diesel oil mixing

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I would like to make some comments about oil mixing, that is mixing different brands of oil, the thought that it's okay.

We have a diesel generator at a remote site and because of some company politics I won't mention the brand name or the oils involved but talk about the problem in general. This gen/set gets run infrequently but when it runs it's at full load and 3,600 rpm. It gets run for sometimes 3-10 minutes and sometimes for 8-10 hours and anything in between but seldom over 10 hours. Most runs are under 10 minutes and the time between runs is almost always an hour or so and it never sits for more than 2 hours, ever.

The mechanics, trying to be kind to this important engine were changing the oil frequently, sometimes changing it when they were present at the remote site event though the Hobbs meter might indicate well under 100 hours, sometimes less than 50. Because of this ad hoc schedule they would change the oil when they were at the sight and use whatever oil they had on the truck as long as it was one of their diesel rated oils and was 15w-40. Also, because of an oil cooler and associated lines about 10% of the approximately 3 gallons of oil remained behind even if the thermostatic valve was open.

Well, there was a problem. At about a quarter of the expected engine life based on previous experience with this engine/generator, the engine shut down on a short run and would not restart, no oil pressure. On tear down the engine was a mess. Scoring on the crankshaft and camshaft, damaged bearings, oil pump pickup screen completely sludged up and oil seals completely shot. The lab told us it was a clash of additives specifically the rust inhibitors and non-zinc vs zinc anti-wear additives. The oil and water failed to keep separated and the resulting mixture was not a good lubricant. Evidently because of short runs and a very large oil sump the crankcase always had some moisture present that was never burnt off until a long run. Because the oil and water never mixed this was not a problem in the past twenty years with this kind of setup at several sites. The clash of rust inhibitors and anti-wear additives in the presence of moisture killed the engine long before is time. It was determined that rebuilding the engine was not feasible and a new long block was ordered. You can bet that there are some new maintenance requirements in place and mixing brands of oils is now prohibited.

I think that when oil experts answered the question about mixing engine lubrication oils their answer was that the oils would mix with each other, that they were miscible but there was no guarantee that the resulting homogeneous mixture would meet any previously accepted standards for either oil.
 
Originally Posted By: 901Memphis
Sounds like it didn't get up to temperature enough, which would have had the same problem with any oil.


No, this exact kind of setup at 7 sites has been working for almost 20 years with no problems, same engine, same generator, same controls, same enclosure. A very similar setup has been in operation since the late 50's when the DEW line was completed in that area, no problems. The lab stated that it was definitely the clash of additives in the different oils. The moisture was not the cause but was one of the contributing factors in the severity of the failure.

3 of the sites are at or north of the DEW line in Alaska. No problems. Same operational setup. Very similar total hours. The failure was in the desert in south eastern California. Ambient temperature at the time of the failure was 98F, humidity 46%, no wind. The problem here is that to get to this site is a 2 hour drive off the paved road sometimes in 4 wheel drive. The service truck is big and the ride is ruff. It's not a very popular part of the service route. Even one less trip is a blessing.
 
Originally Posted By: OneEyeJack
I think that when oil experts answered the question about mixing engine lubrication oils their answer was that the oils would mix with each other, that they were miscible but there was no guarantee that the resulting homogeneous mixture would meet any previously accepted standards for either oil.


That's ALL the compatibility test tests for.

That it doesn't form a split salad dressing when mixed, frozen, cooked, and re-frozen.

The test doesn't test for anything other than the mix splitting.
 
So the answer should be, never ever mix brands of engine oil or oils from the same manufacturer that are of different spec's.

In the case of the gen/set failure it was at the only site where there was a source for different brands of oil. All the other sites use one brand, one viscosity. They did not mix brand of oil because they could not. Nothing else was available.
 
Originally Posted By: OneEyeJack
So the answer should be, never ever mix brands of engine oil or oils from the same manufacturer that are of different spec's.


The standard test tests for stable miscibility of the test oil versus six different standard test oils (not every oil on the shelf).


In the case you have, the specs (zinc versus non zinc) are wildly different additive packs. So you've found a (rare) case where individual oils that mix with all 6 of the reference oils don't get along with each other...possibly every additive was operating at a fraction of it's normal concentration/effectiveness.

If the oils were closer to being "typical" it's far less likely that you would have had a problem.
 
Originally Posted By: 01_celica_gt
I agree with shannow, what exactly are they testing for?

I don't see how mixing of different oils can cause failure...


We sure found out that mixing can cause a problem. And no matter how rare this problem was it is preventable by not mixing oil. The lab repeated the test on a second sample with the same well defined results. The damage noted on the tear down along with the lab results are a very clear indication that mixing oils may work most of the time it's not worth the risk. We compared the oil of 3 similar sites and they tested just fine, same setup but with one brand of oil, same spec's, always. The 3 sites were picked because although the setups were identical, the oils were from 3 different popular brands available almost everywhere.

