Author Topic: Bubbles in engine oil  (Read 341 times)

raueda1

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Bubbles in engine oil
« on: 06 May 2021, 11:26 PM »
I was alarmed today to discover that my engine oil was quite foamy.  This was immediately after driving at highway speed and at high ambient temperature (90F ?).  However, after idling for a few minutes the foaming subsided and the oil level was fine.  The bubbles were fairly large, say 1-2mm.  The oil wasn't at all whipped into a mousse as when mixed with coolant.  Oil pressure is normal and there's no knocking or other signs of oil issues - just foamy after driving.  I recall using a zinc additive, can't recall exactly which one though.  Thoughts on what this means and how worried I ought to be?  If at all?  Thanks and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

BCK1963

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Re: Bubbles in engine oil
« Reply #1 on: 07 May 2021, 12:04 AM »
Dave, as long as the oil remains clear and there is not severe odor of gasoline I woudn't  worry.
Did you glance into the reservoir or did you notice it on the control stick?  I recall to have seen bubbles on a control stick before (don't remember the car, though), so it can happen.
You mentioned the most important aspect yourself:  No signs of white mouuse due to emulsified coolant.
Bernd

1976 Merc 6.9  since 2013
1974 Caddy CdV   since 1992  (for sale)

daantjie

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Re: Bubbles in engine oil
« Reply #2 on: 07 May 2021, 10:25 AM »
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Bubbles in engine oil
« Reply #3 on: 08 May 2021, 09:28 PM »
Well, that's quite the grist!  Anyway, thanks gentlemen for the remarks.  I made it back home today through the amazing topography of Nevada at relatively high speed and without a hitch.. I guess I shouldn't be too surprised since oil pressure has always been fine - if the foaming were really an issue I guess the engine would have been toast long ago.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

BCK1963

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Re: Bubbles in engine oil
« Reply #4 on: 09 May 2021, 04:09 AM »
Very interesting link but the guy focuses on the advantages of oil suppy on race cars, which is clear given his profession.
The apparent reason for using a dry sump engine in our 6.9 is space: An engine with wet sump would be considerably higher and would not have fit under the hood.
Another area where dry sump engines are often used is tanks: The need to maintain the silhouette of a tank as low as possible makes dry sumps the engine types of choice. I know that particularly for Maybach engines for german tanks of the 30s and 40s. Despite those engines the Tiger I and Tiger II tanks were not exactly 'low', and ceasing oil supply during sharp cornering was not not really an issue for them  ::)
Bernd

1976 Merc 6.9  since 2013
1974 Caddy CdV   since 1992  (for sale)

raueda1

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Re: Bubbles in engine oil
« Reply #5 on: 13 May 2021, 08:24 AM »
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,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: Bubbles in engine oil
« Reply #6 on: 13 May 2021, 04:46 PM »
>>>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,
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).
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Nabstud

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Re: Bubbles in engine oil
« Reply #7 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 Hubble the oil.
1975 280S - Australian delivered

raueda1

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Re: Bubbles in engine oil
« Reply #8 on: 14 May 2021, 07:57 AM »
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.
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.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

slfan

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Re: Bubbles in engine oil
« Reply #9 on: 06 June 2021, 07:21 PM »
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
1978 - 450SEL 6.9 - 3170
1978 - 450SEL 6.9 "Parts Car" - 2973

Rolo

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Re: Bubbles in engine oil
« Reply #10 on: Today at 02:29 PM »
I had a lot of bubbles for 2 oil changes after my rebuild.  But, the oil near the intake was solid with the bubbles only near the top.  I still get a few bubbles after hard running.

raueda1

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Re: Bubbles in engine oil
« Reply #11 on: Today at 06:24 PM »
I had a lot of bubbles for 2 oil changes after my rebuild.  But, the oil near the intake was solid with the bubbles only near the top.  I still get a few bubbles after hard running.
That's good news IMO.  Not a coincidence I don't think.  After rebuilding I dumped the first fill after only 100 miles, so there could well have been residual break-in additives, detergents, etc carrying over.  No bubbles now.  Thanks and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0