Many water pump kits—especially on popular Toyota applications—include two different gaskets. That leads to one critical question: which one do you use? The short answer is: only one gasket, and it must match the design of your pump and the condition of the mating surfaces. This article provides a technician-oriented, step-by-step guide to identifying the correct gasket, preparing the surfaces, selecting the right sealant (if any), and installing the pump so it seals the first time.

Why Some Kits Include Two Gaskets (Toyota Example)

Several Toyota engines (and many other makes) have used different water pump and gasket styles over a model run. To cover these variations, aftermarket kits sometimes include two gaskets. You will commonly see:

  • Metal shim gasket (stamped steel or stainless): Thin, rigid, precise. Intended for clean, flat, machined mating surfaces.
  • Non-metal gasket (paper/fiber/composite or molded rubber on a carrier): Slightly compressible. Better at conforming to minor imperfections or pitting.

Because pumps and housings may vary by production date, supplier, or engine revision, the kit covers both possibilities. Your job is to identify which gasket matches the pump and housing on the vehicle—and to use only that one.

How to Choose the Correct Gasket

Use this decision process before you open any sealant:

  1. Identify the pump design: Compare the new pump to the pump you removed. Look for:
    • Gasket interface style: flat machined face vs. a groove for a molded rubber seal.
    • Dowel locations and coolant passage shapes.
    • Any pre-applied seal or coating on the new pump.
  2. Match the gasket shape and thickness: Lay each new gasket on the pump. Bolt hole positions and coolant port geometry must align exactly. If the engine used a molded rubber gasket or an O-ring style seal, only use that style—do not substitute paper or metal.
  3. Evaluate mating surface condition:
    • Clean and flat aluminum/iron surfaces with no pitting: a metal shim gasket is typically preferred.
    • Minor pitting, erosion, or the need for a little conformability: use the paper/fiber/composite gasket.
  4. Follow service information: OEM service procedures override general rules. If the manufacturer specifies a particular gasket type or sealant method, follow it.
  5. Never stack gaskets: Doubling gaskets can misalign the pump, alter belt tracking, reduce clamping load, and cause immediate leaks.

Quick checklist before you bolt the pump

  • New pump casting matches the old one (ports, dowels, bolt pattern).
  • Chosen gasket matches what came off and lays flat with all ports unobstructed.
  • Mating surfaces are clean, flat, dry, and free of old sealant.
  • Hardware, holes, and threads are clean and ready.
  • Sealant choice is confirmed by service info and surface condition (or skipped if not required).

Surface Prep That Prevents Leaks

Sealing success starts with surface preparation. Allocate time here; it pays off.

  1. Remove old gasket material:
    • Use a plastic razor scraper or dedicated gasket scraper at a shallow angle.
    • Avoid aggressive abrasive discs on aluminum. If you must use a bristle-style surface conditioning disc, run at low RPM with light pressure and keep the tool flat to prevent gouging.
  2. Clean the surfaces:
    • Use a non-chlorinated brake cleaner or acetone on a lint-free towel to remove oils.
    • Do not let solvent drip into the exposed bearing of a pump or into the coolant passages.
  3. Check flatness and defects:
    • Run a straightedge across the housing. Minor staining is fine; pitting, grooves, or raised lips from previous scraping need correction.
    • Lightly dress raised areas with a fine flat stone, keeping it perfectly flat.
  4. Prepare bolt holes:
    • Chase threads with a tap or thread chaser. Blow debris out (wear eye protection).
    • If any bolt threads enter a wet hole (coolant passage), plan for thread sealant as specified.

Tip: Don’t use RTV to “make up” for poor surfaces. If the surface is badly damaged, repair/replace the component or use the compressible gasket type approved for the application.

Sealant Strategy: When to Use It and When to Skip It

Not every gasket needs sealant. Use the minimum product required to hold the gasket and seal micro-voids.

  • Install dry when specified: Many metal and paper gaskets are designed to seal dry on clean, flat surfaces.
  • Adhesive/tack to hold in place: A light mist of high-tack adhesive or spray gasket tack can hold a thin metal or paper gasket during assembly. Apply to the gasket only, let it get tacky, then place.
  • Metal shim gaskets on very flat surfaces: Consider a copper gasket spray to improve micro-sealing. Light, even coats. Avoid heavy buildup near ports.
  • Paper/fiber gaskets on imperfect surfaces: A thin film of non-hardening sealant (e.g., aviation-grade) can help. Apply sparingly with a brush; avoid squeezing excess into coolant ports.
  • RTV silicone: Use only if the service procedure calls for it, or at specific joints where two housings meet. If needed, use a sensor-safe, low-volatile RTV and a very thin bead. Allow proper skin/cure time per product instructions before filling with coolant.
  • Molded rubber/O-ring style gaskets: Usually installed dry. A touch of silicone-safe lubricant may help positioning; avoid petroleum grease that can swell rubber.

Do not over-apply sealant. Excess can extrude into coolant passages, break off, and circulate through the system, potentially clogging heater cores.

Water Pump Installation and Torque Sequence

With surfaces ready and the correct gasket selected, proceed methodically:

  1. Dry fit: Confirm the pump and gasket sit flush with the dowels engaged and no port obstruction. Verify fastener lengths; some holes are blind and can bottom out if the wrong bolt is used.
  2. Apply sealant if appropriate: Follow the strategy above. Keep sealant out of bolt holes and passages.
  3. Place gasket and pump: Align dowels first. Hand-start all bolts at least several threads to ensure no cross-threading or misalignment.
  4. Snug in stages: Bring the pump down evenly. Snug bolts in a crisscross/star pattern to distribute load.
  5. Torque to spec: Use an inch-pound or low-range torque wrench where applicable. Water pump fasteners are often small; typical values can be quite low. Always follow the vehicle service information for exact torque and any sequence or re-torque instructions.
  6. Sealant cure: If RTV was used, respect the product’s skin and cure time before adding coolant. Many products require 1+ hour before exposure and full cure in 24 hours; check the label.

