Cooling System¶
The 2000 Honda GL1500 SE Gold Wing uses a pressurized, liquid (50/50 ethylene-glycol) cooling system to keep its 1520 cc liquid-cooled SOHC flat-six within its operating range. Unlike a conventional bike, the GL1500 carries two radiators mounted side-by-side behind the front wheel (behind the plastic grille, ahead of the engine), fed by a single filler/pressure cap, each with its own electric cooling fan. This page documents the full system — coolant type and capacities, the thermostat, water pump, fans and fan switch, temperature sensor/gauge, hoses, the pressure cap, the reserve tank, and the refill/bleed procedure — with all values given in both metric and imperial units. Specifications are drawn primarily from the Honda GL1500 factory service manual; flagged items should be confirmed against your own manual.
System Overview¶
The GL1500's cooling system is unusual and worth understanding before working on it:
- Twin radiators. Two radiators sit behind the front wheel, behind the front fork legs and the plastic front grille. Air enters the front and exits out both sides of the fairing. Both radiators are plumbed to a single radiator/pressure cap and a single reserve tank.
- Two electric fans. Each radiator has its own electric cooling fan. Both fans are wired to switch on together, triggered by one thermostatic fan-motor switch.
- Thermostat is located at the top of the engine, between the two radiators (a notoriously awkward spot to service — see Common Issues).
- Water pump is engine-mounted at the front of the crankcase, sharing a housing area with the oil pump and carrying the tell-tale weep (inspection) hole.
- Pressure (radiator) cap is hidden under the right-side steering-head trim/fairing pocket — NOT in the open like a car.
- Reserve (overflow) tank is reached behind the left top inner cover.
- A carburetor coolant thermal valve routes warm coolant to the carburetors to aid cold-start driveability (a GL1500 carbureted-engine feature; the later fuel-injected GL1800 does not have this).
⚠️ Safety — never open the system hot. The factory manual is explicit: "Do not remove the radiator cap when the engine is hot. The coolant is under pressure and could scald you." Let the engine cool fully before removing the pressure cap. Check coolant level only at the reserve tank.
Coolant Type & Mix Ratio¶
| Item | Specification |
|---|---|
| Coolant type | High-quality ethylene-glycol antifreeze with corrosion inhibitors, silicate-free, formulated for aluminum engines |
| Recommended factory mix | 50% antifreeze / 50% distilled water (pre-mixed Honda HP coolant is 50/50) |
| Water | Distilled water only — never tap/mineral/salt water (scale and corrosion attack the aluminum and the water-pump seal) |
| Honda OEM coolant | Honda HP Coolant / Pro Honda HP Coolant (pre-mixed 50/50) |
Why silicate-free matters (GL1500-specific): silicates in some "universal" antifreezes act like fine grit. On the GL1500 they score the water-pump's ceramic mechanical seal and lead to premature weep-hole leaks (see Water Pump). Use a silicate-free, aluminum-safe coolant.
Freeze / boil protection by mix ratio (factory data)¶
| Mix (distilled water : ethylene glycol) | Freezing point |
|---|---|
| 55% : 45% | −32 °C (−26 °F) |
| 50% : 50% (recommended) | −37 °C (−35 °F) |
| 45% : 55% | −44.5 °C (−48 °F) |
| Boiling point (50/50 mixture) | Temperature |
|---|---|
| Unpressurized (cap off) | 107.7 °C (226 °F) |
| Pressurized (cap on, system pressurized) | 125.6 °C (258 °F) |
Do not exceed ~60% antifreeze; higher glycol concentration actually reduces heat-transfer and freeze protection.
