Good Diagnostics Saves Money in Auto Repair
- Tyler Betthauser
- Jul 18
- 10 min read
No less than 25% of our customers this week have come to our shop after previous shops attempted to replace parts on their vehicles without a proper diagnosis. In the end, those customers spend more on repairs in the medium term when they do not demand that a facility prove a root cause with evidence showing that specific variables are causing a problem. Auto repair is no different from any other technical discipline: observe a phenomenon, define a set of hypotheses, document those hypotheses, determine the tests, collect the data, attempt to prove the null hypothesis, determine the root cause, make a change by replacing the part or educating the customer, and retest. This is an astoundingly simple process that nearly all of us learned in middle school science class. However, it can be exceedingly difficult to maintain enough discipline to abide by these principles. Consistent results happen when technicians maintain composure and leverage the scientific method.
A prime example of this diagnostic philosophy in action involves a customer with a 2019 Ford Expedition. These vehicles feature the 3.5L EcoBoost V6, an engine notorious for expensive failures outside of warranty. After returning home from a vacation in northern Michigan, our customer noticed that upon startup, the vehicle would make a loud ticking and clanking sound. Our shop also observed that within a few seconds, the initial clattering would cease. For 30 to 60 seconds more, however, the engine would continue making a metallic ticking sound before eventually quieting to the point where only the high pressure fuel pump could be heard.
Based on that audible inspection alone, a technician could possibly be forgiven for chalking the issue up to the infamous cam phasers, timing chains, and guides. The previous shop also noted diagnostic trouble codes including P0299, P0365, and P0369, a combination they had likely seen a thousand times. Repair facilities often welcome these cases because the job, while complex for a do-it-yourself owner, is straightforward for a building full of technicians who perform it frequently and efficiently relative to the billed labor hours. The financial incentive structure laid out by this standard book time model is obvious.
Every shop has an operational incentive to generate a profit. Repair shops and dealerships are businesses that employ people with families, pay taxes, and help communities thrive by keeping citizens moving when vehicles invariably fail. However, there is a major caveat to how different business models handle risk. When historical data and Technical Service Bulletins show that a specific cold-start rattle on the 3.5L EcoBoost is isolated to cam phaser locking pin wear or timing chain stretch in the vast majority of occurrences, a high volume facility operates on a base rate assumption. Performing an exhaustive baseline evaluation (such as plumbing mechanical oil pressure gauges, removing spark plugs for cylinder borescoping, and tearing down intake tract piping to measure turbocharger shaft play) adds significant billed labor and bay time. If a shop applies hours of comprehensive diagnostic testing to every vehicle presenting with a startup rattle, they increase the upfront invoice for every customer by several hundred dollars. Across a volume of one thousand vehicles, that represents thousands of hours in labor billed to consumers whose bottom end internal components were ultimately healthy.
The fundamental flaw in this volume based model is that it transfers the statistical tail risk entirely onto the individual consumer. When a flat rate service center plays the statistical odds, they are wagering the customer's capital rather than their own liability. When the base rate assumption holds true, the customer avoids paying for diagnostic hours and the shop turns the bay over rapidly. When that assumption fails, the customer absorbs the entire financial impact of a ruined engine. This tension represents a foundational conflict between two different operating philosophies:
Throughput Optimization: High volume service centers and dealerships are structured around standardized repair paths. They treat vehicles as a statistical aggregate, relying on pattern recognition to process the maximum number of repair orders with minimal operational friction. The system is designed for speed, standardized labor times, and immediate efficiency, accepting that a small percentage of edge cases will result in severe secondary failures.
Micro-Level Reliability Engineering: Root cause diagnostic facilities treat each vehicle as an independent mechanical system. Under standard engineering and quality control principles, ruling out high severity failure modes is mandatory before executing capital intensive repairs. This method prioritizes total cost of ownership and long term asset security over immediate bay turnover.
There are certainly instances where both approaches need to be appropriately used. It certainly is not feasible to diagnose everything to death. But, our point is the incentive structures currently in place have influenced corporate cultures such that overcoming the default behavior is difficult--and even discouraged. Profit drivers are an incredible incentive to nudge decision makers away from prioritizing quality over quantity. The nursing community calls this the normalization of deviance. An organization can clearly outlay in their stated values that quality is the most important; however, small behaviors that do not immediately result in measured poorer quality end up becoming normalized because it takes time for the effect to take hold. By the time effects are felt, organizations have adopted these new anti-patterns as normal and quality becomes far less important when immediate returns are rewarded immediately.
