Mercury MerCruiser Quicksilver V8 Distributor Cap 805759T1 | Thunderbolt IV & V
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Mercury MerCruiser Quicksilver V8 Distributor Cap 805759T1
Part Number: 805759T1
Brand: Mercury Marine / Quicksilver (Genuine OEM)
Official Product Type: Distributor Cap Assembly — GM V8
System: Ignition — Thunderbolt IV & Thunderbolt V HEI
GTIN: 745061491458
What This Is
The 805759T1 is the current genuine OEM distributor cap for MerCruiser GM V8 engines equipped with Thunderbolt IV or Thunderbolt V HEI ignition systems. It is constructed from PBT/PET with solid brass terminal inserts for resistance to heat, warpage, corrosion, and electrical pitting. The current OEM package includes the distributor cap gasket.
Important: The 805759T1 is the distributor cap only — it is not the cap-and-rotor kit. The related kit is 805759Q3 Cap & Rotor Kit.
Compatible Applications
For use on MerCruiser GM V8 sterndrive and inboard engines equipped with the Thunderbolt IV / Thunderbolt V HEI distributor:
- 5.0L / 305 CID V8 (sterndrive & MIE inboard — 230 MIE / 5.0L MIE)
- 5.7L / 350 CID V8 (sterndrive & MIE inboard — 260 MIE / 5.7L MIE)
- 7.4L / 454 CID V8 (sterndrive & MIE — 454 MAG Alpha, 454 MAG Bravo, 7.4L MIE)
- 8.2L / 502 CID V8 (502 MAG Bravo, 8.2L MIE)
- Selected MerCruiser performance V8 packages
Do not select by displacement alone. MerCruiser used multiple ignition systems across similar V8 engine families. This cap is specifically for the Thunderbolt IV / Thunderbolt V HEI distributor family. Not sure? Send us your MerCruiser engine serial number and we'll confirm fitment.
Superseded / Alternate Part Numbers
805759T1 supersedes: 805759T2, 805759A5, 805759A2, 805759A1, 16457A4, 43557A1, 43557, 90746A1
Historical Mercury application data for superseded caps in this family covers numerous GM 305, 350, 454, 502, and performance V8 packages.
When to Replace
Replace the distributor cap when:
- Internal terminals are burned, pitted, or heavily corroded
- Carbon tracking is visible inside the cap
- The cap is cracked or heat-damaged
- Moisture intrusion has caused corrosion inside the cap
- Ignition misfire has been traced to the cap
- Hard starting or rough running is caused by degraded distributor contacts
- Renewing as part of a scheduled ignition tune-up
Inspect the rotor, ignition wires, and distributor sensor at the same time.
Service Interval
Replace as part of a scheduled ignition tune-up or when symptoms above are present. Mercury recommends inspecting ignition components at regular service intervals — refer to the engine service manual for your specific model and serial number range.
Related Parts & Kit Contents
- 27-805760 — Distributor Cap Gasket (included with current OEM cap package)
- 805759Q3 — Cap & Rotor Kit (cap, gasket, and rotor for Thunderbolt IV/V — best value for a full tune-up)
- 13524T1 — Rotor Assembly
- 10-90926 — Distributor Cap Screw (4 required per assembly)
- 87-892150Q02 — Distributor Sensor Assembly
Installation Notes
- Mark spark-plug wire locations before removing the old cap
- Transfer wires one at a time where practical
- Inspect the distributor for moisture and corrosion
- Confirm the cap gasket is correctly seated
- Inspect the rotor for burning or wear — replace if in doubt
- Verify firing order before starting the engine
- Follow the applicable MerCruiser service manual procedure for your engine
Parts Desk Insight
The most common fitment mistake on this cap is selecting by engine displacement rather than ignition system. The 805759T1 belongs to the Thunderbolt IV / Thunderbolt V HEI distributor family. Engines with a later Delco-style ignition — which looks similar externally — require a different cap and rotor. If there is any doubt about which ignition system is installed, verify via the engine serial number and parts diagram before ordering.
Technical FAQ
Q: Does this cap include the rotor?
A: No. The 805759T1 is the cap assembly only (gasket included in current OEM packaging). See 805759Q3 for the complete cap-and-rotor kit.
Q: How do I know if my engine has Thunderbolt IV or Thunderbolt V ignition?
A: The distributor cap on Thunderbolt IV/V systems is secured by four screws. The Delco EST system, used on some later V8s, has a different cap style. Confirm via your engine serial number and the Mercury parts diagram.
Q: My engine is a 5.7L — will this fit?
A: It depends on the ignition system, not just the displacement. Many 5.7L V8 MerCruiser engines use this cap, but not all. Confirm via serial number.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.