Caravan Engine Oil Cooling & Indication Diagnostics
Explore the named components, make a prediction, then connect the supplied result to the system. This workshop adds coached practice alongside the course handbook and assessed lab.
PT6A-140 oil collection, heater return and Caravan cooling
Locate the accessory gearbox (AGB), reduction gearbox (RGB), tank and four scavenge-pump elements. Follow the selected PT6A-140 collection path, then distinguish the three heater-return conditions from the separate airframe-cooler and cooling-air paths.
Select a named component and follow the condition-labeled connection. The internal front and external front elements return oil into AGB; the internal rear element pumps AGB-sump oil through the heater. The external rear element feeds the cooler route from RGB. The optional heater-return thermostat determines whether that heater oil joins the cooler feed or returns directly to tank.
Recorded state: before the supplied change
Green outlines identify components named in the selected exercise record; they do not indicate a healthy component.
Named connections and what each arrow means
- PT6A-140 cooler-feed line / under-engine hose → Airframe cooler and its own vernathermPhysical relationship: Under-engine hose to selected cooler oil route
- Cooling air, fins, shrouds and seals → Airframe cooler and its own vernathermPhysical relationship: Air through core fins carries heat away
- Airframe cooler and its own vernatherm → EX outlet check valve C100490-1Physical relationship: EX cooler outlet oil path
- EX outlet check valve C100490-1 → Oil tank: two differently described return entriesPhysical relationship: Aft-permitted outlet / upper return
- EX shutoff valve and control cable → Airframe cooler and its own vernathermPhysical relationship: Actual shutoff position changes normal-route availability
- PT6A-140 cooler-feed line / under-engine hose → EX relieving check valve 2650121-118Physical relationship: EX alternate feed when required cracking condition exists
- EX relieving check valve 2650121-118 → Oil tank: two differently described return entriesPhysical relationship: Upward bypass return toward tank
- EX shutoff valve and control cable → EX relieving check valve 2650121-118Physical relationship: Closed shutoff plus supplied pressure/cracking condition
- Actual temperature bulb or probe → Installed harness, indicator and display branchInformation / signal: Connected actual sensor, or explicitly substituted test input
- Internal front scavenge element → Accessory gearbox sumpPhysical relationship: No. 2 collection discharges into AGB
- External front scavenge element → Accessory gearbox sumpPhysical relationship: Nos. 3/4 nose-up pickup discharges into AGB
- Accessory gearbox sump → Internal rear scavenge elementPhysical relationship: AGB sump supplies internal rear element
- Internal rear scavenge element → Oil-to-fuel heaterPhysical relationship: Internal-rear discharge through heater
- External rear scavenge element → PT6A-140 cooler-feed line / under-engine hosePhysical relationship: RGB return downstream of external rear element
- Oil-to-fuel heater → Optional engine heater-return thermostatPhysical relationship: Only where optional engine valve is fitted
- Optional engine heater-return thermostat → PT6A-140 cooler-feed line / under-engine hosePhysical relationship: Fitted/warmer: all or part joins cooler-feed line
- Optional engine heater-return thermostat → Direct heater return at 5-o'clock bossPhysical relationship: Fitted/cold: bypass open, direct return
- Oil-to-fuel heater → Direct heater return at 5-o'clock bossPhysical relationship: No engine valve fitted: external tube direct return
- Direct heater return at 5-o'clock boss → Oil tank: two differently described return entriesPhysical relationship: 5-o'clock passage, outside deaerator tray
PT6A-140 cooler-feed line / under-engine hose
Carry external-rear/RGB return and any selected warmer heater-return flow toward the cooler.
Supplied record: Not observed in this supplied record
How it works with the rest
This cooler-feed line is downstream of the external rear scavenge element. The external rear element supplies RGB-sump oil. With the optional engine heater-return thermostat fitted, all or part of warmer heater-outlet oil can join this line downstream of the pumps. The fitted cold and no-engine-valve heater returns instead go directly into the tank through the 5-o'clock boss and do not use this cooler route.
What the evidence must show
Identify which branch supplied the line. Do not draw heater oil back through the RGB scavenge pump or assume every AGB return reaches the cooler.
Selected: PT6A-140 cooler-feed line / under-engine hose
Follow the change through the system.
Two supplied PT6A-140 engine-return records use the same installed engine thermostat. Compare its cold/open-bypass state with its warmer cooler-routing state. These are descriptive records, not instructions to run an engine or manipulate a valve.
Before the recorded change
PT6A-140 engine thermostat fitted; cold/open-bypass record. Heater oil returns directly through 5-o'clock passage into tank, outside the deaerator. RGB external-rear oil retains its own cooler route.
Next observation
Choose your prediction before revealing the supplied result.
Reference: Supplied P&WC PT6A-140 Maintenance Manual 3075742 Revision 23.0, March 3, 2025: 79-00-00 pp.2–3, Figure 2 p.5 and engine thermostatic bypass/check valve p.7. Clock labels identify the named fittings; no viewing convention is inferred.
Course applicability and study references
The detailed engine-flow map here is PT6A-140 specific, based on P&WC 3075742,79-00-00. The PT6A-114/-114A airframe cooler and legacy indication comparisons remain separately identified in TM-042; this map does not establish an earlier-engine internal schematic. Select installed equipment and the stated condition before tracing a route. Supplied records are learning examples; actual work uses complete current applicable engine and aircraft instructions.
- PT6A-140 pressure supply, four scavenge elements and three heater-return conditions
Supplied P&WC Maintenance Manual 3075742 Revision 23.0, March 3, 2025: 79-00-00 pp.1–3, Figure 2 p.5, tank/pump/filter p.6 and engine thermostatic bypass/check valve p.7. Internal-front No. 2-bearing oil and external-front Nos. 3/4 nose-up oil enter the AGB sump. Internal-rear AGB oil passes through the oil-to-fuel heater; external-rear RGB oil has its own cooler circuit. The fitted cold, fitted warmer and no-valve heater returns remain separate; no clock viewing convention or earlier-engine internal route is inferred.
- External return and distinct cooling-air path
Supplied D2078 Revision 42: 79-00-00 p.1 Apr 1/1996; 79-20-00 pp.201,204 Jan 1/2018; 79-20-05 pp.201,203,206,208 Apr 1/2019; legacy high-temperature troubleshooting Figure 101 sheet 1, 79-30-00 p.102 Dec 1/2012. Airframe cooler/upper return, fins/shroud/seal evidence and component-versus-installed-system boundaries.
- PT6A-140 alternate route and thermal record
79-20-05 p.201, Figure 202 sheet 2 p.205, Figure 204 p.210 and p.211 Apr 1/2019. C100490-1 aft outlet flow, separate 2650121-118 upward relieving return, actual shutoff position and forward body arrow. EX functional record uses 120°F/185°F, five minutes each and minimum 0.100 inch increase. Earlier 79-20-00 p.204 uses 150°F/178°F; no task interchange or quantitative thermal-flow model.
- Part-selected analog test and engine boundary
79-30-00 p.201 and pp.501–503/Figure 501/Tables 501–502 Dec 1/2012. 2606015-1/-2/-3 use Table 501; -4 uses Table 502. Controlled resistance at disconnected J14 exercises included harness/indicator, with actual bulb and physical temperature excluded. Actual sensor, restoration, engine servicing and chip-material work retain their applicable tasks; no engine-internal procedure is supplied here.
Original learning diagrams and supplied training records explain the stated relationships. Current aircraft-effective instructions and authorization govern actual maintenance.