Switch from oil to sinthetic

my friend said it is not good to switch from oil to sinthetic when changing your oil from your car. is that true?

First it’s synthetic…And synthetic oil IS oil. Your friend is completely WRONG. You can switch back and forth between regular Dyno oil and Synthetic all you want without any problems what-so-ever. You can even mix them as much as you want.

A long time ago, there were some engines that didn’t handle the switch very well, and those stories have survived and become folklore. With modern oils and modern engines, there is nothing to worry about. Switch back and forth as much as you want.

Our fleet uses conventional motor oil and I use synthetic in our POV’s. They go into the same barrel at the shop and wanna know what happens when they mix?

It forms a stringy polymeric sludge. Without testing, I can only guess at the mechanism behind this, but I absolutely do not change oil types or brands due to the possibility of polymerization.

Me being a "nuts and bolts’ type guy and not being a chemist I had to resort to my favorite text book to answer this.

“Never mix synthetic oils with petroleum-based oils. Also, it is best not to switch from petroleum oils to synthetic oils on an engine that has many miles on it”

This is straight out of the book,and it my biggest suprise of the day.

Confusing the situation even more is the statement “Engine oils are available that are blends of mineral oils and synthetics to keep the cost down”.

Automotive Technology: a Systems Approach, Jack Erjavec 4th edition

I will quote some sentences from the owner’s manual for our 08 GM car with a dohc V6 engine.

Your vehicle’s engine requires a special oil meeting GM Standard GM4718M. Oils meeting this standard may be identified as synthetic.

When adding oil to maintain engine oil level, oil meeting GM Specification GM Standard GM4718M may not be available. You can add substitute oil designated SAE 5W-30 with the starburst symbol.

Substitute oil not meeting GM Standard GM4718M should not be used for an oil change.

Bottom line: You may add a quart of 5W-30 non-synthetic oil to the synthetic oil in the engine. GM makes engines. Does Mr. Erjavec?

I will use your analogy, GM makes itself bankrupt, has Mr Erjavec made himself bankrupt?

“Dyno” oil? For dynamometers?

How were you able to determine the sludge was a result of mixing synthetic oil with regular oil?

I haul my used oil away for recycling about once a year. Sometimes before I haul it off, I pour it from one container into another. There is often a sludgy substance that has settled to the bottom. This isn’t a mix of various types of oil, or even various brands. It is simply dirty oil that has had a chance to sit and settle. Isn’t it possible that is what you are seeing?

From the Mobil1 web site:
“Mobil 1 is fully compatible with conventional motor oils, semi-synthetic motor oils and other synthetic motor oils, should it be necessary to mix them. However, it is important to note that the superior performance of Mobil 1 will be reduced by diluting it in any way.”

I’d think they’d be risking lots of damage claims if this wasn’t true.

I cannot not speak to the results of mixing the oils, but I can offer an anecdote regarding my experience with switching from conventional to synthetic.

Switched from Castrol GTX to Mobile 1 last year in all four of my cars.

1997 BMW with 120k miles with slight valve cover leak, started leaking BADLY from the valve cover after the oil change. I replaced valve cover gasket. It still leaks.

1997 BMW with 220k miles with no leaks, started leaking from valve cover when synthetic oil was used. I replaced valve cover gasket. This one seems to be holding.

1991 Volvo 240 with 280k miles. Started leaking from valve cover gasket after oil change. I have replaced valve cover gasket TWICE since then (tried different brands of gasket). Current gasket leaks only a little.

2004 BMW 330 with 70k miles, switched from Castrol Syntec (which isn’t really synthetic, but BMW uses it and calls it synthetic). Car started leaking from valve cover gasket about 2k miles after switching to Mobile 1.

By the way, synthetic oil stinks really badly when it burns on the exhaust manifold. My whole family is bagging on me because all the cars stink now. I will be switching oils again.

Mazda specifically warns AGAINST use of synthetic oil in the rotary engine in my RX-8 . . . even went so far as to send me a video and warranty update about it. This is in addition to the warning in the owners manual. I personally think that it’s too expensive and would rather change more often with dino, JMO. Rocketman

Based on your anecdotes, is it possible you didn’t properly install the valve cover gaskets? Personally, I know how easy it is to mess up gasket seals when installing them. Even when I have a professional do the job, it is hard to find someone who can do the job in a way that makes the seals last.

I have had similar problems with my '98 Civic, even though I have always used conventional oil. About 2.5 years ago, I had my valve cover gasket replaced by a professional. In less than two years, it was leaking again. The whole time, I used one type and one brand of oil.

Please let us know if you continue to have these problems after you switch back to conventional oil. If switching back solves your problems, I will gladly eat my words.

If using synthetic oil is causing the oil to leak from a Valve Cover gasket…then it should be leaking EVERYWHERE. The oil there is NOT under pressure.

As for Castrol Syntec NOT being synthetic…Mobil-1 is NOW using the same manufacturing process to make their Full Synthetic (API Group III base oil). Amsoil is a Group IV synthetic.

Like from dynosaurs. Like the triglyceridoptopuss. That’s where triglycerides come from.

Sorry. The devil made me do it.