What's this hole or connection on the left side between muffler & engine? (L3650)

[J-H]

I have a Kubota L3650, early '90s. The hole/tube thing in this picture is on the left side of the engine, inboard and mostly below the muffler, and above and rear-wards of the alternator.
What is it? Is there supposed to be a hose connecting here, or some kind of cap?

Context
After finally getting my bush hog fixed (simple slip clutch cleaning, once I knew the bush hog had a clutch and how to get it apart), I started mowing a few days ago again. After a little while, I noticed smoke coming out of the left side of the engine. I parked the tractor, and was able to identify a hole below the alternator; exhaust was coming out, as well as a little bit of oil that had sprayed onto several things. This ended up being a lower engine oil fill cap area. I got a new cap, put about 1/3 qt oil in (my ballpark on how much I probably lost), and press-fit the cap in. Hurray!

I fired up the tractor again, and it seems louder, with what I'd describe as a clattery type noise. The extra noise and some exhaust both seem to be coming from the tube/hole. There's no oil spraying, but I feel like this is probably something that should not be open, and like if it was sealed, everything would sound normal.

I included the above context in case it's another press-fit cap and losing two caps in short order is indicative of some wonky overpressure problem or other underlying issue.
I'm the only one who takes the side cover off, so I don't know how anything would have gotten loose aside from normal vibrations of bush hogging. I've had the tractor for about 3 years with no issues like this before.

It's been really frustrating trying to find info, because the Kubota shop manual has a bunch of line drawings of individual components, which doesn't help. I feel like I could have simply solved this if someone somewhere had an actual photograph of the entire engine put together, including caps and hoses, with each part labeled.

The only reason I was able to solve the previous missing cap issue was because I found a random forum post where someone had a "what's this random hole" question for it, and one of the answers gave the correct name and part number. I found nothing on this part. Hopefully we can get an answer to this, and I've phrased it well enough that someone 10 years from now gets an answer from this too.

 

[GeoHorn]

Can’t quite tell from the pic…. but some exhaust systems have a rain-water drain below the muffler/exhaust manifold …in case water gets in there and needs a way out.

 

[Fordtech86]

Does the tube lead up to the valve cover? Im not familiar with your tractor but Im guessing its the crankcase vent. Also if its pushing the oil fill caps out while running I would suspect excessive crankcase pressure.

 

[J-H]

It's actively blowing exhaust when the engine is running, so if it's a rainwater exhaust, something's malfunctioning.
I think the engine is a bit under-powered (not enough back pressure?) but have no way to measure/prove it.

Here's a better picture. The muffler blocks it... I may have to take off the top engine cover to get better visibility.

How would I measure my crankcase pressure?

 

[GeoHorn]

A water column could be used to subjectively observe crankcase pressure but I don’t know that there’s a specification for it.

 

[GSD-Keegan]

I believe that is going to be excessive crank case pressure….and probably why you were missing the lower plug. Usual cause is worn piston rings. I think I would Be starting with a compression check

 

[rScotty]

It's actively blowing exhaust when the engine is running, so if it's a rainwater exhaust, something's malfunctioning.
I think the engine is a bit under-powered (not enough back pressure?) but have no way to measure/prove it.

Here's a better picture. The muffler blocks it... I may have to take off the top engine cover to get better visibility.

How would I measure my crankcase pressure?

View attachment 63878

It looks like the crankcase breather, and even has the sort of oily look that you expect on that part.
I'd replace the hose and keep an eye on the end to see that it is expelling oily fumes and not a lot of raw oil. Oilyness at the tip of the hose is normal.

I've never heard of crankcase pressure being measured. Generally crankcase pressure goes up as an engine gets older because the blowby - mostly past pistons - increases. Not that we know that yours is too high. That kind of oiling on the crankcase pressure breather hose in your picture looks entirely normal to me. Nothing is broken - except you may want to replace the missing hose.
Eventually things just get older. As long as the engine starts reliably it can still go for a long time. Having somewhat higher crank case pressure all by itself without other symptoms won't affect anything. It's a symptom; not a cause. I've seen engines so old & worn the breather hose has a sock on the end that runs into a tin can to catch the oil drips.
Our old farm truck has had a lot of blowby (sock and tin can type) for about 40 years now. Runs fine. Check the oil often and don't be afraid to use it.

