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Old 07-17-2019, 11:44 AM   #1
Rich-CO
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Default Mixing synthetic and regular oil

Hello all-----Is it ok to mix synthetic and regular oil?

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Old 07-17-2019, 11:51 AM   #2
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Default Re: Mixing synthetic and regular oil

Yes, several oil companies sell it already mixed. I use NAPA brand in my Lincoln
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Old 07-17-2019, 12:00 PM   #3
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Default Re: Mixing synthetic and regular oil

Hmm. Interesting to hear this. Back in my snowmobiling days, it was a definite no-no. Nobody ever gave a good reason, though.
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Old 07-17-2019, 12:07 PM   #4
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Default Re: Mixing synthetic and regular oil

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Originally Posted by tubman View Post
Hmm. Interesting to hear this. Back in my snowmobiling days, it was a definite no-no. Nobody ever gave a good reason, though.
One requirement for an oil to meet a standard (such as SJ, etc.) is that it has to be compatible with all other oils meeting that same standard.
There were a lot of myths and misunderstandings floating around in the early days of synthetic oil. Much like with the zinc "issue" today.
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Old 07-17-2019, 12:23 PM   #5
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Default Re: Mixing synthetic and regular oil

NAPA's synthetic blend!
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Old 07-17-2019, 01:13 PM   #6
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Default Re: Mixing synthetic and regular oil

Same weight and type, no problems mixing.
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Old 07-17-2019, 01:25 PM   #7
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Default Re: Mixing synthetic and regular oil

Motorcraft 5W20 synthetic blend, recommended for my wife's Explorer.
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Old 07-17-2019, 02:03 PM   #8
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Default Re: Mixing synthetic and regular oil

I was just getting ready to post what Bob posted! Ford recommends a blend on their newer cars.
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Old 07-17-2019, 05:43 PM   #9
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Default Re: Mixing synthetic and regular oil

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Same weight and type, no problems mixing.
It doesn't even have to be the same weight.
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Old 07-17-2019, 07:14 PM   #10
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Default Re: Mixing synthetic and regular oil

Thanks for all the excellent responses.
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Old 07-17-2019, 08:39 PM   #11
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Default Re: Mixing synthetic and regular oil

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Originally Posted by Rich-CO View Post
Thanks for all the excellent responses.
Rich
Agree.

Is it also a myth that once you use synthetic you canít go back to regular? I assume yes
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Old 07-17-2019, 10:06 PM   #12
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Default Re: Mixing synthetic and regular oil

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Agree.



Is it also a myth that once you use synthetic you canít go back to regular? I assume yes
I've read the opposite. They say going synthetic on an old dirty conventional oil engine can cause leaks because of the cleaning action synthetic is good at. And I experienced that myself first hand. I bought a O/T car with 200,000 miles and put about 10,000 more miles on it. Then I switched over to Royal Purple and lost a cam seal within 1,000 miles. Bad luck, just a fluke...? I don't know, but that's why I'm hesitant to put synthetic in my flathead.
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Old 07-17-2019, 11:24 PM   #13
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Default Re: Mixing synthetic and regular oil

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I've read the opposite. They say going synthetic on an old dirty conventional oil engine can cause leaks because of the cleaning action synthetic is good at. And I experienced that myself first hand. I bought a O/T car with 200,000 miles and put about 10,000 more miles on it. Then I switched over to Royal Purple and lost a cam seal within 1,000 miles. Bad luck, just a fluke...? I don't know, but that's why I'm hesitant to put synthetic in my flathead.
But your flathead doesn't have lip seals like your modern car (unless it has some modern adaptation, in which the new style seals should be made for use with synthetic).
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Old 07-17-2019, 11:33 PM   #14
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Default Re: Mixing synthetic and regular oil

I ran Mobil-1 20W-50 in the original engine in my '51 before I put the new engine in. I didn't see any increased leakage while I was using it.

Last edited by tubman; 07-18-2019 at 09:09 AM.
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Old 07-17-2019, 11:41 PM   #15
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Default Re: Mixing synthetic and regular oil

Here we are talking oil. I've read if you have a dirty engine don't use synthetic as it bonds to dirt and can clog the works. Now seals and synthetic? I've used what was cheap.



I think most use oil that is cheap and change it. I could probably use corn cooking oil in my car for 1k miles and probably be fine if I changed it back.



