Caterpillar 1673
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar 1673 is an on-highway diesel truck engine, not a complete vehicle: Caterpillar built the engine only and sold it to independent truck manufacturers, who mounted it in their own chassis with their own transmission and axles. It covers three factory generations. The base 1673 (serial prefixes 70B/74B/83B, from around 1961) is a naturally aspirated inline-six of 8.6 liters (525 cu in) displacement, rated around 220 hp, with some truck installations derated to about 200 hp. The updated 1673B (prefix 78B, from about 1963-64) shares the same 8.6 liter displacement class but is rated higher, around 245-254 hp, using precombustion-chamber injection fed by a scroll-type metering pump. The 1673C (prefixes 69D/76R, introduced around 1967) is a full redesign at 10.5 liters (638 cu in), turbocharged, rated around 250-270 hp, later production moving to sleeve-metering and direct injection. Dry engine weight runs roughly 790-880 kg (1750-1940 lb) depending on series. All three trace back to Caterpillar's D333 industrial/tractor engine family rather than a clean-sheet truck design, and independent builders including Oshkosh, Kenworth, Peterbilt, and Diamond T offered the 1673 across their own truck lines through the 1960s and into the 1970s.
The line moved in two real steps. The 1673B was Caterpillar's factory response to early reliability trouble on the base 1673: head cracking, occasional block cracking, spun bearings, and a leak-prone brass-ferrule and rubber-grommet head seal. The 1673B addressed some of this but kept the same displacement class and stayed behind Cummins and Detroit Diesel competitors on durability. The 1673C then broke from that lineage with a larger-bore block shared with the D333C industrial engine, a turbocharger, and stronger overall durability; that same block and architecture carried forward into the Caterpillar 3306, which took over as Caterpillar's mainstream inline-six on-highway and industrial engine into the 1970s and beyond. In today's used and parts market, the 1673 matters mainly to vintage and heavy-haul truck restorers keeping period trucks running, and to owners who value its fully mechanical, pre-electronic design for straightforward field diagnosis and rebuildability. Because Caterpillar retired the 1673 line decades ago, parts supply leans on salvage cores and cross-application with the D333/D333C and early 3306 family.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Caterpillar 1673 specifications
Engine
| Model / series | 1673 truck diesel engine, released around 1960; revised as 1673B (early-mid 1960s) and redesigned as 1673C (introduced 1967). The 1673C shares its architecture with the D333C industrial/tractor engine, later renamed 3306. |
| Configuration | Inline 6-cylinder, 4-stroke-cycle diesel, 2-valve cylinder head on both 1673B and 1673C |
| Displacement | 1673 / 1673B: 525 cu in (8.6 L). 1673C: 638 cu in (10.5 L) |
| Bore x stroke | 1673 / 1673B: 4.5 in x 5.5 in (114 mm x 140 mm). 1673C: 4.75 in x 6 in (121 mm x 152 mm) |
| Gross power | Base 1673: about 220 hp (164 kW), with some truck installations derated to about 200 hp (149 kW). 1673B: about 245-254 hp (183-189 kW). 1673C: about 250-270 hp (186-201 kW). Figures vary by configuration/series. |
| Aspiration | 1673C documented as turbocharged; base 1673 and 1673B were naturally aspirated |
| Governed speed | 2200 rpm (documented for 1673B) |
| Emissions tier | Not applicable - pre-emissions-regulation era engine, no certified tier |
Weights
| Engine dry weight (1673B) | About 1940 lb (880 kg), as built (bare engine, not installed) |
| Engine dry weight (1673C) | Not documented in available sources |
| Operating weight | Not applicable - this is a truck engine sold separately from the chassis, not a complete machine with a published operating weight |
| Ground pressure | Not applicable to a standalone engine |
Dimensions
| Transport length/width/height | Not documented - no factory transport dimensions published for the bare engine |
| Wheelbase / track gauge | Not applicable - engine only; wheelbase is a function of the truck chassis (e.g. Oshkosh, Peterbilt), not the Cat engine |
| Ground clearance | Not applicable to a standalone engine |
Performance
| Travel speed | Not applicable - road speed depends on the truck chassis and transmission, not documented as an engine spec |
| Governed engine speed | 2200 rpm (1673B); not documented for 1673C |
| Gradeability | Not documented for this engine |
Service capacities (summary)
