Using fluid analysis as a diagnostic tool

Editor’s note: This is Part Two of a three-part series on RV health and wellness.

By Wayne Hulit
CEO, Cedar Mountain RVI

In Part One, we explored how truckers use fluid analysis to determine the optimum time to change the oil in their rig so that they get maximum value out of the investment in their oil, and savings by avoiding premature oil changes.

The reasons are largely technical, but each oil change they avoid will reduce their oil expense by 8 percent. Those savings are reinvested in routine Oil Analyses. That’s a smart investment and cheap insurance against a $15,000 repair bill.

On the technical side, the reason is that the defining value of oil — applying an even coat of oil on the engine’s moving parts — is contaminated over time to the point where that coating begins to thin, and wear on moving parts like pistons and bearings increases, ultimately leading to engine failure.

Fluid analysis - towed RVWe recognized that all RVers don’t come from the trucking industry and don’t have a trucking background. But our Class A RVs are built on truck technology. As full-time RVers, we may not be putting 100,000 asphalt miles a year on our engines and transmissions, but the miles that do accrue are often at dusty campgrounds with uneven road surfaces.

How can we use fluid analysis to help save money by not over spending on premature oil changes yet keep tabs on the health and wellness of our RV? Let’s look at some of the ways we can use the science of fluid analysis to inform us of the health and well being of our RV.

We’ll look at two cases. Case I is a vehicle that had a single oil analysis performed; and Case II is a vehicle that routinely had oil analyses performed over a period of months. First, we’ll examine Case I using its single oil sample and attempt to diagnose the health of the vehicle. Then we’ll compare and contrast it to the diagnosis of Case II. In both cases, the vehicles roll 12 months of the year.

Oil is the Blood of an Engine

Like blood to the body, oil brings healthy anti-oxidants (additives) and lubrication (base oil) to the engine’s internal moving parts such as crankshaft, bearings, piston, camshaft, rocker arms and other vital engine components to keep it functioning properly. Oil manufacturers developed a regime of chemical additives such as boron, potassium, calcium, molybdenum, and other elements blended into the oil to promote the engine’s longevity by creating a frictionless environment and reducing the effects of oxidation to the engine’s vitals.

Over time, the reservoirs of additives deplete due to temperature, pressure, and acid build up. Metal parts wear adding to further contamination, and the oil must be replaced.

Like a blood test, an oil analysis for your engine is a snapshot in time of the condition of the oil, and assigns values to the additive elements, oxidizing contaminants, and trace metals present in the oil that accumulate inside the engine. Analysis of the oil provides clear predictors of component behavior.

Oil analysis catalogs metals associated with component wear such as iron, copper, lead, tin, nickel and others as well as contaminant elements. The science assigns values for wear from normal to critical.

Typical values for some wear metals:

  • Copper – less than 15
  • Lead – less than 15
  • Tin – 9 or lower
  • Chromium – 9 or lower
  • Aluminum – 9 or lower
  • Iron – 30 to 60

Iron is the main wear metal because many vital engine components are iron including the engine block itself, crankshaft, rocker arms, bushings, etc. A high level of iron can be indicative of excessive wear on cylinder walls. High levels of copper and lead indicate wear on bearings for crankshaft, camshaft, or piston rods.

Fluid analysis - readout

The oil analysis above is for Case I. In this example both iron and lead levels have been tagged “abnormal” for Iron at 94, and “critical” for Lead at 51. By themselves, these numbers are out of range.

Another set of values to watch are those of the contaminants such as silicon, sodium, and potassium. Elevated levels of silicon indicates the presence of fine grains of sand and grit which have passed thru the air filter and become suspended in the oil. Accumulated levels of soot result from unburned fuel.

As these levels increase, the grit and soot becomes blended with the oil lubricating the bearings and causes wear, further contributing to the increased levels of iron, copper, and tin. It also increases the viscosity of the oil turning it black and giving it a mayonnaise-like consistency.

Contaminants such as soot, fuel dilution, and water are major contributors to shortening the life of oil. In particular, soot and fuel dilution are the “yin & yang” of unhealthy oil. Fuel dilution can be caused by several things such as clogged or leaky fuel injectors. Excess fuel leeches into the oil reservoir through the cylinder, past the piston rings, and dilutes the oil lubricating it.