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Old 07-17-2019, 11:50 PM   #16
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Default Re: Mixing synthetic and regular oil

Make of car and year varies. My VW modern car requires "full" synthetic oil.
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Old 07-18-2019, 08:45 AM   #17
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Default Re: Mixing synthetic and regular oil

If you have a turbo (My F150 3.5 Ecoboost has 2) it is better and recommended to run the synthetic as it doesn't "coke" on the shafts like non synthetic oils will due to the heat involved. I don't run synthetic in my flatheads as they seem to mark their territory enough as it is and I don't want to chance worsening that.
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Old 07-18-2019, 09:12 AM   #18
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Default Re: Mixing synthetic and regular oil

I have been doing it for at least 15 yrs now. At one time synthetic was expensive. no more.
I would always make sure there was at least 1 qt of synth in my car, because it will save your engine, should it run dry for any reason.


walmart sells 5 qts of synth for a little over 15. at this point and it is a moot point, if worried about cost.


I run it in my lawn tractor, A's and all cars and vehicles. nothing better.
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Old 07-18-2019, 09:54 AM   #19
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Default Re: Mixing synthetic and regular oil

Saw a TV show not long ago were a few old cars were driven across the country. One of the old cars was a Ford flathead. This show was sponsored by Shell Oil. The flathead Ford driver said Shell ran several test to determine the best oil to use in the flathead for the cross country trip. The oil Shell provided to the flathead drivers was the synthetic mix 10W 40. Just my 2 cents worth.
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Old 07-18-2019, 10:20 AM   #20
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Default Re: Mixing synthetic and regular oil

All motor oil is compatible. That's an SAE requirement. Since I have a '40 with no lip type main seal, I run straight 30W Rotella. That 10w, etc. wants to drip out the rear. 30w doesn't. No freezing in San Diego so it's fine. You can mix weights, synthetic, etc. No problem.
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Old 07-18-2019, 01:10 PM   #21
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Default Re: Mixing synthetic and regular oil

Aviation is where the ester based synthetics started out for high temperature operations in turbine shaft and turbojet engines. Using mineral oil in them would be a disaster. In reciprocating aircraft engines, they tried straight synthetic oils but had problems so it was discontinued. Aircraft engines run hotter than the automotive engines due to them being air cooled.


Some of the misconceptions likely came from those problems but they have what are called semi-synthetics now. The engines would fail with those oils in the helicopters down here in Texas. They can only use straight grade 100 SAE 50 oils if they want them to last to TBO. Airplanes can and do get up to altitudes where the temperature is down right cold so it works OK for the most part. Helicopters general stay down low where there is better density for lift.

Last edited by rotorwrench; 07-20-2019 at 09:25 AM.
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Old 07-18-2019, 03:03 PM   #22
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Default Re: Mixing synthetic and regular oil

oil "base" stocks don't differ much in their own category (synthetic or petroleum). The rub comes in downstream, each manufacturer (for lack of a better word) adds their own additive package/chemical magic to those base stocks.
I'm not a chemical engineer so I don't know what happens when you "mix and match".
My .02?? I think this falls in the same category as guys trying to raise the octane rating of gasoline using off the self chemical stews.
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Old 07-18-2019, 03:06 PM   #23
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Default Re: Mixing synthetic and regular oil

all I'm saying is those guys are a hell of a lot smarter than I am
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Old 07-18-2019, 09:21 PM   #24
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Default Re: Mixing synthetic and regular oil

Lot of different oil options. Royal purple has some stuff with high zinc ratings. Or using a semi diesel straight 30w. Thick though.


Pertaining to the comment "I think this falls in the same category as guys trying to raise the octane rating of gasoline using off the self chemical stews."


Not sure why anyone would need to boost octane on a standard or slightly modified flathead. Octane in the 30s,40,50 was around 70 octane at best. Octane in the 20s was around 40 and gas was dirty. There is a reason I can get a hit and miss engine to a running heat and switch it to fire on kerosene (15 octane).

Last edited by Tinker; 07-18-2019 at 09:38 PM.
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Old 07-19-2019, 09:06 AM   #25
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Default Re: Mixing synthetic and regular oil

Tinker
I'm not suggesting any of us would want to raise the octane running a flathead. What I am saying is some people [itinerant racers mainly] attempt to raise the octane [essentially reformulate gasoline] using chemical stews available at the local parts store. Pure snakeoil.

