Ambiguous Trim
Question: I have a 1995 Sea Ray with a 4.3LX Alpha One package. The boat is equipped with the Quicksilver 3000 throttle/shifter. The power trim button is very temperamental. Using the "trailer" switch causes the drive to go up with no problem, but the up/down buttons only work some of the time.

You have to toggle up and down several times, and then it will work. Is this a problem with the switch on the throttle, or should I be looking in the back end?

Marc Richardson
Kitchener, Ontario

Answer: I would say that there is a 60 percent chance that the problem is in the switch on the throttle assembly. In order to resolve the problem if it is in the Quicksilver unit, you will have to replace the switch and check the wiring. But before you do that, check the connections at the trim pump to the trim limit switch that is located on the drive.

Make sure the connection is secure and absent of corrosion. The other strong possibility is that the trim limit switch mounted on the gimbal ring is defective. In order to test this, bypass the trim limit switch by connecting the two wires together that go to the switch with a jumper wire.

Generally, the wire looks like a black lamp cord and is plugged into the trim pump harness. Do not confuse the wire with the trim gauge wires, which are identical, but are usually connected into the engine harness that goes to the gauges. If the trim switch works correctly with the jumper wire in place, then it will be necessary to replace the trim limit switch on the gimbal ring.

Too Cool
Question: I recently purchased a 2000 PowerQuest Stryker, with a 7.4 MPI (315-horsepower) MerCruiser engine. The problem is that my water temperature gauge does not move at all.

I tested the circuit and gauge by grounding the sender wire and the gauge pegged, which indicates that it is working. I then replaced the temperature sending unit.

The temperature gauge still won't climb to a normal operating temperature. After the engine is run and then shut off a few minutes, the gauge will climb a little. As soon as the engine is started, the gauge reading goes back down. Is the temperature gauge indicating the temperature of the incoming water, and not the actual running temperature?

Eric Pursche
Zion, Ill.

Answer: The water temperature gauge is supposed to read the engine running temperature, not the temperature of the incoming water. It is obvious that the incoming water is influencing the engine running temperature because the temperature drops when you restart the engine. It is possible that your gauge is inaccurate or that the sender is the wrong range or type for the gauge.

Being that you do not know how long the gauge has been reading low, it may have always been this way. In order to verify the temperature and validate the gauge reading, connect a Scan Tool or digital diagnostic tool to the engine diagnostic plug. If the reading is near the same as indicated through the ECM, the gauge is reading correctly and your engine is running too cool.

It is likely that your thermostat is defective or possibly installed incorrectly. It is also possible that the wrong gasket was used on the thermostat housing, which may be allowing water to bypass the thermostat when it is closed. The thermostat is installed in conjunction with a sleeve on most engine models similar to yours.

Sometimes, the technician accidentally installs the parts in the wrong order. If this is the case, the thermostat does not function correctly. I would purchase a new thermostat and the correct gaskets. Then refer to the Mercury manual for your engine to make sure you are installing the parts correctly.

Aerated Oil
Question: I have a Volvo Penta 496 "Mag" engine in my boat and the oil pressure gauge starts to fluctuate when I run above 4,500 rpm. The oil pressure gauge indicates a steady 60 psi up to around 4,500 rpm. Above 4,500 rpm, the gauge starts to fluctuate between 40 and 50 psi. If I back off the throttle a couple hundred rpm, the gauge once again becomes steady and returns to 60 psi.

Do you have any ideas what the cause of this problem is? It just started to happen this season.

Evan Sherris
Vernon, B.C.

Answer: An unsteady reading or fluctuations on your oil pressure gauge is an indication of aerated oil. If the problem just started this season, we need to investigate what has changed. The first thing I would do is verify the accuracy of your oil pressure gauge by connecting a mechanical oil pressure gauge to the engine. Sometimes, the sending unit starts acting up at the higher pressure levels, which will give you a faulty reading at the gauge. If a mechanical oil pressure gauge connected to the engine indicates the same fluctuations as the electric gauge, your problem is being caused by aerated oil.

