c/diesel-mechanics

Pro tip: stop using the wrong grease on your fifth wheel plate

I keep seeing guys at the shop grab whatever tube of grease is closest and slap it on the fifth wheel. That's a fast way to have a bad day. Most general purpose greases can't handle the heat and pressure, they just turn to liquid and wash off. I learned this the hard way about six months ago on a Peterbilt 579 that came in with a loud clunking sound. The plate was bone dry and starting to gall. Now I only use a proper fifth wheel grease, the kind with high moly content. It stays put and keeps things quiet. What brand do you guys trust for this job?

Overheard a trucker at the diner complaining his DEF heater failed for the third time this winter in Fargo

Found a weird trick for getting a stuck 6.7 Powerstroke turbo oil feed line loose

Had one of those lines on a 2015 F-250 that was seized solid, even with a line wrench and heat. Out of ideas, I sprayed it with a mix of ATF and acetone, let it sit overnight, and it came off with a normal ratchet the next morning. Anyone else have a go-to mix for frozen parts that's not just PB Blaster?

Heard a guy at the Freightliner dealer in Springfield say he never flushes coolant systems

He was telling another tech he just drains and refills because it's faster, and that the flush machines are a waste of time. That's a fast track to silicate dropout and clogged heater cores, especially on those newer Detroit engines with extended life coolant. How many of you actually run a proper chemical flush and reverse flush with every coolant service?

Appreciation post: A talk with a retired guy at the truck stop in Billings

I was grabbing coffee before a job and got talking with an old timer who used to run a fleet shop. He said, 'We used to set injector timing with a dial indicator and a steady hand, listening for the change in the engine's hum.' I've only ever used the laptop and software. It made me think, do we lose a feel for the machine when everything is just a screen and a code? How many of you still use those old school methods sometimes?

Had a 6.7 Powerstroke's high pressure fuel pump grenade on me last Thursday, sent metal through the whole system.

It was on a 2017 F-250 that came in running rough. The customer said it just lost power on the highway. Pulled the fuel filter and found glitter. Tore into it and the CP4 pump was toast. Now we're looking at replacing the pump, lines, rails, and injectors. Quote is over $8k in parts alone. Has anyone found a decent aftermarket kit for this, or is it just a bite-the-bullet OEM situation every time?

My old man told me to never trust a 'quick fix' additive for injector knock, and I should have listened

I had this 6.7 Powerstroke with a nasty knock that wouldn't go away. A guy at the parts counter swore by this 'Diesel Doctor' additive, said it would quiet it right down for $40 a bottle. My dad, who wrenched on semis for 30 years, always said those bottles are just expensive bandaids and to find the real problem. I bought the bottle anyway, poured it in, and the knock got softer for about 50 miles. Then it came back worse than ever. Turns out I had a failing injector cup, which the additive just masked for a bit. Ended up costing me over a grand to fix it right after I wasted time and money on the snake oil. Anyone else have a story about a 'miracle' fix that just made things worse?

Vent: I keep seeing guys torque head bolts dry on 6.7 Powerstrokes

The manual clearly states to lubricate the threads and the underside of the bolt head with clean engine oil... but I've watched three different techs in my shop just run them up dry this month. That changes the clamping load and risks uneven seating or a future leak. Am I the only one who still follows the factory spec to the letter on this?

Had a squirrel drop a whole walnut into a 6.7 Powerstroke's intake boot

This was at a farm shop in rural Ohio, we were doing a routine service. The truck had a weird whistle we couldn't pin down. Pulled the intake tube and this perfect, whole walnut just rolled out onto the shop floor, lmao. The owner said he parks under a tree and the little guy must've been stocking up. Now I always give the air box a quick visual before I even hook up the scanner. Anyone else find weird stuff in engine bays?

Honestly, I just realized my 2015 Duramax started idling smoother after I switched to a different fuel filter brand last month.

Just dropped $250 on a new fuel pressure test kit and it found a problem in 10 minutes.

We had a 6.7 Powerstroke with a hard start that was eating up hours of diag time. The old gauge setup was giving weird readings, but this new kit showed a slow bleed down from the secondary filter housing right away. What's your go-to tool that paid for itself fast?

A 2007 Duramax with a weird injector knock had me chasing my tail for a full weekend.

I swapped the injectors, checked the balance rates, and even pulled the valve covers before I found a tiny crack in a high-pressure fuel line fitting. How often do you guys see something simple like a bad line cause a noise that sounds exactly like a mechanical failure?

Working on a logging truck in Oregon taught me to check the simple stuff first

I was out near Coos Bay last fall, trying to figure out why this old Mack wouldn't build air pressure past 60 psi. Spent half a day convinced it was the governor or a bad compressor. My buddy, who's been at it for 30 years, walked over, listened for about ten seconds, and just pointed at the air dryer purge valve. It was stuck open just a hair, a five minute fix. I felt pretty dumb for overcomplicating it. Since then, I make a point to run through the basic, cheap parts before I even think about pulling something major. What's your most recent 'should have checked that first' moment on a diesel rig?

