Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Does the engine oil lose its properties if it is drained in the pan and returned back

Is the synthetic engine oil hygroscopic (like brake fluid, or AC compessor oil)? Does the oil lose its properties if it is drained in the pan and returned in engine again an hour later?
Yesterday I had to drain the engine oil and then put it back into the car, because my car’s drain plug had a leak and I had to replace the washer. I drained the oil in a plastic oil pan. The oil stayed for about an hour in the drain pan covered with a piece of paper to prevent some dust to get into the oil. You understand that the drain pan in which the oil has been left for an hour is not hermetically sealed and the oil has been in contact with the air all the time. Before I pour the oil into the engine I filtered it, so the procedure stretched so long.
Тoday I checked the oil level and noticed some yellow thing on the dipstick that looks like a mayonnaise? I suppose this is moisture / condensation in the oil? Is it yesterday’s draining and returning oil a cause?
The oil was replaced a full synthetic oil a week ago, and after that I’d noticed the leak that I successfully eliminated yesterday!

Others might not agree but I see no problem . I would drive and get the engine at operating temp for a while and check the oil level daily for a week or so .

1 Like

I do not see a problem, as long as everything was clean.

The mayonnaise probably is air/water/oil. When you drained the oil, it was left behind on the dipstick - in fact more of it may have formed while the crankcase was empty and the dipstick was not bathed in oil.

The oil sitting in the open was not harmed. You may have nothing wrong at all, just normal residual moisture in the crankcase. Be alert for signs of a problem with the PCV system or a head gasket leak, but don’t be surprised to find there’s no problem.

1 Like

What makes an oil function properly is the base stock which is 75% and the ADDITIVES which make up the rest. As oil is used in the engine, the additives are depleted, and the oil loses its capacity to do all those things it usually does. Filtering used oil only removes some solid particles and leaves an additive-depleted oil.

Re-refined oil is cleaned up in an industrial plant and new ADDITIEVS are added to make it about as good as the original oil.

A down to earth comparison would be to take the used water form your mothers washing machine, filter it and expect it to wash more clothes!!!

What you are doing makes no sense; leave the re-refining to commercial firms!

Drive on

I see no problem here

I don’t know if you checked the oil level cold or hot. Suggest making sure the cold level is correct, then driving it a few miles on the freeway. Shut the engine off, and check it after a few minutes. Chances are you won’t see any “mayonnaise” at that time. If needed, top off to reach the correct level

The drain plug washer . . . is it nylon, aluminum, copper, rubber, or what?

Depending on the material, it may be best to replace it at every oil change. Think of it as heading off future problems. For instance, I’ve rarely seen the copper washers seal perfectly when reused

Docnick, you missed the fact the oil had been in the engine for one week.

Check the PCV system. Condensation is the most likely cause for the mayonaise and it showed up after finishing the work because you were very attentive.

Sorry; I thought OP was trying to get extra life out of used oil.

Keep monitoring the dipstick for the oil condition, but I expect that problem will disappear as your drive the car a few times. I’ve done the same thing before when a situation develops where I have to drain the oil to fix something, and that batch of oil has only recently been installed. I just drain it out into a clean pan lined with a new garbage bag liner, sieve it to make sure it is clean to re-use, then pour it back in. Never had a problem. I use conventional dinosaur oil, but I wouldn’t expect synthetic to be any different. As the engine heats up the PCV system should scavenge any remaining moisture out of the crankcase. That’s part of its job, as in normal operation some combustion gasses inevitably get into the crankcase, and the two major combustion gasses are CO2 and H20.

1 Like

Normally I’d so no problem, but that yellow “mustard” of undisclosed origin would suggest something in there. It might have been residue from coolant in the pan or something else. Me? I’d change it again because I’d sleep better.

1 Like

The moisture that has accumulated in the dipstick tube has probably been there long before you changed the oil. The dipstick tube doesn’t get as hot as the inside of the engine so it is common for condensation to develop there.

1 Like

Engine oil is in contact with atmosphere all the time. Plenty of moisture is in contact with the oil and is removed by the PCV system. Engine oil is far more stable than those other fluids and doesn’t try to pull the moisture from the air.

I’m with the majority here. I can’t imagine that the oil having been out of the vehicle has any impact on the stuff you are seeing. My instincts also are the same as those that suspect water and or coolant, but I would give it a good hot run a few times and then worry if I still was seeing it. Cool post.