oil change interval for synthetics

Hi Folks,
I switched to fully synthetic 5W-40 about a year ago and am wondering what oil change interval to use now. The manual says 6 months or 7 500 miles, but I am wondering if that's too often now that I am on synthetic and considering how the car gets used:
- yearly mileage of 3000 miles
- very few trips less than 10 mins
- worst case (very rare) cold start of 10 degC (50 degF), most starts would be above 15 degC (60 degF)

So how often do you think I should change it?

Thanks

I am not sure that anyone knows exact answer to your question but my gut tells me that if you change your synthetic oil it every 2 years or about 7000 miles in your case you should be fine. However, instead of listening to my ( or anyone's guesses) I would suggest that you take an oil sample every few months and send it to a lab for testing. That will give you an realistic and accurate answer if your oil is still good or it's broken down and ready for change...you can take oil sample from oil pan drain bolt, and at least in US test kit costs about $15-30 (iirc) - you simply mail it in and get your results back in a week or two.

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igor325
...take an oil sample every few months and send it to a lab for testing. That will give you an realistic and accurate answer if your oil is still good or it's broken down and ready for change...you can take oil sample from oil pan drain bolt, and at least in US test kit costs about $15-30 (iirc) - you simply mail it in and get your results back in a week or two.

Thanks Igor. Can you tell me who does it in the US? That'll help me find an Aussie equivalent.

I would say, change oil every year weather it needs it or not, even synthetics but I like to think I have a special connection with my machinery. You love yours, right?

Cheers, Rick

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nomis3613


Thanks Igor. Can you tell me who does it in the US? That'll help me find an Aussie equivalent.

See:
http://www.blackstone-labs.com/

http://www.oaitesting.com/#auto

Also you might find this read interesting
http://neptune.spacebears.com/cars/stories/oil-life.html

Regards,
Igor

Once a year is a minimum, doesn't matter if it is synthetic or dyno-age fluid.

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Michiel 318iS
Once a year is a minimum, doesn't matter if it is synthetic or dyno-age fluid.

Well actually it does matter whether it is synthetic or not.

I have used synthetic for over 35 yrs now for some 1 400 000 kms on 7 BMWs, the last being 660 000 kms on my present E30 88 325is and the oil change intervals that i have been using and continue to use are between 20 000 kms (12 000 miles) and 40 000 kms (24,000 miles) and I have not suffered any engine problems due to insufficient oil changes.

I really don't see why people use a once a year minimum, especially when not doing a lot of mileage. Even the interval calculators on our E30s will give at least 12000 miles between changes.

BTW, a sort of disclaimer - I used to make the base stock synthetic oil for Castrol when plant manager for BASF in Canada, so i do have some idea on the benefits of true synthetics.

Salut, Bob p.

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Bob P 325is 88

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Michiel 318iS
Once a year is a minimum, doesn't matter if it is synthetic or dyno-age fluid.

Well actually it does matter whether it is synthetic or not.

I have used synthetic for over 35 yrs now for some 1 400 000 kms on 7 BMWs, the last being 660 000 kms on my present E30 88 325is and the oil change intervals that i have been using and continue to use are between 20 000 kms (12 000 miles) and 40 000 kms (24,000 miles) and I have not suffered any engine problems due to insufficient oil changes.

I really don't see why people use a once a year minimum, especially when not doing a lot of mileage. Even the interval calculators on our E30s will give at least 12000 miles between changes.

BTW, a sort of disclaimer - I used to make the base stock synthetic oil for Castrol when plant manager for BASF in Canada, so i do have some idea on the benefits of true synthetics.

Salut, Bob p.

But Bob, all those short trips and small mileages, there has to be a lot of condensation build up of water in the motor. After a year, regardless of mileage, my oil is shot and looks it! I don't need an oil analysis to tell me. Just eyeball it in the drain pan!, which is span clean before hand. In fact (when I switched over to synthetic oil) I was surprised how played it looked after a years use and how much crap was in it... Rick

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rkj

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Bob P 325is 88

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Michiel 318iS
Once a year is a minimum, doesn't matter if it is synthetic or dyno-age fluid.

Well actually it does matter whether it is synthetic or not.

I have used synthetic for over 35 yrs now for some 1 400 000 kms on 7 BMWs, the last being 660 000 kms on my present E30 88 325is and the oil change intervals that i have been using and continue to use are between 20 000 kms (12 000 miles) and 40 000 kms (24,000 miles) and I have not suffered any engine problems due to insufficient oil changes.

I really don't see why people use a once a year minimum, especially when not doing a lot of mileage. Even the interval calculators on our E30s will give at least 12000 miles between changes.

