By Bob Teague

TRY COPPER

Question: I have a 24-foot Sea Ray with a 400-cubic-inch small-block. I have a problem with the exhaust manifold gaskets. The starboard rear cylinder keeps leaking. What are the best gaskets to use?

Otto Isbill
St. Clair Shores, Mich.

Answer: If you are continuing to have a problem with the exhaust manifold gasket blowing out, there is a cause that needs to be addressed. It is likely that your manifold is warped and less pressure is being applied to the gasket on the one port. You may be able to resurface the mating surface, or the manifold might have to be replaced. Once the exhaust manifold is installed, it should be retorqued after the engine has been run.

Most of the engines that we build have CMI headers on them. In the past, we had experienced some problems with the gaskets blowing out. Usually the cause was that the header bolts loosened.

Periodically tightening the bolts normally solves the problem. A couple of years ago, we started using a solid copper header gasket. This change has eliminated the problem. With the solid copper header gasket, even if the header bolts loosen, the gasket survives and the exhaust leak can be fixed by simply tightening the header bolts.

SCE Gasket Co. in California makes solid copper gaskets for just about every application. They do have a solid copper exhaust manifold gasket for your engine.

MORE STING FOR THE STINGRAY

Question: I have a 2005 Stingray 23SX with a MerCruiser 496 Mag HO engine and a Bravo One X drive with a 1.5:1 gear ratio. Right now the boat runs 70 mph on GPS at 4,900 rpm spinning a 25"-pitch lab-finished Mirage Plus three-blade propeller.

The engine broke the crankshaft, which led to some pretty bad damage. The engine warranty is no longer in effect. I've been offered a good deal on a new Mercury Racing HP525EFI or HP600SCi engine with the XR drive.

Which one of these engines would be a good choice for my boat? Should I opt for the 1.35:1 or the 1.5:1 gear ratio? What kind of speed could I expect with these engines?

Anders Olsen
Copenhagen, Conn.

Answer: Usually I would say that you can never have enough power and speed. But in your case, I think the HP600SCi might be beyond the needs and capabilities of your boat. If your boat is running 70 mph with the 496 Mag HO, you can expect speeds well into the 80s with the HP525EFI. All things being equal, if you can keep the boat under control, you would probably see speeds in the 90s with the HP600SCi.

If a three-blade prop works well on your boat, the indication is that the X dimension is relatively deep. Because of that, I would stick to the 1.5:1 gear ratio. With the additional power, you will need to go up 3 or 4 inches of pitch. If you go to the 1.35:1 ratio, the boat might be sluggish out of the hole, and you may have some issues managing the torque with your single-engine boat.

With either engine package, you should consider installing a good set of trim tabs or K-Planes to control chine walk at the upper speeds. I definitely advise that you also install full hydraulic steering. At a minimum, the boat should be outfitted with a dual ram outside assist steering system.

TOO HOT FOR THE SEAL

Question: I have a 1998 Mirage 257 with a MerCruiser 502 Magnum and a Bravo One outdrive. Recently the engine got hot due to a bad water pump impeller. After replacing the impeller, everything seemed fine other than a drip coming from both exhaust pipes where the Captain's Choice enters the pipes.

As I understand it, there is an O-ring and a bushing that seals these points on both pipes, and that they will fail if the engine becomes too hot. My question is: What do I need to do to replace these seals? The Captain's Choice enters on the inside side of both pipes.

Casey Crowe
Newcastle, Calif.

Answer: All non-water-jacketed exhaust systems require adequate cooling water in the exhaust stream to protect the rubber hoses, flappers and diverter systems from damage. If your exhaust got hot enough to melt the seals on the diverter butterfly shafts, you should probably look for some other damage to rubber parts.

You can contact GIL to obtain the parts to rebuild your diverters. It will be necessary to remove them from the boat in order to rebuild and reseal them. It is probably something that you can do yourself. Or you can send them to GIL to be rebuilt. You should inspect and probably replace anything that is rubber in the exhaust and tailpipe system.

The 4-inch exhaust hoses can have the inner liner fail when they get too hot but may appear OK on the exterior. Internal flappers are the first thing to fail due to a lack of cooling water. Check for flappers in the top of the "bullhorn" that routes the exhaust through the hub as well as in the hull-mounted exhaust tips. If there is part of a flapper missing in the "bullhorn," it might be wedged in the passage near the bottom. It is important that you find all the parts to ensure that the exhaust flow is not hindered or blocked.

