[finn]

OMC Sterndrive Repair more

[BCuser]

Exhaust manifolds for OMC Cobra and 800 models [links]

[jchysk]

Cobra upper/lower unit

[sniff]

• Available for GM 262 4.3 liter V6 and 4 inline cylinder motors. Chevy GM 5.0 liter, 5.7 liter 305/350 CID V8 small block center rise replacements.
• Conversion kits for older Ford V8 'log style. Exhaust bellows, risers, elbows and engine gaskets.
• We ships to United States, Canada, Australia and International. Standard OEM manufactured castings can have uneven internal wall thickness due to their casting processes.
• GLM Marine uses a ‘lost foam casting ’ process, allows for more accurate casting of the wall between the water-jacket and gas area.
• This prevents thin spots in the wall which lead to premature failure. The GLM Marine brand is also designed with a larger water cooling area, up to 40% more compared to original OEM models.
• This can help reduce the overall temperature, leading to longer gasket life. The internal area has also been designed to prevent back pressure or excessive turbulence.

here

[MeatPopsicle]

Moving on to the thermostat, the next possible culprit of an overheating problem in the cooling system. Figure 6 shows the typical thermostat arrangement in the thermostat housing. Most thermostats are designed to open at 160 degrees water temperature. As long as the thermostat opens as designed, everything is fine, if it doesn't then overheating will surely result. To test the thermostat, remove and place in pan of water on cook stove. With a reliable thermometer, heat water until thermostat opens. It should open at approx. 160 degrees. If it does not, discard and replace with new thermostat. [links]

[kaja]

Now that you hopefully understand the basics of the cooling system, lets look at the source of the process, and the things that can go wrong, causing an overheat situation. more

[0x0]

^Click to enlarge^
Figure 2 shows the typical "enclosed" cooling system. This configuration utilizes contained antifreeze in the main part of the motor and also uses a heat exchanger much like the purpose of a radiator in an automotive application. The difference being instead of relying on air flow to cool the antifreeze, fresh seawater is pumped through the heat exchanger and then exits the boat through the exhaust. more

[alanahbing142]

There are two types of cooling systems commonly found on inboard/outboard boat motors.

[Nagilum]

Figure 1 shows a typical fresh water dependent cooling system. With this system, the motor is totally dependent of fresh seawater being present to provide proper cooling characteristics. Fresh seawater is normally drawn by a belt driven pump from a thru hull fitting in hull of boat on inboards, or by water pump in stern drive through the lower unit water passages on an inboard/outboard, and then exits the boat through the exhaust.

[Troutner]

Finally, the third most common reason of an overheat problem with the cooling system can be attributed to clogged water passages, usually in the exhaust manifolds. Since most exhaust manifolds are made of cast iron, rust and corrosion are always present. If you have an overheating problem, and the impeller and thermostat are in good shape, remove the riser from the exhaust manifold Figure 7, and inspect water passages for blockage. if the passages are blocked, its basically the same thing as the thermostat not opening, and water circulation is not allowed to escape through exhaust as designed.

[FreddyFender]

Question: Do the Mercruiser Engines equipped with the Dry Joint Style Exhaust AND Closed Cooling systems circulate antifreeze through the exhaust manifolds?

[brightside]

Answer: Mercruiser has made changes over the years between 1/2 and FULL cooling systems. The driving factor for this was the same reason that always seems to govern manufacturers and their products; cost. Up until 1992 Mercruiser had almost always configured their marine cooling systems, both raw water and fresh water cooling systems, such that they included warm manifolds. However in 1992 when Mercruiser introduced the 502 mag EFI motor the intake plenum was so large that it interfered with the standard thermostat housing and therefore prevented them . Therefore Mercruiser set out to determine if there were functional issues to back up the concerns that the exhaust manifolds could not be allowed to run colder than engine temperature. Mercruiser performed a significant amount of functional testing with the cold manifold systems and the resulting effect of condensation. They determined through this testing that no functional damage resulted that could be attributed to the cold manifolds. Therefore starting in 1992 with the introduction of teh 502 Mag MPI Mercruiser offered the first of several engines with the cold manifold style cooling system.

[dust]

However around the 2000 model year Mercruiser realized that the cost of warranty related to condensation induced engine damage had escalated significantly over the past 8 years and was becoming a real issue. Therefore when the 8.1L engine was released in 2001 it was determined that there was no achievable way to introduce this new engine with a warm manifold type cooling system. Therefore several specific system designs were implemented on this engine to allow it to also be released with the cold manifold type cooling system. However in 2002 the decision was made that going forward all new designs would be done while including a warm manifold cooling system unless this was just not possible. [links]

[maye]

Place the boat in the lake not a pail of water or garden house with rabbit ears being placed on lower water pick area. This work great for outboards and Mercruiser lower units but not for 400-800 series lower unit do to the fact that unit is located in the upper gear case.

[jonathanfrank]

Install a radiator flush kit between the water pick tube up from the intermediate housing and the thermostat housing and check water flow. there should be a steady flow of water at 550 to 600 rpm. water should not have large amount of bubbles as water flow out of it.

[florencte24]

OMC did sell a flushing adapter kit OEM number 172914 for years 1979 to 1985. This was installed in place of old split bearing water cover reusing the same plate and gaskets. [links]