By itself, it will lower oil’s viscosity. The component of fuel that is not fully combusted in the cylinder will result in soot which is scraped down into the oil sump by the piston rings. Because of the increased soot, the oil’s viscosity is raised but its ability to lubricate is reduced, and contributes to a black mayonnaise condition.

Fluid analysis - oil balls

Sodium and potassium are chemicals present in antifreeze. The presence of these chemicals in the oil are a clear sign of a leak in the cooling system which can enter the engine from a blown head gasket, crack in the cylinder head or block, or exhaust gas recirculation (EGR) for engines so equipped.

These elements mix improperly with the oil creating small abrasive “oil balls” which seep into the fine tolerances between moving parts contributing to a sandpaper-like effect that deplete lubricating additives such as molybdenum creating severe wear and eventual failure. It has a thickening effect on the oil which will, like plaque in blood vessels, causes poor circulation, clogs oil pathways and oil filters, producing oxidizing acid build up inside the engine.

In fact, contamination from the sodium and potassium in antifreeze glycol is the number 1 cause in diesel engines of premature filter failure and poor lubrication.

Viscosity of the oil is affected negatively by the presence of contaminants and wear metals suspended in it. They present an unhealthy acidic contaminant (TAN) which counteracts the normal lubricating properties of the oil (TBN). New oil has a TBN value of 5-15. As the acidic TAN value goes up, the TBN goes down, viscosity thickens into black mayonnaise.

When the TBN value approaches 5.0, that’s an optimum time to change the oil. This is the singular reason for taking multiple oil samples for analysis. By observing the trends and changes in the variables such as wear metals, contaminants, and values for the TBN, it’s easy to predict the onset of an unhealthy condition inside your engine. Under normal conditions, it pinpoints the optimum time for an oil change.

Beware of Black Mayonnaise

So, let’s now look at our oil analysis reports and perform some diagnostics on the engines looking for minor or major signs of concern. For Case I, the sample was taken from a Class A motorhome with gasoline engine, using 15W40, after about 8,000 miles on the oil with approximately 70,000 miles on the vehicle and engine. The oil sample was thick and black and had a mayonnaise-like consistency.

Fluid analysis - oil sampleFirst, it’s important to note, that this is a single sample, only a snapshot of the engine oil, taken alone. There are no preceding reports which we can use to spot trends of increases in wear metals or contaminants.

We start with the viscosity value of 10.9. Comparing it to a typical viscosity value of 15.0 it is low. While the oil is thick, the TBN value is low at 4.29; typical values range from 5-15. With a low TBN but mayonnaise-like consistency, it indicates that the oil is high in contaminants. The intersection of high acidic contaminants and the low ability of the oil to provide adequate lubrication have crossed, indicating an optimum time for an oil change.

We can’t draw any conclusions from the normal values for the additives since the brand of oil was not specified, and manufacturers’ additive values vary widely. We judge some of the additives have low values for their “typical” ranges but aren’t flagged as abnormal by the analyst.

Reading left to right on the wear metals, we see a value for iron at 94. Typical values for iron are 30-60; we can infer possible cylinder wear. We might want to pair it with fuel dilution values to see if there’s any correlation. The value is low which might indicate an earlier fuel injector leak that was resolved but which might have created permanent damage to the piston rings and cylinder walls.

We can see that the values for copper (24) and lead (51) are out of range. While the copper is not flagged and lead is listed as severe, we can compare them against typical values. copper and lead values should be less than 15. Their values indicate wear on the bearings, rocker arms, bushings etc. Which of the contaminants might be contributing to this wear? Fuel dilution does not seem to be a factor in this oil analysis.

What about silicon? It’s possible that fine dust might be passing thru the air filter. The presence of silicon doesn’t always mean dirt. Engines with oil bypass filters will catch up to 99 percent of this contaminant. But if there is no bypass filter, or it’s clogged, silicon grit might be the culprit.

Since the value is relatively low for this sample, we can’t conclude that dirt doesn’t play a part. (A trend or increased jump from 4 to 25 in silicon might be worrisome.) Again remember, that without multiple samples, there are no trends, so we’re trying to pinpoint potential problems using a single sample.

Now let’s look at the value for Sodium. Since we know that high levels of sodium will cause “oil balls,” which are sources of abrasion suspended in the oil, that easily seep into the tolerances between the piston walls and piston rings, we can see that the value of sodium (63), though not flagged as abnormal, might be cause for concern.

