A J's Service Marine, Inc. Frequently Asked Questions

Frequently Asked Questions About Marine Service

These are some of the questions customers ask us about the problems they encounter with their boats. If you have a question, e-mail me with it. Questions with the broadest interest will be added to this section. I will try to respond to all serious queries. Please no questions about outboards, I do not service them at all.

Mercruiser trim
I have a 1987 wellcraft antigua with 454 mag. and alpha 1 outdrive. The trim/tilt does nothing. I checked the fuse and it is good .Any ideas? Mark

A. Find the trim pump. There are 2 solenoids. 1 is up blue wire, 1 is down green wire. Jump these solenoids to see if the pump is working. If the trim is not working but the trailer button works, the sending unit on the OD is probably defective. Also, the switch could be defective.

Cracked Block?
I am looking at buying a Baja with twin 502s in it. When looking at the boat I noticed that each engine had a freeze plug blow out which means it probably wasn't winterized properly. How can I check if the block or head is cracked? What else should I look for that could have broke during freezing? Thanks, Mike

A. The exhaust manifolds are most susceptible to freezing and cracks. Pull spark plugs and look for water signs. If the spark plug tip has rust on it water was present at one time. Pull the dipstick. If it is overfull there could be water in the oil. If all looks well, startup and run engines. Visually inspect manifolds and block for external cracks. Water will be present if cracked. Find a reputable Mercruiser dealer to perform an engine survey and sea trial. It will be well worth the few hundred dollars charged should there be a problem.

OMC Outdrive Question...I think....
Hi A.J., I sort of tripped over your faq while looking for a source for OMC Outdrive manuals. You have a terrific amount of information already there and I appreciate the "to the point" way you answer questions. Here's the problem (which I am asking on behalf of my husband and son). We have two boats with OMC outdrives that have the same problem which leads me to believe they most likely have the same cause. Both sound like they want to start, point of fact one did, was shut off and now won't start again. One is 1988, the other either an '88 or '89. Both boats were bought at auction so have no background on either. My thought is that perhaps there is something equivalent to a "neutral safety switch" in a car. In other words, there are some things that need to be in place before it will start. Boy, am I not explaining this well, but if I knew what I was talking about, I might have been a boat mechanic. I had also been told there was some type of reset needed in the event the boat overheated. If you wouldn't mind answering those two questions (is there a neutral safety switch type thing and is there a reset?), I can either say "I told you there was one of those" or "you were right, there isn't one of those" to my husband and son. Thanks a lot, A.J. Regards, Beth D.

A. There is or should be a neutral switch in the control handle. If the handle is in either gear the starter will not activate. If, when trying to start, all you get is a clicking sound, the slave solenoid might be defective. There are three solenoids on the back of the engine. One to start, two for the trim system. If the engine spins over but doesn't start, check for ignition, check for spark. I recommend buying a shop manual for your particular engine. Clymer shop manuals, Seloc publications. Good luck

Hard cold start 3.0 mercruiser
I have a 1998 Sea Ray 180 with a 3.0 mercruiser. I am the second owner. The boat and motor have approx. 120 to 130 hrs. The first owner had the 100 hr. serv. at about 70 hrs. I had the service about 6 hrs. ago. Since the service, it has been very difficult to start when cold. I even start it at home with the hose connected and it is an ordeal. When the engine does try to start, it shakes and seems as if the timing is off. It never back fires. Once it starts, no problems later while on the lake. Prior to my service, it always started, no matter how long it has set, 1st time, every time.
While it was being serviced, they corrected an oil leak coming from the timing cover gasket. Not sure if the timing could have been altered, but ever since, its a real bear to cold start. During this service, I replaced the prop with a Turbo stainless that is a 14.25X21P that was supposed to be the same as the aluminum that came on the boat. My speed is a little better, but the rpm's top out at about 4000 to 4100 instead of 4500 - 4600. I can not figure this because my original prop I now find is a 23 pitch. My rpms should be too high if these pitches are correct. I have not verified the pitch of the Turbo prop yet nor have I tried the boat with the old prop installed again. Any ideas of the hard cold start and lower top end rpm's. Could they be related? Thank you. Dennis T.

