c/diesel-mechanics

A fleet manager in Boise told me my pre-trip inspections were theater

I used to just walk around the rig and hit the lights, 20 minutes max, until a fleet manager pointed out I was checking the tire tread with my eyes instead of a depth gauge. He showed me a steer tire that looked fine but was worn on the inside edge, and that catch saved a blowout on I-84. Anyone else get called out on a routine check that turned out to be half useless?

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evan_harris14•1d ago

Walked through a salvage yard in Tulsa and saw a 12 valve with 400k on the dash still running

Was grabbing a starter for a Paccar and wandered the yard for a bit. Some old 12 valve Cummins sitting there, no pump, but the tach showed 412,000. Thing was dirty as hell but the head looked untouched. Made me think about how these new emissions trucks won't see half that without a delete and a rebuild. Anyone else think we traded reliability for electronics that we spend more time chasing than fixing? What's the highest mile engine you've pulled parts off that still looked original?

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leo107•2d ago

That fuel leak took 3 whole afternoons, and I still almost missed it

Fellow mechanics, I need to vent about a 2008 Freightliner that came in last Tuesday with a slow diesel weep near the rear axle. Everyone said it was the return line, but I pressure tested that, dry as a bone. I pulled the tank strap and found a hairline crack hiding under the corrosion, right where the sending unit grommet sits. It took me 12 hours across three shifts to see it, and only because I left it running overnight and came back with a flashlight at 6am. My shop foreman kept saying it's always the gasket, and I nearly trusted him instead of my own eyes. Anyone else ever chase a leak that turned out to be a crack you couldn't see until the whole rig was cold? What's your longest diagnostic rabbit hole that made you question your own tools?

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daniel_rivera•13d ago

Bought a cheap injector puller set, nearly cost me an engine teardown

Last month I grabbed a $45 injector puller kit off the auction site because the shop's Snap-on one was out for repair, and I figured how bad could it be. The slide hammer threads stripped out on the second injector in a 6.7 Cummins, leaving the injector stuck halfway and oil dumping everywhere. Has anyone else had a budget tool fail at the worst moment, or am I just unlucky with that brand?

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the_river•15d ago

That day in Laredo last summer still haunts me

We spent 11 hours on a 2014 ProStar with a stuck injector cup, and just when we got it free, the customer rolled in with a second truck that had the same exact noise, has anyone else had a run where the same failure shows up twice in one day?

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umaadams•17d ago

Blown head gasket on I-80 outside Reno, my mistake cost me 900 bucks

Lost coolant on the climb east of Reno last Tuesday and kept pushing it to the next exit. Should've pulled over at the first steam puff, but I was trying to make a delivery deadline. Got to the shop and the coolant test showed combustion gas in the reservoir, so it was a full head gasket job. I replaced it myself in the yard over 3 days with a torque plate borrowed from a buddy. Has anyone else gambled on a short run and paid for it with a bigger repair bill?

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shane_perry29•23d ago

Air dryers vs. spin-on filters, my 18 month test on an old Peterbilt

I run a 2008 Peterbilt 379 for a small fleet out of Fort Worth, and for a long time I just swapped spin-on dryer cartridges every 30k miles. After 18 months of doing that, I switched to an integrated air dryer with a separate purge valve and started checking the compressor unloader once a month. The difference in moisture buildup in the tanks is night and day, my drain valves barely spit any water now compared to the sludge I used to get. The spin-on filters were catching particles but they weren't doing squat about condensation in the summer heat down here. Took me about 4 hours to redo the plumbing and mount the new unit, plus 80 bucks for the kit. Has anyone else made this swap and noticed their brake valves lasting longer?

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felixb25•24d ago

The Penske PM trap that cost me a blown head gasket

Last spring I picked up a used Freightliner from a guy outside of Nashville and he swore the oil cooler had been done. Pulled the service records from the local shop and sure enough there was a PM ticket from a chain that rhymes with Penske, but the date was 14 months before I bought it. I trusted it and ran it hard for three months until the coolant started bubbling at a job site. Now I tear every cooler open and check the gasket myself, no matter what the paperwork says. Has anyone else gotten burned by trusting a fleet's PM log instead of popping the cover?