Coolant Capacity¶
The factory service manual gives three distinct figures — be sure you are using the right one for the job at hand:
| Capacity | Volume | Notes |
|---|---|---|
| After disassembly (full dry fill of an empty system) | 4.1 L (4.3 US qt, 3.6 Imp qt) | Total system volume — use when refilling a system that was completely drained/rebuilt |
| After draining (routine change, incl. reserve tank) | 3.8 L (4.0 US qt, 3.3 Imp qt) | What you actually put back during a normal coolant change via the drain bolt — a small amount stays trapped in the engine/hoses |
| Reserve (overflow) tank | 0.55 L (0.6 US qt, 0.5 Imp qt) | Expansion tank volume |
The "after disassembly" total of 4.1 L is the authoritative figure (it matches the GL1500 General Specifications table). Some owner/forum sources quote ~3.5 L — that figure is not the GL1500 system capacity and should not be used. Buy 4 US qt (≈3.8 L) of premixed coolant for a routine change, plus a little extra to top the reserve.
Radiator & Pressure Cap¶
Radiators¶
| Item | Detail |
|---|---|
| Configuration | Two radiators, side-by-side, behind the front wheel / front forks, behind the plastic grille |
| Plumbing | Single shared filler neck and pressure cap; single reserve tank |
| Fans | One electric fan per radiator (two total), wired to run together |
Pressure (radiator) cap¶
| Item | Specification |
|---|---|
| Cap relief pressure | 0.75–1.05 kg/cm² ≈ 74–103 kPa / 0.74–1.03 bar (11–15 psi) |
| Location | Under the right-side steering-head trim / fairing pocket |
| OEM cap part number | 19045-MZ3-405 ⚠️ (also reported as 19045-MY3-621 on some catalogs — confirm against your VIN/parts fiche) |
| Common aftermarket cross-reference | Stant 11233 / NAPA 703-1406 ⚠️ (forum-sourced; verify fitment & rating before use) |
- The factory cap value in kg/cm² (0.75–1.05) converts to about 74–103 kPa. The "11–15 psi" figure printed in the manual is the rounded equivalent and is what most owners quote.
- A pressure cap raises the boiling point (~3 °F per psi of cap pressure). A weak/leaking cap causes coolant loss into the reserve and chronic low level; a stuck-closed cap over-pressurizes hoses and the reserve tank.
- DIY check: have the cap pressure-tested; it should hold and relieve within the 74–103 kPa (11–15 psi) range. Replace it if it cannot hold pressure or the rubber seal is hardened/cracked — a cheap, common fix for mystery coolant loss.
Thermostat¶
| Item | Specification |
|---|---|
| Begins to open | 80–84 °C (176–182 °F) |
| Fully open | 93–97 °C (199–206 °F) |
| Minimum valve lift | 8.0 mm (0.31 in) when heated to 95 °C (203 °F) for 5 minutes |
| OEM part number | 19300-611-005 (fits GL1500 incl. SE; shared across several Gold Wing models) |
| Location | Top of the engine, between the two radiators (under bodywork) |
| Housing | Plastic thermostat housing with an O-ring; housing reported ~US$30 ⚠️ (price varies) |
Inspection (bench test): suspend the thermostat in heated water with a thermometer (do not let it touch the pan). It should remain fully closed below ~80 °C, begin to open in the 80–84 °C band, and lift at least 8.0 mm by 95 °C. A thermostat that is open at room temperature, or that never lifts 8 mm, is faulty. A stuck-closed thermostat is a listed cause of overheating; a stuck-open one causes slow warm-up and a gauge that never reaches normal.
Service note (GL1500-specific): the thermostat is one of the most awkward jobs on the bike — owners describe it as "they put the thermostat on the floor and built the Wing around it." It typically requires removing front bodywork and partial radiator access. Soak the housing bolts repeatedly with penetrating oil before attempting removal (corroded/seized bolts are common — replace the O-ring and inspect the plastic housing for warping while you are in there).