There are certainly instances where both approaches need to be appropriately used, as it is not feasible to diagnose every mechanical anomaly to death. However, the incentive structures currently in place have influenced corporate cultures such that overcoming default behavior is difficult and often discouraged. Profit drivers serve as an incredible incentive to nudge decision makers away from prioritizing quality over quantity.
In aerospace engineering and safety culture, this phenomenon is known as the normalization of deviance, a term coined during NASA accident investigations. An organization can clearly state in its core values that quality is the highest priority; however, small shortcuts that do not immediately result in measurable failure end up becoming accepted practice because the negative consequences take time to materialize. While corporate managers may view strict adherence to fast, standardized repair bulletins as a way to control process variance, that same rigidity discourages deeper investigation. By the time the cumulative effects of missed underlying failures are felt by consumers, organizations have adopted these shortcuts as normal operating procedure, and quality becomes far less important when short-term volume is rewarded immediately.
By spending extra time conducting a thorough upfront investigation, we saved our customer thousands of dollars and avoided a potential $15,000+ engine replacement later.
The Car Conservatory believes that these additional checks should be the standard of due care before such a large job is undertaken, has been documented as a lessons learned internally, and will be standard going forward.
We discuss more in depth the key checks we will perform going forward.
Ecoboost Turbochargers
Ecoboost engines are twin-turbocharged. They have two turbochargers that are positioned on either side of the engine. Inside of the turbocharger is a turbine that compresses the air it takes in--which drastically increases the velocity of the air and compresses it. The 3.5L EcoBoost turbochargers use a journal bearing design rather than a ball bearing design. The shaft spins on a thin cushion of pressurized engine oil within brass bushings called the Journal Bearings. The turbo is also comprised of a specialized 360-degree thrust bearing handles the axial (forward and backward) loads created by exhaust gas pressure. Finally, the components float completely on oil, preventing metal-on-metal contact during operation.
The design choice informs how to inspect the turbochargers for wear. Once a technician gets access to the turbochargers they assess whether the turbine has excessive play. Not an exact science, but sufficient for making the risk assessment about whether turbos need to be replaced while performing surgery on the truck. Journal bearing turbos (like the factory 3.5L EcoBoost) naturally have a noticeable amount of side-to-side play when the engine is off. Conversely, ball bearing designs have virtually zero perceptible play when dry because they are mechanically supported by physical bearings rather than a fluid cushion. A small, distinctly noticeable wiggle is perfectly normal for this journal bearing design. When the engine is off, the shaft is resting loosely inside its brass bushings. Once the engine starts, oil pressure fills that gap and centers the shaft. While wiggling the shaft side-to-side, pull or push it toward the outer housing. The compressor wheel blades must not touch the metal walls of the housing. If you feel it "scrape" or see score marks on the housing, the bearing is shot. There should be absolutely zero noticeable in-and-out play. If you pull the compressor nut toward you and push it back toward the engine, and you can feel it click, chunk, or slide back and forth, the internal thrust bearing has failed. A failed thrust bearing will immediately destroy the oil seals.
While finger checks are a reasonable approach for most diagnosis, they are certainly far from perfect. This is where critics of excessive diagnosis might have their strongest argument. Ideally, measurements would be done with a micrometer and a dial indicator. We feel a test like this is sufficient given the time constraints. Most turbochargers probably should not be replaced until true failure anyways.
Luckily for our customer, the turbos seemed to be fine and there was minimal blow-by.
Cylinder Health
A key piece of the puzzle is whether cylinders are healthy. Many parts can be replaced on an engine which are vastly more cost effective than the cylinder heads themselves. The spark plugs were removed and a borescope inserted into the cylinder. Here is where our concerns about the engine health were validated.
Bore scoring manifests as vertical grooves in the cylinder bore, with severity ranging from minor, manageable marks to deep grooves that cause significant engine damage. Detection through borescope inspections is crucial to prevent failure. Symptoms such as excessive oil consumption, smoke on startup, ticking noises, and loss of compression can indicate scoring. Causes sometimes might be faulty fuel injectors or vacuum leaks. Ultimately, bore scoring leads to compression loss, oil contamination, and eventual engine failure.
