Automotive Parts for Merc 5.0 MPI Engines

Water U Lookin' At

Water U Lookin' At

Member
Jan 2, 2007
71
Washington, DC
Boat Info
300 Sundancer 2002
Engines
5.0 MPI, Bravo III Drives
All,

I'm trying to determine which GM parts can be used for our 5.0 MPI engines. Anyone ever done this cross reference before?

For example, our spark plugs, AC 41-932's, are $18 from Sea Ray, but one can go to Advance Auto Parts and get them for $6. There must be many other instances of this gross mark up in other parts. Please let us all know.

Eddie
 
Water U Lookin' At,

My understanding (mostly from this board) is that automotive parts are not compatible for marine applications.

Stick with parts from dealer or marine stores that are made specifically for use with your boat.

Others please chime in!

Gregg
 
Especially plugs.....If I am not mistaken they are specific for marine application for anti-corrosion.
Last thing you want is corrroded plugs in your block...for a measly 12$$$ savings
 
In the case of spark plugs, if you confirm that the part number is absolutely the same, then by all means by them from an auto parts store. Don't let them sell you one that their book says 'is the same heat range'. Get the exact same brand and number only.

The same would go with older motors with distributor caps, rotors, etc.

However, it is critical that starter motors, alternators, and distributors on a marine motor be 'ignition protected', that is, that they are shielded to lessen the possibility of igniting gas fumes. These must be marine rated parts. It's just not worth the savings in buying a car part to risk you and your families safety.

I saw a big explosion this past summer on an older boat that had been leaking fuel from a bad fuel line. By sheer luck, they were close to the marina and the port people were close with their little work boat and pulled them from the water. A couple of miles farther out and they might have been lost. Gas fumes and electricity are scary things when they get together...

John
 
I agree about sparks in the engine compartment, but I kinda doubt they marinize the distributor and other parts for these engines. What makes the engines proper for marine applications is the raw water cooling system and exhaust, and the mating with the stern drive, I think. I've yet to see any special marinizng process on any merc part I've bought for the engine.

I've saved $200 in spark plugs for my 2 V8s and now I'm just trying to do the same for other pieces.... Every little bit adds up fast. Sea Ray charges $2K plus for winterization, which I do myself for about $150-$200. I figure there has to be someone that has researched this before me to save money on their maintenance...

Eddie
 
You will learn that Mercruiser does indeed design lots of parts for the base GM engines. Ignition components are almost always designed for the harsh marine enviornment to handle mositure, ingnition or spark leaks and longevity. Lots of folks think that plugs and ignition wires for example are lots cheaper from the parts house only to find that they replace the wires annually and that plugs may not even last a season.

Hope your approach works out for you...............
 
Thanks for the feedback Frank. I would like to think things are marinized, but the parts aren't lasting any longer than the automotive parts, or even as long right now. So, why pay more for them? At least that's my theory. I'll keep everyone informed of what I find out. I might even do a side by side comparison, of at least the ignition coil, when I purchase it to see the difference first hand.

Eddie
 
I found marine Dist and rotor at autozone. The one on my boat wasn't marine, it was auto - the only place my boat had EVER been was the SR dealer. Go figure.
 
I take what Frank said and the USCG info very seriously. That's why i want to do a side by side comparison. It sounds like the marine parts are just sealed to prevent moisture from entering the parts, whereas the auto parts are vented b/c they can be, due to the larger amount of air flow in a car's engine compartment.

I want to save money like everyone else. So, I think it's good to have these conversations in this forum to see if anyone finds the best/cheapest source for qualified products. As far as making sure you're getting the right part, marinepartsexpress.com has schematics for all Mercruiser engines on their site. Their prices are a little better than the dealer, but with shipping costs it evens out. So, the search continues!