Water Pump¶
| Item | Detail |
|---|---|
| Type | Engine-mounted centrifugal pump, belt/gear driven off the engine |
| OEM part numbers | 19200-MN5-040 (early), 19200-MY4-020 (~1992–96), 19200-MAM-A60 (later) ⚠️ — supersessions exist; the current pump fits all GL1500 (1988–2000). Confirm the correct number for a year-2000 SE on the parts fiche. |
| Seal | Mechanical seal: spring-loaded stationary carbon/rubber face running against a polished ceramic ring in the impeller; coolant lubricates the seal faces |
| Weep / inspection hole | Drilled between the coolant-side mechanical seal and the bearing; an escape path for coolant that bypasses the seal |
Weep-hole leak = failed seal. If coolant (or a crusty coolant stain) appears at the weep hole, the mechanical seal has failed. Do not plug or epoxy the weep hole — that only forces coolant into the bearing and destroys the pump faster. The correct fix is to replace the pump (or rebuild the seal); replace the related O-rings/seals while it is apart. Silicate-laden or neglected (old) coolant is the usual cause of premature seal wear.
⚠️ Water-pump-to-engine fastener torque values are not clearly itemized in the sample service-manual data consulted. Confirm the cover/mounting-bolt torques against the factory manual before reassembly.
Cooling Fans, Fan Switch & Relay¶
| Item | Specification |
|---|---|
| Fans | Two electric radiator fans (one per radiator), run together |
| Fan control | Thermostatic fan-motor switch that grounds the fan circuit |
| Fan switch turns ON | 98–102 °C (208–216 °F) |
| Fan switch turns OFF | A few degrees below the ON point as coolant cools ⚠️ (exact OFF spec not separately listed in the manual table) |
| Fan switch location | Bottom of the left radiator |
| Fan switch OEM part number | 37760-MT2-003 |
| Wiring | Fan switch on a Black wire (it grounds the fans); coolant temperature gauge sender on Blue/Green |
How it normally behaves: at steady highway speed the fans may never run (airflow is sufficient). In traffic, idling, or low-speed riding on a hot day, coolant reaches ~98–102 °C and the switch grounds both fans until temperature drops a few degrees. On the dash gauge this typically corresponds to roughly the 3/4 mark when the fans engage (the thermostat opening shows near 1/4) ⚠️ (gauge positions are owner-reported, not a factory spec).
Testing the fan switch: disconnect it and bench-test like a thermostat — suspend the sensing tip in heated oil/water with a thermometer and an ohmmeter across the switch; continuity (closed) should appear at ~98–102 °C. Alternatively, jumper the switch connector to ground (with ignition on) to confirm the fans and their wiring/fuse are good. A faulty fan switch (or blown fan fuse/relay) is the classic cause of overheating only at idle / in traffic while highway temps stay normal.
⚠️ Whether a separate fan relay is used (vs. the switch grounding the fans directly) varies by description across sources. Confirm the exact fan circuit (switch, relay, fuse) on the GL1500 wiring diagram for your year. Fan-switch installation torque is listed in the manual's torque table but could not be read cleanly from the source consulted — verify before tightening (over-torquing into the aluminum radiator tank risks cracking it).
Temperature Sensor & Gauge¶
The dash temperature gauge is driven by a separate coolant temperature sensor (thermo unit) from the fan switch.
| Item | Specification |
|---|---|
| Gauge sender OEM part number | 37750-PC1-004 ⚠️ (widely listed for GL1500; confirm year-2000 SE applicability) |
| Sender location | On/near the thermostat housing, top-rear of the radiators |
Coolant temperature sensor resistance (factory test values)¶
| Temperature | Resistance |
|---|---|
| 60 °C (140 °F) | 104 Ω |
| 85 °C (185 °F) | 44 Ω |
| 110 °C (230 °F) | 20 Ω |
| 120 °C (248 °F) | 16 Ω |
- Resistance falls as temperature rises (negative temperature coefficient). Measure with an ohmmeter at a known coolant/oil temperature and compare to the table to diagnose a gauge that reads wrong or pinned.
- Normal running: the gauge needle should settle around the middle once warmed up and hold steady. A needle that climbs toward the top in traffic but recovers on the move points to fan/fan-switch problems, not necessarily the engine.