A. Ask the shop how exactly did they repair the leak. If the timing was adjusted it could be the cause of both of your problems. Also old or contaminated fuel can cause poor performance. Gas starts to lose its octane inas little as 3 - 4 weeks. A 6-year old boat with less than 100 hrs. makes me suspect of poor fuel or carb problems. Make sure your repair shop has qualified Mercruiser techs. AJ

Outdrive Gear ratio?
I have a 5.0 Mercruiser carb model with /alpha one 1.47 gear ratio. My problem is I live in an area where the altitude of the lakes I use is from 1200-2500 feet. It seems the gear ratio, is to high, so I had to re-prop the boat for wakeboarding & water skiing. I was wondering about changing the gears to 1.62 ratio. I wanted to know is this worth doing, from a cost standpoint. The boat is 3 years old, and is a 19' Just wondering if it can be done, and is it expensive?

A.(a) Before doing a gear ratio change, make sure the engine has been adjusted for height altitude running. This is very important. Then, if the engine is running right, it should push a 19' boat quite well with only reproping.
What size props before and after. What is WOT (wide open throttle). What is the boat not doing that you want it to, i.e., more top end, faster hole shot, etc.

Q.(b)I am currently running a 15 x 16 RH 4 blade Aluminum. I use this for water skiing & wakeboarding for hole shot, and to get on plane quicker my WOT with this prop is around 4500, with a top speed of 42 mph. I also use a 14 1/2 x 18 4 blade Aluminum when the water is a bit to cold to go into, about the same wot, but top end is 47-48. They said it is adjusted for this altitude, but I noticed most of the other boats, with 5.0 carb engines all run 1.62 Alpha One, with 14 1/2 x 18 or 15 x 19 and have no problem with hole shot, or planning. I would think with the 15 x 16 4 blade, I should easily be able to reach 480-5000 rpm, and hit the rev limiter, would you agree?

A.(b) Looks like you have done your homework. Check timing. Advance can be increased by 2 degrees. Also carb can be leaned out slightly. A 1.62 ratio will definitely help. If you set the boat up this way, it will perform correctly at height altitude only.
P.S. The gear set is about $370.00 plus labor to install

Q.I am new to boating purchasing a used 1998 18' Rinker with 4.3L mercruiser. I have noticed that when 'zooming' as my kids call it, the temperature rises to just above 180. 'revving' the engine in neutral quickly cools back to 160. The starboard manifold (one piece) is noticiably hotter than the port. I have just had the circulating pump replaced the an AC Delco marine (I am dubious about this - but go along with it) I know it has spent time moored in saltwater but has around 200 hours, any pointers would be appreciated. Thanks, Mark

A."Zooming" works the engine very hard with full throttle starts and quick stops after high speed runs. If you notice the temp increase when you slow down, this is normal. If temp is above 180 while under way, this is hot. Probably raw water pump in outdrive. If you are running the engine on a hose attachment, one manifold will overheat. They should be the same temp when running in the water.

Q.I have a question regarding the grade of oil I should use in My 1984 120 HP Mercruiser inboard-outboard. The manual says "use only Mercury Quicksilver gear oil". Is any good grade of hypoid 90 gear oil acceptable or should I stick with the Quicksilver oil? This unit has a mechanical shift. Thanks, Lindy

A.Mercruiser has gone to a synthetic outdrive oil and recommends it in all of their outdrives. You need 1 quart. Not more than $12.00. AJ

Q.I am considering buying a boat with a 1994 Mercruiser 5.7 with an alpha 1. The engine seems to run well, but when I touch the risers, one is very hot and the other is very cool. Is this a problem? (The engine doesn't seem to overheat.) R. Keech

A.If you are running the boat on a hose, this is common. The hose cannot supply enough water. One manifold will get less water than the other. If it does this when you are in the water, you have a problem. AJ

Q. I just purchased a boat with a Mercruiser GM 5.7 and Mercruiser stern drive. The boat runs well, but it is several years old and I am wondering what should be inspected or changed so that I can expect to run all season.

A. That is a good question and shows that you realize that boats need a lot of maintenance on a regular basis to deliver reliable service. You didn't say whether the boat has been used in fresh or salt water so I will cover both situations.

