Mix them you will be okay.

If your car is leaking oil DO NOT use synthetic oil. Synthetic oils have a higher flow rate than conventional oils which allows them to leak at a much higher rate. This is simply because the oil flows thinner.

Do not confuse the flow rate of the oil with the viscosity (weight) of the oil. They are two totally different things, 10w 30 conventional and 10w 30 synthetic will NEVER flow at the same rate.

For future reference any ticking sound coming from the head will generally become louder with a non-conventional oil as well.


As for mixing brands, I don't really see any harm in it. But again, I really would go and buy some good conventional oil until you fix that leak.

OP you are fine mixing oils if that is what you need to do.

If your car is leaking oil DO NOT use synthetic oil. Synthetic oils have a higher flow rate than conventional oils which allows them to leak at a much higher rate. This is simply because the oil flows thinner.

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Please elaborate. I want to know what you're talking about.

Alright, thanks guys.. I always use synthetic because f what I was told is that it's better for my car.. The leak will be fixed soon, so I'm by to worried about how much it's leaking.. Ill jut be sure to keep an eye out for it. Thanks for everyone's answers!

EDIT: I believe leak to be coming from the oil cap.. But it's leaks out about half already in about 1k miles.. Seems like a decent leak to me, and not just the seal in the oil cap.. But if anyone has had a oil cap leak about how much did ya leak?

pauleyman said:

Please elaborate. I want to know what you're talking about.

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If I'm correct, synthetic oil is a lot thinner. While this is what makes it better than conventional oil, it also makes it more susceptible to leaks.

Instead of swapping to conventional, go ahead and fix the leak.

Also, there are some additives like Lucas that can either make the oil much thicker, or coat the insides of the engine with a thick gunk to seal out small oil leaks.

pauleyman said:

OP you are fine mixing oils if that is what you need to do.



Please elaborate. I want to know what you're talking about.

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Gusu is 100% right.. Synthetic oil has a higher flow rate.. flow rate is defined as mass of a substance which passes through a given surface per unit of time. When you don't change your oil it will eventually combine with combustion gases and causes the oil to become acidic. So with synthetic oil you can go longer between oil changes because it will take longer to become acidic. Both conventional and synthetic have the same viscosity but in very basic terms synthetic oil is much thinner because of its higher flow rate. So if you put in synthetic oil in a engine that has a minor oil leak, it can cause that oil leak to become worse because it is "thinner" it can leak past seals, etc, at a greater rate. So if you are using conventional and your engine leaks a few drops, if you change to synthetic it will now leak more than just a few drops. It will leak more because it can pass through the worn or broken seal easier. Using synthetic will not cause oil leaks but it can make existing oil leaks worse.

Perhaps ill try the sealant from Lucas.. That way I can rule out a small leak.. Anyone know why it's called? Can prob pick it up from autozone.

with the thick gunk to seal out small oil leaks.

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I don't think I'd want GUNK in my motor.

Get a new oil cap. Rubber gasket on the cap has prob a hairline crack causing your leaking. Hope you're not seeing leakage from end seals.

Gusu is 100% right.. Synthetic oil has a higher flow rate.. flow rate is defined as mass of a substance which passes through a given surface per unit of time. When you don't change your oil it will eventually combine with combustion gases and causes the oil to become acidic. So with synthetic oil you can go longer between oil changes because it will take longer to become acidic. Both conventional and synthetic have the same viscosity but in very basic terms synthetic oil is much thinner because of its higher flow rate. So if you put in synthetic oil in a engine that has a minor oil leak, it can cause that oil leak to become worse because it is "thinner" it can leak past seals, etc, at a greater rate. So if you are using conventional and your engine leaks a few drops, if you change to synthetic it will now leak more than just a few drops. It will leak more because it can pass through the worn or broken seal easier. Using synthetic will not cause oil leaks but it can make existing oil leaks worse.

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We're way off topic here but I still want more information on this. Synthetic oils do not have as many viscosity enhancers in them as a standard oil as they do not need them so they have a tendency to maintain their viscosity properties over a wider time frame and rate of shear. The rate of shear is where they really shine. I did a few lab tests on them years ago and I saw no evidence of synthetic being any thinner than conventional even at elevated temperatures. What is your objective data regarding the topic please?

What I was wonderin' -

For simplicity sakes: the difference between dino and synth oils is the construction of the oil molecules.

Dino oils have various sizes of molecules in which they break down more readily under hot and cold conditions (why the recommended 3mo/3K oil changes when driving conditions are mainly town driving, and why dino oils are always used during motor break-in periods-you put synth oil in during break-in periods and the motor will never get broken in and rings will never seat), where with synth oils, the molecules are the same size, thus making the oil more durable (why some synth oils can stay in the block a lot longer-just change the filter at least every 5k miles and why AMSOIL can advertize 15k mile oil changes) which are great for turbo appl due to the durability against the cold and heat.

I've seen 20w/50 synth oils be as thick as dino oils in as much as 5w/30 synth oils be as thin as the same in the dino version.

Thus, going back on topic: If you're a quart low and only have a quart of dino, the two will mix together with no problems-just the mix of the two will slightly reduce the durability of the synth oil - and eventually an oil change will be needed.

-DSM