Garage > Mechanicals

Bubbles in engine oil

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raueda1:
Well, this issue continues to bug me.  I just read and reread the service manual which has a very detailed description of the design and components of everything.  A couple things stand out to me.  First, the oil tank has perforated baffles to defoam the oil from the oil return pump.  Second, the oil filler tube in the tank extends fairly deep into the tank.  Yet foam is coming up quite high in the filler tube, meaning that it must extend pretty far down into the tank.  It's almost like the system is under pressure. 

Does it make any sense that it IS under pressure somehow?  That the crankcase breather system isn't working right so the crankcase IS under pressure and blowing through the oil return?  I'm going to try to chase that down and make sure that the crankcase breathing isn't blocked somehow.

Regardless, I'm going to change the oil ASAP based on another theory, though it might be far fetched.  The car is running on the second oil change after rebuild last spring.  At that time the initial start was with break-in oil.  Once running OK that was changed with regular oil and run a few hundred miles (should remove traces of the break-in oil, assembly lube, etc).  Oil was then changed again.  Is it possible that there was still enough rebuild oil residue that foaming being promoted (reduced surface tension from residual break-in additives)?

I'll report on my findings.  Any other theories would be very welcome, particularly observations on your own cars.  One of my ongoing challenges in this whole business is figuring out what's just normal.  Thanks and cheers,

raueda1:

--- Quote from: raueda1 on 13 May 2021, 08:24 AM --->>>snip<<<

Does it make any sense that it IS under pressure somehow?  That the crankcase breather system isn't working right so the crankcase IS under pressure and blowing through the oil return?  I'm going to try to chase that down and make sure that the crankcase breathing isn't blocked somehow.

Regardless, I'm going to change the oil ASAP based on another theory, though it might be far fetched.  The car is running on the second oil change after rebuild last spring.  At that time the initial start was with break-in oil.  Once running OK that was changed with regular oil and run a few hundred miles (should remove traces of the break-in oil, assembly lube, etc).  Oil was then changed again.  Is it possible that there was still enough rebuild oil residue that foaming being promoted (reduced surface tension from residual break-in additives)?

I'll report on my findings.  Any other theories would be very welcome, particularly observations on your own cars.  One of my ongoing challenges in this whole business is figuring out what's just normal.  Thanks and cheers,

--- End quote ---
Changing the oil got rid of the foam.  Completely, not a single bubble.  So maybe my theory was right.  I hope so, cause if not then something else happened to the oil to make it foam so easily, though I can't imagine what.  Engine seems to run fine but I hope that something terrible wasn't happening while the foaming was going on.  I'd hate to do 2 rebuilds in as many years.   :-[  Guess I'll find out soon enough (gulp).

Nabstud:
Nice outcome. Did you use the same oil?

I would have thought the oil would leak out the seals under pressure rather than Hubble the oil.

raueda1:

--- Quote from: Nabstud on 13 May 2021, 11:33 PM ---Nice outcome. Did you use the same oil?

I would have thought the oil would leak out the seals under pressure rather than bubble the oil.

--- End quote ---
Same oil, Castrol GTX 20W-40. I think some others here use it as well.  The car doesn't really leak, just a couple small drips.  In fact, the car didn't lose any oil at all since rebuilding last year and 6000 miles ago.  There are a couple mildly drippy struts.  Struts will be rebuilt very soon which should solve that.  Interestingly all the drips seemed to decline with more driving.

slfan:
Dave,

I had a similar situation a few years ago.  If I recall correctly, there are round seals (mini-donuts) that are attached To the hoses that connect the oil tank to the bottom of the engine (oil pan I guess is the name).  Despite not leaking, one of my hoses was missing this round (resembled a mini-donut) seal.  Once this seal was installed, I never again had the foaming problem.

Regards,
Angel

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