Assuming the engine starts easily and runs smoothly at all throttle settings, you probably don't need to worry about a major tuneup. What you do need to worry about is the condition of the elbows or risers that sit on top of the manifolds. Even on fresh water cooled engines -- with antifreeze in the engine -- the risers deal with hot raw water all the time the engine is running. Once the engine is shutdown, the risers at least partially drain and let in air. Heat, air, and moisture are eventual death on all cast iron. When raw salt water is added to the equation, things get worse quickly.

Pull the risers and carefully inspect them. If they look rusty or are flaking off inside, replace them. Once they fail and begin leaking water into the exhaust mainfold, you are risking a suddenly ruined engine. If you pull the dipstick and warm oil looks like a milkshake, you already have water in the engine and have to act quickly to change the oil and filter and determine where the water is coming from. As with any engine, there are several possible causes of water in the oil -- blown head gaskets, cracked block or head, bad manifold -- but the most likely culprit is the riser and that should be checked first.

Okay, the risers look good and just show a layer of carbon inside. Great! Replace the gasket -- never reuse a manifold or riser gasket -- and move on.

Next remove the outdrive. This allows you to inspect the gimbal bearing located in the transom assembly. The bearing should turn smoothly with no rough spots. If it is rough or frozen, replace it. The area inside the "boot" or driveline bellows should be dry. If there is any water there, the boot is leaking somewhere and must be replaced. Also inspect the shift bellows. This little rubber boot can sink a boat in a hurry if it leaks and the bilge pump quits.

If either of these boots shows signs of weathering or cracking, replace them before they bite you. Boats kept in salt water usually grow barnacles on these boots and barnacles can cut a hole in the flexible rubber without warning.

Next inspect the u-joints on the outdrive. If these are rusty or muddy, you are getting water on them and they are probably ruined and require replacement.

While water usually enters from the bellows, it can also come in from the outdrive itself. When the seals fail on the outdrive, you get an oily mess inside the boot. If lower seals fail, the goop is laden with water.

If the driveline area is clean, you are getting there. Next drain the oil from the outdrive. There should be little or no water mixed with the gear oil. If there is a substantial amount of water, say more than a half ounce, you probaly have a lower seal that has failed and the outdrive will need to be disassembled and seals replaced. If the oil is clean and no chunks of metal sticking to the magnet on the plug, go on to the next step.

Most outdrives have the raw water pump inside the outdrive wrapped around the vertical shaft. This pump should be replaced each season and more often if you operate in sand, mud, or grass. If this pump fails, you will overheat the engine quickly and have some really expensive problems. Replace it!

Remove and inspect the prop and look for fishing line wrapped around the shaft. This stuff can eat seals like crazy. While you are at it remove any small dings on the edges of the prop with a file. If there are serious dents or curls, replace or rebuild the prop.

When all of this has been done, reassemble the outdrive and pressure test it before refilling it with gear oil. If it holds 10 psi for a few minutes, release the pressure and refill with marine grade gear oil.

Inspect and replace any zincs that are corroded away, get a fresh gasket set for the outdrive, lubricate the u-joints if they have fittings and put the whole thing back together. You should be set for a season.

Once everything is back together, put water to the engine and start it up. While it is warming up, check the ignition timing and reset it if needed. Once the engine has warmed up and the oil is hot, change the oil, oil filter, and the inline fuel filter. Restart and look for leaks. If the antifreeze in fresh water cooled engines is more than a year or two old you might want to flush it out and add fresh water and antifreeze. The mixture should be at least 50/50 but you can add up to about 75% antifreeze for extreme conditions. Be sure and dispose of the old antifreeze where dogs can't get to it. Antifreeze tastes sweet to dogs and will kill them if they drink it!

That's it! Go have fun!

Q. My engine is hard to start and has hesitation when I give it throttle under load. Sometimes, it backfires through the carburator. Is my timing off or what?

A. The timing could be off, but likely your engine is starving for fuel. When under no load, an engine requires far less fuel than when it is pulling hard. It sounds as if the accellerator pump has quit and maybe some stuff has grown in your carb, restricting or disrupting fuel flow. All fuel contains some moisture and little hard deposits can form inside the carb itself. Usually the solution is as simple as a carb rebuild. In a few cases, however, your only fix is to actually replace the carb. I have seen carbs that simply would not take a rebuild -- even by a remanufacturing plant.