Carburetor Coolant Thermal Valve¶
A GL1500 carbureted-engine feature: warm coolant is routed to a thermal valve at the carburetors to improve cold driveability, shutting off the warm-coolant circuit once the engine is up to temperature.
| Item | Specification |
|---|---|
| Starts to close (49-state) | 78–82 °C (172–180 °F) |
| Starts to close (California model) | 58–62 °C (136–144 °F) |
This component does not exist on the fuel-injected GL1800. If you have unexplained idle/driveability quirks tied to engine temperature, the thermal valve and its small coolant hoses are worth inspecting.
Hoses & Clamps¶
- The system uses standard formed coolant hoses between the engine, the twin radiators, the thermostat housing, the reserve tank, and the carburetor thermal-valve circuit, secured with screw-type water-hose clamps.
- Inspect hoses for swelling, hardening, cracking at the clamp lands, and chafing where they pass bodywork. Replace any hose that is spongy or weeping; replace clamps that are corroded or have lost spring tension.
- Because so much bodywork must come off to reach the cooling system, it is good practice to replace suspect hoses, the thermostat O-ring, and the pressure cap as a set while everything is open.
⚠️ Individual coolant-hose OEM part numbers are not listed here — look them up on a parts fiche (e.g. partzilla / cmsnl / bikebandit) for 2000 GL1500SE under the Radiator / Water Pipe groups before ordering.
Reserve (Overflow) Tank — Checking Level¶
| Item | Detail |
|---|---|
| Location | Behind the left top inner cover (turn the handlebars fully right for access) |
| Level marks | Coolant should sit between the LOWER and UPPER marks (the two rectangular openings) on the dipstick built into the reserve-tank cap |
| When to check | With the engine at normal operating temperature, engine OFF, bike upright |
| If low | Remove the reserve-tank cap and add coolant mixture up to the UPPER mark; reseat the cap firmly |
- Check level at the reserve tank only — do not open the pressure cap to "check" coolant.
- Chronic low reserve level with no visible leak usually means a weak pressure cap (losing coolant past the cap), a small external leak, or the start of a water-pump weep-hole leak.
Coolant Change & Bleed/Refill Procedure¶
Interval: Honda specifies replacing the coolant every 2 years (mileage-based references cite ~38,000 km / 24,000 miles) ⚠️ — confirm the exact interval/table in your owner's manual; coolant degrades on a time basis regardless of mileage.
Tools/supplies: ~4 US qt (≈3.8 L) of pre-mixed silicate-free 50/50 coolant (a little extra for the reserve), a drain pan (5 qt+), basic hand tools to remove the lower front cowl, and distilled water if flushing.
Drain¶
- Let the engine cool completely. Place the bike upright on the centerstand.
- Remove the lower front plastic cowl to access the drain bolt under the water pump.
- Remove the pressure cap (under the right steering-head trim) to vent the system.
- Place the pan and remove the drain bolt; let it drain fully (~3.8 L will come out).
- Empty the reserve tank as well (siphon it out, or remove and empty it).
⚠️ Drain-bolt torque is not stated in the article/manual data consulted — reinstall with a new sealing washer if applicable and torque to the factory value (confirm in the service manual). Do not overtighten into the soft pump housing.
Optional flush¶
- Refill the system with distilled water only, run the engine to operating temperature (until the fans cycle), let it cool, drain, and repeat until the water runs clear. Drain the reserve each cycle. Always do the final fill with proper 50/50 coolant.
Refill & bleed¶
- Reinstall and tighten the drain bolt (with its washer).
- Slowly pour coolant into the radiator filler neck until full; pause to let trapped air rise and bubble out, topping up as it settles.
- "Burp" the system: briefly crank/start the engine to circulate coolant, watch the level drop as air escapes, and keep adding coolant.
- With the cap still off, idle the engine until it reaches operating temperature and the fans switch on (this proves the thermostat has opened and circulation is established). Keep topping the filler neck as the level falls.
- Once warm and the level is stable, install the pressure cap.
- Fill the reserve tank to the UPPER mark.
- Let the engine cool, then recheck the reserve level and top to UPPER. Recheck again after the next ride or two — it is normal to need a small top-up as the last air works out.
