Cooling System Leak Diagnosis

A real-world example of something I was trained to do at school is leak diagnosis using air pressure and soapy water. The potentially leaking system is pressurized with a manual air pump or with compressed air with a regulator to control specific pressure, and soapy water is sprayed on any potential areas where the leak could be. Radiators, charge air coolers, fittings, sealed connections, hose and line ends, are the primary culprits. That does not exclude hoses or lines themselves as they might have holes enough to cause a leak. We have done this in the school shop on things like the Charge Air Cooler on a Series 60 to find the source of a leak.

So, back to the real world example. I changed the water pump on a Duramax (more on that in another post), and after completing the installation found that the system held neither vacuum nor pressure. I pressurized the cooling system to 15 psi and sprayed soapy water all over. Eventually, I heard a fizzing sound. Crawling under the truck, I noticed that a pipe that enters the rear of the water pump was foaming quite heavily. The source of our leak. This connection has a simple dry non-metal gasket.

Off came the water pump again, and inspection of the flanges (which were straight-edged) and gasket gave no obvious hints as to why they would be leaking. I put a special silicone sealant on the gasket, reinstalled the water pump and pressurized and tested the system the following morning with no obvious signs of our leak.

Soapy water tells us where the leak is located.

Evidence of the leak on the gasket.

Reflection:

Sometimes the root cause of the problem is not entirely obvious, even when you have located and inspected where the problem occurs. Using a silicone sealer solved the leak, and we will have to leave it at that. I don't have the answer to this one, but in the end the fix was simple. Perhaps others have possible insight into the root cause? Curious minds would like to know, if so.

Wire Repair

Apologies for the lack of updates on the blog since graduation, illness and work have kept me exhausted. As my former energy and enthusiasm returns, I will make at least weekly updates henceforth.

I have done many things since my last post, ranging from oil changes and fuel filters to basic scan tool work and injector replacement, electrical diagnostics, and more additions to my toolbox. As I am several weeks behind, rather than writing it all up as one or several posts of my weekly activities, I will present them as single activities per post mixed among my current work. Such as a new tool, or the injector replacement.

For today's topic and what I did at work today: wire repair. A Volvo dump truck which had multiple wiring issues involving missing or damaged insulation, and a toggle switch which needed replacement.

Damaged insulation at the toggle switch terminals.

New toggle switch and a choice of two heat-shrink crimp connectors.

I chose the red, smaller one suitable for 16 gauge wire. This is the finished product, before putting the switch in its mounting and testing to ensure the lights it controls work. They did.

Connecting a fresh piece of wire to replace a damaged section. Again, heat-shrink connectors were used.

My reflection:

I am starting to get decent at basic wire repairs. I prefer the use of heat-shrink connectors, but they are not always necessary (in the cab, for instance). In my learning process, I have trashed a few of these crimp connectors as my crimping tool (Snap-On brand) can punch through their insulation if you're not careful. My final attempt in the last picture had zero connector casualties and no mistakes, as I am getting a decent feel for the crimping process. Third attempt at wire repair, third time is the charm?

Finals

This week was our final exam for Electronic Diesel Engine Controls. Heavy emphasis on the test was put on use of electronic service information, wiring diagrams, and using a scan tool in conjunction with service information to troubleshoot sensor and wiring problems.

Late-model Freightliner Coronado, used to pull a code for bad turbo intake sensor for our final exam. Our teacher had simply unplugged the sensor.

Reflection:

With finals over, it gives a lot of time to reflect on all the lessons learned and experiences had over my 3 years in the Auto-Diesel shop. My education was not just a matter of learning how to wrench on vehicles. It was learning how to be confident in my abilities and get engaged, even if I make mistakes. It was about interacting with and getting along with my class mates, my teachers, and potential customers. It was about building a pathway to my career.

What is next for me? Tomorrow I go full time at my current place of employment, and say good bye to the Auto/Diesel shop which I have called home for 3 years. This isn't the end, it is just the beginning. I will stop by whenever time permits to see how the place where I got my start is doing, and I will keep my instructors informed of my activities in the Automotive/Diesel Truck world on a regular basis.

It has been, quite an experience!

GMC Sierra 5.3L Final Assembly

This week in class, with permission from my instructor Jeffrey Starkey, my team worked on my GMC Sierra 1500, which was in the shop for repairs originally as part of another class which I helped with. It has a 5.3L gasoline engine, but for the purposes of our class it is very much "electronic engine controls," even if not a diesel. It had been my hope to get the truck finished that day and pulled out of the shop.

Most of the engine work had been done, all that needed to be finished on it was valve covers, the radiator fan, coolant hoses, and of course... electrical connections to sensors and other electrical components. Final step was engine oil and coolant (which we used water to flush the system).

We got everything hooked up and started the truck. Whoops! Coolant leaks everywhere, and a bad idle. What did we do wrong?

