It's OK to mix engine oil brands, types, and viscosity...

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Originally Posted by OVERKILL
Originally Posted by y_p_w
I don't do it intentionally, but there's always a blending whenever there's an oil change and a different oil is used or the manufacturer has changed formulations. I remember having 4 different bottles of Kendall 10W-30 that were labelled exactly the same way, but they were clearly different by smell. Some engines apparently keep about 30-40% of the previous oil when changed.

I suppose there's always the possibility that a witch's brew can create strange interactions. I remember one guy working in an engine testing lab said that the occasional mixing of different additive packages could result in two different 5W-30s with a viscosity maybe in the 20W-40 range.


I'm interested in the source of that claim. That's like an engine with a 5L sump only draining 3L of oil and taking a 3L change capacity. I don't believe I've ever run across that. About the closest I can think of would be the old double-hump Ford oil pans where somebody neglected to drain the front part of the pan, but even then, that wouldn't be 2L of oil.

My wife's 2002 Civic LX lists a 3.2 quart change amount without a filter. The owner's manual says 4.4 quarts total capacity. So that's more than 27%. It's certainly possible to do an oil change (still at the min level on the dipstick) where it's within specs with 30% of the oil still remaining. But these numbers are rounded up/down so I'm not sure. Still - there's a good deal of oil left when there's an oil change. Not sure what the number should be when talking about minimizing compatibility issues, but even with a filter it's more than 20% of the previous oil in there.

I heard the original Boxster was kind of large. I know it was about an 8-9 quart change, but I can't find the total capacity.
 
Originally Posted by Patman
My LT1 calls for 7 quarts of oil but it only takes 6 quarts to show full on the dipstick after an oil change, but even that's only 15% getting left behind.

I do find it a bit odd that the owner's manual says to use 7 quarts, because if someone just used that figure without double checking on the dipstick first, they'd overfill this engine by a quart. The engine probably takes 7 quarts right from when it's brand new and doesn't have any oil in it at all yet, but that's not the number that should be listed in the manual for subsequent oil changes.


Or the dipstick isn't an exact representation of capacity and there may be a fudge factor for consumption.
 
Originally Posted by y_p_w
Originally Posted by OVERKILL
Originally Posted by y_p_w
I don't do it intentionally, but there's always a blending whenever there's an oil change and a different oil is used or the manufacturer has changed formulations. I remember having 4 different bottles of Kendall 10W-30 that were labelled exactly the same way, but they were clearly different by smell. Some engines apparently keep about 30-40% of the previous oil when changed.

I suppose there's always the possibility that a witch's brew can create strange interactions. I remember one guy working in an engine testing lab said that the occasional mixing of different additive packages could result in two different 5W-30s with a viscosity maybe in the 20W-40 range.


I'm interested in the source of that claim. That's like an engine with a 5L sump only draining 3L of oil and taking a 3L change capacity. I don't believe I've ever run across that. About the closest I can think of would be the old double-hump Ford oil pans where somebody neglected to drain the front part of the pan, but even then, that wouldn't be 2L of oil.

My wife's 2002 Civic LX lists a 3.2 quart change amount without a filter. The owner's manual says 4.4 quarts total capacity. So that's more than 27%. It's certainly possible to do an oil change (still at the min level on the dipstick) where it's within specs with 30% of the oil still remaining. But these numbers are rounded up/down so I'm not sure. Still - there's a good deal of oil left when there's an oil change. Not sure what the number should be when talking about minimizing compatibility issues, but even with a filter it's more than 20% of the previous oil in there.

I heard the original Boxster was kind of large. I know it was about an 8-9 quart change, but I can't find the total capacity.


What's the with filter capacity? I find the "keep the filter" thing a weird Honda quirk, most marques include the filter in the change capacity.
 
That's what bothers me about dipsticks, it's hard to tell for sure if they are accurate. I much prefer the electronic oil level in my wife's BMW, there is no guesswork involved there.

But FWIW, other LT1 owners I've talked to that change their own oil also mention they see the level on their dipstick as full after adding only 6 quarts.
 
Originally Posted by Patman
That's what bothers me about dipsticks, it's hard to tell for sure if they are accurate. I much prefer the electronic oil level in my wife's BMW, there is no guesswork involved there.

But FWIW, other LT1 owners I've talked to that change their own oil also mention they see the level on their dipstick as full after adding only 6 quarts.


Sure, but I'd expect GM might be a little "generous" with the dipstick capacity so that it masks some consumption during an OCI, given how infrequently folks check their oil nowadays.
 
Originally Posted by OVERKILL
Originally Posted by y_p_w
My wife's 2002 Civic LX lists a 3.2 quart change amount without a filter. The owner's manual says 4.4 quarts total capacity. So that's more than 27%. It's certainly possible to do an oil change (still at the min level on the dipstick) where it's within specs with 30% of the oil still remaining. But these numbers are rounded up/down so I'm not sure. Still - there's a good deal of oil left when there's an oil change. Not sure what the number should be when talking about minimizing compatibility issues, but even with a filter it's more than 20% of the previous oil in there.

I heard the original Boxster was kind of large. I know it was about an 8-9 quart change, but I can't find the total capacity.


What's the with filter capacity? I find the "keep the filter" thing a weird Honda quirk, most marques include the filter in the change capacity.

I heard it used to be fairly common in the 60s and 70s. I did oil changes on an '89 Integra and a '95 Integra GS-R and both specified an oil and filter changed together every time.