| Fuel tank | Not applicable - fuel tank is chassis-mounted, not part of the engine spec |
| Engine oil | Not documented in available sources |
| Cooling system | Not documented in available sources |
| Hydraulic system | Not applicable - this engine model has no published hydraulic system data |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
1673 fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (with filter) | Not published in any surviving factory literature found in this search. The 1673 is a 1960s/70s mechanical inline-six (525 cu in on the 1673/1673B, 638 cu in on the 1673C), sharing block architecture with the D333 industrial engine and the later 3306. Comparable Cat inline-six crankcases of this displacement class typically fall near 30-38 L (8-10 US gal) with filter, but no verifiable OMM figure specific to the 1673 could be confirmed. Verify against the original operator's manual for the exact serial-number break. | Factory guidance predates Cat's modern branded oil line. Period service literature for this engine family called for a diesel engine oil meeting the Series 3 (later API CC/CD) classification, graded by climate: SAE 10W for cold starts, SAE 30 for normal temperate operation, and SAE 40 for sustained high ambient/heavy load service. Treat any listing citing a specific modern branded product for this engine as unverified. |
| Cooling system | Not documented in publicly available sources for the 1673 specifically. Total system volume on inline-six engines of this era and displacement is normally in the 25-40 L (7-10 US gal) range for the engine circuit alone, but chassis-mounted radiator volume varies by the truck builder, so no single figure applies across installations. Confirm with the specific chassis OEM cooling system spec plus the engine OMM. | Era-correct guidance called for water with a corrosion/rust inhibitor (a compounded coolant, not a modern extended-life glycol formula, which postdates this engine). Cold-climate operation called for the addition of a glycol-base antifreeze rated to the expected ambient low, per the period cold-weather starting aids section of the OMM. |
| Fuel tank | Not applicable from the Caterpillar engine OMM. The 1673 was sold as a power unit to independent truck manufacturers; fuel tank sizing and mounting were set by the chassis builder, not by Caterpillar. | No capacity or brand fluid specified by Caterpillar; use diesel fuel meeting the era's ASTM No. 2-D specification per the engine OMM's fuel section. |
| Transmission / powertrain compartments | Not applicable. The 1673 is a standalone diesel engine; transmission was supplied and specified by the truck chassis manufacturer, not covered in the Caterpillar engine OMM. | No fluid recommendation exists for this system since it falls outside the engine OMM's scope. |
| Final drives | Not applicable. Final drive/axle hardware on trucks powered by the 1673 belonged to the chassis builder's driveline, outside Caterpillar's engine documentation. | Not covered by the Caterpillar 1673 engine OMM. |
| Hydraulic system and tank | Not applicable. The 1673 is an engine-only product; it has no Caterpillar-specified hydraulic system. | Not covered by the Caterpillar 1673 engine OMM. |
| Axles / differentials | Not applicable. Axle and differential hardware was sourced and specified by the truck manufacturer, not Caterpillar. | Not covered by the Caterpillar 1673 engine OMM. |
| Grease (chassis/engine fittings) | Spec only; no metered quantity published for the 1673 engine's own grease points. | Period multipurpose chassis grease, NLGI Grade 2 lithium-base, per the general lubrication chart typical of engines and machines of that era. No further OMM-specific detail found. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar 1673 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 50 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 6,000 h |
|
| Every 12,000 h |
|
Servicing the 1673 beyond the schedule
Predictive maintenance and fluid analysis
Run scheduled oil sampling on the 1673's Series 3 lubricant to catch bearing and cylinder wear before it reaches the crankshaft, since this engine has no ECM to flag it electronically. Track fuel dilution and soot loading, because a worn scroll-type (or later sleeve-metering) injection pump shows up first as fuel-thinned oil. On the 1673C, log boost pressure and exhaust manifold temperature at a fixed load point every interval; a slow boost drop or temperature climb flags turbocharger wear or fouled injector spray patterns before it becomes a hard failure.