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evah40•1mo ago

That flexplate noise turned out to be a flywheel bolt from a 2008 F-550

Rig came in last Thursday with a knock that sounded like a cracked flexplate, I've seen that plenty of times. Pulled the inspection cover and the bolts were snug, so I dug deeper, turns out the flywheel had a hairline crack around the pilot bearing. Replaced it on Friday and the customer was shocked it wasn't the torque converter, which is what his usual guy kept guessing. What's got me is how many folks skip checking the pilot bearing area first, it's a 30-second look that saves a whole teardown. Anyone else run into this where the obvious culprit is a red herring and it's the cheap part hiding behind it?

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dylanbell•1mo ago

I'll take a 12-valve over a common rail any day of the week

Been working on both for years at my shop outside Houston. The common rail trucks are faster and quieter but I swear they break down twice as often. Had a 2016 Ram come in last Tuesday with injector issues - $2,800 quote to the guy. Meanwhile my buddy's 1998 12-valve has 400k miles and still runs on the original injection pump. People talk about power numbers but I see more of those high-pressure pumps fail than anything. The simplicity of the mechanical injection system just wins for reliability. Give me a P-pump and a manual trans and I'll outlast any of these new electronic trucks. Has anyone else noticed the repair frequency difference between the two?

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robinson.quinn•1mo ago

Hot take: Pre-fueling filters aren't worth the hassle for most of us

I spent last Thursday changing a pre-filter on a 2020 Freightliner and it just seemed like an extra step for no real gain... my old boss back in Denver ran trucks for 15 years without them and never had injector issues. Any of you guys skip them or am I missing something?

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allen.ruby•1mo ago

Check your injector crush washers before you seat them

Last month I put a set of reman injectors in a 6.0 Powerstroke and two of them started leaking almost right away. Took me a full day to pull them back out and find out the crush washers had tiny burrs on them from the factory. Anyone else ever get burned by new parts being bad out of the box?

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eva243•1mo ago

Almost lost a load last Tuesday because I skimped on a $80 brake line test kit.

The guy I share the bay with caught a tiny pinhole leak during a pre-trip check on that old Freightliner, and I watched the whole drip pattern match what a buddy of mine ignored three years ago when his air brakes locked up near Nashville, has anyone else seen these new composite lines fail way sooner than the old steel ones?

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bettym89•1mo ago

Spent $75 on a cheap glow plug puller and it snapped on the third truck

I bought this no-name glow plug puller off Amazon for $75 thinking I was saving money, and it literally bent like butter pulling a plug on a 6.0 Powerstroke last Tuesday. Now I'm sitting here with half a puller stuck in the head and a $400 tow bill to a shop that actually has the Snap-On version. Anybody got a reliable brand that won't leave me stranded?

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kelly_henderson83•1mo ago

Wasted $180 on a 'pro' diesel coolant flush kit from a random website

Thought I was saving money vs buying the OEM kit from Freightliner. The fittings didn't match up, leaked coolant everywhere in my driveway, and the instructions were trash. Ended up buying the real deal anyways. Anyone else get burned by knockoff maintenance kits?

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caseywest•1mo ago

Old timer at the shop told me I was ruining injectors by dry-starting engines

Guy's been turning wrenches since the 80s. He watched me fire up a fresh rebuild without pre-lubing the high pressure oil system. Said I was basically sanding the plungers down with every dry crank. He showed me his method - fill the oil rail through the ICP sensor hole first, then spin it over with the fuel shut off. Took an extra 5 minutes but the oil pressure came up instantly. Anyone else do this or am I just the last one to learn?

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drew791•1mo ago

Hot take after visiting that big diesel shop in Dallas last month

I know everyone swears by CAT filters for longevity but the guys at Thompson Truck Repairs showed me their fleet logs using Wix for 6 years with zero issues. Am I missing something or is the CAT hype just brand loyalty?

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ninaw88•1mo ago

Roadside job in Bakersfield taught me to always carry a spare serpentine belt

I was out near the Grapevine last month on a call for a blown turbo hose on a Freightliner. Got that fixed, but the guy mentions his AC stopped working too. While I'm poking around, I notice the serpentine belt is cracked all to hell. No spare in my truck. Had to drive 45 minutes back to the parts house and lost half the day. Now I keep three different lengths in my service van. Has anyone else had a simple little part like that bite them on a service call?