But for this car I really hate changing the filter. The oil is easy. I can do it flat on the ground without jack stands or ramps. I've got ramps (and the recommended wheel chocks), but I hate using them. But the filter drains on the axle and I'd rather not deal with the ramps if I could help it.

But again, I really think in this day and age oil filtration is overrated. For my WRX, Subaru went to this teeny-tiny filter and they didn't stress about it lasting an entire OCI. I recall someone here commented in the oil filter forum that modern engines barely put out anything that needs filtration unless there's something seriously wrong and where the filter isn't going to save anything.
 
Originally Posted by OVERKILL


Sure, but I'd expect GM might be a little "generous" with the dipstick capacity so that it masks some consumption during an OCI, given how infrequently folks check their oil nowadays.


One thing that really used to bug me with the 98 Corvette I had for 9 years was that it's dipstick would show full for the entire OCI but when I drained the oil it would be a quart low! I couldn't never figure that one out, and it just added to my hatred of the conventional dipstick.
 
Originally Posted by Triple_Se7en
Originally Posted by Nickdfresh
It's probably okay, but not smart.

Baloney
30 years doing it with no issues and you are calling me a dummy?
hahahahaha..... now that's not smart.


It seems like you run the same oil in every listed vehicle?
 
Says here, not a good idea to mix oils or add oil additives to today's oils, Pennzoil for the last 50+
cheers3.gif

https://www.machinerylubrication.com/Read/31107/oil-lubricant-additives
 
Originally Posted by Triple_Se7en
Originally Posted by Nickdfresh
It's probably okay, but not smart.

Baloney
30 years doing it with no issues and you are calling me a dummy?
hahahahaha..... now that's not smart.


Nothing has blown up...that's all...that's not science...and having done it for 30 years doesn't make you a scientist or tribologist.

The oil manufacturers tell you it's not good practice and to avoid it.
The engine failures that HAVE occurred (there's SAE papers on it) have been catastrophic loss of pumpability at relatively benign temperatures. The oil becoming a 20W would not be apparent in a lot of case (*)
The formulators on BITOG suggest that it's not good practice, and that the first place to see issues is the failure of the "W" grade".

The MISCIBILITY standards simply meant that the oils are mixed with 7 reference oils, cooled, heated, and cooled again, and they don't split like salad dressing or drop out chunks...they don't test ever oil with every other, or any actual performance test other than splitting or blowing chunks.

Essentially...that nothing is likely to blow up


(*)BTW, you suggest that if the "W" grade fails, that it's engine design at fault...could you please elaborate on the mechanism.
 
If I have oil left over it goes into the OPE's. I've eliminated that problem by trying to use the same oil in all vehicles. The Ranger takes 4.5 quarts the Van takes 4 the F150 takes 5 and the 4Runner takes 5.5 so it seems to work out. I'm not a chemist so I don't mix. When I drain the oil mine keep less than a half quart hidden in the engine.
 
Originally Posted by Nickdfresh
It's probably okay, but not smart.



Today the baseoils add packs between brands are more similar than ever.
 
Originally Posted by OVERKILL
... What's the with filter capacity? I find the "keep the filter" thing a weird Honda quirk, most marques include the filter in the change capacity.
Most manuals I remember gave capacity both with and without filter. My Prius manual does, and the service manual also shows dry fill capacity, so we can easily compute the residual percentage. (4.7-4.2)L/4.7L = 10.6%, which is probably typical.
 
Originally Posted by CR94
Originally Posted by OVERKILL
... What's the with filter capacity? I find the "keep the filter" thing a weird Honda quirk, most marques include the filter in the change capacity.
Most manuals I remember gave capacity both with and without filter. My Prius manual does, and the service manual also shows dry fill capacity, so we can easily compute the residual percentage. (4.7-4.2)L/4.7L = 10.6%, which is probably typical.


10% is a heck of a lot more reasonable than 30-40%.

BTW, none of my Mopar manuals, going back to 2006, list capacity without the filter, it is given with filter exclusively, FWIW.
 
if the alternative to a mix is low or overused oil, i will take the witch's brew anyday. i lived overseas for 30 years mostly in nonwestern countries, seen alot of oddball, unsophisticated but effective car use and care. in north america ive mixed brands of synthetic, noneuro spec, close but not exact weights to top off a former mb c280 and current vw passat 2.5 without issue a few thousand miles before the 10k dealer change. for a simple toyota like my yaris (you should see the beatings that ever-running yarii take in the philippines and indonesia) i wouldn't think twice mixing at the regular oci even with unmatched weights.
 
I agree that modern engines, especially DI and/or turbo/supercharged engines, are generally harder on oil than older carbed or port/TB injected engines. So if I owned one, I would be very particular about the lubricants with those vehicles. But I've never owned one.
I avoid mixing *substantial quantities* of different oil brands/viscosities. E.g. I'm OK mixing 1 quart brand X 10w30 with 4 quarts brand Z 5w30, no worries at all. But I would try to avoid mixing 2 quarts brand X 20w50 plus 2 quarts brand Y 0w20 plus 1 quart brand Z 5w30. There probably wouldn't be an issue, not in the vehicles I own, but it just doesn't seem right to do this. I've used lots of different brands and grades over the years, and with the residual used oil left in the engine of a different brand/grade, I've never had any issues.
 
There's a few guys here arguing that it's dangerous because you're mixing oil properties, blah blah blah.

I don't believe it one bit.
 
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