The problem was also aided by the oil left in the oil cooler and lines which was about 10% of the total capacity of about 3 gallons. The lab said there was probably enough oil with the offending additive left behind to set the process in motion. After the oil pressure safety circuit was taken out of the system the engine did turn over one revolution on the starter, it was not seized. The bearing manufacturer said the problem happened within a couple of house of operating time, that it was definitely not long term and it was not a sudden failure, either. The oil filters were completely plugged up, too. There was no rust visible anywhere inside the engine but the bottom of the oil pan was discolored and there were some tiny specs of bearings and piston rings in a layer of sludge in the pan but no evidence of excessive heat. If the oil pressure safety switch had not shut the engine down there soon would have been a dramatic failure.
 
Originally Posted By: 01_celica_gt
I agree with shannow, what exactly are they testing for?

I don't see how mixing of different oils can cause failure...


No, the Standard that people here rely on "that means that oils must all be compatible, mix away" only checks for miscibility and that they don't separate.

There are no tests for water separation, anti-corrosiveness, or wear protection on the blends, nor any test that ensures that the mix meets any of the standards that either new oil meets.
 
It sounds to me that the difference between the failed gen/set and all the others is not only the mixing of oils, but the frequency at which it was changed and mixed.

If I understand what you're saying correctly and translated it into a typical automobile "mixing" schedule, that would be like me draining two quarts of oil from one of my vehicles every week and replacing those two quarts with "whatever I happened to have on the shelf," thus ending up with who knows what in the motor. I would say that is radically different than mixing 3 quarts of 15W40 with two quarts of 10W40 and driving for five thousand miles under normal operating conditions.

Now, having said that, I will add that back in the late 80's, I was changing the oil in my old Chevy. I had a bunch of different oils on the shelf that had been opened, some with a little, some with as much as half a quart. I mixed it all together and poured it all in the Chevy. After a few hundred miles, the oil had a horrible stink that I can only describe as a burnt acid smell. I drained the oil into a pan and replaced with five quarts and changed the filter. I remember putting the oil in a five gallon bucket and putting it in the shed. The next day, when I opened the shed door, the stink was overpowering. I assumed then that the additives in the oil "clashed" and created some kind of unholy mixture.

For me, that was a one time event as over the years I have mixed various brands and weights of oils together with no problem, (even mixing different kinds of used oils together to put in old beater cars). Could it be that like yours, this was a rare event of radical additives attacking each other?
 
Does anyone know of two additives that are used in oils that are known to not mix well or cause a chemical reaction? I have never heard of such a thing happening like that with an engine.
 
Originally Posted By: morepwr
Does anyone know of two additives that are used in oils that are known to not mix well or cause a chemical reaction? I have never heard of such a thing happening like that with an engine.


Me neither, at least not with modern oils formulated to diesel specs.

It seems as if we're shooting into the dark unless we know what oils were used and what labs reported this?

Stuff inside an engine can fail, like a faulty oil pump.

Quote:
The lab told us it was a clash of additives specifically the rust inhibitors and non-zinc vs zinc anti-wear additives.


I would like to know how they determined this.
confused2.gif


Did they use afetrmarket additives in addition to the diesel rated oils?

Something doesn't add up here.


For a dry desert environment with those temps, even 10 to 15 minute run times should be sufficient. In Alaska, the run times would have to be increased.
 
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Hi,
OneEyeJack - You said this;

"Because of this ad hoc schedule they would change the oil when they were at the sight and use whatever oil they had on the truck as long as it was one of their diesel rated oils and was 15w-40."

IMO it seems to me there is a great chance that the lubricant's specification(s) were incorrect for the engine

I've seen this type a failure a number of times and it has almost always been traced back to the incorrect lubricant being used
 
Originally Posted By: Doug Hillary
Hi,
OneEyeJack - You said this;

"Because of this ad hoc schedule they would change the oil when they were at the sight and use whatever oil they had on the truck as long as it was one of their diesel rated oils and was 15w-40."

IMO it seems to me there is a great chance that the lubricant's specification(s) were incorrect for the engine

I've seen this type a failure a number of times and it has almost always been traced back to the incorrect lubricant being used


That's what I was thinking but decided to comment with the remark "Interesting". I was waiting for our resident experts to weigh in, I'm glad you commented.
 
I am going to hope that any lube used would have been API CJ-4 approved, as it's been out for 7 years now ... I would also presume that any lube used would have been a reasonably consumable brand name or big house brand, and not some boutique brew from an expensive blender. So I must suspect that any/all additives would have been reasonably compatible.

More info is always better; would be helpful to understand the lubes in play, the lab, etc. However, I also understand the hysterical way some here will over-react to brand "X" and brand "Y" co-mingled, and forecast the doom of all engines that ever had more than one flavor in the CC.

I find it hard to believe that the add packs clashed with such severity that it caused this issue, as claimed by the lab. However, I am more certainly a noob when it comes to the real chemistry, and that's why Mola's input is vital here. Few, if any, understand the additive market as well as he.


I would have to think it would have been some "also used" (uninformed but well intended) extra additive made it's way in there, and not one that came from the bottle. But I doubt with such money down the drain that anyone will 'fess up to it.
 
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