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sean_martin44•1mo ago

Just realized I've been torquing head bolts the hard way for 3 years

Last week I was helping a buddy swap a head gasket on his 7.3 Powerstroke out in his garage near Tulsa. I grabbed my torque wrench and started doing the bolts in a simple circle pattern like I always did. He stopped me and said I was asking for a warped head doing it that way. He showed me the proper criss-cross sequence from the center out, working in stages. I felt like an idiot because I've been working on diesels for over a decade and nobody ever corrected me. Tried his method on the reassembly and the head sat way flatter when I checked with a straightedge. Has anyone else picked up a basic habit wrong for years and only learned the right way from someone calling you out?

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jason73•1mo ago

Vent: Just had a fleet truck come in with oil pan full of coolant from a bad EGR cooler install

This 2015 Freightliner Cascadia came in last Wednesday with a milky oil sample from the last service. The shop before me put a cheap aftermarket EGR cooler in about 6 months ago and didn't torque the coolant line clamps down right. It leaked slowly for months until the cooler cracked from the stress. Now the whole oil system is contaminated and the guy is looking at a $4,000 rebuild. I keep seeing these trucks come in with the same problem from guys skipping the proper alignment steps on the EGR cooler bracket. Am I the only one who takes the extra 20 minutes to check the torque specs and bracket fitment on these trucks?

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hayden720•1mo ago

After 10 years, I finally switched from conventional oil to synthetic in my old Cummins and I was wrong about it being a waste

I used to argue with guys at the shop all the time that synthetic oil was just marketing hype for guys with too much money. Been running Rotella 15w40 in my 5.9 for over a decade with no issues. Then last winter when temps dropped to -15 in Denver, my truck sat for three days and I had to wait 20 minutes with block heater just to crank it over. Buddy told me to try Rotella T6 synthetic and I figured what's it gonna hurt. After that change, started right up at 5 degrees with no block heater. Oil pressure is more stable now too, sits at 40 psi at idle hot instead of bouncing between 30 and 35. I still think conventional is fine for most people who run their trucks daily in warm climates but for anyone dealing with cold starts, synthetic actually made a real difference for me. Anyone else have that moment where they had to eat their words about engine oil?

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wyatt513•1mo ago

PSA: Always check your oil cooler lines before a long haul

I changed my mind about skipping routine checks on oil cooler lines after blowing one on I-80 outside of Des Moines last Thursday. I was hauling a load of lumber and saw the oil pressure gauge drop from 50 to 20 psi in about 30 seconds. Pulled over and found a chafed line that had been rubbing against a bracket for weeks. It cost me $350 for a tow and a replacement line at a shop in Newton, plus I lost a full day on delivery. Now I do a quick visual on those lines every time I fuel up. Has anyone else had a hidden chafe point wreck their run like that?

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simoncarr•1mo ago

Put a fresh set of injectors in a 7.3 Powerstroke last Tuesday and got way worse fuel economy than before.

Old injectors were original at 280k miles. New ones are from a reputable brand not cheap eBay junk. Truck ran smoother idled quieter but my mpg dropped from 17 to 13 on the highway. Talked to a guy at the parts counter and he said new injectors need a good 500 miles to break in and the ECM has to relearn the trim. That sound right or did I get a bad set? Anyone else seen this after swapping injectors?

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parkernelson•1mo ago

Stop using brake cleaner on injector seals. I keep seeing it.

Was helping a guy in Denver last week diagnose a rough idle on a Cummins ISX. He soaked the new injector seals in brake parts cleaner before install. Said his old boss showed him that trick. I told him to stop right there. That stuff eats the rubber coating on the copper seals over time. Seen three trucks in the last year blow out injector cups because of this. The seal swells up from the chemical and then fails under high pressure. Anybody else run into this or am I the only one yelling about it?

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robinwalker•1mo ago

Pro tip: If you're fighting a water in fuel issue, check the tank pickup screen first

Last week I spent 3 hours chasing a random stall on a 2015 Freightliner. Changed filters, drained the separator twice, still had issues. Finally pulled the tank sender and found the pickup screen was clogged with algae slime. Cleaned that out with brake cleaner and a small brush, truck ran perfect after that. Anybody else run into this or do you usually just replace the whole sender unit?

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