Teague On Tech: Q & A with Bob Teague June 2022

As seen in Speedboat Magazine’s
JUNE 2022 Issue.

Water Flow

Dear Bob:

Q. My boat is equipped with a MerCruiser 7.4L Bravo One package. I am having a high speed overheating problem and the local marina is having trouble figuring it out. They’ve replaced the raw water pump, thermostat, and exhaust risers, but the engine still overheats at higher rpm. Any suggestions you can provide would be awesome.

Todd Walker
Marina Del Rey, CA

Left: Remote water pick-up kit with drive side shower.
Right: Corroded transom water passage.

If your engine maintains proper operating temperature at idle and low RPM, the problem is not associated with the thermostat. Exhaust risers or manifolds that are excessively rusty in the water passages can cause a flow restriction, but this is also not likely your problem. If you have destroyed a water pump impeller in the past, there could be impeller particles blocking water flow at the first oil cooler in line on the outlet side of the raw water pump. Similarly, if you do not have a sea strainer in your boat, and you do your boating where there is grass, leaves, bark or other debris in the water, the water passages in the cooler could be clogged with the foreign matter causing a flow restriction. If you suspect that the cooler water passages are clogged, you can back flush the system by disconnecting the 1¼” hose that supplies the thermostat housing assembly and flowing water backwards through the system with the hose disconnected from the outlet side of the raw water pump. It is best to place the raw water pump end of the hose in a bucket or direct it through a screen so that it is possible to detect the effectiveness of this operation. In stubborn cases, it may be required to remove the oil cooler and run a 1/8″ aluminum welding rod backwards through the water passages to dislodge the debris. The bottom line is that your problem is associated with water flow restriction.

It is most likely that the flow restriction is not related to any of the conditions described above. It is more likely that you have a flow restriction in the supply hose that passes through the transom assembly. There is a molded hose that connects from the bell housing (that is attached to the gimbal ring) to the inner transom where the engine water supply neck is bolted. A 1¼” water supply hose is connected to the water neck on the transom that in turn connects to the raw water pump. The molded hose in the transom assembly is held in place with plastic wedge inserts that screw into the hose itself and apply pressure to the housings that the hose passes through. On older boats, especially ones that are used in salt water extensively, we have seen many instances where the housings start to corrode around the hole where the molded supply hose passes through. The corrosion grows and puts pressure on the outside wall of the hose. Eventually, enough corrosion accumulates to collapse the hose and the insert to the point that there is a very small passage for water to flow through. In order to fix this problem, you will need to remove the drive and the water neck on the inner transom plate. If the corrosion condition exists, it will be immediately apparent. The repair consists of removing the screw-in wedges and the hose. Then it will be necessary to remove the corrosion and restore the condition of the holes where the hose passes through. Sometimes the original surface can be restored with JB Weld. Install a new molded hose with new screw-in insert wedges. The hose and inserts are available from your Mercury dealer.

In very severe cases, the inner transom is so damaged that a hose cannot be reinstalled. If this is the case, you will need to replace the transom assembly in order to keep the water system stock. As an alternative, you can install a TCM block off plate on the inner transom and thread the hole in the bell housing with a 1″ NPT tap, install stainless steel allen pipe plug omitting the molded hose completely. Then, install a bottom or transom pick up for engine water supply similar to what is done on many high performance boats.

If you install a remote water pick-up, it is highly advisable to also install a sea strainer in line before the raw water pump. The drive receives cooling from the water that passes through it. If you replace the drive water pick up with a hull mounted water pick up, it will still be necessary to have water flowing through the drive. This can be done by drilling a hole into the water passage on the left side of the upper housing. Use a 23/32″ drill and thread the hole with a ½” NPT tap. Install a flare to a ½” NPT 90 degree adapter and connect a hose to it that is routed to a top mount drive shower assembly. This way, water will be force fed through the drive while the boat is under way (which will provide internal drive cooling), and then will be directed to the top of the upper hosing for additional cooling. Aftermarket drive shower kits that utilize a flexible hose can be adapted to the side fitting in the drive housing.

Comp Pro Magnum XD Rocker Arms

Dear Bob:

Comp Cams Pro Magnum XD rocker arms and Mercury posi-lock.

Q. I noticed that you recommend the Comp Cams Ultra Pro XD Pro Magnum rocker arms. Will the part number 1820-16 rocker arms fit under the Mercury 500 EFI valve covers?

Ed Martell
Fountain Valley, CA

The Competition Cams Pro Magnum XD rocker arms (part #1820-16) is an excellent choice as a replacement for a stud mounted rocker arm on most big block Chevy applications. On the Mercury Racing engines including the 500 Carb, 500EFI, 525EFI, 600SCI, and 700SCI as well as any engine using the GM based valve covers, Comp rocker arms will fit without modification. This is true as long as the stock length valves are used. In most cases, it is necessary to use the .970” tall posi-locks that were provided with the engine to ensure clearance under the valve covers instead of the longer ones provided with the new rocker arms.

In cases where the engine is modified and longer valves are installed to accommodate higher performance valve springs with increased installation heights, it may be necessary to modify the sealing surface of the valve cover so a shim style GM valve cover gasket can be installed in conjunction with the O-ring valve cover seal which raises the valve cover about 1/8″.

For your chance to be featured in Teague On Tech, email your questions for Bob Teague to Ray@speedboat.com.

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