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  1. #1
    Cadet
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    Default Differences between auto and marine engine parts

    Hello all,Was wondering if someone that really knows th answer would post a reply.What is the difference in parts on a boat engine and an auto, the obvious points are that a boat engine runs most time at a current RPM versus a car which varies. But having (by experience) tried with little success to use a auto engine (even though exact same CID and manufacture) the auto engine would not last even after re-build.Now several years and boats later my enquiring mind would like to discover the real engineering differences.Thanks in advance.

  2. #2
    Captain
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    Default Re: Differences between auto and marine engine parts

    SOME DIFFERENCES BETWEEN AUTOMOTIVE & MARINE ENGINESFor those of us in the marine industry, a common occurrence is to be questioned by customers about auto vs. marine parts. A common scenario is to have a customer ask for a replacement part for his boat. The part in question is a starter for a 350 cu.in. GM block. You give the customer a price, and he looks at you with a blank look on his face. He, then states (very angrily) "I can get one at the local auto retailer for $29.95". In the marine industry, this little scenario occurs all the time. Many boaters are unaware of the difference between an automotive and a marine engine and their respective accessories. The most notable differences include the exhaust systems, the cooling systems, the electrical systems, and the fuel systems. Additionally, items such as heads and cams are usually different. For the purpose of this article, we will only be hitting the highlights on select systems. In regard to the cooling systems, one of the major differences is found in the water-circulating pump. This is especially noticable when you have a raw water cooled engine. Unlike their automotive counterpart, a marine pump works in an open cooling system. This type of system is extremely corrosive to the pump. Therefore, the pump must be altered for longevity. A marine pump has a special ceramic seal, stainless steel backing plate, and a bronze impeller to resist corrosion. An automotive style pump, with its stamped steel impeller, would fail due to corrosion in a short time.The electrical systems in a marine application are also extremely specialized. In an automobile, any gasoline vapors that accumulate will readily dissipate through the bottom of the engine compartment. However, a boat with its sealed engine compartment, does not have that luxury. Therefore, any spark could literally cause a boat to explode. All electrical components in a boat are either completely sealed or specially vented to prevent such a catastrophe. This includes the starter, alternator, distributor, and many other engine electrical components. Carburetors typically have what is known in the industry as J type fuel bowls. These allow for the extreme vibration, pitching and yawl experienced on boats. This allows fuel to be drawn in exteme conditions and keeps fuel from being ejected from the carburetor barrels.Heads and cams are set up for a completly different torque curve. A marine engine must develop most of its torque on the low end of throttle range. This allows for the ability to use a single gear transmition system. Think of it this way:You get in your carStart it upDrive to the highwayPut your foot to the floor and hold it there for an hourIts a little different, well for most of us.Although we have only briefly touched on some of the differences between an automotive and marine application; hopefully, it will serve to remind us that there is a difference, and that the reasons for these differences need to be shared with our customers and friends in the boating community. Hopefully, when shared, this information can eliminate some of the "blank stares" in regards to parts, and maybe prevent some dangerious situations.

  3. #3
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    Default Re: Differences between auto and marine engine parts

    The biggest Danger, Fire, Explosions, Some Auto parts are not designed to be put in closed areas where gas fumes could really ruin your day. An altanator looks very much alike, Auto vs. boat engine, Mixing the two could be your last mistake. Be Safe, See Ya

  4. #4
    Commander f_inscreenname's Avatar
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    Default Re: Differences between auto and marine engine parts

