AC Delco MR43-LTS Long-Reach Vortec Marine Spark Plug | GM 4.3L V6 & 5.7L Vortec Engines | Replaces MerCruiser 33-862029, NGK TR5, Crusader R030008A & Champion RS9YC | Sold Individually

AC Delco MR43-LTS Long-Reach Vortec Marine Spark Plug — GM 4.3L V6 & 5.7L Vortec Marine Engines | Replaces MerCruiser 33-862029, NGK TR5, Crusader R030008A & Champion RS9YC | Sold Individually

AC Delco MR43-LTS is a conventional long-reach marine spark plug for GM 4.3L V6 and 5.7L (350 cid) Vortec marine engines used in MerCruiser and Crusader stern drive and inboard applications. Long-reach (LTS = Long Thread, Tapered Seat) design required by Vortec cylinder heads. Replaces MerCruiser 33-862029, NGK TR5, Crusader R030008A, and Champion RS9YC. Sold individually — order the quantity needed for your engine.

Part Specifications

• Part Number: AC Delco MR43-LTS
• SKU: ACD-MR43-LTS
• Plug Type: Conventional marine spark plug — long-reach, tapered seat (LTS)
• Application: GM 4.3L V6 and 5.7L Vortec marine engines
• Replaces (MerCruiser): 33-862029
• Replaces (Crusader): R030008A (see also: Crusader R030008A Spark Plug 5.7L GM)
• Replaces (NGK): TR5 (see also: NGK 2238 TR5 V-Power Spark Plug)
• Replaces (Champion): RS9YC
• Sold As: Individually (single plug) — order quantity to match your engine’s cylinder count

Cross-Reference & Replacement Guide

• MerCruiser 33-862029: OEM plug number for MerCruiser GM 4.3L V6 and 5.7L Vortec stern drives and inboards. If your MerCruiser service manual or existing plugs show this number, the MR43-LTS is the AC Delco replacement.
• Crusader R030008A: OEM plug for Crusader 5.7L GM Vortec inboard engines. The Crusader R030008A is available as a pre-labeled replacement — the MR43-LTS is the individual AC Delco equivalent.
• NGK TR5: The NGK 2238 TR5 is the NGK V-Power equivalent for the same GM Vortec marine applications. The MR43-LTS is the AC Delco alternative to the NGK TR5. Both are conventional plugs for the same application.
• Champion RS9YC: Champion marine plug equivalent for the same GM 4.3L V6 and 5.7L Vortec application. The MR43-LTS is the AC Delco replacement.

MR43-LTS vs MR43-T — Long-Reach vs Short-Reach

The MR43-LTS and the AC Delco MR43-T share the same heat range (43) but have different thread reach and seat designs. They are not interchangeable:

• MR43-LTS (this listing): Long-reach, tapered seat. Required for Vortec cylinder heads (GM engines produced from approximately the mid-1990s onward with the Vortec combustion chamber design). The longer thread reach positions the electrode correctly in the Vortec combustion chamber.
• MR43-T: Short-reach, tapered seat. For pre-Vortec GM V8 cylinder heads (older GM marine engines produced before the Vortec redesign). Installing a short-reach plug in a long-reach (Vortec) application leaves the electrode recessed and can cause misfires, hard starting, and poor combustion efficiency.
• How to confirm which plug your engine needs: Check the existing plug’s thread length and compare to the MR43-LTS spec, or verify the correct plug part number in your engine service manual. Vortec engines are typically identified by the “Vortec” designation on the intake manifold or in the engine model name.

Compatible Marine Engine Applications

• MerCruiser 4.3L MPI V6 (Vortec): GM 4.3L V6 Vortec engine used in MerCruiser Alpha and Bravo stern drive configurations. OEM plug: MerCruiser 33-862029, replaced by MR43-LTS.
• MerCruiser 5.7L (350 cid) Vortec: GM 5.7L small block Vortec engine used in MerCruiser stern drives and inboards. OEM plug: MerCruiser 33-862029, replaced by MR43-LTS.
• Crusader 5.7L GM Vortec inboard engines: Crusader inboard engines based on the GM 5.7L Vortec block. OEM plug: Crusader R030008A, individual equivalent: MR43-LTS.
• Other GM 4.3L V6 and 5.7L Vortec marine applications: Any marine engine using a GM 4.3L or 5.7L Vortec block that cross-references to MerCruiser 33-862029, NGK TR5, or Champion RS9YC may use the MR43-LTS. Confirm against your engine documentation before ordering.
• Verify before ordering: Confirm the MR43-LTS is the correct plug for your engine model and year by checking your service manual or comparing to your existing plug part number and thread reach.

Application Notes

• Sold individually — order the quantity matching your engine’s cylinder count: 6 plugs for a 4.3L V6, 8 plugs for a 5.7L V8
• Verify the correct gap specification for your engine in the service manual before installation
• Thread in by hand for the first several turns to avoid cross-threading; torque to the specification in your engine service manual
• Apply anti-seize to plug threads if specified by your engine manufacturer, particularly for aluminum head applications
• Inspect and replace at the interval specified in your engine service manual; conventional plugs in marine service typically have shorter service intervals than platinum or iridium plugs
• Fouling patterns on a conventional plug (oil fouling, carbon fouling, ash deposits) can indicate engine and fuel system conditions worth investigating at each service

Additional Information

• Vendor: AC Delco
• SKU: ACD-MR43-LTS
• Part Number: MR43-LTS
• Replaces: MerCruiser 33-862029 | Crusader R030008A | NGK TR5 | Champion RS9YC
• Product Type: Boat & Engine Maintenance / Spark Plugs
• Plug Type: Conventional marine, long-reach tapered seat (LTS)
• Application: GM 4.3L V6 and 5.7L Vortec marine engines
• Sold As: Individually (single plug)
• Country of Origin: USA
• HS Code: 8511.10 (spark plugs — verify for your import classification)

Frequently Asked Questions

Q: What is the difference between the MR43-LTS and the MR43-T?
A: Same heat range (43), different reach. The MR43-LTS is the long-reach version for Vortec cylinder heads (mid-1990s and later GM marine engines). The MR43-T is the short-reach version for pre-Vortec GM V8 engines. They are not interchangeable — installing the wrong reach plug can cause misfires and poor performance. Verify which plug your engine requires in your service manual.

Q: Does the MR43-LTS replace MerCruiser 33-862029?
A: Yes — the MR43-LTS is the AC Delco replacement for MerCruiser 33-862029, the OEM plug for MerCruiser GM 4.3L V6 and 5.7L Vortec stern drives and inboards.

Q: Is the MR43-LTS the same as the NGK TR5?
A: Yes — the MR43-LTS is the AC Delco equivalent of the NGK 2238 TR5 for the same GM Vortec marine engine applications. Both are conventional long-reach plugs. Choice comes down to brand preference.

Q: How many plugs do I need?
A: Order the quantity matching your engine’s cylinder count — 6 plugs for a GM 4.3L V6, or 8 plugs for a GM 5.7L V8. This listing is for one (1) individual plug.

Q: Will the MR43-LTS work in a pre-Vortec GM V8 engine?
A: No — the MR43-LTS long-reach design is for Vortec cylinder heads only. Pre-Vortec GM V8 marine engines require the short-reach MR43-T. Installing a long-reach plug in a short-reach application can cause the electrode to contact the piston, creating a serious engine damage risk. Verify which plug your engine requires before ordering.