The presence of high levels of sodium indicate seepage of antifreeze into the oil, creating the conditions for “oil balls” and excess wear on cylinder walls (iron=93) and crankshaft or piston bearings (copper=24, lead=51).

The increase of wear metal values indicates severe wear on the main components of the engine’s vitals. The presence of high levels of sodium indicated from this sample would likely point to it as a culprit for wear in this engine. As indicated earlier, the TBN number of 4.29 indicates the need to change oil immediately. But the presence of high wear metals values and contaminants are a clear sign to replace this oil and get another sample after 2,500 miles – especially since there is only 8,000 miles on this highly contaminated oil.

What is causing this problem? A relatively easy diagnostic would be to check for a blown head gasket, using a compression test of the cylinders. On the other hand, if that test shows nothing, a more serious problem might be a cracked cylinder head or engine block. Again, without previous samples, there’s no way of knowing whether a previously replaced bad air cleaner was the cause of an increase in wear metals from this sample.

Likewise, the presence of sodium in this sample, which might not have appeared in previous samples, paired with high levels of silicon, would indicate possibly a “new” problem.

In Part I, we made the point that letting your oil get too dirty can lead to a “blown engine”. Without an oil analysis, changing the oil is merely guesswork and rote procedure. Our analysis of this engine points to an impending failure if the oil is not changed immediately. There is no guesswork needed on this sample.

What the long term disposition of this engine will be is hard to say. Changing the oil at a recommended 25,000 interval and hoping for the best doesn’t seem likely to produce a happy outcome considering all the “damage” we see from the 8,000 mile sample. A better strategy is to use the science of the oil analysis as a diagnostic tool: replace the oil now and take another sample soon afterwards to monitor the condition.

If it continues to show high levels of wear metals and contaminants, it’s further cause for concern about the health and wellness of this RV and a corrective action will be necessary.

Fluid analysis - chart

Discipline, Not Guesswork

Let’s look at Case II. This vehicle is a Class A truck with a diesel engine that has nearly 900,000 miles on it and uses 5W40 oil. The oil analysis report above is actually an eight-month history of oil analyses. Each sample taken at roughly 30-day intervals and 15,000 miles over the course of 100,000 miles.

Notice there have been NO oil changes in eight samples, though oil has been added — more than twice the total capacity of 11 gallons. The oil filter has been changed. The analyst has flagged this report in the “abnormal” range and advises that the oil’s viscosity is “moderately high.”

A trend analysis of each of the elements generally shows an increase in wear and depletion of additives. But spikes in the trend analyses can be correlated with other factors. For example, looking at the viscosity, we see it spikes at a time of increasing values for wear metals, and a spike in the lead value. Iron is increasing at an alarming rate, though the analyst gives it a green light.

The increases in aluminum and chromium, while not substantial, when combined with oil consumption points to the pistons. Chromium typically flakes off from piston rings. Worn piston rings lead to lower compression and lower combustion chamber temperatures leading to a buildup of soot, which contributes to the increase in viscosity.

Fluid analysis - ironThis sequence is leading to decreased oil flow to the piston cylinders thus causing increase in wear and the rise in the iron value. We can see that changing the oil filter – most likely a recommendation by the analyst – did not help. A contributing factor is the depletion of the additive molybdenum. We can see this on the third sample, it practically “flat lines”. Since molybdenum is critical to creating frictionless surfaces in cylinder walls, its depletion can be directly tied to the increase in iron values.

And when lead is compared on the same graph, we can see that the lead spike can also be traced back to the depletion of molybdenum. The increase in lead value is more disconcerting than increases in the iron value. Lead is a sacrificial metal used in bearings. A corresponding appearance of copper values, a main component metal for bearings, simultaneously with spikes in lead is pointing to a problem with the main crankshaft bearings.

Fluid analysis - leadAt this point, an engine overhaul is seriously on the table for Case II. This vehicle has upwards of 900,000 miles and there is no information on the overall condition of it. At 100,000 per year, the vehicle is likely 10 years old. It’s possible that the owner switched to a grade of oil with less of the critical additives during the period of the third sample.

Nonetheless, by monitoring the engine’s condition thru the science of fluid analysis, the owner was able to get another 80,000 miles and another year’s service out of the vehicle. There was no guesswork involved, there will not likely be an unexpected outcome. The discipline of the oil analysis has given the owner a clear picture of the next step.

