mixing engine oil

Has anybody heard of mixing synthetic oil with conventional oil and it turning to road tar, and ruining the motor, or is this a extreme case??

Oil is cheaper than rebuilting an engine.
Why mix oils?

Sounds like a fairy tale to me. You would just loose much of the benefits of using synthetic oil.

If you read the comments on the container what you said is baloney....for an acceptable word used on this forum.

Secondly, surely you are aware that Synthetic Blends, that are very popular and have been for years, are the process of mixing chemical and organic compounds..........Some areas of the country that are in a salty and/or high humidity environment have proven that mixing the two types of basic compounds results in economy of scope, better temperature extremes protection, and increased protection from internal metallic rusting. Besides the blends offer a cost advantage.

NOT a common issue.

I know of a guy who has had his oil changed for YEARS at a relative's shop and has had them use half synthetic with NO negative issues. (Dunno if there are any POSITIVE bennys EITHER, LOL!)

You can even buy ''synthetic blend'' motor oil with the blending already done for you.

Hogwash! Been using the Ford synthetic blend for a long time.

(quoted from post at 08:42:17 03/02/23) Has anybody heard of mixing synthetic oil with conventional oil and it turning to road tar, and ruining the motor, or is this a extreme case??

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That was something going around what, 20+ years ago when synthetics were first hitting the market? Have not heard it in a long long time. Not sure why you'd dredge it up now after synthetic oils have proven themselves time and again.

If there is any chance at all of a reaction it will be in the additive packages. Two additives liking each other a little too much and merging to form something new. IF it happens it is EXCEEDINGLY RARE. It is not in the best interest of an oil company putting out a product with an additive that reacts with additives in other products. They want to GAIN market share, not shoot themselves in the foot.

a good synthetic oil will not do that. they are compatible with conventional oils, but as others say you loose more benefits of watering down the synthetic that you ever gain.

IF turning to tar happened a cause could be that the synthetic oil cleaned a very dirty engine out and the gunk that broke loose and settled somewhere else is what they saw.

I've been an AMSOIL dealer for quite a while and the one car i didn't flush the engine out when i converted the car (after i bought it) from conventional (or what every the quicky lube place the previous owner used put in it) to full synthetic it plugged the filter after a coupe thousand miles and I had a light rattle at start up. swapped a new filter and no issues after that for about 100,000 miles before i sold the car. Since then i always use engine flush when switching. The older and dirtier the engine (and/or an engine that is not running right and has gas/fuel or antifreeze in the oil) could have that issue. maybe not but good chance of it.

not sure how the synthetics would behave if the old engine oil had stop leak or STP, lucas or other cure in a bottle snake oils in it.

for the $ blends are worth bothering with... having said that AMSOIL JUST came out with a 50%+ blend of diesel and hydraulic oils so.. ???

I just heard it yesterday, i use conventional oil in all my tractor/pickups,it sounded extreme to me too,so sorry to be so uninformed !!!

I heard something like that back in the mid '70s.

Never seen it happen. I suspect it was just fear mongering of something new. I even heard if it was low, and you didn't have any synthetic oil, to top it up with water! How ridiculous was that!

Besides, when you change oil, there is still some left that doesn't drain out. If they were incompatible, the problem would start right there.

Would I mix them just to be doing it, no. But if I had to top up and it was dangerously low, I would.

I heard that 20-30 years ago and was even told if I mixed regular oil and synthetic in the truck transmission it would do something like that also. I have mixed both before in cases of keeping levels up then whrn time came for changing just drained out and filled with my choice of oils. In the semi I keep synthetic 50 in the transmission for shifting in cold weather and never change it for warm weather. It now has over a million mmiles on with no issues so guess it is fine. I have mixed rearend oils in the past for the same reason and same mileage with no problems and no tars or other oil problems. I run a synthetic 75/90 in the rear ends less drag in cold weather with it.

If their oil turned to road tar I would expect it had more to do with lack of changing it or coolant mixing with the oil than the mix of conventional and synthetic.

Sounds to me like it's a carryover from back in the 60s when I always heard that mixing different brands of oil would cause them to coagulate.

Question anything you hear when old men, restaurants, and/or coffee are involved at any level.

I used that oil in the Wife's 2003 Mercury Mountainer since it was brand new and traded it with over 215,000
miles, the 4.6L V8. The car had it's share of problems but NOTHING in the engine ever gave problems. I've
still got a few quarts of the blend in the shop, been using it to top-up the wife's 2015 Edge with 2.0L 4 cyl.
Has 97,000+miles and uses half a quart between oil changes.
There's SO much mixing of chemistry in today's motor oil, how's anyone going to tell which part of oil is
which? After 10 miles it all looks the same.

If that was the case synthetic blend oils wouldnt be manufactured. Ive heard other things about mixing but this is a new one. Tar you say? Like hard chunks made from carbon blowing past rings or like 5 quarts of molasses?

I know of one person that happened to in about 1983 or 4. My neighbor farmers had an F250 almost new maybe an 81. They put synthetic oil in it and it locked up the oil pump. In 1983 one of my college professors was a salesman for Conklin products. They sold lubes and even liquid fertilizer. He gaves us students a nice lube demo and talked about synthetic oil. At that time he said it had to be what he called Para synthetic or it would congealed with regular oil. The only way he said their pure synthetic could be used was if you started with a freshly rebuilt engine. Keep in mind this was the early 80's.

I've been using whatever oil I have handy or is cheap for over 100,000 miles on my car. Conventional, blend or synthetic. I bought it with 150 some thousand on it for $250 because it needed a rear driveshaft. It has bad valve stem seals so it burns a little oil. It's got 270,000 on it now and I drive it 90 miles round trip to work and back every day so I'm thinking the different oils hasn't hurt it any!

You forgot alcohol.

Has anyone noticed that GM builds engines that only run synthetic oil, like the Corvette. And it is widely held that you are to never put synthetic oil in a new engine because it needs friction to seat the rings. The answer is, they run the engines by electric motors without a pan or ignition to break them in before they are started. Separate oil systems and filter systems. JUst information you did not know you needed!!