Corrective and common repairs
Expect head cracking and spun main or rod bearings on early 70B/74B/83B and 1673B engines, the same trouble that forced Caterpillar's own 1963-64 factory update. The brass-ferrule and rubber-grommet head seal is the recurring leak point; replace both whenever a head comes off, not just the gasket. On the 1673C, turbocharger shaft seal weep and injector nozzle carbon-up are the common wear items. Diagnose all of it mechanically, through compression checks, injector pop-testing, and boost or exhaust readings, since there is no fault code to read.
Overhaul and rebuild points
A top-end job on the 1673 means pulling the head, checking for the known cracking pattern around valve seats and injector bores, and replacing valves, seats, and the head-seal ferrules and grommets together. Inframe work means checking the block for that same cracking tendency before honing or reboring, since a marginal casting will crack again under load. The 1673C shares its larger-bore block with the D333C and early 3306, so machining data and rebuild practice from that later family are the most practical guide now that the 1673 line itself is long retired.
Seasonal and environment servicing
Cold-weather operation calls for a lighter SAE-graded Series 3 oil and a glycol and corrosion-inhibitor coolant mix sized to the expected low temperature, since these engines predate factory ether-start or block-heater integration. In hot, dusty service, shorten the air cleaner interval, and remember the naturally aspirated base 1673 and 1673B lose more power to heat and altitude than the turbocharged 1673C, which compensates better at elevation. Check the fuel-water separator more often in humid or high-condensation storage and duty conditions.
1673 common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| 9L-0481 | Oil Filter | Lubrication service | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
1673 attachments & work tools
Work-tool / attachment ecosystem
The 1673 is a 1961-era Caterpillar on-highway diesel truck engine, not an earthmoving or material-handling machine model. It was sold as a power unit installed by outside truck builders into their own over-the-road chassis. No bucket, fork, grapple, blade, or breaker work-tool line exists for it because it does not belong to a Caterpillar construction or work-tool equipment class.
Coupler / mounting system
Not applicable to this model. The 1673 bolts into a truck chassis as a fixed powerplant; it has no front linkage, quick-coupler, or pin-grabber interface for exchanging work tools, unlike wheel loaders or excavators.
Hydraulic kit / PTO arrangement
Factory literature for the 1673 covers the engine proper: cooling, precombustion-chamber fuel injection, and lubrication systems. No hydraulic-kit or work-tool circuit is documented for it. Any power take-off for dump beds, winches, or mixer drums on a 1673-powered truck was engineered and fitted by the truck or body builder, not offered as a factory work-tool option.
Factory configuration / series notes
Three distinct builds exist and should not be merged: the original 1673, rated around 220 hp; the updated 1673B, a 4.5 in x 5.5 in bore/stroke unit of about 525 cu in rated near 245-254 hp; and the later redesigned 1673C, a 4.75 in x 6 in bore/stroke unit of about 638 cu in rated roughly 250-270 hp (varies by configuration/series), which shares its basic design with the D333C industrial engine later renamed 3306. Chassis guarding, PTO provisions, and mounting were set by the truck manufacturer's frame, not by a factory equipment-guarding option list.
