What is this breather tube/pipe connected to?

Does anyone know what this tube is or is connected to? And also why it would be spewing oil? This is on a 2016 GRiSO 1200 8V SE

I’d rather not take the fuel tank off, but near as I can tell it’s routed along the right side of the fuel tank (yellow arrows) and seems to end at the front of the tank (unless it actually continues to the left side of the tank—but as I said, I haven’t taken the fuel tank off and would rather not, if I can help it). Thanks.

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My guess is Crank case breather tube open to air. All CARC models have that tube loose than can be arranged to exit most often on the left side of the engine up under the airbox.

The only big pipe that should be 'open to air' is the gearbox breather - it usually lies next to the throttle swivel on the LHS & usually doesn't belch anything. If it's that you are fine (just smell it & check it's gear oil)

If (I think it is !) it's the big line you arrowed then it's line 12 in parts diagram below, the 'blowby gas' after oil droplets are separated flows back to the airbox in this line. It runs across under the RHS side of the tank, drops under the airbox & then should be attached to the airbox on the LHS lug (according to my 2009 bike !) or RHS lug on other bikes.....worst thing about it not being connected is the crap that gets sucked into the airbox unfiltered. Check if the airbox lug is open on LHS (and check RHS as some models may have same return lug on RHS)

PS: If yours has RHS airbox lug return set up, the pipe has just come off & slipped down 1 inch south of it & easy to just push back on. If mine looked like yours it would mean somebody has cut the pipe short & just left it damgling there !

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I think you’re correct that the line I arrowed is #12 on the parts diagram. And according to the parts diagram, that line should be clamped to the air box and not open to air, no? In other words, should it be clamped to the nozzle (for lack of a better word) that I circled in red on these two pictures?

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Correct.

On the front of the airbox are two spigots. The RH one is for the vent hose from the oil separator/collector box behind the steering head. The LH one is for the hose for the stepper motor.

It is very important that both hoses are attatched. Also check the two airbox drains are attached, unfractured and plugged.

So if I’m understanding this correctly, there shouldn’t be any sludge coming out of that breather tube, it should just be gases going into the air box, yes?

If that’s the case, what would be the cause of this sludge? And where did my hose clamp go???

There will always be gas expelled from the crankcase as it is always positively pressurised by blow-by past the rings and the pumping action of the pistons. The gas inside the crankcase is a fog of oil droplets as they are whipped up by the cyclonic forces of the spinning crank and the streamers of oil flowing out of the bearings in the engine and off the crank.

These gasses and the oil droplets in them are passed out of the engine from the two breather hoses that come off the plates on the back of the cylinder heads that cover the backs of the cams and cam sprockets. These sprockets have a flinger plate outboard of them that is designed to fling the gasses outward as they pass and this encourages the oil droplets to hit the surfaces inside the head where surface tension will encourage them to stick and then drain back to the sump. Some oil particles though will remain in the gas and be expelled up the hoses to the breather/separator box behind the steering head where, once again, it is hoped that they will settle out on the walls of the box and then drain back down the pipe that goes from the box to the back of the sump you can see adjacent to the sump drain plug.

By now it is hoped that the vast majority of the oil will of separated from the gasses that have been expelled and these gasses now pass down that pipe, that on your machine has become disconnected, and are fed into the airbox where any remaining and residual hydrocarbons and oil droplets should be fed back into the engine with the incoming fresh air and burnt in the combustion process reducing the amount of hydrocarbons released into the atmosphere and helping keep the environment clean.

There will always be some oily residue coming down that hose from the separator box and it is that mess that you are seeing on the end of the hose. The thing is it can be minimised very simply and you want to do this, not only because excess oil expelled this way can pool in the airbox and clog and damage the throttlebodies but it can also pollute the incoming charge and promote detonation and, in severe ashes, carbon build up in the combustion chambers.

Minimising it is really simple. Don’t fill the engine to the ‘Full’ mark on the dipstick! Oil, being a liquid is effectively incompressible. Gas on the other hand, isn’t! The more oil you have in the crankcase the higher the pressure in the case and the closer the oil in the sump is to the crank leading to greater windage and more oil particulates in the gas. Put simply, the more oil there is in the engine the harder the condensor/return system has to work and the greater the chance that it will be overwhelmed and end up with *Too much* oil being expelled into the airbox.

People tend to try and keep the oil at the ‘Full’ mark on the stick. Don’t! The factory specifies way too much. If you just fill it to half way between the ‘Add’ and ‘Full’ marks and don’t keep adding any more you will find that the oil level will stabilise somewhere between that point and the ‘Add’ mark on the stick after a few rides. That is your engine’s *Happy Place* and you can, if you wish, mark the stick at that point and use it as your new ‘Full’ mark. There is no need to worry, there is lots of oil in a Guzzi big block engine. It won’t do it any harm.

Thanks Pete, that explanation is really helpful. I’ll try and reattach that tube later today. As far as I know, everything else seems to be attached properly. I bought this bike pre-owned, so it had all its fluids changed before I got it—but I never thought to check the oil level! Will definitely keep an eye on it going forward.

I'll add that in the 21k miles I've put on my GRiSO, I've yet to need to add any oil.

And Pete, in reading your excellent explanation of the breather system. I occurred to me that running at higher rpm would encourage more oil to get drawn into the intakes., as the droplets are moving faster so might not get time to settle out early in the game. I typically ride under 4k rpm, and rarely exceed 5k rpm. Perhaps that contributes to low oil consumption?