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Foamy stuff in the oil lid

I am writing about a 2007 Chevrolet Suburban and for the last few months, have noticed that the car is losing oil. I have to put in a quart of oil about every 3 weeks. I have brought it in to the mechanics and asked them to look for a leak and they can’t find anything. They have changed the oil, replaced the evap hose, but the car is still losing oil. Just did a lot of driving this last weekend and the oil went all the way down, to the point of when I started it this morning, I got a huge amount of blue smoke out the back. When I took off the cap to add oil, I noticed this mustard yellow, foamy stuff on the lid. Never saw that before. Does anyone have a clue as to what might be going on?

That usually indicates a lot of moisture in the oil. How’s the coolant level?

Tester

Yes, coolant contamination of oil appears as a nasty, snot-like foamy brown stuff…usually up at the (cooler) top of the dipstick tube.

Check for coolant loss, oil slick at coolant filler neck, and compression check to diagnose a potential head gasket issue.

Good Information Supplied, But Some Missing Information Begs Unanswered Questions.

Prior to “Just did a lot of driving this last weekend,” was the vehicle used for frequent short trips or is it driven a lot regularly where it can get up to full operating temperature when it’s used ?

Is the temperature gauge (if equipped) reading in the normal range and is the heat output in the cabin adequate ?

As has been asked already, is the coolant level in the radiator and reservoir at “full” and fairly clean looking ?

Has it been cold outside where you live (below freezing 32*F) ?

Did the mechanics check the PCV (Positive Crankcase Ventilation) system and/or replace the PCV valve ?

Moisture will form and accumulate in a normally running engine that does not regularly get warm enough (short trips, cold running engine, bad thermostat, etcetera) and can cause problems like the moisture you’re seeing on the oil fill cap. Also, excessive moisture has been know to freeze in the PCV valve and could lead to oil unusual oil consumption.

CSA

+1 for CSA

Foam in the engine is always a bad sign. I had a lot of blowby in my 1977 Dodge Colt, and it overtaxed the PCV valve. So I made a draft tube, as used in old cars to let the gasses out directly into the atmosphere. I was breaking the law, but the car only had a limited life left before being scrapped.

Milky stuff on the dipostick, foam anywhere in the engine spells serious trouble.

How many miles are on this Subie?
How’s it been maintained?

First let me start by saying that the cloud of blue smoke when you start up in the morning is caused by oil leaking past the valve stem seals and down onto the back of the intake valves and/or in the cylinders (where the intake valves stopped in the open position) and being drawn into the cylinders and burned when the engine is started. This is an advanced wear condition of the valve stem seals.

The rest of the oil may be getting past the rings due to wear AND is definitely being drawn past the valve stem seals and into the cylinders and burned whenever you decelerate and the vacuum in the cylinders spikes.

In addition to the leaky valve seals, oil can get burned for two reasons, and both go hand-in-hand. (1) worn cylinders combined with worn and tired rings allow much too much oil to remain on the cylinder walls when the piston goes down in the intake cycle. It then gets pushed back up into the cylinders by the compression rings and gets burned. That same wear allows “blowby”, a condition wherein combustion gasses pass by the rings and pressurize the crankcase. That pressure can push excess oil up into the cavity under the valvecovers where it can be ingested through the PCV valve and burned. That pressure can also force oil past worn and tired “main seals”, which seal the ends of the crankshaft to prevent leakage of oil from the crankcase.

In short, you’re likely burning oil via worn cylinders and rings, as well as through worn out valve stem seals, and pushing it past worn out main seals and cam seals. I truely think that at this point the place to start is with a good compression test. Post the results back here.