While scoring is a physical groove, scorching appears as darkened, discolored, or "melted" patches on the piston sides and cylinder walls. It is caused by intense heat and friction when protective oil films break down. In the case of this Expedition, the cylinder walls take on a blue hue in spots. There are a few different causes. One potential is insufficient oil film—whether from using the wrong viscosity, fuel flooding the cylinder (fuel wash), or extended oil change intervals—allows raw metal-to-metal contact. Another potential cause in certain engines, microscopic debris from deteriorated coatings or worn components gets trapped between the piston and the wall, plowing grooves into the metal. Drivers can also be a cause as well! Overheating or running an engine hard before it reaches operating temperature causes the piston to expand faster than the cylinder, leading to uneven wear and scuffing.
While there are signs of physical damage in the cylinder, spark plugs can also hold clues about another concerning sign: oil fouling. Oil fouling occurs when liquid lubricating oil enters the internal engine combustion chamber and coats the firing end of a spark plug. This oil creates a thick physical barrier over the center and ground electrodes, preventing the ignition system from arcing cleanly across the electrode gap and igniting the air-fuel mixture.
An oil-fouled spark plug has a distinct visual appearance compared to normal wear or dry carbon fouling:
Wet, Shiny Surfaces: The firing tip, ceramic insulator nose, and metal shell are covered in a wet, glossy, black or dark brown coating of engine oil.
Greasy Sludge Buildup: Unlike dry, sooty, matte-black carbon deposits caused by a rich air-fuel mixture, oil fouling presents as a thick, greasy, or sludgy residue.
Bridged Electrode Gap: In severe cases, oil and ash deposits accumulate between the center and ground electrodes, physically bridging the gap and shorting the ignition path.
Oil fouling is a indication of internal mechanical wear or component failure that allows excess oil into the cylinder. Primary sources include:
Worn Piston Rings or Cylinder Walls: When piston compression rings or oil control rings lose tension, wear down, break, or stick, they fail to scrape oil off the cylinder walls during the piston stroke, allowing oil to bypass into the combustion chamber. Given the damage we observed in the cylinder itself, we think this was the cause here.
Worn Valve Guides and Valve Stem Seals: Degraded rubber valve stem seals or excessive clearance between valve stems and guides allow cylinder head valvetrain oil to be drawn down into the intake port and combustion chamber during the intake stroke.
Blown Cylinder Head Gasket: A failure of the head gasket seal can allow pressurized oil from engine block oil feed passages to leak directly into adjacent combustion cylinders.
Faulty Positive Crankcase Ventilation (PCV) System: A clogged or malfunctioning PCV valve causes excessive crankcase pressure, forcing oil vapor and mist back through the intake manifold into the combustion chambers.
Turbocharger or Supercharger Seal Failure: In forced induction engines, degraded turbine or impeller shaft oil seals can leak pressurized lubricating oil directly into the intake tract or exhaust stream.
The $20,000 Savings
Our customer opted to sell the vehicle as-is to Carvana. Given the preponderance of the evidence from our investigation, The Car Conservatory thinks this is the best choice for the customer. Would we dutifully replace the engine or cam phasers (and all the other components we need to)? We absolutely would do the work for the customer. Our overriding point is that customers need to have all the data to make the decision in the first place. Had additional investigation not taken place, there is a high probability that the engine would have failed soon after doing the extensive repair of the cam phasers and other ancillary components. Ultimately, the customer spent around $567 to avoid a $20,000 sunk cost.
The Way Forward
We are certain this is not a popular approach. But, The Car Conservatory was started because there is a clear misalignment of the incentives most auto repair places have relative to the outcomes and experiences customers demand. For years, our team passively collected hundreds of narratives from customers describing their horrid experiences. For months we did extensive research and interviews. As an Engineer at the OEM, I was at least tangentially exposed to exceedingly poor customer experiences through reading thousands of warranty claims.
Decades of bad behavior has tainted the well. We do not, and will not, operate like the typical shop because our desired outcomes that we wish to see are so different than the typical establishment. Would our model rate highly on the list at a private equity firm or on Wallstreet? Certainly not now. But, maybe in the future the singlemindedness around profit correlating to quality is finally so disproven that business has to change. Auto repair shops get most of their customers locally--within a 10-15 minute drive. You eventually run out of customers if you do not build a model that simply treats each repair order as though it is the last time you'll ever see that person.
Did our shop 'lose out' on a lucrative, profitable job? In the short term, yes. But, we feel pretty good their Expedition won't bankrupt them, still got paid for our expertise, and have the opportunity to be top of mind the next go around.
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