Author Topic: Frothy oil sump tank  (Read 353 times)

Rolo

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Frothy oil sump tank
« on: 24 February 2020, 02:53 PM »
Since rebuilding and getting some break in miles, I'm doing some harder than normal acceleration and letting the engine spin higher than you would in daily driving in aid of seating the rings all the way in the cylinder bores.  It's been so long since I've had a healthy motor that I can't recall...

Is it normal for the oil in the 6.9's sump to be all bubbly coming right up to the fill cap after hard running?

daantjie

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Re: Frothy oil sump tank
« Reply #1 on: 24 February 2020, 03:23 PM »
I have never seen this on mine, so I can only speak from my own experience, but this sounds a bit unusual.  Are you sure you did not perhaps overfill the system?  I'm sure you know this but on the 6.9 you check the oil with the motor fully warmed up and running, and only then should it read between the high and low mark on the stick.
« Last Edit: 24 February 2020, 04:58 PM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

Rolo

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Re: Frothy oil sump tank
« Reply #2 on: 24 February 2020, 04:04 PM »
Yes, I check and without the hard driving, no foaming and level is correct.

I'm talking about full throttle to redline driving.  Been years since I've done that.  Pre rebuild, that kind of driving would belch out a huge cloud of smoke that gets you a stiff fine around here.

rumb

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Re: Frothy oil sump tank
« Reply #3 on: 24 February 2020, 04:31 PM »
I've never run across this myself, but quick search it is not a good thing. Air bubbles. : Poor lubrication. Since it is a dry sump even more odd. Overfilling a regular engine the crank would whip the oil.  Is this a new rebuild? Mixed lubricants can cause this. What oil did you use? Maybe assembly lube mixed with the oil could cause this.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

john erbe

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Re: Frothy oil sump tank
« Reply #4 on: 24 February 2020, 06:27 PM »
You're sucking in some air somewhere. Check the hose connections from reservoir to sump. Also that o-ring along flange fitting which extends into sump.

Rolo

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Re: Frothy oil sump tank
« Reply #5 on: 25 February 2020, 12:33 PM »
I will check.  Can you help me with terminology?  The sump is the tank welded to the fender.  What is a reservoir?

daantjie

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Re: Frothy oil sump tank
« Reply #6 on: 25 February 2020, 02:30 PM »
I'm pretty sure in this case dry sump tank = reservoir.  You will see 3x hoses running between the -  let's call it "oil pan" to avoid further confusion - and the dry sump tank.  You will also see the flanges mentioned at the "oil pan" side.  Good to check all these hoses and connections for tightness.
Daniel
1977 450 SEL 6.9 - Astralsilber

Randys01

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Re: Frothy oil sump tank
« Reply #7 on: 25 February 2020, 03:03 PM »
Mr Erbe is  on the money.

TJ 450

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Re: Frothy oil sump tank
« Reply #8 on: 26 February 2020, 05:43 AM »
I recall having this sort of frothing when the sump hoses were leaking. It took two or 3 refits and some hylomar on the paper gaskets to get it leak free, and I'm thinking that flat ring could be your issue. As an aside, I wouldn't be too heavy handed (footed?) with the engine if you haven't done many miles. That's my opinion anyway, until any teething issues like this are sorted .

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

john erbe

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Re: Frothy oil sump tank
« Reply #9 on: 27 February 2020, 05:12 PM »
Regarding the o-ring, that was the problem I had. Symptoms were that (1) the oil pressure gage  did not peg at start-up and (2) when the car made I believe a left hand turn the pressure would drop.

john erbe

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Re: Frothy oil sump tank
« Reply #10 on: 27 February 2020, 05:20 PM »
Also, to save time, just check first the suction hose from the reservoir. The other is the return but unfortunately I dont recall which is which.

rumb

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Re: Frothy oil sump tank
« Reply #11 on: 28 February 2020, 03:51 PM »
diagrams
« Last Edit: 28 February 2020, 04:05 PM by rumb »
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

Rolo

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Re: Frothy oil sump tank
« Reply #12 on: 02 March 2020, 04:05 PM »
Thanks all for the tips.  Did any of you experiencing frothing have oil leaks?

alabbasi

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Re: Frothy oil sump tank
« Reply #13 on: 02 March 2020, 10:04 PM »
I had that happen to me a while back, it turned out that I was low on oil. I would also notice the oil pressure drop on fast left turns. The problem went away when I added a couple of quarts of oil.
With best regards

Al
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TJ 450

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Re: Frothy oil sump tank
« Reply #14 on: 03 March 2020, 12:23 AM »
I had oil leaks externally at all three fittings.

I would change the oil again and confirm it is at the correct level as Alabbasi said above (operating temp, engine running).

It there are leaks present or if this doesn't sort it out, I would double check all the O rings if you can.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500