One of the causes of aerated oil in the pan is overfilling your crankcase. Your engine should never be run with the oil level above the full mark on the dipstick. When the oil level is too high, the windage created by the crankshaft rotating assembly can pick up the oil from the sump and whip it up, which causes air in the oil. There is a windage tray installed in your oil pan to protect the oil in the sump from the windstorm that is being created in the crankcase.

This tray is spot-welded to the pan on some models and is attached to studs extending from the main bolts on other models. Some engines have both windage trays installed. It is possible that the windage tray has broken loose inside the pan and is no longer protecting the oil in the sump from being whipped up by the rotating crankshaft. I have seen instances where these loose parts have been sucked up against the oil pump pickup resulting in catastrophic engine failure.

It is also possible that the pickup on your oil pump has fallen off in the pan. The lower portion of the oil pump is usually submerged in oil and the pickup extends to near the bottom of the pan. As the engine increases in rpm, oil flow is increased, but then takes longer to flow back to the pan. The result is that the oil level in the pan drops to a lower level during extended high rpm use. If the oil pump pickup has fallen off, or is otherwise defective, the pump may be picking up air as the oil level lowers in the pan away from the pump itself.

I would first check to make sure that your oil level is not too high. If it is, lower it to somewhere between the add mark and the full mark. Then run the boat to see if the situation improves or gets worse. If the symptom gets worse when the oil level is lowered, then it is likely that the oil pump pickup has broken loose. If the oil level has no effect on the symptom, then I would suspect that there is a problem with the windage tray in the pan. In any case, do not continue to run the engine at a point where the pressure drops and fluctuates or engine damage will occur. Figure it out and fix it.

Chevy Heads
Question: Can you tell me what cylinder heads MerCruiser used on the 1987 330-hp 454 Magnum engine package?

Keith Bevins
Taylor, Mich.

Answer: The 330-hp version of the 454-cubic-inch MerCruiser engine was not referred to as a Magnum. The Magnum version of the engine was rated at 360, 365 or 385 horsepower depending on the model and induction system. The 330-hp engine was a marine version of the GM 454 truck engine. It was a Mark IV big-block Chevrolet with small intake runner oval port iron cylinder heads. Typically, the exhaust valves also had rotator assemblies under the valve springs.

The Magnum version of the 454 engine is a marine version of the Chevrolet high-performance 454-cubic-inch engine. This engine uses the larger rectangular port intake runner Mark IV cast iron heads that are similar to the heads first found on the LS-7 hot rod motor that was first available around 1970. Both the oval port and rectangular port heads I am referring to are "open chamber" design.

The very early models of these heads are not suitable for use with today's unleaded gasoline because they were not fitted with hardened exhaust seats. These heads cannot be retrofitted because there is not enough material in the casting around the exhaust seats to properly install a hardened seat insert.

Generation V and VI GM cylinder heads should not be used on your Mark IV engine because of water sealing problems with the head gaskets. If you are thinking of reworking or upgrading your heads, don't. The best solution is to select one of the many aftermarket head assemblies that are offered specifically for marine use.

I have had good success with head assemblies available from Edelbrock and World Products (Merlin). I also would consider going with aluminum heads, which better dissipate the heat that is generated by today's gasoline formulations. Edelbrock has a marine head assembly that is anodized and has a smaller 110 cc chamber. Using this head will result in raising your compression a little, which will improve the engine's performance.

Fluctuating Drive Lube Level
Question: I have a 1997 27-foot Fountain with a Mercury HP500 motor. My Bravo drive started leaking after two days of use. I took it to a Fountain dealer in my area for service. They told me that the bottom section of the drive needed to be rebuilt. They stated that some nut had come loose and messed up the threads. The repair cost $2,600.

Now, when I run the boat, the drive oil reservoir fills up when running the boat and drops to a level that sets off the alarm when the boat is stopped. Do you have any suggestions on what the problem might be?