Refill quantity: expect to use about 3.8 L (4.0 US qt) for a drain-and-fill; up to 4.1 L (4.3 US qt) if the system was fully drained/disassembled and dry.
Operating Temperatures (quick reference)¶
| Event | Approx. coolant temperature |
|---|---|
| Thermostat begins to open | 80–84 °C (176–182 °F) |
| Thermostat fully open | 93–97 °C (199–206 °F) |
| Cooling fans switch ON | 98–102 °C (208–216 °F) |
| Coolant boil (50/50, cap on, pressurized) | 125.6 °C (258 °F) |
| Coolant boil (50/50, unpressurized) | 107.7 °C (226 °F) |
A healthy GL1500 runs with the gauge near mid-scale, the thermostat cycling around 80–97 °C, and the fans kicking in only at low speed / idle on hot days.
Common Cooling Issues & DIY Notes¶
- Overheats only at idle / in stop-and-go, fine on the highway → fans not running. Suspect a faulty fan-motor switch, blown fan fuse, bad fan relay (if fitted), or a seized fan motor. This is the single most common GL1500 cooling complaint. (Manual's overheating causes also list low coolant, stuck-closed thermostat, carbon build-up, poor fuel, wrong ignition timing, lean mixture.)
- Coolant weeping from the water-pump weep hole → the mechanical seal has failed. Replace the pump (or seal); never plug the weep hole. Often traced to old or silicate-containing coolant.
- Chronic low coolant with no obvious leak → weak pressure cap (cheap first thing to replace and pressure-test), small hose/clamp seep, or early weep-hole leak.
- Slow warm-up, gauge never reaches normal → thermostat stuck open (or missing). Overheating with a cold lower hose → stuck closed.
- Thermostat replacement is labor-intensive on the GL1500 (buried between the radiators). Plan for bodywork removal, soak seized housing bolts with penetrant in advance, and replace the O-ring and inspect the plastic housing for warping while in there.
- Use only silicate-free, aluminum-safe coolant and distilled water — protects the water-pump seal and the aluminum engine.
- Air pockets are the usual cause of a post-refill overheat or fluctuating gauge — always burp the system (idle to fan-on with the cap off) and recheck the reserve after the first rides.
See also: Engine Specifications · Lubrication / Oil System · Torque Specifications · Maintenance Schedule ⚠️ (sibling-file names/numbers assumed — adjust links to match the actual file set).
Sources¶
- Honda GL1500 Factory Service Manual — Cooling System & Specifications section (sample PDF): https://www.aservicemanualpdf.com/Samplepages/SM-1994%20Honda%20Goldwing%20GL1500%20Manual.pdf
- Honda GOLDWING GL1500 Owner's Manual, Specifications (cooling system capacity), ManualsLib p.111: https://www.manualslib.com/manual/598692/Honda-Goldwing-Gl1500.html?page=111
- Honda GOLDWING GL1500 Owner's Manual, Coolant / reserve-tank check, ManualsLib p.30–31: https://www.manualslib.com/manual/598692/Honda-Goldwing-Gl1500.html?page=31
- Honda GOLDWING GL1500 Service Manual contents (thermostat / temp gauge sections), ManualsLib: https://www.manualslib.com/manual/817941/Honda-Goldwing-Gl1500.html?page=151
- goldwingdocs.com — "How to change (and optionally flush) your coolant" (GL1500 DIY): https://goldwingdocs.com/forum/viewtopic.php?t=31083
- goldwingdocs.com — "How to check your coolant" (GL1500 DIY): https://goldwingdocs.com/forum/viewtopic.php?t=10957
- goldwingdocs.com — "Thermostat" (GL1500): https://goldwingdocs.com/forum/viewtopic.php?t=8158
- Steve Saunders Goldwing Forums — "GL1500 fan switch": https://goldwingfacts.com/forums/2-goldwing-technical-forum/344465-gl1500-fan-switch.html
