulled the unit.
With the rich mixture your smelling sounds like it's pulling to much air and that pulls to much fuel from the carb and will pull the oil through the breather tube. Check the easiest stuff first.
If you pull the valve cover be careful with the gasket or be ready to get a new one. One good thing it's running there hard to trouble shoot when there not running. Just take your time back away so you can kind of look at the whole unit sometimes when your right up on them you only see one spot.

[MEXICOWANDERER]

Very high oil consumption via combustion can be easily detected by running a finger round inside the tip of the tailpipe. A finger wet with oil is proof the oil is running through engine internals trying to be combusted.

Blow-by past the top compression and 2nd piston rings will pressurize the crankcase causing lube oil to vent out of crankcase access holes. High blowby defeats the operation of the bottom oil ring and encourages much higher oil consumption.

The 1st thing I would do is a wet/dry compression test on both cylinders. A cylinder leakdown tesr is better but it takes an intelligent tech to perform a leakdown test.

[jayhorowitz]

Thank you for all of the great responses. The reed valve is my next avenue of attack. I am not familiar with the reed valve - its purpose, what it looks like, and most importantly how to diagnose whether it is causing my oil consumption issue. What am I looking for?

Based on Chris Bryant's diagram it seems easy to access. Is there anything that I should be aware of (or wary of) in removing the cover from the crankcase to access the reed valve? I assume this should be done with the generator cold.

Regarding the dipstick, I am fairly certain that it is the original. The O-ring appears to be in good condition and it seals well.

Kpackpackkelley, do you think that I should have those things done even if the reed valve resolves the issue? I'm running 10W-40 per the temperatures that I camp in. Thank you for the service manual offer. I have a copy of it and have been learning/reading/glazing over it for days 🙂

[Kpackpackkelley]

You need to find a good small engine mechànic to tighten all the gaskets around the carb , air filter housing , and head. Gasket to spec and then set the valves to spec.
If it's not cold weather run 30 wt oil as the manual specs.
If you need the service manual pm me your email and the complete model number.

[westend]

Could the weird choke assembly issue I described in the original post have anything to do with oil consumption? It looks like the choke does fully open after the engine has been running, only that the housing assembly is wonky.

It might. There are some engines I've worked on that an interference in the air delivery resulted in excess oil consumption. Is the valve cover breather tube connected to the air box on the exterior or interior of the air filter? If the breather tube is connected to the air box on the exterior side of filter and the oil consumption was from the breather tube, the air filter would be saturated with oil.

The only significance I can make out of the exhaust heating duct and the breather tube both being off is that it's possible that someone was working on the intake or a backfire happened.

You should check on the valve cover side of the breather tube and see if there is a reed assembly or metering plug and if that is operable.

I guess we could assume that the dipstick is the stock one and that oil levels are measured accurately? I've had a few Onans and Kohlers that I remember it was impossible to keep oil levels at "full". The engines either consumed the oil through the rings or drew it in though the breather tube. None of them retreated to the "add" level unless there was a secondary leak.

Chris B posted while I typed. The breather tube reed valve is now a top suspect.

[Chris_Bryant]

I would bet on the reed valve being stuck- an easy fix:
.

[jayhorowitz]

UPDATE:

A couple of days ago I fully drained the oil and replaced it with 1.6 quarts of 10W-40 dino. The generator still starts easily and runs fine, but the oil consumption issue is hasn't gone away. An hour or two of generator time under load took the dipstick reading from Full nearly all the way to Add. At least switching to dino oil has made it cheap to keep the oil level topped off while I troubleshoot!

I removed and checked the breather tube for obstructions and didn't find any, and user "427435" suggested that I next check the breather leaf valve, the process for which I'll need research. Fortunately I have a solid solar array and battery bank so the generator issue isn't pressing, but I definitely want this solved.

I've also noticed exhaust fumes in the RV (setting off the CO detector) after ~1 hour of running the generator, but I've had that issue since before the oil change. Stupidly (I think), the exhaust pipe doesn't even fully extend beyond the side of the RV, terminating underneath the RV a few feet below a huge (closed, of course) window - RIGHT where the CO detector is. When I look at the breather valve I'll also check for cooling/venting obstructions (mud daubers were an issue in lots of areas when I bought the RV), attempt to clean out the muffler by removing the plug, and - if I can see it - look for any cracks in the exhaust pipe at the muffler connection. Warm/hot exhaust blows strong from the exhaust pipe and I haven't seen any residue of any kind in the pipe.

Could the weird choke assembly issue I described in the original post have anything to do with oil consumption? It looks like the choke does fully open after the engine has been running, only that the housing assembly is wonky.