All 1673 assemblies by section
Every catalogued assembly group for the Caterpillar 1673. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
1673 Diesel Truck Engine
Accessory Drive
Aftercooler
Air Cleaner
Air Compressor And Drive--Part 1 Of 2--Field Installation
Air Compressor And Drive
Air Compressor And Drive--Part 2 Of 2--Field Installation
Air Compressor And Drive--Field Installation
Air Compressor And Drive--Low Mounted
9l584 Air Compressor Assembly
| 9L***84 | Air Compressor Assembly | 1 |
9l1167 Air Compressor Assembly
| 9L***67 | Air Compressor Assembly | 1 |
9l1375 Air Compressor Drive Group
| 9L***75 | Air Compressor Drive Group | 1 |
4l7805 Alternator--12 Volt, 60 Ampere
| 4L***05 | Alternator Assembly | 1 |
Camshaft
Connecting Rod And Piston--6 Required
Crankshaft
Crankshaft Bearing Replacement Groups
Cylinder Block And Covers--Side View--Part 1 Of 2
Cylinder Block And Covers--Front View--Part 2 Of 2
Cylinder Block And Covers--Front View --Part 2 Of 2
7m4403 Cylinder Block Assembly--Type 2
| 7M***03 | Cylinder Block Assembly | 1 |
7m4403 Cylinder Block Assembly--Type 1
| 7M***03 | Cylinder Block Assembly | 1 |
Cylinder Head And Valve Mechanism--End View--Part 2 Of 2
Cylinder Head And Valve Mechanism--Side View--Part 1 Of 2
Electric Starting (24 Volt) And Alternator (12 Volt)
Electric Starting (24 Volt) And Alternator (12 Volt)--(9l460 N/S)
| 9L***60 | Electric Starting | 1 |
Exhaust Pipe
Fan And Drive
Fan Belts
Fan Mounting And Drive
Flywheel (9l667 N/S)
| 9L***67 | Flywheel | 1 |
Flywheel Assemblies
Fuel Filter And Priming Pump
Fuel Injection Valves And Lines
Fuel Pump Housing And Governor
2m4050 Fuel Pump Housing Group
| 2M***50 | Fuel Pump Housing Group | 1 |
8h9794 Fuel Transfer Pump Assembly
| 8H***94 | Fuel Transfer Pump Assembly | 1 |
Gasket Kits
Governor Control
9l240 Governor Group--Type 1
| 9L***40 | Governor Group | 1 |
9l240 Governor Group--Type 2
| 9L***40 | Governor Group | 1 |
Manifold
9l3586 Manifold Conversion Group
| 9L***86 | Manifold Conversion Group | 1 |
5l2537 Motor Assembly--24 Volt--Part 1 Of 2
| 5L***37 | Motor Assembly | 1 |
5l2537 Motor Assembly--24 Volt--Part 2 Of 2
| 5L***37 | Motor Assembly | 1 |
Oil Cooler And Water Lines
Oil Filler, Breather And Fumes Disposal (9l483 N/S)
| 9L***83 | Oil Filler, Breather And Fumes Disposal | 1 |
Oil Filter (9l481 N/S)
| 9L***81 | Oil Filter | 1 |
Oil Lines
9l1282 Oil Pump Assembly
| 9L***82 | Oil Pump Assembly | 1 |
9l455 Oil Pump Assembly
| 9L***55 | Oil Pump Assembly | 1 |
9h2256 Pump
| 9H***56 | Pump Assembly | 1 |
9l1225 Solenoid Fuel Shut-Off Group--12 Volt
| 9L***25 | Solenoid Fuel Shut-Off Group | 1 |
4m1812 Solenoid Switch Assembly
| 4M***12 | Switch As-Solenoid | 1 |
4l8393 Tachometer Drive Group
| 4L***93 | Tachometer Drive Group | 1 |
Turbocharger And Mounting
8m5354 Or 9l982 Turbocharger Assembly
| 9L***82 | Turbocharger Assembly | 1 |
9m3557 Water Pump Assembly
| 9M***57 | Water Pump Assembly | 1 |
9l2279 Water Pump Assembly
| 9L***79 | Water Pump Assembly | 1 |
Attachments
9l380 Air Cleaner Group--14 Inch Dynaclone--Type 2
| 9L***80 | Air Cleaner Group | 1 |
9l380 Air Cleaner Group--14 Inch Dynaclone
| 9L***80 | Air Cleaner Group | 1 |
9l2190 Air Compressor Assembly--Type 2
| 9L***90 | Air Compressor Assembly | 1 |