BTW, a sort of disclaimer - I used to make the base stock synthetic oil for Castrol when plant manager for BASF in Canada, so i do have some idea on the benefits of true synthetics.

Salut, Bob p.

But Bob, all those short trips and small mileages, there has to be a lot of condensation build up of water in the motor. After a year, regardless of mileage, my oil is shot and looks it! I don't need an oil analysis to tell me. Just eyeball it in the drain pan!, which is span clean before hand. In fact (when I switched over to synthetic oil) I was surprised how played it looked after a years use and how much crap was in it... Rick

If there is a lot of crap in the oil, then you need better filters. The colour of the oil means little if the viscosity and lubricating properties are still intact.

As for moisture...your exhaust system is the only thing that really gets hurt by it. It only takes on good run with the engine up to operating temp to burn off any build up of condensation. The moisture is evaporated and vented out into the intake manifold.

I think too many people worry too much about oil changes and a lot of the nervousness has been instilled in them by the oil companies and the car makers who are in partnership with them.

I run synt in my car, which gets very little use, and change it every spring. Anything less, to me, seems foolhardy considering the cost of a change.

'93 190E 2.6 » days
'92 318ic » weekends
'85 280TE » resto



Edited 1 time(s). Last edit at 12/27/2009 10:02PM by ducatipaso.

Moisture only evaporates when the oil gets at temperature, which can take quite a while. And even then you need a number of miles before most of the moist gets vented out.

I agree that oil can last a lot longer when conditions are good (long periods of operation, without overheating). Trucks were getting oil changes every 120.000 km (when I was working at a trucking company) just because they run longer stints.

All considered, what's more expensive: an oil change every year, or an engine swap after a couple of years?

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Michiel 318iS
Moisture only evaporates when the oil gets at temperature, which can take quite a while. And even then you need a number of miles before most of the moist gets vented out.

I agree that oil can last a lot longer when conditions are good (long periods of operation, without overheating). Trucks were getting oil changes every 120.000 km (when I was working at a trucking company) just because they run longer stints.

All considered, what's more expensive: an oil change every year, or an engine swap after a couple of years?

Depending on mileage traveled and the conditions, I do change my oil at least once a year. It works out to an average of about 12,000km with synthetic.

I think the people we're talking about here are the ones who religiously change oil every 3 to 5,000m or every three to 4 months; just because that's what they've been taught to do.

It takes a lot of abuse to cause an engine to wear out in a couple of years. Not changing the oil would be the least of the causes for that kind of premature wear.

Hi,
Thanks to everyone for the replies. I'm leaning towards yearly changes now, which I can do no probs. I'll send off a sample to be tested just to be sure. I won't stretch it to 120,000km(!), but 6 months seemed a bit overkill when the car would only do about 1,500km in that time.

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rkj

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Bob P 325is 88

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Michiel 318iS
Once a year is a minimum, doesn't matter if it is synthetic or dyno-age fluid.

Well actually it does matter whether it is synthetic or not.

I have used synthetic for over 35 yrs now for some 1 400 000 kms on 7 BMWs, the last being 660 000 kms on my present E30 88 325is and the oil change intervals that i have been using and continue to use are between 20 000 kms (12 000 miles) and 40 000 kms (24,000 miles) and I have not suffered any engine problems due to insufficient oil changes.

I really don't see why people use a once a year minimum, especially when not doing a lot of mileage. Even the interval calculators on our E30s will give at least 12000 miles between changes.

BTW, a sort of disclaimer - I used to make the base stock synthetic oil for Castrol when plant manager for BASF in Canada, so i do have some idea on the benefits of true synthetics.

Salut, Bob p.

But Bob, all those short trips and small mileages, there has to be a lot of condensation build up of water in the motor. After a year, regardless of mileage, my oil is shot and looks it! I don't need an oil analysis to tell me. Just eyeball it in the drain pan!, which is span clean before hand. In fact (when I switched over to synthetic oil) I was surprised how played it looked after a years use and how much crap was in it... Rick

Rick, I think that Numis indicated that he did not take 'short trips' and the climactic conditions he stated aren't severe nor very conducive to condensation buildup.
At any rate, looking at oil has never been a good way to know what state the oil is in. The only thing that counts is are the original properties of the oil still present, eg. viscosity, shear strength, pour point acid number etc.. Finding sludge, etc in the oil pan doesn't indicate how the oil is doing, in fact, it might be indicating the the oil is doing a good job, one of the 'jobs' being keeping the particles in suspension so that they drop out in the oil pan, out of harm's way! BTW, most of that sludge etc is caused by combustion process and unburned fuel, causing varnish etc., which the synthetics can better deal with than conventionals and for longer.
I go by my years of experience in using synthetics (and conventionals) in both my cars and in the plants that I have operated, in stating that, in general, people need not change synthetic oils as often as some would claim.
There is one circumstance, however, when I would change oil often and air filters - sandy desert conditions. In those circumstances it is pointless to use synthetic, anyway, since the change intervals are so short.

