Crankcase pressure

Hi Peter,

 I've put many a spring in an oil hose (probably a 100+) and have seen and heard of a hundreds engines doing the same without issues. I see it done in coolant hoses too. Even MFG's do it.  I see this on several other forums. By doing this I have seen oil temps drop by 15F - 20F when they were on the high side by allowing better unrestricted oil flow. More oil flow is better than just pressure alone. Having a hose reduce its radius due to some collapse will cause back pressure and higher temps. In 20 years of adding a spring (only when it's needed to keep an oil hose from collapsing) I have never seen or heard of any issue. Plus if needed I will reroute a hose to make it straighter and stay wide open at times..

Someone can cause an issue if done improperly. . 

Hi Roger,

I am aware of the use of springs for this purpose. Personally I have no doubts whatsoever myself. However, the report and its findings draw some attention. 

My focus here is more on the crankcase pressure (ambient plus 0,3bar = max) as I recon it would be fairly easy to have it monitored. But I have never ever seen or heard of such a set up.

Regards

Peter

Collapsing Oil Hose/ High Crankcase Pressure

I am intrigued -

(The following is Speculation)

Collapsing Oil Hose:

How would you even know this is happening?

How can it happen in the first instance?

The cooled oil supply, is from the tank, via the oil cooler, to the pump. It reasonable to suggest, that this is the only hose that may experince a degree of negative pressure ie has the potential to a collapse.

In the "normal" course of events, a collapsed hot oil hose would regain its shape very quickly after engine shut down - if true, a suspect oil heating/crankcase pressure problems, would be hard to blame on the hose.

It seems to me that the only potential for oil hose collapse, is in the cooled oil side of the circuit and could only happen if the engine rpm was increased, such that the oil pump created a significant negative pressure, in this hose, due to the oil being "thick" due to insufficient heat up time.

OR

This engine is fitted with an oil thermostat that malfunctioned, thereby partially/totally blocking the oil return to the pump. precipitating a hose collapse.

High Crankcase Pressure

The crankcase pressure is essentially controlled by the hot oil to tank return line venting, via the oil tank, breather hose, to atmosphere (nil potential for blockage). Partial/total blockage of this line is the only way of raising the crankcase pressure (short of piston ring failure).

What mechanism could lead to a hot oil return line part/total blockage?

Part/total blockage could only be caused by a internal component failure blocking the crankcase oil exit.

The hot return oil line, under posative pressure, will not, under normal conditions, collapse. 

What say you?😈

Sean, I do follow your description and have no intention to argue against any of it. Obviously “the report” I am referring to contains “findings” that do not match experience, e.g. using springs in oil lines to prevent them from blocking oil flow e.g. in tight bends. That’s why it caught my attention and yours.

One feasible point they make is that blow by gas which forces the oil back up to the oil tank may increase to an unhealthy extend under circumstances. Perhaps they had blockage in mind or bad piston rings. It reads like Rotax has established the ‘0,3 bar above ambient’ rule to protect certain seals that may fail otherwise and cause loss of oil. If that’s correct, I wonder if it makes sense to monitor crankcase pressure.

Too high and too low crankcase pressure seems to have some potential to cause grief.

Hi Peter Kl,

I guess I was trying to visualise/put into words what I see as a highly unlikly scenarios -hose collapse & a separate (I think) crankcase pressure concerns.

I suspect that an actual hose collapse is precipitated by something else, therefore deal with the something else and it won't happen - no need for hose anti collapse springs.

Excessive crankcase pressure, again some other factor is at play - having a gauge to warn you of this unlikly event will probably not prevent the problem occurring as its likly some internal disintegration would have to happen to block the oil/vent/drain. 😈