That is in the same vein as people mixing oils; the home hotrodder outthinking engineers and oil companies who have spent many years and bazillions of dollars developing additive packages.
But hay, whatever turns your crank.
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Old 07-19-2019, 11:13 AM   #26
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Default Re: Mixing synthetic and regular oil

Quote:
Originally Posted by Gene1949 View Post
Tinker
I'm not suggesting any of us would want to raise the octane running a flathead. What I am saying is some people [itinerant racers mainly] attempt to raise the octane [essentially reformulate gasoline] using chemical stews available at the local parts store. Pure snakeoil.

That is in the same vein as people mixing oils; the home hotrodder outthinking engineers and oil companies who have spent many years and bazillions of dollars developing additive packages.
But hay, whatever turns your crank.
Gene, thanks for sharing some common sense! (which seems to be in short supply these days!)
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Old 07-20-2019, 12:52 PM   #27
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Default Re: Mixing synthetic and regular oil

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Originally Posted by tubman View Post
I ran Mobil-1 20W-50 in the original engine in my '51 before I put the new engine in. I didn't see any increased leakage while I was using it.
I run Mobil 1 15w50 in all of my old and air cooled engines. The mustang, dirt bikes, lawn mowers, pressure washers, etc all get it.

It's the only Mobil 1 that has the full amount of zinc for flat tappets. It being synthetic makes it work better in the cold, and stands up to heat a lot better... hence the reason using it in air cooled engines that tend to cook the oil. I've used it for decades in these applications. The 15w50 is also thick enough for flatheads, as I don't feel comfortable running thin stuff in these engines. Very affordable in the 5 quart jugs from Walmart, Advance Auto parts, Autozone, etc.

My $0.02
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Old 07-20-2019, 03:50 PM   #28
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Default Re: Mixing synthetic and regular oil

You are correct Mike. To the best of my knowledge, all oil that is at least 50 weight has high amounts of zinc. I started using it when I had a case left over from my dirt track days. The hemi in my racecar had an enlarged oil pan, dual filters and a large oil cooler when meant it took 13 quarts of oil for a change. When I built the car, all the old timers told me "hemi's need lots of oil". Changing the oil in that car was more of a financial decision than anything else.
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Old 07-21-2019, 09:40 AM   #29
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Default Re: Mixing synthetic and regular oil

With the racing oils, I think Mobil puts more zddp in there than is actually necessary for all but racing. Most all the figures I've seen on the subject put the nominal useful value at 1200 ppm per container for best anti wear results. Amounts above that actually start to get relatively acidic and can affect other materials in the engines. A person has to keep in mind that the stuff is made for racing with very hard use and constant oil changes and not for normal driving and setting for several months in the garage. I'm not saying a person shouldn't use it but be aware of what it's really for.

Last edited by rotorwrench; 07-21-2019 at 09:46 AM.
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Old 07-21-2019, 10:02 AM   #30
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Default Re: Mixing synthetic and regular oil

High zinc levels and detergents "don't play well together" is what the applications engineer at the Lucas Oil booth said. That's why the racing oils aren't meant for on road use. He said racing oil has little or no detergent and should be changed very frequently.
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Old 07-21-2019, 01:43 PM   #31
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Default Re: Mixing synthetic and regular oil

Synthetic oil is light years ahead of conventional oil, but beware that one of the qualities of full synthetic is its ability to flow.When we rebuild an engine we advise the owner to avoid full synthetic on early engines as it can, and does, leak around the crank seals
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Old 07-22-2019, 08:26 PM   #32
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Default Re: Mixing synthetic and regular oil

Quote:
Originally Posted by Gene1949 View Post
Tinker
I'm not suggesting any of us would want to raise the octane running a flathead. What I am saying is some people [itinerant racers mainly] attempt to raise the octane [essentially reformulate gasoline] using chemical stews available at the local parts store. Pure snakeoil.

That is in the same vein as people mixing oils; the home hotrodder outthinking engineers and oil companies who have spent many years and bazillions of dollars developing additive packages.
But hay, whatever turns your crank.

I think we agree?, I can come off sometimes being serious when I'm not.


"Racers" certainly have cause for increasing octane ratings. Drag in my thinking.

As far as a regular old flathead, MMO shots in the gas never hurt. Pertaining to fuel in my flathead anyway. Not that I'm buying cases, but always have a couple bottles. MMO does nothing to the octane rating. Just a little help to lube the valve assemble. Just something I do once and a while.


as far as oil, see I posted here #15. Explains my thought. Just change it.
.

Last edited by Tinker; 07-22-2019 at 09:24 PM.
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