- Steve Saunders Goldwing Forums — "GL1500: Cooling Fan Temperature Sensor": https://goldwingfacts.com/forums/2-goldwing-technical-forum/311237-gl1500-cooling-fan-temperature-sensor.html
- Steve Saunders Goldwing Forums — "GL1500 Water Pump - where is the weep hole?": https://www.goldwingfacts.com/threads/gl1500-water-pump-where-is-the-weep-hole.671105/
- Steve Saunders Goldwing Forums — "Coolant temp GL1500, where does it read on your gauge?": https://www.goldwingfacts.com/threads/coolant-temp-gl1500-where-does-it-read-on-your-gauge.386793/
- Steve Saunders Goldwing Forums — "GL1500 Radiator Location?" / "GL1500 Radiator Fan Operation?": https://www.goldwingfacts.com/threads/gl1500-radiator-location.377194/
- goldwingparts.com — Honda GL1500 Thermostat OEM #19300-611-005: https://www.goldwingparts.com/products/thermostat-2
- cyclemax.com — GL1500 OEM Water Pump (19200-MN5-040 / 19200-MY4-020 / 19200-MAM-A60): https://cyclemax.com/products/gl1500-oem-water-pump
- goldwingparts.com — GL1500 Water Temperature Sending Unit OEM #37750-PC1-004: https://www.goldwingparts.com/products/water-temperature-sending-unit-5
- Amazon — Radiator Fan Switch, replaces OEM #37760-MT2-003 (GL1500): https://www.amazon.com/XMT-MOTO-Radiator-VTX1800-Replaces-37760-MT2-003/dp/B0757F2YTZ
- buymachineryparts.com — Radiator Cap 19045-MZ3-405 (Honda GL1200-1500 compatible): https://www.buymachineryparts.com/products/radiator-cap-19045-mz3-405-compatible-with-honda-vt500-1100-gl1200-1500
- maintenanceschedule.com — Honda Gold Wing GL1500 Maintenance Schedule (coolant interval): https://maintenanceschedule.com/honda-gold-wing-gl1500-maintenance/
⚠️ Items to Verify¶
- Coolant capacity figure: 4.1 L (full/disassembly) and 3.8 L (drain) come from the factory General Specifications and the cooling spec table and are well corroborated; the ~3.5 L value seen on some sites appears to be an error — do not use it. Confirm 4.1 L total against your own manual.
- Radiator cap OEM part number: 19045-MZ3-405 vs. 19045-MY3-621 differ across catalogs; verify the correct cap for a 2000 GL1500SE on the parts fiche. The Stant 11233 / NAPA 703-1406 aftermarket cross-reference is forum-sourced — confirm rating (11–15 psi) and physical fit.
- Water-pump OEM number for year-2000 SE: three superseding numbers exist (19200-MN5-040 / -MY4-020 / -MAM-A60); confirm the currently-supplied number on the fiche.
- Coolant temperature gauge sender (37750-PC1-004): widely listed for GL1500 but confirm year-2000 SE applicability and that it is the gauge sender (Blue/Green) vs. the fan switch (37760-MT2-003).
- Fan switch OFF temperature: the manual lists the ON window (98–102 °C); the exact OFF/reset temperature was not in the spec table consulted — verify.
- Fan circuit details (relay vs. direct ground, fuse rating): sources differ on whether a dedicated fan relay is used; confirm against the GL1500 wiring diagram for the 2000 model.
- Torque values: drain-bolt, thermostat-housing, water-pump cover/mounting, coolant-temperature-sensor, and fan-switch torques could not be read cleanly from the available service-manual extract. Look these up in the manual's Torque Values table before reassembly (over-torque into aluminum radiator tanks / pump housing risks cracking).
- Coolant hose OEM part numbers: not listed here — look up under the Radiator / Water Pipe groups on a parts fiche for 2000 GL1500SE.
- Coolant change interval (mileage): "2 years" is solid; the 24,000-mile figure is from a third-party maintenance-schedule site — confirm in the factory owner's manual.
- Cross-reference sibling-file links (engine, lubrication, torque, maintenance) assume a file-naming scheme; adjust to match the actual document set.