    Here we go again. Some parts are diffrent some are not. A motor is a motor. No you cant take a motor out of a car and put it in a boat. It would work but a car motor is set up for a diffrent RPM. But a lumbering truck motor.... Its just diffrent specs on what makes the motor tick (cam and maby valve springs). Its the same cam maker marine/auto but for a car (lobe/lift) its set up for H.P. not torque like for a boat. Most auto places have the cam you need for a boat. You just have to tell them the specs you want and you find that it was used in a 78 pick up also. A quality part is a quality part. Cheep is cheep marine or auto. Bolt ons are diffrent. Dist cap is diffrent but the dist is not. Alt has a tin shield (spark arester) on it and cost 100% more. Why? As for a starter. Ya it may last longer (marine) but for two bolts and two wires I will change it every well.. Mines been on for five years and still have not had any problems. Have to get back to you. I can get five for what it costs for one so that is at least 25 years on average. I dont know anyone that had a starter that lasted 25 years. I know I will catch alot of B-S for my opinion,but its mine. I just use common sence. Where marine parts are needed they are used,where quality auto parts can be used or are direct replacement I dont see any reason to pay 100% mark up just because the store is on the water. Mark
    It's Not About Being Noticed, It's About Being Remembered. ResurrectionMarine.com
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  5. #5
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    Default Re: Differences between auto and marine engine parts

    Marine starters have the screen as well...Look at your insurance... Will they pay if automotive parts are installed? My familly is worth more than a few extra bucks saved!! Just my thoughts!!

  6. #6
    Commander f_inscreenname's Avatar
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    Default Re: Differences between auto and marine engine parts

    Looking at a exploded view (Clymer man/Volvo )of a Delco-Remey,Autolite and Bosch starters. Dont see the "screen" you are talking about. Second,I have a starter from a Ford 302 (mercruiser) and a starter of a 302 car motor on my bench now. The only exterior diffrence I see is a Mercruiser sticker on it. Over the same model number thats on the car starter. I grew up on a 18 acre island off the coast of Maine. The only way there and back was by boat, they were our life lines. Also (not braging,a lesson learned) with a row boat my 70 year old grandmother and a 12 year boy (myself) saved 2 loboster fishermans lives when there boat cought fire and burned to the water line a 150 yards from our dock. Most of my hair was burned off because they couldnt swim with all there gear on,so we had to get close enough to where they could reach the transom. Boy glass boats burn fast and hot. I am not one to take risks on the water. I know what can happen!P.S. Dont get personal. Thanks Mark
    It's Not About Being Noticed, It's About Being Remembered. ResurrectionMarine.com
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  7. #7
    Admiral SS MAYFLOAT's Avatar
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    Default Re: Differences between auto and marine engine parts

    Something that I want to add to this topic. If you are using automotive parts and an accident happens, then when the Coast Guard does there investigation and finds automobile parts on the engine, look for a big fine! That is when you really wished you spent the bucks for the marine parts.
    BEER........Helping ugly people find true Love since 1862

  8. #8
    Captain
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    Default Re: Differences between auto and marine engine parts

    Naahhhh..Not personal Just wanted you to know that marine starters do have the screens inside. Outside they look the same.

  9. #9
    Senior Chief Petty Officer
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    Default Re: Differences between auto and marine engine parts

    When I had Mick Gray build my MerCruiser Chev 350 engine...he asked me if I wanted to spend the extra bucks for a marine gasket kit. I don't recall the specifics...but I know there was a considerable difference (other than the price) between the marine gasket kit & the standard automotive kit. Oil & coolant leaks in the bilge are not at all desirable...so I opted for the marine gaskets. Seems to me the marine gaskets were thicker...less likely to leak? Trent...can you explain the differences?I think the key here is, as FNScreen said...to use common sense when it comes to which parts must be "marine"...which can be "automotive". It's dangerous to say, "an engine is an engine is an engine...so why pay more for parts with the word marine stamped on?". At the same time for example...if a fan belt (alternator belt...etc...) from Napa will fit my engine just fine...why pay three to four times more for one that says Mercury on it!!

  10. #10
    Captain
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    Default Re: Differences between auto and marine engine parts

    The main difference in the gasket sets are that the metal components of the gasket sets are stainless steel for corrosion resistance.