Buddy Grierson
Upper Marlboro, Md.

Answer: It is likely that the check valve in your drive lube reservoir is missing. A Bravo drive is supposed to operate with slight internal positive pressure as it gets warmer. In the stock drive lube reservoir cap, there is an orange "umbrella"-shaped rubber check valve that allows air to enter the reservoir, but not escape. As the oil heats up in the drive, it expands. The expansion of the oil due to heat combined with the windage created by the rotating gears results in the oil expanding into the reservoir.

With the check valve in place, pressure is created in the drive and drive lube reservoir, which minimizes the amount the oil level rises. As the drive cools, air is drawn past the check valve to prevent a negative pressure condition or vacuum in the drive. If a vacuum is created, water will be sucked in past the prop shaft seals contaminating the drive oil.

The orange "umbrella" piece that is used in the stock cap is the identical part that is used for the check valve in a Holley carburetor bowl for the accelerator pump. So, if your local Mercury dealer does not have one, go to the carburetor shop or auto parts store.

Many aftermarket drive lube reservoirs do not have check valves installed in them. If they do not, then they are not properly suited for the intended use.

After you obtain and install the proper reservoir cap with a check valve in place, I would start over by draining your drive and properly filling it from the bottom. This is done by pumping the oil in the plug at the bottom that is behind the propeller with the upper side plug out. Once oil runs out the side plug, install the side plug and continue pumping oil until it appears in the drive lube reservoir and rises to the proper level.

Quickly remove the fill hose and replace it with the plug and washer (make sure the washer on both plugs are in good condition and in place). The cap must be off the drive lube reservoir during the filling process. Replace the cap making sure the gasket and check valve are in place and in good condition.

Just Get A Big-Block
Question: I have a 2002 Rinker 270 loaded with every possible option including generator, air conditioning, radar, windlass, extra battery banks, rigid dinghy with a 15-hp motor, and so on. The boat is heavy. If I had to guess, the weight of the boat is more than 9,000 pounds.

The boat is a bit underpowered with the stock 300-hp, 5.7 MPI engine with a Bravo Three drive. I can cruise at 28 mph with just my family (wife and two kids), but if two adults are added to the load, I cannot get the boat on plane. Would it be worth it to add a supercharger? What kind of performance gains would I get?

I mainly would like to have midrange improvements as I'm more concerned with cruising speed than top speed, but improving both would be nice. I know a big-block would be best, but adding a supercharger seems a lot easier and less expensive.

My Bravo Three drive has a 2.2:1 ratio with 22"-pitch props. Without the dinghy and just my family, the maximum rpm that I can attain is 4,600 to 4,700, which is at the low end of the desired range for the 5.7 MPI engine.

The ideal outcome would be to cruise at the same speed (28 to 30 mph), but drop engine rpm from the current 3,900 to 4,000 down to around 3,200 in order to lower gas consumption. Help!

Fred Moomey
Traverse City, Mich.

Answer: I would not hesitate to install a MerCruiser 496 Mag or 496 Mag HO in your boat in place of the small-block. What you need is torque in order to carry the load. There is no real substitution for cubic-inch displacement when it comes to getting the job done.

I would be reluctant to install a supercharger on your stock 5.7 MPI engine because of the severe load that it is under all the time. Engine reliability could be an issue. You might be able to find a takeout 496 package that is in good condition from someone else who is upgrading to another level. If you replace the entire engine, then you will also have the 5.7 MPI engine to sell to the next guy.

If you install one of the 496 Mag offerings, you will probably be able to go up in prop pitch to at least 24-inch, maybe 26-inch with the 2.2:1 drive ratio. I would be willing to bet that your fuel economy will end up being better overall after the conversion to the big-block package.

Superchillers For 600sc Engines
Question: I have a 1997 Apache Warrior with twin Mercury Racing carbureted 600SC engines. I understand there are some upgrades available, such as SuperChillers and blower pulleys that will increase the horsepower of these engines.

