Determining the Correct 3.0L Mercruiser Exhaust Manifold
Performance Product Technologies Question & Answer Forum
Topic: Mercruiser 3.0L Exhaust Manifolds
Question: I need to replace my Mercruiser 3.0L marine exhaust manifold but cannot seem to locate the same matching part number. Why can't I find the same replacement "cast iron" exhaust manifold part number for my Mercruiser 3.0L marine engine?
Response: Mercruiser has made numerous changes to the 3.0L exhaust manifolds over the past 15 years. This has been due to a variety of reasons including GM dropping to large port cylinder head that the 120 Hp marine engines were equipped with. The original 42673 and 99798 series manifolds used back in the 1980's were replaced by the 806867 series manifolds in the mid 1990's which has most recently been replaced by the 860235 series manifolds. Today Mercruiser only offers the 860235 series manifolds in two different versions to replace these older manifolds. The new 860235 version manifolds from Mercruiser DO NOT have the removeable end caps with gaskets but they are the correct intended replacement part. Note that these currently available 860235 series manifolds only work for the engines using the large bore Mercarb carburetor. Mercruiser no longer offers a replacement manifold for anything using the small bore "rochester" style carburetors that required different mounting pattern dimensions. Also note that the exhaust manifold ports don't match perfectly for the older style large port cylinder heads however the manifold/head gasket compensates for this and will seal it properly. Let us know if you need any further assistance we will be glad to assist!
Part Diagram – 860235A03 (Manifold w/o Bosses) (link to part diagram)
Carburetor mounting bolt pattern is 3.69" x 2.00". There ARE divider walls between the intake ports on this manifold. The A03 DOES NOT have the additional bosses located on the outboard side that were used for mounting the shift linkage components. The Intake/Exhaust ports, Carburetor mounting, and Exhaust outlet are all the same on both the A03 and A04 manifolds.
Part Diagram – 860235A04 (Manifold w/ Bosses) (link to part diagram)
Carburetor mounting bolt pattern is 3.69" x 2.00". There ARE divider walls between the intake ports on this manifold. The A04 DOES have the additional bosses located on the outboard side that were used for mounting the shift linkage components. The Intake/Exhaust ports, Carburetor mounting, and Exhaust outlet are all the same on both the A03 and A04 manifolds (see picture below).
The 860235A03 replaces this 806867A 3, A 9, and A12 manifold shown below that DID NOT have the additional mounting bosses on the outside.
The 860235A04 replaces this 42673, 99798, 806867A 2 and A 8 series manifold shown below that DID have the additional mounting bosses on the outside that were required for mounting the shift hardware.