1994 7.4 GL-DP Exhaust Exits?

[coolbreeze255]

Greetings everyone. I'm new to this forum and new to Cobalt boat ownership. Great boats by-the-way.

I hope this isn't a rehash of an already posted topic. I did a search, but didn't find any info on this subject.

I recently bought a 1994 255 Cuddy with a Volvo Penta 7.4GL Duo Prop setup and a closed cooling system. She's in great condition and ran great. After test driving the boat, the previous owner raised the outdrive and took the boat out of the water, but forgot that the engine was still running. Needless-to-say that caused the raw water pump to shredded its impeller. I bought the boat anyway as the price was right and putting in a new impeller kit isn't quite a big deal for me.

After installing an impeller kit and reinstalling the water pump, I lowered the outdrive into a large tub of water sufficient to submerge the outdrive's raw water intakes, and kept the hose running water into the tub. I started the engine and It looked like the water pump was working well; however, there was hardly any water coming out of, what I'm assuming is the exhaust port - the part that looks like a fishtail above the props. The water instead was coming out of two tube shape outlet ports right below the exhaust bellow and are part of the transom shield casting (see attached picture). I check to make sure that the water pump was actually working by revving the engine (while in neutral), and the water was shooting out of these outlet ports with speed and intensity matching the engine's revs. Also, I brought the engine to normal operating temp and it did not overheat. And the water coming out of the ports was slight warm. I'm not familiar with this type of exhaust setup, so I was wondering if this is normal, or should I be concerned? Any insight on this will be greatly appreciated.

Thanking everyone in advance for your input.

[coolbreeze255]

Just a follow-up...

I was able to speak separately with a couple of old school Volvo Penta mechanics and both of them confirmed that my situation was normal. The two tubes below the exhaust bellow are part of the exhaust system and their purpose is to keep the Y-exhaust pipe from retaining water, especially salt water, which would eventually corrode and rust out. At low rpms, the exhaust water would exit from these tubes, while at rpms above 1500-2000, the exhaust water would exit through the tail fin-like anti-cavitation plate/exhaust port. Mystery solved.

[AsLan7]

.
So glad you found us cb255. I missed your first post. Yes this is correct from my recollection of this system. How difficult was the impeller change? It should have been pretty straightforward. How bad was the old impeller after the previous owner ran it dry.

Any pics of your boat?

And welcome aboard mate.

.

[coolbreeze255]

AsLan7,

Thanks for your greetings. I'm glad I'd found my way here.

Taking off the raw water pump wasn't too difficult. Two bolts and two hose clamps, and the pump came right off. Putting it back on wasn't too bad either; however, I had a bear of a time getting the belt tight enough against the pulleys as there weren't any pry-points to wedge a pry bar against. And clearance between the pump pulley and the crankshaft pulley was only about an inch and a-half, so there wasn't sufficient space to put a spreader between the two pulleys in order to get the belt tight enough. I finally had a friend crawled and squeezed into the left side of the engine compartment and pulled hard on the pump/pulley assembly, while I tightened the mounting bolts. This was enough to get the belt tight to where there was less than a quarter inch of free play at mid-point of the belt, which is about where it supposed to be.

When I took the two hoses off of the raw water pump, some chunks of rubber from the melted impeller were falling out of both the pump and the outlet hose - about half of the rubber impeller vanes had broken off. In order to make sure there weren't any residual chunks of rubber left in the outlet hose going to the heat exchanger, I used a wet/dry shop vac on the outlet hose, which produced quite a bit of rubber chunks and about half gallon of water. I felt much better and safer afterwards about clearing the hose and passages of potential obstructions from the impeller debris.

Rebuilding the pump was fairly straight forward with the help of a YouTube video I'd found. The video had excellent step-by-step instructions with some great tips on the rebuilding as well. Not sure if I'm supposed to place a link to the video here though, but the video is titled: OMC Cobra/Volvo Penta Water Pump (Impeller) Rebuild, uploaded by Michael Romer. You can most likely find it by searching YouTube.

I'd initially ordered a Sierra impeller kit, which left a lot to be desired. For $60, it only came with just the impeller and an O-ring; very skimpy kit indeed. So I ordered a genuine Volvo Penta impeller kit from a local dealer for $20 more. But it wasn't that much better. It came with just the impeller, gasket, O-ring and 3 zinc-plated body bolts. The gasket was of an universal type and paper thin, and the holes did not match the pump body's bolt pattern. Really disappointing! Then, I decided to look on eBay and found a complete rebuilding kit for about $30 more than the Volvo Penta kit. The eBay kit came with everything, including a real, direct fit gasket, O-ring, brass end plate, new bearings, races, seals, spacer, key, snap rings, brass cam, and all new stainless steel hardware. At the end of the day, I now have a newly rebuilt raw water pump.

Here are some pictures of my 255 when I bought it a year and a-half ago. She has about 720 hours and have been well maintained and stored inside. The inside of the cabin looks new as the former owners (there have been 3) hardly used the cabin. With the pandemic and my hectic work schedule, I've finally got around to rebuilding the pump about couple of months ago and just put her in the water this Fourth of July weekend. She runs like a top and purrs like a kitten. And has a lot of giddy-up and go, especially with the duo-prop propulsion.

I'm really impressed with Cobalt boats. The quality of their material and workmanship are truly first class and very obvious. And I'm very fortunate to have found this boat as it's in near mint condition.

Have a great summer and a fantastic boating season.

[coolbreeze255]

I'd tried to attach some pictures, but it didn't work. I'll try again here.

[bruceb58]

Never ever ever run your drive in a large bucket of water. The pump is not designed to suck up water like that. When your boat is in the water, the pump is actually lower than the water level.

Time for another water pump impeller.

Using muffs on those era Volvo drives is next to impossible, what most people do is tee into the line going to the raw water pump and put a flush fitting there...it basically forces water to the pump but not back to the drive.

www.amazon.com/Perko-0456DP7-Marine-Flu ... 1824&psc=1