Had to choose between a 12-valve Cummins rebuild or a new crate motor for a '94 F-350. Went with the rebuild and it's been a year now.

Just realized using a zip tie to hold the fuel line clip open saved me 20 minutes on a 6.7 Powerstroke injector swap.

I was fighting that stupid plastic clip for the third time last Tuesday and remembered a YouTube comment about using a small zip tie to lock it in the open position, which let me slide the line right off without breaking it.

Found out a 6.7 Powerstroke's oil filter holds way more than I thought

I was draining one at the shop yesterday and it took a full 2.5 gallons to refill, which just seemed wild for a filter. Anyone else run into a surprisingly large capacity on a common part?

I was torquing head bolts wrong for years until a guy in Phoenix showed me his trick

I was doing a head gasket on a 6.7 Powerstroke last month, and a mechanic from another shop was watching. He saw me torque the bolts in the order from the manual, then just walk away. He said, 'You're not doing the final quarter-turn angle torque? The manual says to, but a lot of guys skip it.' I had been skipping that step on every single job for about five years, thinking it was just for factory assembly. I went back and did it, and the feel was totally different. Has anyone else found a step in the book they were just ignoring?

Had a customer in Bakersfield tell me his truck was 'just a little loud'

He brought in his 6.7 Powerstroke last month, saying it sounded rough but ran fine. I popped the hood and found three broken exhaust manifold bolts and a massive soot trail. When I showed him, he just shrugged and said, 'It's a diesel, they're supposed to be loud, right?' I had to explain that noise is one thing, but exhaust leaks before the turbo are robbing power and could wreck the turbo bearings. How do you guys get through to customers who ignore clear danger signs like that?

Finally got the hang of reading injector trim codes without the scanner

For years, I'd just plug in the computer and wait for the readout, which was fine until a scanner died on me mid-job at a farm outside Bakersfield. I had a Duramax with a rough idle, and my boss said 'figure it out the old way.' I spent an hour with a multimeter and the service manual, checking resistances and counting the flashes on the injector connector light. Now I can diagnose a bad injector in about 15 minutes without any fancy tools. Anyone else have to learn a manual backup method for a common electronic check?

Finally tried a new torque wrench on my old 7.3 Powerstroke and the difference was crazy

I've always used my old clicker wrench for head bolts, but last week I borrowed a buddy's digital one for a rebuild. The digital readout showed my old wrench was off by almost 15 foot-pounds on the high end, which explains a lot. Has anyone else switched tools and been shocked by the results?

Heads up on those new DEF injector designs from the 2022 model year trucks

We had a fleet of delivery vans come through the shop, all with the same engine. The ones from 2021 were fine, but the 2022 models started showing crystallized DEF clogging the injector tips after only about 15,000 miles. The housing design changed to a smaller, more recessed port that doesn't get as hot. It took us three vans with the same fault code before we spotted the pattern. Now we're telling drivers to run the trucks for a good 20 minutes after a regen cycle to try and burn it off. Has anyone else found a better fix for this, or is it just a bad design we're stuck with?

Warning: a $30 part saved me from a huge headache on a 6.7 Powerstroke last month

The truck had a rough idle and a code for low fuel rail pressure. I spent hours checking the high pressure pump and injectors before I found a cracked plastic fitting on the fuel line coming from the tank. Has anyone else seen those fittings fail on the newer Fords?

Tried to quiet a 6.0 Powerstroke with a 'whisper' muffler from a car show, now it sounds like an angry coffee can.

Pulled a 7.3 Powerstroke glow plug and found the tip was a different length than I expected

I was doing a full glow plug change on a 2002 F-350 that came into the shop last Thursday. Grabbed a new set, part number ZD-11, and went to work. When I pulled the old ones, I measured one and the heated tip was a full 3mm shorter than the new plug. Checked the old box in the truck's glove box and they were the wrong spec, installed by the previous owner. Has anyone else run into a truck running on mismatched plugs for who knows how long?

Had a total facepalm moment about torque specs on a 6.7 Powerstroke

I was replacing the turbo oil feed line on a 2015 F-250 last week, a job I've done maybe a dozen times. Always just gave the banjo bolt a good 'snug' with a 3/8 ratchet, never used a torque wrench. This time, the new line started weeping after the test drive. My foreman walks by, sees me about to crank it down harder, and just says 'spec is 18 ft-lbs, you know that, right?' I'd been going way over that for years. Grabbed a torque wrench, set it, and it sealed up perfect. How many other 'feel' habits are actually wrong? Anyone else have a simple spec they ignored forever?