Electrical troubleshooting on cooling systems

I had two cases where a piece of equipment was brought in for problems with the cooling systems. The gauge would read that the unit is overheating. I did some troubleshooting and found that the thermistor was no longer working properly. I tested it by removing it and comparing the value of resistance at ambient temperature to a resistance chart telling me what the resistance should be at that temperature.

Here's how it works. The unit will have a coolant temperature gauge. The gauge will have a power and ground like everything else but there's a twist. It also has a signal wire coming from a coolant temp sender. The job of the temp sender is to let the gauge know what to read for engine temperature. The sender is something called a thermistor.

In this scenario a thermistor is a resistor located on the engine whose resistance is reduced by heat. As the engine warms up the resistance reduces allowing voltage for the signal wire to increase which increases the reading on the gauge. In other words when the engine's cold the resistance is high causing the voltage for the signal wire to the gauge to be low. As the engine gets hot resistance for signal wire goes down increasing the signal voltage to the gauge.

One method for discerning whether you have a problem with the gauge or the sender is to ground the signal wire to the frame. If the gauge pegs over all the way then most likely there is a problem with the thermistor on the engine. You can troubleshoot further by removing the thermistor and testing it with your multi-meter. At a specific temperature there should be a specific amount of resistance. If your meter is reading a lot more resistance than the thermistor is supposed to have at that temperature then it should be condemned.

Typical thermistor in an engine with signal wire bolted to it

Lug with the S next to it is for the signal wire

coolant gauge on a Gehl skid loader

Dirty deeds done dirty cheap

Birch was sending an IR compressor to auction and one of the ones we were keeping had a bent axle. What management decided to do was swap the axle of the good one we were selling with the bad axle on the unit we were keeping. My job was to put the good axle on the unit we were keeping. The only catch was it was all the way in the back of the yard with no axle on it...yay. I ended up rigging the compressor with a reach lift and some lifting straps with the proper weight rating. Once I got it in the air I installed the axles and tightened the bolts just enough to be able to tow it to the shop. Once I got there I too out the bolts, cleaned them up with a wire wheel, and lined up the axle with the witness marks of the previous axle. That means I'm assuming the axle before was flush, plumb, square and where it needed to be. I was going to take some measurements and see if it was true, but was told that it was good enough and I was splitting hairs. Bolts were torqued with a torque wrench to 240 ft lbs.

Another job that is somewhat unsavory is mast hoses on an industrial forklift. The key is to marking all of your hoses, pulleys, and tensioners. That way you know how to route the new hoses when you install them. What happens is you rip all that stuff off and when you go to put it back together you go uhhhhhhh how did this go again? It just saves you time and prevents a headache. Doosan also likes to put the head of the bolts for their hose tensioners so that you have to line it up and then feed the bolt through the back side where you can't see.

40hr

530hr

Cooling system on Gehl RS5

I ended up working on a reach-lift that I found several problems when I performed my inspection. The line coming off the hydraulic pump was leaking so that had to be replaced with a high pressure hose. Those are always more difficult to maneuver then a regular hydraulic hose, and make getting the fitting started much more time consuming.

It also had a transmission leak running down the side of the bell housing. I washed and and ran it to identify the leak and it turned out to be one of the two plugs on top of the transmission. I changed the o-ring and it stopped leaking.

The third problem was that the coolant gauge never read the engine temperature getting above 120 F no matter how long you ran it. I popped the panel off for the gauge and it had good power and ground. Next I checked the signal wire for the coolant temperature sender which is a thermistor. It was measuring about 8.5 volts at the gauge and the sender. This brought me to the conclusion that the gauge is faulty.

40hr
490hr

Trail king brakes

I ended up working on a 3 axle super tilt trailer that originally came in for hubs to be serviced. Upon inspection the brake shoes and drums were very worn and needed to be replaced. Usually the entire backing plate is replaced because it's usually cheaper in the long run. My coworker did the bearings for the new hubs and the backing plates. It's just five bolts that hold it on to the axle. They're magnetic brakes so all of the wiring had to be spliced. Instead of trying to solder the wires and get the copper to tin with the solder I just used connectors with solder built in. It's much faster and a lot less hassle using them instead of solder and heat shrink. 

There was a pin for the leaf spring that was no longer taking grease and the press fit zerk fitting snapped in the process. I ended up drilling out the fitting and tapping a new hole for a different fitting to be used. I blew out all the metal pieces with an air blower, installed the fitting, and made it take grease with an air powered grease gun. Otherwise it was take the pin out which is not something I wanted to do if I could avoid it. The trick was taking my time and getting the tap perfectly straight for nice threads because if I made a mistake then I was hosed.