Hardware notes:

  • Thread sealant: If any bolts enter a coolant passage, apply a non-hardening thread sealant with PTFE as specified.
  • Clean washers and bolt heads: Grit between a washer and the casting can reduce clamp load.
  • Do not use anti-seize unless called for; many torque specs assume clean, dry threads.

Refill, Bleed, and Leak Check

Coolant type and bleeding procedures matter as much as the gasket install.

  1. Flush if needed: If the old pump shed debris or coolant was contaminated, flush the system.
  2. Use the correct coolant: Match OEM chemistry (e.g., Toyota Super Long Life Coolant for modern Toyotas). Avoid mixing types; if changing chemistry, perform a complete flush.
  3. Vacuum fill if available: A vacuum fill tool reduces trapped air and speeds bleeding. Otherwise, use a spill-free funnel.
  4. Heater on HOT: Set HVAC to full heat to open the heater core circuit.
  5. Initial fill: Fill slowly at the radiator or surge tank. Squeeze upper radiator hose to burp air.
  6. Warm-up and bleed: Start the engine. Run at 1,500–2,000 rpm intermittently as the thermostat opens. Watch for air bubbles and top off as needed.
  7. Cap and test drive: Once the system stabilizes at operating temperature and heater output is hot, cap the system. Perform a short test drive with varying load.
  8. Final check: After cool-down, recheck level and inspect all around the pump and gasket seam for weeping.

Inspect the weep hole on the new pump. A few drops immediately after installation can be residual; ongoing wetness indicates a seal issue.

Troubleshooting After Installation

If you encounter leaks or noise:

  • Leak at the gasket seam: Most commonly due to incorrect gasket choice, poor surface prep, or uneven torque. Remove, clean, and reinstall with the correct gasket and torque sequence.
  • Coolant weeping from the pump weep hole: Internal seal failure or contaminated sealant during fill. Verify belt tension and pulley alignment; replace the pump if the seal is compromised.
  • Belt misalignment or squeal: Stacked gaskets or debris trapped under the pump can alter pulley position. Confirm pump is seated flat on dowels and only one correct gasket is installed.
  • Overheating or no-cabin-heat: Air pocket in system. Re-bleed; consider vacuum filling. Check thermostat operation.
  • Persistent air bubbles: Possible head gasket combustion leak or trapped air elsewhere. Perform block test if symptoms persist.

OEM vs. Aftermarket Gaskets and Pumps

Both OEM and quality aftermarket options can work when matched correctly. Consider:

  • Fit and finish: OEM and premium aftermarket gaskets typically have tighter tolerances and consistent port alignment.
  • Material: Modern composite or molded rubber gaskets outperform old-style cork. Avoid cork unless specifically specified by the manufacturer.
  • Completeness: Some kits include new O-rings, seals, and hardware. Always replace any O-rings removed.
  • Service data: If OEM service information specifies a unique gasket or sealant procedure, follow it regardless of the brand.

Pro Tips to Improve First-Time Seal Success

  • Photograph the original gasket orientation before removal. It’s easy to misorient a symmetric-looking gasket and block a passage.
  • Use alignment dowels. If missing or corroded, replace them; they control the pump’s centering.
  • Dry-fit bolts by length in a cardboard template. Mixing lengths can bottom out bolts and reduce clamp load.
  • Replace the thermostat and serpentine belt while you’re there if age/wear warrants. Cooling system reliability is cumulative.
  • Mark each fastener after final torque with a paint pen to confirm sequence completion.

FAQs

Do I use both gaskets if my kit includes two?

No. Use only one gasket, the one that matches the pump and the engine’s mating surface design. Stacking gaskets reduces clamping force, can misalign the pump, and often causes leaks.

Metal or paper: which should I choose?

Use the metal shim gasket on clean, flat, machined surfaces. Use the paper/fiber/composite gasket if you need slight conformability due to minor pitting or surface irregularities. If the application uses a molded rubber gasket or O-ring, use that style only.

Should I use RTV on a water pump gasket?

Only if the service information calls for it or at specific joints. Many gaskets are designed to be installed dry or with a light adhesive/tack only. If RTV is specified, apply a thin, even bead, avoid ports and bolt holes, and follow cure times.

Is OEM always better for gaskets?

OEM gaskets are reliable and often preferred. Quality aftermarket gaskets can perform equally well if they match the application precisely. Avoid outdated cork materials unless specified by the manufacturer.

What torque should I use on water pump bolts?

Always follow the factory service manual. Water pump fasteners are often small and require relatively low torque. Over-torque can distort the pump or strip threads; under-torque can cause leaks.

Can I use sealant to fix a pitted surface instead of replacing the housing?

A thin film of non-hardening sealant with a compressible gasket can bridge minor imperfections. Significant pitting or gouges should be repaired properly or the component replaced. Excess sealant is not a substitute for flat, clean surfaces.

Shop Cooling System Service Tools

To execute the steps in this guide, see our Cooling System Service Tools for proper surface prep, accurate torque, and clean bleeding.

  • Gasket scrapers, plastic razor blades, and flat stones for clean, flat surfaces.
  • Thread chasers and sealant applicators to prep fasteners.
  • Vacuum fill tools and spill-free funnels to reduce trapped air.