Compare & Contrast

Comparing the two cases, we see that in Case I, the lead value is at an alarming level for 70,000 miles with no sense of how it got to this condition. Whereas by using a constant monitoring of Case II’s condition thru frequent oil analysis, it’s easy to see that while lead is not at an alarming level, the trend is very likely to get it there in the next sample or two.

While the analyst for Case II suggested running another 1,000 miles before taking the next sample, in Case I, the analyst advised changing the oil immediately and taking another sample in 2,500 miles.

Clearly, by taking another sample for Case I, the engine conditions may show that the lead value to be an anomalous spike with no cause for concern other than the possible antifreeze intrusion, which may be a different problem altogether. Without another sample, the Case I owner has no way of knowing how serious the problem is or whether a breakdown is imminent. As a single sample, the report is alarming.

As one in a series where conditions trend towards a more “normal” wear on a 70,000 mile engine, the owner will be able to sleep better at nights.

For the owner in Case II, the last sample provided insight into either getting a new vehicle or preparing for an overhaul. Changing the oil will replenish the depleted additives, but with the large oil consumption, enough engine wear has occurred that it’s not likely to make a difference.

For Case I, until the next sample is taken, the owner is in for a little nail biting. In order to prepare for an orderly future, Case I’s owner will need the data only the science of fluid analysis can provide. Data in order to make a disciplined decision, not one of guesswork.

In Part Three, we’ll lay out an RV health and wellness strategy that includes regular check ups and tools to help you monitor your progress. In the long run, keeping your RV healthy will give you and your family great peace of mind. And it will increase the resale value of your RV enormously. You don’t want the headache. And no one wants yours.


Wayne Hulit is CEO of Cedar Mountain RVI. The company provides an important fluid analysis service to dealerships and RVers alike. Check their website at for more information and download our whitepaper describing the importance of fluid analysis for an RV and listen to RV Daily Report’s Podcast 117 featuring Tom Johnson, president of JG Lubricant Lab, discussing the importance of fluid analysis.

Greg Gerber

Greg Gerber

A journalist who has covered the recreation vehicle industry since January 2000, Greg Gerber founded RV Daily Report on April Fool's Day in 2009. He also serves as the editor of the publication and website. As an Eagle Scout, he has enjoyed camping for decades and has visited every state except Hawaii. A DODO -- Dad of Daughters Only -- to three young women, he has two grandchildren as well. He currently splits his time between Wisconsin, Texas and Arizona. Greg can be reached at

Leave a Comment

  • Toni Calzone says:

    Hope the next part discusses what a lot of users may like to see what letting a unit sit more and not racking more than 6000 miles a year. Comparison should show diesel and gas verison. Sitting units have their own consequences so the oil interval change needs to be different. I have the oil anslysis done at least every two years lately and the oil does get changed within at least 15 months between. been doing this since owned the unit in 2004. analysis has not been out of range. Although it takes having the mechanic in the shop made sure they are given the sample container purchased to fill and the shop not loosing the results after they mail it or remember to so takes a bit of monitoring to make sure done . Shops normally do not see a number of rvers ask for it so it falls thru the cracks.
    Now that I am a more experienced owner would not think or buying or selling a unit without the oil analysis done and a record from the shop that changed the transmission oil to see how long ago done and miles on unit. A unit may have 100000 miles on it but if maintenance was done right it will go another longer length of mileage use without expensive repairs.

  • Chris Carty says:

    Great fluid analysis article! I have been doing fluid analysis since my early days as a jet mechanic in the U.S. Navy repairing multi-million dollar aircraft.
    As a RV Inspector, I always recommend buyers opt for fluid analysis on any RV they are considering buying, as a means of knowing what the current mechanical condition the engine, transmission and generator may be (especially on RV’s without documented maintenance logs/records). Looking at the fluid/oil on a dipstick does not provide any (factual) data about the component’s condition or when the last fluid change was performed.
    Too many auto/RV/motorcycle operators do not use fluid analysis to keep track of lubricant condition or condition of the component degradation over a period of time. Performing fluid analysis over a long period of time is invaluable for identifying abnormal wear of sacrificial metal components which may lead to preventative maintenance actions that may avoid more expensive repairs.
    I will be sharing this article with all of my RV buyers to help them make an educated decision on whether to buy or pass on their next RV purchase.

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