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Dave R · 04-20-2010, 08:47 AM

I have the same engine in my boat.

The exhaust flappers are a wear item. They are very cheap and very easy to change. You need to pull the elbows off the manifolds to change them, so have new gaskets (again, cheap) handy and make sure you get bring the engine serial number when you buy the Mercruiser (I assume it's a merc...) gaskets. The right gaskets for your engine likely have restrictor holes to create a bit of cooling system back pressure. A lot of people use the wrong gaskets in this application.

While the elbows are off, you'll have a perfect opportunity to check the elbows and manifolds for excessive corrosion. If you need new manifolds and risers, OEM are the best. GLM parts are OK if you know someone with a machine shop that can mill the gasket mating surfaces flat.

I agree that it's likely been run hot, but I would not sweat it. If you are serious about buying the boat, replace the impeller before you head out on the water. While the pump is off the block for impeller replacement, disconnect the hose that goes to the oil cooler from the thermostat housing and back flush the oil cooler, fuel cooler, and power steering cooler. Odds are good there's bits of failed impeller in them. It's a simple procedure that adds 3 minutes to the impeller job.

Compression on a 150 hour 7.4 should be around 140 to 150 PSI. However, if it's checked cold, it'll likely be way off. If it is off, check again after the test run.

That engine should run to 4500-4600 RPM at WOT

Good luck!

04-20-2010, 08:47 AM	#4
Dave R Senior Member Join Date: Jul 2004 Posts: 2,985 Thanks: 246 Thanked 744 Times in 444 Posts	I have the same engine in my boat. The exhaust flappers are a wear item. They are very cheap and very easy to change. You need to pull the elbows off the manifolds to change them, so have new gaskets (again, cheap) handy and make sure you get bring the engine serial number when you buy the Mercruiser (I assume it's a merc...) gaskets. The right gaskets for your engine likely have restrictor holes to create a bit of cooling system back pressure. A lot of people use the wrong gaskets in this application. While the elbows are off, you'll have a perfect opportunity to check the elbows and manifolds for excessive corrosion. If you need new manifolds and risers, OEM are the best. GLM parts are OK if you know someone with a machine shop that can mill the gasket mating surfaces flat. I agree that it's likely been run hot, but I would not sweat it. If you are serious about buying the boat, replace the impeller before you head out on the water. While the pump is off the block for impeller replacement, disconnect the hose that goes to the oil cooler from the thermostat housing and back flush the oil cooler, fuel cooler, and power steering cooler. Odds are good there's bits of failed impeller in them. It's a simple procedure that adds 3 minutes to the impeller job. Compression on a 150 hour 7.4 should be around 140 to 150 PSI. However, if it's checked cold, it'll likely be way off. If it is off, check again after the test run. That engine should run to 4500-4600 RPM at WOT Good luck!