Respectfully, Bob p.

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Michiel 318iS
Moisture only evaporates when the oil gets at temperature, which can take quite a while. And even then you need a number of miles before most of the moist gets vented out.


I agree that oil can last a lot longer when conditions are good (long periods of operation, without overheating). Trucks were getting oil changes every 120.000 km (when I was working at a trucking company) just because they run longer stints.

All considered, what's more expensive: an oil change every year, or an engine swap after a couple of years?

Actually the moisture evaporates when the oil temperature gets close to 100 C, which doesn't take very long in the engine where the oil is in contact with rotating and moving parts near the cylinders, maybe 30 secs. Also, where did this condensation come from? How did it get into the oil system in the first place, since that system is pretty well sealed?


I would agree, IF an engine swap were to occur after a couple of years and 12000 miles, which won't occur even with conventional oil.

Salut, Bob p.



Edited 1 time(s). Last edit at 12/29/2009 01:34PM by Bob P 325is 88.

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Bob P 325is 88

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rkj

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Bob P 325is 88

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Michiel 318iS
Once a year is a minimum, doesn't matter if it is synthetic or dyno-age fluid.

Well actually it does matter whether it is synthetic or not.

I have used synthetic for over 35 yrs now for some 1 400 000 kms on 7 BMWs, the last being 660 000 kms on my present E30 88 325is and the oil change intervals that i have been using and continue to use are between 20 000 kms (12 000 miles) and 40 000 kms (24,000 miles) and I have not suffered any engine problems due to insufficient oil changes.

I really don't see why people use a once a year minimum, especially when not doing a lot of mileage. Even the interval calculators on our E30s will give at least 12000 miles between changes.

BTW, a sort of disclaimer - I used to make the base stock synthetic oil for Castrol when plant manager for BASF in Canada, so i do have some idea on the benefits of true synthetics.

Salut, Bob p.

But Bob, all those short trips and small mileages, there has to be a lot of condensation build up of water in the motor. After a year, regardless of mileage, my oil is shot and looks it! I don't need an oil analysis to tell me. Just eyeball it in the drain pan!, which is span clean before hand. In fact (when I switched over to synthetic oil) I was surprised how played it looked after a years use and how much crap was in it... Rick

Rick, I think that Numis indicated that he did not take 'short trips' and the climactic conditions he stated aren't severe nor very conducive to condensation buildup.
At any rate, looking at oil has never been a good way to know what state the oil is in. The only thing that counts is are the original properties of the oil still present, eg. viscosity, shear strength, pour point acid number etc.. Finding sludge, etc in the oil pan doesn't indicate how the oil is doing, in fact, it might be indicating the the oil is doing a good job, one of the 'jobs' being keeping the particles in suspension so that they drop out in the oil pan, out of harm's way! BTW, most of that sludge etc is caused by combustion process and unburned fuel, causing varnish etc., which the synthetics can better deal with than conventionals and for longer.
I go by my years of experience in using synthetics (and conventionals) in both my cars and in the plants that I have operated, in stating that, in general, people need not change synthetic oils as often as some would claim.
There is one circumstance, however, when I would change oil often and air filters - sandy desert conditions. In those circumstances it is pointless to use synthetic, anyway, since the change intervals are so short.

Respectfully, Bob p.

Thanks Bob, That oil pan inspection (in a clean pan, I use it on all the bikes and cars) is more of a test for whats not there then anything else; if I don't see coolant or metal parts I'm smiling and as it drains into the dump can you really do get an idea why you drain your oil when its hot. After three years (I don't ride That often but...) my new race bike still has a metal flake bottom of the drain pan. This coming year/season I'll change over to synthetic.

Out here, on the east end of the island, it is actually rough conditions. We're kind of out at sea here great for sailing but not so good for motors.

Rick

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Bob P 325is 88

Also, where did this condensation come from? How did it get into the oil system in the first place, since that system is pretty well sealed?


Salut, Bob p.

I've often wondered the same thing. I spent a couple of years driving 4 miles each way to work and I never saw any evidence of moisture in my oil.