9l2190 Air Compressor Assembly--Type 1
| 9L***90 | Air Compressor Assembly | 1 |
3l517 Air Motor
| 3L***17 | Air Motor | 1 |
5l2231 Air Starting Motor Assembly
| 5L***31 | Air Starting Motor Assembly | 1 |
9l918 Air Starting Motor Group
| 9L***18 | Air Starting Motor Group | 1 |
9l1116 Alternator Assembly--12 Volt, 60 Ampere
| 9L***16 | Alternator Assembly | 1 |
9l1149 Alternator Mounting And Drive Group
| 9L***49 | Alternator Mounting And Drive Group | 1 |
9l1725 Alternator Mounting Group
| 9L***25 | Alternator Mounting Group | 1 |
9l1117 Alternator, Mounting And Drive Group--12 Volt, 60 Ampere
| 9L***17 | Alternator, Mounting And Drive Group | 1 |
Auxiliary Drive Pulley
9l1223 Auxiliary Drive Pulley Group
| 9L***23 | Auxiliary Drive Pulley Group | 1 |
Crankshaft--Field Installation
9l1145 Exhaust Elbow Group
| 9L***45 | Exhaust Elbow Group | 1 |
9l658 Exhaust Flange Group
| 9L***58 | Exhaust Flange Group | 1 |
9l939 Fan Mounting And Drive Group
| 9L***39 | Fan Mounting And Drive Group | 1 |
9l907 Fan Spacer Group
| 9L***07 | Fan Spacer Group | 1 |
9l906 Fan Spacer Group
| 9L***06 | Fan Spacer Group | 1 |
9l1612 Fan, Air Compressor, Alternator And Drive Group--Part 2 Of 2--Type 1
| 9L***12 | Fan, Air Compressor, Alternator And Drive Group | 1 |
9l1612 Fan, Air Compressor, Alternator And Drive Group--Part 1 Of 2--Type 1
| 9L***12 | Fan, Air Compressor, Alternator And Drive Group | 1 |
9l1612 Fan, Air Compressor, Alternator And Drive Group--12 Volt, 60 Ampere--Part 2 Of 2--Type 2
| 9L***12 | Fan, Air Compressor, Alternator And Drive Group | 1 |
9l1612 Fan, Air Compressor, Alternator And Drive Group--12 Volt, 60 Ampere--Part 1 Of 2--Type 2
| 9L***12 | Fan, Air Compressor, Alternator And Drive Group | 1 |
8h4681 Primary Fuel Filter Group
| 8H***81 | Filter Group-Primary Fuel; Primary Fuel Filter Group | 1 |
9l693 Flywheel Housing Conversion Group--Type 2
| 9L***93 | Flywheel Housing Conversion Group | 1 |
9l763 Flywheel Housing Conversion Group--Type 1
| 9L***63 | Flywheel Housing Conversion Group | 1 |
9l763 Flywheel Housing Conversion Group--Type 2
| 9L***63 | Flywheel Housing Conversion Group | 1 |
9l693 Flywheel Housing Conversion Group--Type 3
| 9L***93 | Flywheel Housing Conversion Group | 1 |
9l693 Flywheel Housing Conversion Group--Type 1
| 9L***93 | Flywheel Housing Conversion Group | 1 |
9l1736 Fuel Filter Mounting Group--R.H.--Rear Mounted
| 9L***36 | Fuel Filter Mounting Group | 1 |
9l687 Glow Plug Group--24 Volt
| 9L***87 | Glow Plug Group | 1 |
9l1103 Glow Plug Wiring Group--24 Volt
| 9L***03 | Glow Plug Wiring Group | 1 |
9l1151 Glow Plug Wiring Group--12 Volt
| 9L***51 | Glow Plug Wiring Group | 1 |
Governor
Governor And Rack Limiter
9l914 Governor Control Extension Group
| 9L***14 | Governor Control Extension Group | 1 |
9l685 Hydraulic Pump Mounting Group
| 9L***85 | Hydraulic Pump Mounting Group | 1 |
Name Plates And Transfers
| 2M***31 | Plate; Serial Number On R.H. Side Of Cylinder Block And R.H. Side Of Loader Frame | 1 |
| 4B***58 | Screw (Identification Plate) Mounting | 2 |
| 5L***85 | Plate; Warning And Information On Flywheel Housing | 2 |
9l755 Oil Filler And Breather Group--Top Mounted
| 9L***55 | Oil Filler And Breather Group | 1 |
9l1135 Oil Filler And Gauge Group--R.H.