  11. #11
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    Default Re: Differences between auto and marine engine parts

    A nifty item is that some automotive engines turn in a different rotation than a marine engine. A few years ago a friend ( with considerable experience) replaced his engine with an automotive type. Most all went fine even with the start up and running the engine. BUT when he put it in forward he went backwards. He pulled the engine reversed the rotation. Then I asked him why he did not change the pitch direction on the prop? = Dumb look.was the answere.

  12. #12
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    Default Re: Differences between auto and marine engine parts

    the starter, and the alternator are not the same, yes, then will bolt on, and work,but the game wardens if they look in engine bay they will ticket you for not having Coast Guard approved electrical system parts.

  13. #13
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    Default Re: Differences between auto and marine engine parts

    just a stupid question, but If you have a 25 year old mercruiser and somebody stuck a chevy II starter on it 19 years ago before you bought it, and acounting for wear and tear how is it going to look any differant externally than a marine one?not trying to be a jerk or anything but that's a bit like a park ranger looking through my catalytic converter. Why would a game warden look in an engine ocmpartment, if I'm not mistaken there would be neither fish nor game in there only propulsion.

  14. #14
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    Default Re: Differences between auto and marine engine parts

    Please ignore the above reply, I was sleepy and crabby and I am a cheap skate who would by a used bar of soap if given the chance.

  15. #15
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    Default Re: Differences between auto and marine engine parts

    Some good information listed...thanks for a good laugh " NeedMercHelp "

  16. #16
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    Default Re: Differences between auto and marine engine parts

    Well guy's and of course gals (if any),I started a very lenghty discussion, but with little technical meat as to what my question was enquiring.I don't want to start a war between the dealers and die hard people with "marine part is a marine part" and the other side which says "a quality part is a part".My question was more of what captain alluded to in one of his earlier responses in where the cam is lobed different etc.....which is really obvious since a marine engine red line is MUCH lower (usually) then a car engine.But more specifically, are the main, rods and cam bearing of a different compound? and the like.Please, Please lets get quickly away from the hard lines of what one preferres as parts and what ones livelyhood might be.As for Coast Guard investigations during a motor boating incident (having been one) please let me tell you that the engine "components manufacture" is NOT one of the critical things we used to go look at.Adriano

  17. #17
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    Default Re: Differences between auto and marine engine parts

    I believe your main question deals with internal parts, so I will spill out my knowledge on that. I do know that the head gaskets are of a different material to prevent corrosion. As far as bearings, they are in the same oil as a car engine, don't know of any Marine 10W40 as of yet. I have never seen or heard of different bearings. The Cam should be tuned to your liking. From what I have seen, Cars need torque because there is less slippage from your tires to the road. In a boat, horsepower is used when you get that motor turning 3500-5000 rpm, there is plenty of "slippage" until the prop catches up with itself. I have never even heard of the torque specs on a boat motor. Anyhow, just what I know.

  18. #18
    Commander f_inscreenname's Avatar
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    Default Re: Differences between auto and marine engine parts

    Like I said befor. "mercruiser buys the same core 305 motor that chevy trucks div buys (same with Ford). Just a diffrent cam. The rest is mercuiser bolt ons and merc stickers on the parts they could keep.
    It's Not About Being Noticed, It's About Being Remembered. ResurrectionMarine.com
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  19. #19
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    Default Re: Differences between auto and marine engine parts

    Thanks Big_Al and f_inscreenname, guess the reason why car engines directly ported to boats burn up/die so quickly, must be that cam lobe cause excessive heat and wear on the rings, bearing components.Thanks to all.

  20. #20
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    Default Re: Differences between auto and marine engine parts

    I did have an alternator problem last year with my 3.0L OMC I/O (1987 vintage). The case bolts that hold the front to the back case had 1 stripped and 1 broken bolt. I had the alternator checked and repaired at a local auto/electric parts store. One of the case bolts that was stripped was backing out and grounded on a terminal so they bench tested the regulator and it failed. They were full aware that this was a marine part and assured me that presented that pressented no problem.I guess my question is what should I look for or am I OK?

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