Eddie
 
I don't want to beat this horse to death, but some differences between marine and automotive parts are not obvious and are quite subtle. It is fairly simple to see how a carburetor bowl vents, but you cannot readily see the seal between the bendix and motor on a marine starter, you cannot easily tell the difference between new shiney auto wiring and tinned marine wiring. Then there is the whole metalurgy thing.......is that silver contact on your automotive ignition rotor cadmium plated steel or is it tinned or stainless steel? Are the contact ends on your cheaper automotive spark plug wires cadmium plated steel (lasts till about dark tomorrow on a salt water boat) or brass?

If I am going to invest the effort, time and money to service my own boat, then I'm going to remove the unknowns from the equation and use only high quality marine parts......I do my own maintenance and I only use OEM parts on my boat. If your car decided to quit on you, you pull over, dial up AAA and read a magazine while you wait on the tow truck. Some of us boat in pretty unforgiving locations and a parts failure can mean a real serious inconnvienence.

Something not mentioned in this thread is that there is a marine aftermarket just like there is in auto parts and if you wish to economize on parts cost, you would be better served looking there than at auto parts.....the name Seirra comes to mind and I believe that NAPA and Carquest both have some marine parts in their listings. You just have to specify that you want marine parts.
 
I can confirm for you that the fuel filter on the 5.0 engine is different for the car engine. I bought both and cut them apart and the auto model is inferior in several ways. I purchased the car filter because it is less than $10 vs. over $50 for the Mercruiser filter. I'm only buying the mercruiser filters for my boat if no other reason than they are built from Stainless steel.
 
There is probably another difference as well. I suspect the Mercruiser filter media inside the can is a "water block" type of paper that will not let water pass thru.
 
Marine parts are almost always different then car parts. The differences are for two reasons: First they are different to protect the lives of those onboard the boat, and second to withstand the unique conditions of the marine environment. The wrong parts very definitely can be life-threatening. Also, remember that simple component failure of things like distributor caps and spark plugs can absolutely bring on massive engine damage. This is a very risky area to try to save money.

One other thing... The comparison testing you are talking about has already been done. That is what led to the marine components in the first place.
 
Do marine insurance policies dictate using marine designated engine parts or OEM parts? I've never looked at my policy on this issue since I use OEM parts (for that matter, I bite the bullet and let the dealer do the service while the engine/boat is still under warranty).

This is not an area where I would feel comfortable not using OEM -- I'll cut out a trip during the season if I want to save money....although I have no problem trying to find the OEM parts for the best price....
 
I only know of one disallowed claim...it was about 15 years ago and involved a guy who replaced his carburetor with a Holley off-road automotive carburetor without proper bowl venting. He blew the side out of a very nice Chris Craft when fuel leaked into the bilge after a backfire.

I guess this would fall in the category of contributory negligence.
 
If only we had a stupidity exclusion, my life (insurance life) would be alot easier.

Wesley
 
Most automotive engines adapted for marine use are, for the most part, identical to their automotive vehicle counterparts; the 'long block' is the same in nearly every case. Electrical, fuel, certain gaskets and cooling are the components that are modified for marine use.

Electrical components are designed specifically to eliminate/minimize the possibility of sparks/arcing in the engine compartment; fuel systems are designed to minimize the possibility of leaks/fumes entering the engine compartment; and the necessary alterations to the cooling system should be obvious.

Electrical system and fuel systems parts should only be replaced with marine approved/grade components. Internal engine parts can be safely replaced with regular automotive replacements, since that it what they are, originally.

The automotive distributor, as long as it is electronic pick-up (i.e., NO breaker points), will work, but the power curve (controlled by moving weights under the pick-up plate) may not provide optimum performance for the marine application. The marine distributer cap connectors and plug wires are designed to continue operating normally even if they get wet.

Don't gamble with you life on the water.
 
There are actually many differences in internal components as well. The camshaft for example is very different to provide a better torque curve (and prevent the reversion of cooling water that is being talked about in other threads). Also, things like valve return springs, rocker assemblies, and freeze plugs are different. In some cases like the 454 Magnum and 502 Magnum, the cranks, rods and pistons are forged.
 
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