| 9L***35 | Oil Filler And Gauge Group | 1 |
9l1273 Oil Filler And Gauge Group--L.H.
| 9L***73 | Oil Filler And Gauge Group | 1 |
9l1709 Oil Filler And Gauge Group
| 9L***09 | Oil Filler And Gauge Group | 1 |
9l1402 Oil Filler And Gauge Group
| 9L***02 | Oil Filler And Gauge Group | 1 |
9l1617 Oil Filler And Gauge Group
| 9L***17 | Oil Filler And Gauge Group | 1 |
9l1230 Oil Level Gauge Group
| 9L***30 | Oil Level Gauge Group | 1 |
9l1089 Oil Level Gauge Group
| 9L***89 | Oil Level Gauge Group | 1 |
9l1073 Oil Level Gauge Group
| 9L***73 | Oil Level Gauge Group | 1 |
9l490 Oil Pan Group--Front Sump--Type 1
| 9L***90 | Oil Pan Group | 1 |
9l490 Oil Pan Group--Front Sump--Type 2
| 9L***90 | Oil Pan Group | 1 |
9l2103 Exhaust Elbow Adapter Group--4 Inch
| 9L***03 | Pipe Group-Exhaust | 1 |
4h5076 Air Precleaner
| 4H***76 | Precleaner Group | 1 |
9l358 Shock Mounting Group--Rear
| 9L***58 | Shock Mounting Group | 1 |
8h1913 Motor Assembly--Part 1 Of 2
| 8H***13 | Starting Motor Assembly | 1 |
8h1913 Motor Assembly--Part 2 Of 2
| 8H***13 | Starting Motor Assembly | 1 |
9l1146 Starting Motor Group--12 Volt--Part 1 Of 2
| 9L***46 | Starting Motor Group | 1 |
9l1146 Starting Motor Group--12 Volt--Part 2 Of 2
| 9L***46 | Starting Motor Group | 1 |
5l8735 Solenoid Switch Assembly
| 5L***35 | Switch As-Solenoid | 1 |
1673 serial number reference
On these 1960s-70s Cat truck engines the serial/model tag is a small metal plate riveted to the block; as with most Caterpillar diesels of this era it is commonly located on the left side of the block near the fuel injection pump, or on the valve cover - this location is general Caterpillar convention rather than an 1673-specific documented spot, so check both areas. If the tag is missing, the number may also be stamped into the block itself. The number reads as a 3-character prefix followed by a sequential serial (e.g., 70B12345); the prefix identifies the specific engine model in the family (base 1673, 1673B, or 1673C), not a build date, so match it against a model-prefix chart rather than reading a year out of the digits.
