DIESEL Workshop investigates why the starter motor is not always to blame for a faulty starter motor.
So you think your starter motor is on the blink (again!), and with a full truck you’re sitting idle by the side of the highway halfway between where you came from and where you want to be, with a deadline looming and a crusty and inconsiderate client. And you’re cursing why your repairer can’t put a decent starter in your rig instead of the obvious Chinese/American/European piece of junk he’s used.
While we know from fleet managers the average cost of a starter breakdown is between $2,500 and $5,000 (or more than five times the cost of the starter), we also know that often the starter isn’t the cause of the starter problem. So before you rip out the Chinese/American/European piece of junk and look for a better quality unit, take the time (and cost) to have your truck’s electrical system analysed to see exactly where the problem may lie.
It’s important to know that modern heavy-duty starters are not designed to be cranked under low voltage. Just three or four starts on a good starter under low voltage can dramatically shorten the life of your starter, and this damage will be obvious when tearing the starter down, so you’ll likely end up having a warranty claim denied.
Why does engaging the starter under low voltage shorten its life? It’s because of the way electricity works. When the trucks electrical system is operating at less than the required voltage it generates a higher current flow than the system is designed for. The higher current generates excessive heat.
It is not uncommon for this heat to reach levels where it welds the moving parts inside the starter motor and it can even create a fire. Most commonly it causes carbon from the brushes to create a film on the commutator. This film sets up resistance which exacerbates the slow cranking and low voltage issues, thus further shortening the starter life.
Often when you replace a starter motor that has failed and the new unit cranks better, the immediate conclusion is that the problem is solved. In actual fact, if the slow cranking of the old unit was due to low voltage issues, the new unit will quickly follow suit unless the underlying problems are resolved. So often when the new unit fails prematurely (after operating fine for a few weeks or months) the immediate assumption is a poor quality starter.
SO BEFORE WE BLAME THE STARTER MOTOR, LET’S DIAGNOSE WHAT’S GOING ON WITH YOUR SYSTEM.
While cranking problems can be frustrating, identifying and correcting the root cause does not have to be. The first step is to identify the symptoms. In a cranking system, you can divide your symptoms into one of three possible troubleshooting categories:
Slow Crank: The starter will crank, however, the engine RPM is too slow to start the vehicle.
Click No-Crank: The solenoid clicks but the starter doesn’t crank.
No-Click No-Crank: The solenoid doesn’t click and the starter doesn’t crank.
Once you’ve identified which problem you’re dealing with, then you can start to remedy it. For all issues, the initial troubleshooting is the same: you start with the batteries.
STEP 1 - Begin at the batteries: Charge the batteries and perform a load test on each battery in the battery bank. If any batteries aren’t up to spec they need to be replaced or you will shorten the life of the other batteries and compromise the health of the starting circuit.
STEP 2 - Perform a voltage drop test: Once the batteries pass your tests, perform a voltage drop test on the starter main cables. The starter voltage drop should be less than .5V total on the cranking circuit. This is an important step and is often the cause of a slow cranking complaint. Yet voltage drop also is a leading cause of click or no-click complaints because almost every vehicle manufacturer uses the heavy positive post, located on the starter solenoid, as a place to pick up the current used to supply the control circuit.
STEP 3 - Identify the specific issue: Until now, the diagnostic path has remained the same regardless of the complaint. Now is where you address the specific issue.
Slow Cranking: For the starter to be cranking, the control circuit would have to be working. So, if battery and cable checks are within specification and the vehicle still cranks slowly, then it’s a slow cranking problem and it’s time to replace the starter.
Click No-Crank: Check the control circuit. If the starter does not contain an Integrated Magnetic Switch, or IMS, then a voltage drop test will need to be performed on the vehicle control circuit. If the starter does have an IMS switch function, then the technician will have to verify that the vehicle’s control circuit is providing voltage to the starter IMS.
No-Click No-Crank: When this occurs, power is not being sent to the solenoid, making it very unlikely that the issue is related to the starter motor.
A diagnostic tool can help you diagnose the complete starting and charging system, including the alternator, batteries, starter motor and wiring. The diagnostic tool can perform a full system check in about 25 minutes, making it a great investment for your workshop.
SO IN A POOR STARTING ENVIRONMENT, OR WHEN A STARTER MOTOR HAS FAILED, WHAT COULD BE WRONG?
Batteries – By now you should have tested your batteries and replaced any that were faulty. Don’t be tempted by the false-economy of leaving one poor quality battery in a bank of four. And you should look at your battery cabling, as this can often be less than optimum from new. In the diagram below, the top illustration shows the original battery cable layout, which results in the two inner batteries working hard and the outermost two never receiving optimum charge. In the diagram below (Pic 1) shows an easy solution to balance the workload of the battery banks.
If your batteries were not at full charge, your alternator capacity may not be up to the needs of your rig. How old is it? A standard brushed alternator is good for 100-150,000km, a long brush alternator up to 300,000km and we have seen brushless alternators last for over a million kilometres. You get what you pay for. Also if you’re hauling more than one trailer or have additional lighting or other load on your electrical system, the standard alternator output may not be sufficient to run your truck and adequately charge your batteries.
Providing you have a quality brand alternator, you can trust the claimed output, and your auto electrician should be able to work out your requirements. If your alternator is running at or near capacity just to run your truck, there’s a fair chance it’s not getting the chance to charge your batteries between starts. But remember, before you invest in a high output alternator, check the wiring for size. Most truck manufacturer’s use the narrowest cable they can get away with so there’s a chance your new high output alternator may be wasted on undersized cabling.
It is amazing how many electrical problems are caused by simple wiring issues. Undersized cable is often at fault, or it can be poor quality or corroded terminals. Remember any voltage drop over half a volt is a problem. Finding voltage drop is easy and fixing it is often just a matter of increasing your cable size.
Battery master switches are common in many heavy duty applications and intelligent battery switches and rollover devices are mandatory in fuel haul vehicles. The quality of the battery switches in the Australian market varies wildly, and we have seen switches with well over half a volt of voltage drop across the terminals. Look for a quality battery switch with less than 0.1V voltage drop across the main contacts.
Finally is your starter motor up to scratch? While most starter motors fitted new are up to the task, many aftermarket replacements simply do not live up to the claims they make. If you’re having starter issues and think the starter motor may be the problem, the first choice would be to fit the original equipment starter, or a manufacturer endorsed upgraded alternative.
A warning should be raised about the claims made by many suppliers of aftermarket heavy duty starters, as the kW output claimed is often well above what can be achieved. In the case illustrated above, a claimed 7.8 kW output was found on test to be a little over 5.0 kW, or good for up to an 8-litre engine rather than the 15-litre engine it was designed for. The red lines illustrate the genuine unit fitted by the original manufacturer, the black lines represent its aftermarket replacement.
So while starter motor failures are frustrating and costly, immediately blaming the much maligned starter motor for the problem may just end up costing you more in the long run. Our recommendations for avoiding starter problems would be:
- Analyse your complete charging and starting system at the first sign of starting problems, or earlier as part of preventative maintenance. Remember just three or four cranks under low voltage can dramatically shorten the life of your starter.
- Invest in an electrical diagnostic tool, or find a reputable repairer that has one and knows how to use it.
- Stick with the original equipment manufacturers or known quality brands. If there is an OE upgrade, consider it next time your starter comes up for replacement.
- Make sure your electrical equipment, particularly your alternator, is up for the job, taking into consideration any modifications to your truck since new.
When you take into account the cost of your truck being off the road, a little spent on preventative maintenance and invested in quality parts will pay off tenfold over the life of your truck.