Starting this thread to share some of my experiences around the job sites. Background: independent contractor with 9 years of Cat dealer field experience, contracting to a large highway/infrastructure contractor. We have a large variety of iron in the fleet from old to new technology. Dozers from a D5G to a D10N with most of the grading work being done with the new D5 next gen machines and D6N machines. Excavators from a 308 and (4) 374s and everything in between. Backhoe loaders, brooms, hoe rams, hoe packs, soil compactors, wheel loaders and a fleet of triaxles to top it off. 20+ miles of highway and a few large warehouse building pads in construction currently, starting a new infrastructure job in the city next month. All of this with 3 field technicians, we stay busy year round. I like sharing knowledge with other technicians and believe we build on each other’s experiences. Hopefully this will bring value or at least entertainment factor.
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In my experience…
- Thread starter ahart
- Start date
Cat 349F: complaint, high soot load. Machine running a hydraulic breaker busting up asphalt road bed and wouldn’t regen on its own. Hooked ET and immediately noticed engine temp was too low and wouldn’t warm up efficiently. After getting warm enough to do a manual regen, machine would instantly cool off. Installed 2 new thermostats and machine would then regen on its own. 
D6N PER prefix. Complaint: engine oil leak. Appeared to be coming out around crankcase filter housing, pulled filter and was full of sludge as were the tubes coming off of the breather housing. Pulled outlet tube off of the NRS cooler as this is a common place to coolant entry on these engines (Perkins C6.6,) dry there. Put 10 psi on the cooling system and let set for several hours while doing some other jobs. Came back to 3.5 psi on the gauge, cracked open engine oil drain valve and there were a few drops of coolant coming out. Drained cooling system and installed new water pump, #2 most common point for coolant entry on a Perkins in my experience. Once old pump was off, both weep holes were packed full of dirt. There is a purge valve on the back side of the crankcase filter housing that was releasing the oil from the filter housing due to extreme restriction. Cleaned crankcase filter system and installed new filter. Changed engine oil and filter. 
We talk a lot on this forum about checking transmission clutch pressures. Some may not fully understand what’s going on there. As shown in first photo, the modulation valves are where I have my pressure gauges hooked to. On this particular machine (D8T) there are two directional clutches and 3 speed clutches. One directional clutch is engaged and one speed clutch is engaged in any given gear. The modulation valve receives an current supplied by the powertrain ECM to control which clutch is engaged and how fast it is engaged. The second photo is a digital indicator group that I use when checking pressures. They are expensive but I like them better than dragging out test hoses and physical gauges for this situation. Physical gauges are still utilized when I need to see what the needle is doing, hard to see that on a digital unit. This meter will read between 0 psi and 10k psi depending on which transducer you use and channel 1-2 will read differential pressure 
8000 hrs on machine, no guarantee it happened at the same time. It just got bad enough that they got cold. I’ve seen several instances of them being stuck on 349 and 980k machines. Recently had a set stuck open on a W900L kenworth with a C15 belonging to my father in law. Seems like you get a rash of them around here
I know a few years back when I was living at the coal mine we replaced these thermostats a lot in the 3516 Engines that were in the 4AR 793C trucks, had 20 of them on site. Thermostats would stick open causing the engine to run cold which would over time cause the rings to stick on the pistons and eventually break. Tell tale symptom of broken rings on a 3500 series is hazing smoke at an idle and/or plugging engine oil filters due to the soot going into the oil.
changing stuff like that one at a time has never made sense to me.
you already did all the work to get to one why not go ahead and hit all of them while you are in there?
Mobiltech
Senior Member
I guess the difference is here in our cold climate if one thermostat is stuck open even 1/16 of an inch you won’t get the engine to warm up at all so we would never see them get that bad . We change a lot of thermostats in the beginning of winter and we do change both.
Nige
Senior Member
I found that the type/condiiton of the coolant used by customers had a major effect on thermostat failures. One particular customer used only a recycled coolant on their 4AR 793C's that they bought from an outside supplier (yes it was the cheapest tender selected by the accountants/logistics kings) and would you credit it they had more overheats and cooling system-related failures than nearly all the rest of the large haul truck operators put together..........
It was amazing. You could walk into the rebuild shop and see a disassembled engine, look at the liners, water pump, etc, and straight away know it was from that particular customer.
Nige
Senior Member
Remind me again. How many iterations of water ferrules went into 3500 engine spacer plates before they settled on the latest version with a stainless steel centre..?
We also changed the temperature regulators every 8k as a preventive measure.
The last place I was at used a coolant from Shell meeting Cat ELC specification and TBH cylinder liners and anything else that came into contact with coolant looked like new @ 16k hours when the engines were pulled for PCR. That's all the proof I need.
We also changed the temperature regulators every 8k as a preventive measure.
I don’t know, seems like I got a publication update every month for awhile. I left at the end of 2015 which is when I stopped paying much attention to the 3500 updates. I traded those for DEF software updates which seemed to be daily there for awhile.
621E scraper, another field tech on the job diagnosed as blown head gasket causing to pushing coolant out of the radiator cap. Got sent over to help put on the lowboy. Opened radiator cap, started machine and instantly a decent stream of coolant shot out of the radiator. I’ve seen many instances of compression in the radiator and never seen one shoot a geyser of coolant out with cap off so I decided to check it out. Noticed coolant residue at the dryer, removed air compressor and disassembled to find this. Called for a reman compressor and left the machine on-site instead of hauling it out for an engine. Lesson: if something doesn’t seem right, check it out for yourself. 
Truck Shop
Senior Member
Not coolant related or cat related--But remove a DD15 or 16 cylinder head, lay the injectors out on the
bench and the possibility is 50% in a 24 hr time frame those injectors will be locked up.
bench and the possibility is 50% in a 24 hr time frame those injectors will be locked up.
Truck Shop
Senior Member
Truthfully-don't know. But does happen frequently. Service manager I've known for years hasn't a clue either.
One of ours went in for a warranty head and six seized all covered on warranty. It's not the first time on a
warranty head replace. I asked if keeping them submerged in fuel would stop it, already been tried.
But there only $980.00 ea if not covered under warranty, so I guess it's not too big of a deal.
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