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MerCruiser GM Engine Identification


MerCruiser purchases engine blocks from General Motors that are sold as complete engines with MerCruiser serial number tags. MerCruiser maintains records of each boat’s original engine serial numbers for warranty purposes. If replacement engines are installed, it is necessary for a MerCruiser dealer to submit the new serial numbers. If this is not done, MerCruiser records will only record to what distributor or dealer the engine was originally shipped, and when, but not associate the engine with a particular boat. Replacement engine blocks do not have MerCruiser serial number tags.

Engine blocks should have three sets of identifier numbers;

  • MerCruiser serial number,

  • GM stamped number

  • GM block casting number that includes a date code of when the casting was made.

MerCruiser serial number:

The MerCruiser engine serial number is generally an aluminum plate that is riveted to the right side of the block. Additionally, most engines have a decal with serial numbers for the engine (and associated drives) on the top of the flame arrestor. Depending upon the engine model, there may be two or three other serial number decals on (removable) engine components.

The MerCruiser serial number records are key for access to significant information. Unfortunately, all of the MerCruiser serial number displays are subject to loss. The aluminum plate is generally lost if the engine block is handled by a machine shop and “hot tanked” for cleaning. The other displays are easily worn away, and of course, lost if the component to which they are applied is replaced.

GM Stamp Numbers:

As a quality control and for the purposes of recall, a “Production Run Number” is stamped on the milled surface of the engine block. We are advised that MerCruiser tries to keep the number of their engines that carry the same number to no more than 200.

MerCruiser Service Bulletin 2002-08 (a confidential document) lists the key for decoding the GM stamp numbers to determine the engine model. For example, the stamp number T02288HJ. The last two characters (“HJ”) of this number indicate the engine model (in this case a 502 engine block), and the last number before the model characters (“8”) indicates the year of production (in this case a 1998 engine, but it could be a 1988, or 1978 engine). The beginning letter is a code for the specific plant where the engine was produced. The numbers “0228” are reported to be a date code which may be read on the stamp numbers from certain plants as DD/MM format. This particular engine may have been built at the “T” plant on 02/28/1998.

Engines which have stamp numbers that significantly vary from this format, such as 7.4-T.1102FCN, indicates by format that this was never a MerCruiser engine.

High performance MerCruiser engines may not receive a stamp number.

GM Block Casting Number:

A number and date code is cast into the engine block when built. We are advised that this number may be common to as many as 10,000 engines. For this reason, the casting number is of little use in identification at the individual engine level. We are also advised by MerCruiser, that a photo of the block casting number is retained as part of the MerCruiser engine serial number documents, but cross-reference information is not available.

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