Vehicle Fluids
Our Laboratory handles a variety of fluid analyses ranging from routine engine oil analysis for wear metals to identification of foreign fluids and solid contaminants in any of the vehicle fluids. This paper reviews the techniques employed in these analyses and some examples of specific problems we have solved.
Routine Oil Analysis
Induction Coupled Argon Plasma Spectrometry (ICAP): Elemental analysis for the presence of telltale wear metals can be performed by ICAP. Metal atoms in solution, excited by an argon plasma, emit light at characteristic wavelengths. The amount of light emitted and the wavelength are detected and through the use of standards the specific metals are quantified.
Either elevated levels or sharply upward trends of the following metals may indicate engine problems.
| Element | Condition |
| Iron | Wear metal from steel and cast iron components throughout an engine |
| Copper | Wrist pin bushings, cam and rocker arm bearings, thrust washers, heater and radiator corrosion products |
| Aluminum | Aluminum block, pistons, oil pump housings,radiator corrosion products |
| Chromium | Rings, exhaust valves, cylinder liners, coolant rust inhibitor |
| Lead | Leaded gasoline, bearings |
| Silicon | Ingested dirt, antifoam additives |
| Sodium | Ingested road salt, antifreeze, oil additive |
For expensive engines, monthly or quarterly oil analysis is a good investment. Wear metal trends permit scheduling of major engine service as well as detection of antifreeze leaks and ingestion of abrasives through intake system leaks.
The remainder of this paper addresses forensic analysis techniques.
Forensic Fluid Analysis
Gas Chromatography (GC): GC is an analytical technique which separates and detects the individual components in a mixture according to their volatility (boiling point). By comparing chromatograms (plots of detected component vs. time) of suspect and reference materials, characterizations and identifications can be made.
Figure 1 compares chromatograms of a transmission fluid with a brake fluid suspected of containing transmission fluid. The brake fluid produced sharp peaks representing molecules of discrete size while the transmission fluid produced many overlapping peaks which represents a broad range of molecular sizes. This analysis proved that no transmission fluid was present in the brake fluid.
(Figure 1. Gas chromatograms of a brake fluid and a transmission fluid - click image to enlarge.)
GC analyses such as this usually require reference samples.
When trace amounts of a contaminant are suspected or when contamination by a material chemically similar to the sample is suspected, GC is the technique of choice. GC can discriminate between chemically similar fluids such as motor oil and transmission oil which are both hydrocarbons but have different molecular size ranges.
Fourier Transform Infrared Spectroscopy (FTIR): FTIR is useful in identification and characterization of both liquid and solid samples. Specific wavelengths of an infrared light source which is shined through or reflected off the surface of a sample are absorbed by the sample's chemical bonds. The spectral absorption is converted to a plot or FTIR spectrum of transmission vs. wavelength. This plot, in essence, is the sample's chemical "fingerprint".
The spectra shown in Figure 2 are of the same brake fluid and transmission fluid samples compared by GC in figure 1. The brake fluid was identified as a glycol and the transmission fluid as a hydrocarbon.
![Figure 2. FTIR Spectra of a brake fluid [a glycol] and a transmission fluid [a hydrocarbon] - click to enlarge](i/resources_NHML_Vehicle-Fluids_fig2_lg.gif)
(Figure 2. FTIR Spectra of a brake fluid [a glycol] and a transmission fluid [a hydrocarbon] - click image to enlarge.)
FTIR can detect gross contamination of a sample by a chemically different substance. For instance, if a transmission fluid were present in the brake fluid at a concentration of 5% or more, it would be detected by IR.
Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS): SEM allows visual analysis of particles at magnifications up to several thousand. EDS applied with SEM allows detection and identification of the elements present in the particles being studied. This combination of techniques is useful for the analysis of unknown solid contaminants such as sand and clay and determining the source of metallic chips and flakes.
Case Histories
The following are some of the problems we have solved using ICAP, FTIR, GC, SEM/EDS, and microscopy:
Thirty five miles after an oil change, the automatic transmission in an automobile failed. GC identified motor oil in the transmission.
A differential failed a few thousand miles after having been rebuilt. It was alleged that the oil was contaminated. A combination of analytical techniques proved it was not.
A highway tractor suffered injector failure due to water contamination of the fuel. FTIR identified the water and EDS detected elements indicating it was sea water. Further investigation by the adjuster revealed the vehicle had been parked at an ocean beach during a storm.
A diesel highway tractor stalled a few hundred miles after its injectors were overhauled. Analysis of the fuel showed it to be gasoline.
Examination of components showed that a crawler tractor was used briefly after sand had been added to the transmission.
After engine failure, sugar was identified in the crankcase and under the filler cap. FTIR showed that the oil had been oxidized while the sugar had not, indicating the sugar was added after the engine failure.
Following magneto failure in an aircraft engine, oil was repeatedly changed and analyzed until all magneto debris had been flushed out.
Following failure of a recently rebuilt transmission, analysis of transmission fluid and solid debris using SEM/EDS, FTIR and GC identified dirt and a form of rust which develops in open air. This indicated that junk yard parts had been used by the mechanic.
Following alleged brake malfunction, FTIR and GC showed that the mechanic had used the correct pads and fluid.
Obtaining Samples
To insure collection of appropriate samples, we recommend a phone call to one of our chemists to discuss your problem, samples and analysis needs. We will send sample containers and advise you regarding sampling techniques.
Reference samples of suspected contaminants may be necessary in incorrect fluids.
January 1, 1995 by V. Ridlon, R. Cunniff
Other Resources
See our Industry Definitions for further insight.
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