I had an interesting short conversation with an Exxon tech support man. He said that the oil samples are best evaluated as a "trend analysis" system. The idea being that the presence of contaminants in one sample are not enough for diagnosis, but rather samples taken at different intervals would let you know if there is an actual problem by seeing if those numbers are increasing or merely remaining stable.
That is a good point on most of the factors. Especially when you don't personally know the oil change history. If it has been an especially long time since the last change either in time or miles, the readings would naturally be higher than a sample taken after a recent or proper oiil change period. It is still a good and valuable practice when seriously considering a bus. A bad analysis whether becuase of wear or neglect would serve as a red flag whereas a good result either means it is in good shape or the oil has recently been changed.
But as it relates to Doug's situation, the presence of Glycol is a concern no matter what. It still doesn't mean that there was enough to do the consequential damage (only physical inspection of the engine can determine that for certain). But it does mean that something is letting coolant into the oil.
I specifically asked him about glycol. It seemed he did not make a real distinction there. I guess that if the content is still within a safe level, a second test would tell you if it were increasing or stable. It still seems to me that you would want to track the problem down early.
Quote from: Lin on March 02, 2009, 12:51:56 PM
I guess that if the content is still within a safe level, ...
I guess that would be similar to my thoughts on it too. if glycol is within the specification limits, then it's fine and is not really a different case than the other factors. But if it is out of limits, it's presence likely indicates a failed gasket/o-ring, not just standard wear that should be followed over time. Coolant is entering the oil and must be remedied asap or major engine damage will follow.
Disclaimer: I am by no means an DD engine expert. But I have learned a lot about things to look out for from several who are. (and I stayed in a Holiday Inn Express once)
That contradicts what I have believed for a long time but I have forwarded the question to my oil analysis lab for their comment. I will post their reply here.
The duty cycle that most busnuts put the oil through will be an oil analysis nightmare, me thinks.
The regular opportunity for the oil to just sit and and the engine condensate, and the oil separate and settle, and whether we get enough mileage before we drag a sample out of it...
Remember, the collective experience of the oil analysis community is with running machines, not sitting machines.
Within certain measures, we need to be careful we don't read the tea leaves too closely, as our samples may be wonky.
I'll be curious as to what these folks might have to say about our extra light, sporadic duty cycles.
happy coaching!
buswarrior
When you change filters just cut them open and observe for any metal. We use oil analysis in the airplane biz but it is based on trend like previously said here. When you cut the filter open you can open the accordion paper element and get a good look. If your engine is coming apart you will see it.
http://www.aircraftspruce.com/catalog/topages/oilfiltercutter.php (http://www.aircraftspruce.com/catalog/topages/oilfiltercutter.php)
If you want to get really creative get some really strong earth magnets and place them on the outside of the oil pan on the bottom. After 6 months to a year drain the oil and drop the oil pan. All metal particles should be stuck at the location of where the magnets are attached. This usually only applies to steel not aluminum or brass or copper.
It makes sense to me that this would apply in all cases but where glycol (coolant) has been found in the engine oil. I suppose in my case there could have been glycol in the oil for some time (prior to my purchase) but since no prior test sample information is present, I would have to agree with HighTech and say that the presence of glycol is probably an indicator of something bad and should be remedied as soon as humanly possible.
Interesting information though and it definitely backs up my theory that there is a lot more information floating around on this forum than I will ever have time to absorb.
Doug
Well guys, I had hoped for more enlightenment but it is what it is:
From: W.T.Tanguay
Metro Tech Systems Ltd.
www.metrotechsystems.ca (http://www.metrotechsystems.ca)
The reason for concern for the Ethylene or Propylene Glycol in used oils is that under the operating conditions of an engine or a transmission the Glycol is a chemical which decomposes the oil with the result of gum and varnish deposits and sludge. Temperature, time of presence of Glycol and quantity of the contaminant are the key factors for the sludge to form. Glycol in new oils is nothing new, that has been around for a very long time but, because it is not there due to an engine problem, it is burned off rather quickly. Also for the Detroit 2-stroke or any other engine for that matter, if there is a small amount of Glycol present and that amount is not increasing, it is likely to be burned off before it can do too much harm. On the other hand if the reported small amount of Glycol is due to an engine or transmission system problem, the next time one checks again maybe too late to save the equipment.
Quote from: bobofthenorth on March 03, 2009, 03:47:50 PM
On the other hand if the reported small amount of Glycol is due to an engine or transmission system problem, the next time one checks again maybe too late to save the equipment.
I think that pretty much agrees with the point that once out of tollerance, Glycol content is too critical to just continue monitoring as one might with other factors that simply indicate wear. Wear is usually a gradual process and you can nurse a tired engine along quite a while if you have to. But a part failure that lets coolant into the oil, will lead to serious consequential damage and total breakdown in fairly short order.