This engine has four blocks with little nipples that go into coolant passages on the heads, two on front and two in back. The front ones are passages for the "coolant air bleed pipe" which connects under the throttle plate to the intake and allows air to bleed out of the cooling system. The rear two are simply there to block the flow of coolant out of the heads.

In my haste to get this vehicle finished, I had put the gaskets to these on wrong, and coolant was leaking out of all 4. Lesson learned! We luckily just had to take them back off, put the gaskets on correctly, and we also put some RTV silicone on them just to be sure of correct sealing.

I drove the truck onto our alignment rack, and found it died on me several times. On Thursday, we found this was due to the MAP sensor not being plugged in.

On Thursday, we fixed these issues and finally got the truck running decently and pulled out of the shop.

First ignition after we fixed the leaks and the MAP sensor was plugged in.

Reflection:

Don't get in a hurry. It's not a race. Take the time to go through your work and ensure it is all correct and up to spec. I made some mistakes through being in a rush and learned well from those lessons

The truck still has some issues which need to be ironed out, such as a misfire. However the big work is done. Just a matter of working out the kinks that were probably not related altogether with the crack in the head we fixed, and as always the learning will continue.

Series 60 Crank/No-Start Diagnosis

This week since my team was absent, I was asked to help a member of another team finish diagnosing a Series 60 with a Crank/No-Start condition. We had a clear hose hooked up from the fuel filter to the transfer pump, which I noticed at starting had little more than air in it.

We also noticed that the filter itself had no fuel, so we put fuel in it and tried starting it again. We found air bubbles forming in the (clear) filter housing. After referring to service literature we found this meant an air leak anywhere between the fuel tank and fuel filter, with perhaps defective housing o-rings. Fuel is sent to the transfer pump past the filter.

Checking, we found one o-ring missing from the small fill cap at the top of the filter. We replaced this. Upon startup, we made more progress but we still had significant problems and the truck would not start.

So I crawled under the truck and started at the fuel tanks tracing the lines back. And this is what I found:

Each line comes in from the fuel tanks to this fitting, and goes out to the fuel filter from there.

At first I noticed a wet spot on the fitting, and after touching it found the line to be loose. I tightened it up and we tried again. This time, we got the truck to start.

Reflection:

Problems can have more than one cause. In our case, and agreeing with our service information, there were 2 causes of this no-start condition and we could not get the truck to start until we fixed both of them.

It made sense to get under the truck and inspect the lines and fittings going to the filter, especially after replacing the missing o-ring did not fix the problem. After we had made sure all was okay, we could verify our fix and move, if necessary, to the next step of diagnosis if we still have issues.

Oil Pressure Sensor Circuit Fault, Code 141 (Cummins N14 Celect Plus)

This week in the shop we did some cleanup. Pretty standard stuff, but while looking for a magnet I found this:

Mechanic ingenuity?

Someone had welded a socket to a long piece of all-thread. What the purpose of this tool was I did not learn.

What I did learn, however, was how to read flash codes on a Cummins N14 Celect Plus in the school's International sleeper truck. Courtesy of some quick research on Cummins Quickserve and Google, we ascertained exactly how to read the code flashed on the dash, and found one code, 141. Once again with the help of Google we found this to be an oil pressure sensor circuit fault. So we printed out a component location diagram and went to look:

Oil pressure sensor location. Right under the ECM on the driver's side, mounted in the block.

The actual sensor on the vehicle.

When we checked the sensor, it was unplugged. Mistake from a previous team? Deliberate bugging? Who knows, but once we plugged the sensor back in, the check engine light went out and we were good to go.

Reflection:

Once again we get back to "keep it simple, stupid," the sensor was simply unplugged. However, that might not have been the only problem with it. So what is the next step in the repair process? Verify that the seemingly obvious fix did indeed correct the problem. In our case, it did. But what if there were wiring issues down the line? Then the diagnostic process would continue, with one possible cause (disconnected connector) eliminated. That would have been our next step, had the check engine light stayed illuminated.

The Importance of Maintenance

This week, due to class cancellations, I will briefly post on something I did at work.

While working on a truck for another issue, it was necessary to unhook the batteries. Part of "modus operandi" where I work is to clean pretty much everything we remove if we are putting the same parts back on. So while I had the battery cables disconnected, I went through all the terminals and cable ends and cleaned them all up. Here is what I found on some of them:

I bead-blasted the cable ends and cleaned the nuts for the terminals up on a wire wheel. We had to replace one cable end because it was so badly corroded.

Reflection:

It's good practice to get into the habit of routinely checking and cleaning things such as battery cables and terminals, especially if you have to disconnect them to work on something else anyway. I routinely clean any electrical connections such as this whenever I have them off. It may take an extra minute or two, but it helps to solve a lot of avoidable electrical problems which are the result of the "green" corrosion pictured above.