| Prefix | Identifies | Notes |
|---|---|---|
| 70B | 1673 (base) Truck Engine | Base 1673 truck engine, introduced 1961 as Cat's first purpose-built over-the-highway diesel, built off the D333 industrial/tractor engine. Six-cylinder, about 114 mm x 140 mm (4.5 in x 5.5 in) bore and stroke, roughly 8.6 L (525 cu in) displacement. Period trade coverage of the launch rates it near 220 hp; some truck installations were derated to about 200 hp - horsepower varies by installation, confirm with dealer or engine spec plate. Fitted to Oshkosh R- and E-series and to Peterbilt and Kenworth highway tractors; also used as a repower engine in International cabover trucks. Manufacturing plant/region not documented in sources found - confirm with dealer. |
| 74B | 1673 (base) Truck Engine | Second serial block for the same base 1673 truck engine as prefix 70B - same D333-derived six-cylinder, ~8.6 L (525 cu in) architecture. This prefix range is directly named on a factory service-manual cover for the 1673, separate confirmation that it belongs to the base model. No prefix-specific spec change documented; treat as a later production batch of the same base model. Confirm exact build-change details with dealer. |
| 83B | 1673 (base) Truck Engine | Third serial block for the base 1673 truck engine, same family as prefixes 70B and 74B. No prefix-specific spec change documented; likely reflects another production run of the original 1673 rather than a configuration change. Confirm with dealer if a running change is suspected. |
| 78B | 1673B Truck Engine | 1673B is a factory update of the base 1673, dating to roughly 1963-64. Six-cylinder, about 114 mm x 140 mm (4.5 in x 5.5 in) bore and stroke, around 8.6 L (525 cu in) displacement, two-valve head, rated near 245 hp. Same basic D333 lineage as the base 1673 but a distinct model line per the serial-prefix chart. Fitted in the same Oshkosh/Peterbilt/Kenworth highway-truck applications as the base 1673. |
| 69D | 1673C Truck Engine | 1673C is a redesign introduced around 1967, built on the newer 4.75 in bore D333C tractor/industrial engine - the same base engine later carried forward as the 3306. Six-cylinder, about 121 mm x 152 mm (4.75 in x 6 in) bore and stroke, roughly 10.5 L (638 cu in) displacement, two-valve head, rated around 250-270 hp (varies by configuration/series). Distinct from the base 1673 and 1673B; do not apply base-1673 dimensions to this prefix. |
| 76R | 1673C Truck Engine | Second serial block for the 1673C truck engine, same D333C-derived redesign as prefix 69D - about 10.5 L (638 cu in), 250-270 hp. Treat as another production run of the 1673C rather than a separate configuration; confirm any running change with dealer. |
Frequently asked questions
What engine powers the Caterpillar 1673?
The 1673 designation covers three factory generations of Caterpillar's own inline six-cylinder diesel. The base 1673 and 1673B displace 8.6 liters (525 cu in), naturally aspirated with precombustion-chamber injection. The redesigned 1673C displaces 10.5 liters (638 cu in) and adds a turbocharger. All three derive from Caterpillar's D333 industrial and tractor engine family rather than a purpose-built truck design.
What does the Caterpillar 1673 weigh?
As a bare engine, dry weight runs roughly 790-880 kg (1750-1940 lb) depending on series, with the turbocharged 1673C at the heavier end. There is no factory finished-vehicle operating weight for the 1673, because Caterpillar sold it only as an engine; the chassis, cab, transmission, and axles came from the independent truck builder, so completed-vehicle weight depended entirely on that builder's configuration.
What replaced the Caterpillar 1673?
The 1673C's larger-bore, D333C-based design carried forward directly into the Caterpillar 3306, introduced in the early 1970s, which became Caterpillar's mainstream on-highway and industrial inline-six for decades afterward. The base 1673 and 1673B had no separate replacement beyond the 1673C factory redesign itself.
What 1673 owners discuss
What's the general reputation of the Caterpillar 1673 truck engine among owners and mechanics?
What engine failure patterns are tied to specific 1673 series?
How does the fuel system differ across 1673 versions, and does it cause problems?
Are there known driveline or chassis wear patterns tied to trucks running this engine?
Are there electrical or sensor issues commonly reported for the 1673?
Is it worth rebuilding an early 1673 or 1673B, or is a replacement engine the better move?
What should a buyer check before purchasing a used 1673 engine or a truck powered by one?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
Need a specific 1673 part?
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