I use synthetic and change at 10,000 miles no matter how long it takes.

Here's a good place to spend a lot of time reading about oil: [www.bobistheoilguy.com]

John

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John Yust

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Bob P 325is 88

Also, where did this condensation come from? How did it get into the oil system in the first place, since that system is pretty well sealed?


Salut, Bob p.

I've often wondered the same thing. I spent a couple of years driving 4 miles each way to work and I never saw any evidence of moisture in my oil.

I use synthetic and change at 10,000 miles no matter how long it takes.

Here's a good place to spend a lot of time reading about oil: [www.bobistheoilguy.com]

John

Yes, that is a good site. BTW, I am not the Bob is the oil guy, but I guess I could be!

Not knowing any more about your driving conditions, I would say that you are still being conservative in your intervals.

If you see water in your oil, it probably isn't water but coolant, which doesn't boil off so readily and indicates a more serious problem.

salut, bob P.

Only when all of the oil is at temperature, all of the moisture can evaporate. And if you've driven an M3 (or any vehicle with a oil temp sensor), you'll know how long it can take.

Moisture gets in when hotter air (which contains moist in most of the cases) gets into contact with colder parts of the engine.

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Michiel 318iS
Only when all of the oil is at temperature, all of the moisture can evaporate. And if you've driven an M3 (or any vehicle with a oil temp sensor), you'll know how long it can take.

Moisture gets in when hotter air (which contains moist in most of the cases) gets into contact with colder parts of the engine.

It is not the oil temperature that counts, but when does the temperature of the water in the oil reach 100 C. If there is any water in the oil system, as soon as the oil water temperature gets to 100 C (not necessarily in the oil pan), the water evaporates. Any pressure built up by this water evaporating is vented through the PCV system. If you measure the temperature of the oil/water film at parts which are already at 300-400 C, then you will know that the water is evaporating at that point and doesn,t need to wait until it reaches the oil pan.

As for the water entering the oil system via hot air contacting colder engine parts, how does the air get into the oil side of colder engine parts? The oil circulation system which contacts the rotating engine parts and cylinder walls, is a sealed system, isolated from outside air. In fact, that is why idle is affected by unsealing the system, such as a loose fitting oil stick or leaking valve cover. The oil system is under pressure, therefore any leaks present usually result in gases and liquids leaking out, not into the oil circulating system.

BTW, my 325is has an oil cooler on it and I have measured the oil temperatures and agree that it takes a while for the oil to reach a high temperature, but remember the temperature measured is after the oil is cooled, not at where the oil has been heated by the engine, which reaches 100 C very quickly.

At any rate, a small amount of water in the oil in the pan is not a problem that one need worry about since this doesn,t affect the lubricating properties of the oil at the lubricating surfaces where there is no water present there.

Salut, Bob p.

A

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Bob P 325is 88
BTW, I am not the Bob is the oil guy, but I guess I could be!

You're are "Bob is the (other) Oil Guy"!!

FWIW, my car also has an oil cooler.

Love this topic!

I agree with most you say, but I still want to comment on it. ;-)

On short trips, water enters the engine through piston blow-by (especially when cold and especially on older engines), just as unburned fuel. On real short trips, even the unburned fuel will stay in the oil system (especially a problem on direct injected engines).
My previous 318iS had a pretty worn engine and after a week of just commuting to work (5 km), I could see a bit of moist in the oil. At that time, the cooling system was still OK. A longer drive for the weekend got that moist out.


And off-topic: moist in transmission oil takes very long to get out, as most systems aren't forcefully vented.

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Michiel 318iS
Love this topic!


On short trips, water enters the engine through piston blow-by (especially when cold and especially on older engines), just as unburned fuel. On real short trips, even the unburned fuel will stay in the oil system (especially a problem on direct injected engines).

And off-topic: moist in transmission oil takes very long to get out, as most systems aren't forcefully vented.

I would worry more about unburned fuel in the oil than a bit of water! The fuel definitely affects the lubricating properties of the oil, but then, the fuel evaporates (or distills) off even at a lower temperature than the water. Just because you 'see' water in a cooled down system, doesn,t mean that there is water when the system is at 100 C teperature. you might just be seeing water that condensed after the system cooled to below the dew point of the air introduced into the system.

I don't know why you keep on insisting that there is water in oil. Oil and water are immiscible and therefore there is very little water in the oil. There can, however, be water in oil circulating systems, but this water usually collects at certain points (oil pans, etc.) and therefore is not present at the points where water would be harmfull, and eventually is evaporated when the system reaches the water's boiling point.

Salut, Bob P.