After that it was install the drums, put the tires back on with a bar, and torque the lug nuts. 

450hr

Motor swap for a Dodge Ram with a 4.7 V8

A friend of mine who works for Portal Way automotive asked for my help with a motor swap. It's a Dodge Ram with a 4.7 V8 so it's a fairly large engine automotive wise. There is also a lot more components to remove or disconnect then if it was on a piece of heavy equipment. We began by draining all the fluid out of the radiator, engine, and transmission. Disconnected all the plugs and the ones that were most difficult were the plugs for the the fuel injectors and the coil packs because they're really hard to get to and the plastic is brittle and frail. Also all of the plugs have these annoying tabs that lock the plug and they must be lifted out of the way before you can disconnect them. We removed the radiator, alternator, belt, hood, transmission cooler, oil cooler lines, and just strapped the ac compressor and components to the side with straps.

Second step was removing the drive shaft and transmission because it's just easier to swap the motor with the dowels on the bell housing out of the way. Of course we had to first unbolt the flywheel of the engine from the plate connecting it to the torque converter. Cool thing I learned about torque converters is when you reinstall them you have to first get the splines inside the drive hub to line up with the transmission input shaft and then get the drive flats on the hub to lock into place by turning the impeller until it pops in. Otherwise you destroy it and you'll be purchasing a new one and possibly a transmission.

We removed the Engine Mounts from the chassis after we got it hooked up to the cherry picker with a load leveling attachment. After that we removed the engine and struggle some getting it out. They have the engine tucked so far back in the engine compartment that a good portion of it it under the fire wall. It wouldn't surprise me if it's recommended to remove the cab first to make it easier. Next update will be installation of the new engine and we might have to take the cab off to get it back in.

50 (40 for work 10 for motor swap)
450

Night Light Pro I series troubleshooting

I received a light tower off the repair line with a complaint that a service light goes out intermittently. There are four service lights on this piece of equipment. Each light has it's own capacitor, step-up transformer, and bulb. It shares a breaker switch with one other light, and there are a number of places a problem can occur. I began troubleshooting at the capacitors with my meter and they all had the proper voltage except when the light would go out obviously. I tested them by changing the wiring for the service lights to different capacitors to see if the problem would follow to a different service light. When it didn't I troubleshooted the step-up transformers and they all were reading the proper voltage output. I continued by switching those transformers to different capacitors to see if the problem would follow thereby telling me if I had a transformer problem or something else going on.

It didn't follow to another service light telling me the capacitors and transformers were working fine. Next I checked the generator output at the breaker switches to see if I possibly had a bad winding in the generator. Both breaker switches had a steady 124 volts coming out of the generator and it didn't drop suddenly which would be an indicator for a generator issue. I shook all the wiring harnesses up to the service lights to see if maybe I had a short to ground somewhere but I couldn't induce a problem. I removed the light bar by the service lights because often times someone doesn't reassemble them properly and wires get rubbed through and ground to the frame.

Didn't find anything so I continued troubleshooting by switching service light wiring at the light bar with grounds from different service lights to see if I had a problem in the wiring from the light bar to the actual service light. Problem didn't follow so I knew the grounds were good. Keep in mind the very first thing I did was check power and ground at the service light elbow right before the service light.

This brought me to the conclusion that the problem was somewhere between the elbow and the actual light bulb itself. I had either a bad light fixture or a bad bulb itself. I switched the bulbs in the service lights to see if the problem followed to a different light. It did and all this dummy had to do was change the friggin light bulb...ugh.

So from now on when I have an intermittent problem with a service light I learned to swap the bulbs around..after checking power and ground at the load of course. One must go to the load as a wise man once said.

40hr
400hr

Service light wiring in light bar. Power, ground, neutral.

Capacitors on the left and transformers on the right.

Breaker switches

Elbow at service light

Light bar disassembled

Big Bertha

I was tasked with performing the 1000hr service on Big Bertha. She's the oldest piece of gear that Birch Equipment owns. She hadn't actually hadn't ran 1000 hours yet but the last person to do it didn't do it properly and water got into the hydraulic tank.

There's no easy drain plug to get to on this tank so I ended up just using a pump to get it out and then cleaning the inside of the tank by hand. It was fairly messy work. The problem from last time was that the previous mechanic didn't glean the gasket area on the tank or the oil filter housing or the lid. Just slapped it together. Eco-Terra is not cheap and that is a fairly large tank.

When it came time to reassemble I made sure that every mating surface was clean down to the machine marks and that black silicone was used as a sealant. You have to treat it as an engine oil pan gasket because essentially that's what it is.

40hr
360hr



40