 

[J-H]

Thank you, so it looks like there's consensus on it being the hose, but not on if I have a bigger problem.

Where does the other end of the hose go to, and what does it connect to?

 

[Fordtech86]

Where does the other end of the hose go to, and what does it connect to?

look at the part diagram I posted. If it is indeed the vent tube it will attach to the front of the valve cover.

 

[J-H]

Oh, okay, and this is the back end attachment.

 

[Fordtech86]

Looking closer at your picture it looks like you are missing this lower section of pipe

 

[J-H]

Does the pipe just hang down and not attach to anything at one end? The diagram has one end going into the engine block and doesn't show where the other end goes.

 

[Fordtech86]

Does the pipe just hang down and not attach to anything at one end? The diagram has one end going into the engine block and doesn't show where the other end goes.

no it doesn’t attach to anything, older tractors just vented them to atmosphere, newer models will route them back to the air inlet side

 

[J-H]

Okay.
I don't understand the physics of how adding a 12" pipe/hose changes the exhaust noise and power that much vs. just having it vent right there. It may work but I don't understand how.

Should be really easy to replace, though!

 

[Fordtech86]

Okay.
I don't understand the physics of how adding a 12" pipe/hose changes the exhaust noise and power that much vs. just having it vent right there. It may work but I don't understand how.

Should be really easy to replace, though!

the pipe won’t fix your problem. Excessive noise/pressure coming from there and it pushing the fill plug out of the engine is a sign of excessive crankcase pressure caused by excessive blow by, which can also cause low power as well. How many hours does the tractor and how has it been maintained?

 

[J-H]

The engine odometer has about 875 hours on it. I bought it used a couple of years ago. The guy I bought it from had changed all the fluids and filters.

Prior to my bush hog issues I had zero engine problems/noise so it's odd to suddenly go from zero to loud/problem overnight. I would expect a blow-by issue (by my understanding, namely more slop between pistons and cylinder walls) to build up over time gradually instead of appearing suddenly.

 

[Pau7220]

The guy I bought it from had changed all the fluids and filters.

it's odd to suddenly go from zero to loud/problem overnight.

blow-by issue (by my understanding, namely more slop between pistons and cyl

I have the same machine with 2200 hours... yes it's the crankcase vent. PO lost the tube so I ran a hose down the engine zip tied to the loader frame below the clutch pedal. FYI... I get nearly zero blow by out of it... no oil film whatsoever. I hope you checked the air filter for proper installation and quality. I check and clean mine after every use. Did you check the integrity of the air intake tubes? Intake noise can be nearly as loud as the exhaust.

Are you sure you're not having an exhaust issue also? I had a split muffler seam I touched up with the mig welder.

Blow by isn't always caused by slop. If you find an air intake issue, "dusting" an engine causes vertical scratches on the rings and cylinder walls resulting in blow by... it can happen in minutes in dirty air, especially with brush hogging dust.

 

[J-H]

I will have to check those parts out, thank you!

 

[J-H]

The hose is on. I don't think it's ever been on in the 3 years I've owned this tractor.

The engine is still really loud and blowing a lot more exhaust than usual. Video here:

Unfortunately THIS thread is one of the top search results for some of my search terms.

So far leading candidates I've found are air filter issues, water in the fuel tank, or injector issues of some kind. I'm not sure any of those also explain the noise.

I'm going to go put 5gal of fresh diesel in soon. If I have a water in the tank issue, that should fix it.

Edit: Air filter is secure/no gaps. It's a bit dirty and I probably will change it soon. More diesel in the tank didn't make a difference, but I only ran the engine for about 30 seconds more. The exhaust is definitely white.
Fuel filter does not have any obvious clogs or gunk on the inside.
No drips of oil out of the new crankcase breather hose, and only minor pressure poofing out of it when the engine is running.

Any input welcomed with thanks...

 

[Pau7220]

That sounds a little ugly for sure. Can you pinpoint the noise? Front cover, upper, lower, clutch area? Cracking injector lines would help pinpoint which cylinder is misfiring... if you feel comfortable running it without risking a catastrophic failure. You can then move the injector to see if it follows the injector. A compression test after that would help would help determine engine condition.