How much power are these motors capable of while keeping things moderately reliable? Are the stock blowers worth keeping and buying chillers or should I work on replacing them?

What would you recommend to get an extra 100 to 150 hp per motor? Are these goals realistic?

Rob Franta
Amherst, Ohio

Answer: Adding the SuperChillers to any blown engine will increase the horsepower while also controlling detonation. I think a realistic expectation for your engines is just short of a 100-hp increase per motor without going crazy on the boost level. I would not hesitate to install intercoolers on your engines, especially with your heavy boat that creates more engine load all the time.

B&M produced the blowers used on the Mercury Racing 600SC and 800SC engines. The design was modified to Mercury's proprietary specifications. The major difference from the standard B&M 420 blower is that the Mercury version has a different snout, idler system and pulley.

In order to install the SuperChillers on your motors, you also will have to purchase the 16-rib drive conversion kit, which consists of new pulleys, a remote-mounted idler plate and spring-loaded idler pulley assembly, and a 16-rib belt. If your blowers are in good shape, this will be the best way to go.

If your blowers are tired, you might think about converting to 6-71s or 8-71s because parts are getting rare. Holley bought the blower line from B&M several years ago and has pretty much let the line die. The Blower Shop makes one of the most commonly used 6-71, 8-81 and 10-71 marine kits on the market. SuperChillers also are available for all makes of the 6-71 through 14-71 series superchargers.

Adding the SuperChillers using your current superchargers will cost $1,495 for the SuperChiller and $895 for the new idler/pulley system. If you elect to replace the superchargers, the Blower Shop 8-71 marine blower kit costs about $3,900 and the intercooler kit sells for $1,695. If you change to the 8-71 blower, you will also need to change your carburetor linkage to the Enderle type, which costs about $125. All of these estimates are per engine. In addition, you will need to add hull-mounted water pickups, dumps, sea strainers and plumbing for the SuperChillers, which will cost about $500 per engine.

All that being said, I would not hesitate to install intercoolers on your engine. The result will be increased horsepower while helping to control detonation. I would expect the top-end performance to increase on your boat about 8 to 10 mph.

Bravo One To XR
Question: I recently upgraded from a Bravo One drive to a Bravo One XR drive. The new drive sheared teeth in the upper unit after only three hours of use. In contacting the selling company, they informed me that since I had "upgraded" and not simply replaced my old drive, I should have purchased a kit.

This kit includes spacers to be installed on the cylinders so the drive cannot be raised as high as the Bravo One. Also, the kit has some kind of part that would be placed in the gimbal housing.

Have you heard of this?

Charlie Vineyard
Moses Lake, Wash.

Answer: The first design of the Bravo One XR drive used a more massive universal joint and yoke assembly in comparison to the stock Bravo One. Because of the larger U-joints, it is desirable to not run them at too much of an angle. That is the purpose of the trim-ram blocks.

Also, if your transom is an earlier model Bravo One, the gimbal bearing has to be changed to the later design that has less of the inner race protruding on the drive side of the bearing. The Spicer version of the XR universal joint assembly is slightly longer. The design of the later gimbal bearing provides the additional room needed. The late-model XR gimbal bearing is easily identified by a red dot on the aft face of the bearing unit.

The aluminum bellows retaining ring also needs to be changed to the later design that is slightly narrower in order to provide adequate clearance for the larger universal joints.

XR drives provided by Mercury Marine for about the last four years no longer have the Spicer heavy-duty assembly with the larger U-joints. So if your drive is a very late model, someone is making excuses.

All that being said, it is very doubtful that the cause of your upper gear failure was because you didn't have the "kit" installed in your boat. There has been a run of teeth breaking off the "forward" and pinion XR gears lately. If your engine is in the 500-hp range or less, was full of oil, and you didn't hit anything, I think the seller should stand behind it if they are a marine business.