In extreme cases of getting the exhaust system too hot, damage can occur to the wood in the transom where the tips pass through. If the rubber hoses that connect to the transom tips are burnt, I would remove the tips, inspect the wood, reseal the wood, and then reinstall and reseal the tips.

MAKE SURE YOU CAN GET PARTS FOR IT

Question: I am buying a 1977 Glastron CVX-16 powered with a Chevy four-cylinder (140 horsepower). Is there anything I should know or look for before I make this purchase?

Timothy Foley
Fall River, Mass.

Answer: Whenever you are purchasing a boat that is 30 years old, you should make sure that maintenance and overhaul parts are available for the engine and stern drive to make repairs that will likely be needed. It has been a long time since Mercury Marine or Chevrolet has produced the engine that is in the boat that you plan to purchase.

WATER IS BETTER THAN LAND

Question: I have a 1999 Baja H2X with a MerCruiser 502 MPI engine. I bought the boat new and it now has 200 hours of use. It has the low water pickup style on the Bravo One drive. Not too long ago, I sucked up sand and filled the sea pump full. After being towed in, I had it back flushed and had a new seawater pump and thermostat installed. I then had issues with the water temperature the first time out, and took it back to the place that worked on it. They said they back flushed the lines again and found more sand.

Now if I cruise around 3,000 rpm or less, the engine water temperature stays normal. But, if I increase the rpm to around 3,500 or more, the temperature gauge fluctuates between about 170 degrees (where it normally stays) and about 190 degrees. The place that worked on it is now ignoring me and refusing to talk to me!

Do you have any idea what could be causing the fluctuating water temperature? I never had an issue with the temperature gauge staying steady at about 170 degrees no matter how hard I ran the boat until this happened. I read your section in Powerboat magazine first in every issue. When it comes to knowledge about boats, you are the man.

Ronnie Watson
Henderson, Ky.

Answer: The reason your engine water temperature is still fluctuating under higher loads is because the cooling is still inadequate. This is most likely because there is still quite a bit of sand in the engine. It also is likely there is sand in the cooling passages of the engine block that is insulating the cooling water from conducting heat away from the cylinders.

As the power is increased, the cooling demand intensifies and the areas that are not being adequately cooled are creating steam pockets. As the steam evacuates from the engine past the water temperature gauge sender, it causes an erratic reading. If this is the case, the drain plugs need to be removed from the block and the engine needs to be flushed vigorously.

The thermostat in your engine is installed in conjunction with a sleeve to hold the thermostat in the correct position. If the sleeve is installed on the wrong side of the thermostat, or if incorrect gaskets are used, the result is that the thermostat will act erratically. Make sure that the thermostat is installed in accordance to the Mercury service manual for your engine and that the required gaskets were used. Some gaskets will fit but may have the wrong bypass holes in them, which may cause the thermostat to operate incorrectly. If there is any sand still in the system, it can jam the thermostat operation as well.

Your engine picks up its cooling water from the drive, then it is routed to the raw water pump. From there, the water flows through the oil and power steering coolers. If an engine starts to overheat under load, it also is likely that the raw water supply to the engine is being restricted in some way. If you picked up sand, it is just as likely that you picked up a few rocks or pebbles. These rocks could be lodged in your drive's water passage and as the water flow in the drive increases, they are forced into a position that blocks the cooling water hose that passes through the transom assembly.

The best way to check for this possibility is to remove the drive from the boat and visually check the drive's cooling passage. While the drive is off, turn it upside down and flush large amounts of water through the inlet passage using your flushing attachment on a clean area so you can see if anything washed out.

Then check the inlet of the rubber hose that connects the cooling passage of the bell housing of the transom assembly. While the drive is off, disconnect the inlet hose from the sea pump and flush water backward out through the cooling water hose in the transom assembly. Then, remove the 1 1/2-inch hose that feeds the engine at the thermostat housing and the outlet hose on the sea pump.

With your garden hose, flush backward with large amounts of water in order to wash any debris out of the inline oil and power steering coolers. If pebbles are involved, it may be necessary to remove the coolers and clean each passage in the cooler with an aluminum welding rod. An aluminum welding rod is best because it is soft and less likely to damage the cooler.

