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.
 
tubman said:
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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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.
 
NAPA's synthetic blend!
 

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I was just getting ready to post what Bob posted! Ford recommends a blend on their newer cars.
 
adileo said:
Agree.



Is it also a myth that once you use synthetic you can’t go back to regular? I assume yes
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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.
 
WABOOM said:
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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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).
 
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.
 
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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.



.
 
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.
 
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.
 
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.
 
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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