Besides poor performance, you run the risk of buring valves or pistons by running too lean. Fix it and you will be glad you did.

Q. What can I do to make my marine batteries last longer. It seems like I am always replacing one of them. I keep my battery switch in the "BOTH" position so they should both be charging, Right?

A. Wrong! Batteries may be discharged in parallel but should never be charged in parallel. Each battery has a slightly different internal resistance. Thus one battery in parallel with another will be overcharged consistently and drastically shorten its life.

Run your battery switch on either "1" or "2" but not "BOTH" when you are running your engine. If you want to start on one battery and switch to the other while running, that is okay as the switches make before break. Just never turn the battery switch to "OFF" while the engine is running. The excessive voltage can damage the alternator, instruments, lights, and expensive electronics.

If you must charge more than one battery from a single source, add an isolator block which feeds both batteries through diodes and protects the batteries. This way your alternator "sees" only one battery -- the one it is running off of -- and you avoid overcharging. I really don't know why this information is not better known and disseminated, but now YOU know the secret. Most batteries used in Marine applications will require replacement every two or three years for reliable starting and adequate supply for the electrical and electronics systems on board.


Q. Hello, I just purchased my first inboard 5.0 [302 ford] I knew it was overheating at time of purchase. If you open the drain in the port side manifold while it is running it does not overheat. Engine runs like a top and no water in the oil. Appears to be pumping sufficient water. Do I have a bad manifold or riser? Thanks

A. I would remove both risers. Inspect risers for clogged water passages. These can be cleaned out. If they break while cleaning they needed to be replaced anyway.

Q. Thanks for the info. I should have done this first instead being the last thing . One had a lot of rust falling out when removed from manifold and the bellows looked a little burned and flaking off. Is it worth taking a chance trying to clean them out some or just replace?

A. I would recommend replacing the risers. If they fail you run the risk of getting water in your engine. If you run in salt water check risers every year.

Grinding when shifting:

Q. I have recently started pleasure boating. I bought a 1988 boat that was repowered in 1997. I believe that the outdrive is the original Alpha I. Sometimes it grinds while I am shifting. Is this enough information for you to troubleshoot? Thanks

A. Lower shift cable might need adjusting if it grinds more in forward or reverse than the other.

Outdrive Oil:

Q. Hi, I was wondering if you had directions on how to change the outdrive oil on a Alpha 1 outdrive. I have a 1995 Searay Sundancer 250 with a Mercruiser 5.7L V8.

A. Remove upper and lower vent/drain screws. Drain old oil. Fill outdrive from bottom - usually 1 quart. Inexpensive pump kits are available where you buy Mercruiser lower unit oil. Unit is full when oil comes out top vent. Hint: Replace top vent screw first. This will prevent oil loss when bottom screw is installed. AJR

Q.Thanks for the quick reply. I have two more questions though about changing the outdrive oil. 1.)Should I lower the unit all the way down when draining the the outdrive oil? 2.)When draining the oil, will the oil in the resouivour in the engine compartment drain too? You don't need to change that also, do you?

A. Place outdrive in full down position to change oil. If you let the outdrive drain all night, yes the reservoir will empty. To stop this, remove reservoir from its bracket. Pinch hose very gently to block the oil flow. AJR

Replacement Carb:

Q.I have a 95 Malibu Response ski boat with a 265hp 5.7 liter chevy. It has never started very well cold and not much better after being shutdown over 6-7 minutes hot. It has a Carter AFB 625cfm carb. It seems that most ski boats are running Holley. Here's the question A. do you agree that the Holley is a better carb for a boat...B. 600 or 650 cfm.....C. Vacuum or mechanical secondaries....I'm thinking 600 with vacuum?

A. First, be certain you use a marine carb NOT an automotive carb. Your choice is a good one. Holley, 600, vacuum advance. Holley is more adjustable than others. Good Luck AJ

Volvo 280 Aquamatic Outdrive Leg:

Q.I need to understand in simple terms the gear ratio in my volvo outdrive. This model comes with overall gear ratio of either: Type 280 B 1.61: 1

Type 280 C 1.89: 1

Type 280 D 2.15: 1

Assuming my engine RPM was operating at 2000 rpm, what would the amount of turns of the prop be for

Type B ______

Type C _______

Type D _______

I need to understand whether the gear ratio of the leg is a reduction of the RPM or an increase. My way of thinking is that at 2000 rpm and a gear ratio of 1.61: 1 that my prop is turning 1242 rpm. Or is it actually 3,220 rpm.