Keep track of what you flush out of the system so you can gauge your success. Make sure that all hoses are securely replaced and clamped. Then reinstall the drive and go give it a test. Good luck.

WATER REVERSION IMMINENT

Question: I just installed a 1999 Mercury Racing 502-cubic-inch, 500-hp carbureted engine in my 1995 253 Checkmate Convincer, and I'm worried about exhaust water reversion. The boat originally came with a MerCruiser 454 EFI Magnum with 385 horsepower outfitted with CORSA Captain's Call diverters.

I later installed a set of Stainless Marine exhaust manifolds and risers on the 454. In order to make the Stainless Marine riser fit with the CORSA system, I had to trim about an inch off the Silent Choice because the new risers were slightly longer than the stock risers. Since 500-hp engines came with GIL-style exhaust, which were available with short risers for Silent Choice systems, can I use the standard length Stainless Marine risers that were on my 454 Magnum? I deleted the Captain's Call system when I installed the 500-hp engine.

Gary Miller
Pasadena, Md.

Answer: Mercury Racing carbureted 500-hp engines were notorious for reverting exhaust water. The combination of the cam profile, slow idle speed and the GIL exhaust system all contributed to the problem. Mercury addressed the problem a couple of times. A service bulletin was distributed requiring the in-gear idle speed to be adjusted higher to about 700 rpm.

Later versions of the engine had GIL risers that were designed higher than the earlier low-swept version. This riser went nearly straight up for several inches and then curved back down to the standard exhaust opening location. The idea was that it was harder for water to climb the hill compared to the lower riser. The later riser also was better for applications where the engine was low in the boat compared to the waterline.

GIL exhaust systems also were required to have a "turbulator" ring installed at the manifold between the manifold and riser sandwiched between two gaskets. This device was a stainless-steel plate that had a lip on the inside angled upward with about a 3-inch opening. The purpose of the "turbulator" ring was to catch water that was being reverted by exhaust pulses and turn it back into steam so it could be evacuated.

CMI developed an Elbow Top header system designed to replace the GIL system on these motors, which eliminated the water-reversion problem. The CMI system was eventually approved by APBA for use on Factory class race boats that had carbureted 500HPs at that time. This CMI exhaust system is still currently available.

The use of any exhaust manifold system with a short riser pipe on a HP500 is likely to result in some exhaust water reversion. If you intend to use your Stainless Marine manifolds, purchase full-length riser pipes that are water jacketed the entire length. The use of "dry pipes" or the CMI E-Top system are the only ways to guarantee that exhaust water reversion will not occur.

Once you get the boat in the water, adjust the idle speed on the carburetor so that it is about 700 rpm while in gear and the boat is in motion. Then take the drive out of gear and make sure that the unloaded idle is not too high that it could cause abuse to the drive when shifting.

502 MAG TO HP525EFI

Question: I have a 2000 Baja Outlaw with a MerCruiser 502 Magnum. I am getting ready to swap the motor and install a 2004 Mercury Racing HP525EFI. What concerns should I have with this motor swap? Is the wiring harness and mounting the same for both motors?

Please provide me with any information you think would be helpful.

Chad Mitchell Springville, Utah

Answer: This should be a very easy upgrade to your boat. The 2004 model of the HP525EFI uses the same 10-pin wire harness connection as your 502 Magnum. All the senders and warning systems will work with your current gauges and alarm.

Later-model HP525EFI engines are equipped with the 14-pin connector. If your engine has the 14-pin connector, you can purchase a harness adapter from Mercury Marine. If the adapter is used, it is necessary to run a separate dedicated 10-gauge power supply wire to the helm for all accessories because the hot wire in the 14-pin system is not capable of supplying the boat's power needs.

The HP525EFI is traditionally supplied with the plate-style motor mount. You can use this mount by installing "L"-angles vertically to your stringers that are in turn bolted to the engine plate mount. You also can remove the plate mount and install the feet mounts off your 502 Magnum. It is better to solid mount the higher-horsepower engine instead of having the rubber feet.

You can either install new L-angles that are higher on the stringers or purchase aftermarket feet that are solid replacements. It will be easier for you to use some type of adjustable mounts when aligning your engine. It is imperative that you use an alignment tool to adjust the motor height during installation.

If your 502 Magnum has the standard exhaust system (without riser spacers) and the exhaust tip holes in the transom are in the standard locations, the CMI "sweeper" headers and standard tailpipes should fit the same dimensions.