A.You are correct. Gear ratio reduces the rotation of the prop.

Rebuilt outdrive:

Q. I recently went thru the pain and expense of having my alpha one outdrive being rebuilt. I was wondering if there is any break-in procedure. The shop that did the work told me that there is not. I would like to be reassured that I was given the right information before I run the risk of future repair.

A. To my knowledge, there is not. The outdrive is only gears and roller bearings similar to the differential on a car. AJ

Automotive carb on boat:

Q. I have a 351 windsor with an automotive carb.It has a heat rise choke.How do i install an electric choke? Also do i install a switch on the console?

A. I'm sorry I can't help you. Automotive carbs are dangerous on boats! AJ


Q. Hello, I just purchased my first inboard 5.0 [302 ford] I knew it was overheating at time of purchase. If you open the drain in the port side manifold while it is running it does not overheat. Engine runs like a top and no water in the oil. Appears to be pumping sufficient water. Do I have a bad manifold or riser?

A. It is very possible that the riser is clogged . Remove both risers and inspect the water passages for restrictions. One is likely corroded closed. Clean or replace as necessary. Note: drain manifold before removing riser. I`m guessing you have a Shamrock boat with a PCM engine .AJ

Spark Plugs

Q. I have a 1988 OMC Cobra 5.7. The spark plug, when looking at the front of the engine all the way back on the right, keeps blowing out the porcelain of the plug. What could cause this?

A.My guess would be detonation caused by an improper fuel/air ratio. Suggest a professional carb rebuild, set timing, spark plugs A.C.-MR43T AJ

Oil Pans

Q. I just upgraded with an engine change from 305 to 350. The engine dealer gave me a pan that the mercruiser windage tray did not fit and told me to remove the try and all would be ok they no longer use them. Well I did so and I have developed oil blowing out of the pan gasket under a lot. I would say it is from the no windage/baffle in the pan and the oil being sloshed around and foaming. They do not agree and say the gasket may not be in right, it is a one piece. I disagree with that theory, and I wonder what your thought may be?

A. If your explanation is correct: THE PAN IS WRONG! The windage tray is necessary. Get away from those guys. AJ

Electronic Ignition

Q. Aj, I found this electronic conversion kit on eBasic Marine and would like to get your opinion as how difficult it would be to hook up. I am concerned on the wire hookups mostly. I would like to know what you think about it and if you have done them yourself? I have a Mercruiser 140... Thanks, I have learned so much from you and your web site.

A. If it is specifically for marine use and for your engine it should work. I am not familiar with this unit. AJ

Air Lock Problem

Q. I have a 5.7, EFI Merc I/O (2 years old) and I was performing the regular maintenance that included changing the fuel filter. My filter looks similar to an oil filter that you simply unscrew and replace. I did everything according to the owner's manual that simply stated "unscrew and discard the old filter and replace with the new one". After replacing the old filter I started the engine and it cranked right over. It ran for about 10-15 seconds and then stopped. I tried unsuccessfully to restart the motor but it would not turn over. My neighbor said it might be an air lock. I unscrewed the new filter and removed it. It was completely dry (no gas inside it). I filled the filter up about 3/4's of the way with gas thinking maybe that would prime it. I put the filter back on and once again tried to start it. The engine just cranked and cranked but would not kick over. It obviously is not getting fuel. Assuming I do have an air lock, are there any tricks I can try that I may be missing before I call a marine mechanic?? Anything you could offer would be most helpful.

A. There is a schrader valve (tire valve) on the fuel rail. Remove the cap, put a rag over it and depress the valve. Fuel pressure runs at 40+ PSI, so protect yourself. Turn ignition on. Fuel pump should run for 2 seconds. Bleed system in this manner until pure fuel comes out, usually two to 3 cycles. AJ





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Al & Debbie Robicheaux
330 Mountain Drive
Destin FL 32541
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