OMC water pump reliability modification.

[Reactivity]

So I picked up a Sea swirl Striper 210 WA a few months ago in very sorry condition. Had two POs and one of them had no interest in properly maintaining or modifying it at all. After months of work and a full engine rebuild, the last problem I couldn't figure out was the water pump. I burned up impeller after impeller on the trailer and in the water. I replaced the adapter plate, and did all number of fixes and restorations before finally deciding it was f****d when it worked right and engineering my own solution. I wanted something that was dead to rights reliable and did not require any major modifications to the cooling system. I read a handful of other forums that performed a similar modifications or added pulley mounted pumps but I think I have added some features that improve reliability.

All you need is a 22-28 gpm self priming 12v pump

(I used this one: https://www.jmesales.com/mp-pumps-fmx-75-12v-dc-sp-self-priming-centrifugal-pump-21-gpm/)

A smaller 2-4 gpm self priming pump (I used a normal wash down pump), 3 brass ball valves, some fittings, and some 3/4" tubing.

The total cost ran about 1000 bucks, but it's a hell of a lot cheaper than replacing the ford 302 when it burns up from lack of cooling. For me the peace of mind of never worrying about the cooling system is worth it alone.


I plumbed it up such that the larger ~21 gpm pump is in series with the normal cooling path, inside the engine bay. All you have to do is remove the impeller from the factory pump and reinstall the pump housing with all the seals and everything. Wire your pump up to a fuse and a switch with suitable current passing ability and you are golden. The thermostat will still regulate flow and allow the engine to come up to temp. I also opted to add an additional line from a washdown pump from a different sea chest that connects downstream of the pump, but upstream of the engine. There are 3 ball valves in series that allow you to isolate the engine, the washdown pump, and the main pump separately. I did this for several reasons:

This gives you the ability to prime the main pump if it loses the ability to self prime.

You can backwash the entire cooling system all the way out to the stern drive intake if it becomes fouled.

You can use the washdown pump as an emergency cooling pump to limp home.

The other advantages of this system aside from massively improved reliability are: You can now verify you have full cooling flow before you ever start the engine whereas before if the impeller did not prime you wouldn't know until it was ruined. You can flush the engine without turning it on. You can backwash sea chests easily. You can replace parts that fail at sea since all moving parts of the cooling system are inboard whereas the factory system is completely submerged when at sea. Once setup correctly the system requires virtually no maintenance and will last the life of the boat (no more replacing impellers).

I ran the engine hard and found the cooling performance to be more than adequate. Amazingly even the 4gpm washdown pump had enough flow to easy run the boat up to 7-8 mph (limited by the location of the sea chest. It loses suction on plane because of the mounting location).

The main disadvantage of this system is the electrical demand. If you don't have a 60+ amp alternator I wouldn't recommend doing this. The pump can draw upwards of 15 amps continuously and that is a considerable load on a small alternator. You also need to be mindful of not running the main pump with the engine off as it will drain the battery very quickly. Conversely you need to remember to start the pump within a minute or two of the engine starting. You may also have issues starting your engine if your battery is a bit flat with the main pump running. I'm still developing and perfecting this design, but for me it's miles ahead of the factory "solution".

 

[Scott Danforth]

why not simply fix what is there? the raw water pump in the Cobra drive is good for cooling a big block. same goes with any of the SX drives.

if its the older stringer drive, the stock impeller also works fine for any engine up to about 260hp.

 

[Grub54891]

Wow. Another engineering nightmare. :-(

 

[Lou C]

Honestly after 20 years with a Cobra I’ve had very few cooling problems. Im not sure what the problem was here…..

 

[Reactivity]

why not simply fix what is there? the raw water pump in the Cobra drive is good for cooling a big block. same goes with any of the SX drives.

if its the older stringer drive, the stock impeller also works fine for any engine up to about 260hp.

Reliability. If that pump fails 10 miles out to sea your options are getting towed and getting towed. If all you ever do is putz around a lake or bay, this is overkill. If you want to take a single engine boat out a good ways offshore, it's nice to have lots of options when things go south.

 

[Reactivity]

Honestly after 20 years with a Cobra I’ve had very few cooling problems. Im not sure what the problem was here…..

My experience with the pump is that it works great when it works. The problem is that when it doesn't work, it will destroy itself with no indication other than the engine overheating. With the price of getting towed, a nice redundant cooling system starts to look like a pretty good deal.

 

[Reactivity]

Wow. Another engineering nightmare. :-(

2 pumps, 3 valves, 2 switches, no changes to existing hardware. It's really not as bad as it sounds.

 

[Scott Danforth]

My experience with the pump is that it works great when it works. The problem is that when it doesn't work, it will destroy itself with no indication other than the engine overheating. With the price of getting towed, a nice redundant cooling system starts to look like a pretty good deal.

a $27 water pressure gauge would tell you if you lost water pressure 30 seconds before an overheat.

 

[Lou C]

With the Cobra pump mounted in the upper gear housing there are only a few things that can cause low water flow & wear on the impeller:
Clogged plastic water inlet screen
Bad water tube gaskets
Water tube has a hole rotted in it
Aftermarket impeller kits sometimes don’t pump right
Clogged water nipple might not allow the impeller to prime easily
On mine I had an issue with barnacles growing on that screen, even when painting it with anti foul paint. Common on boats moored in salt water. This caused low water output and warm running but not overheating. I removed that screen about 9 years ago and no problems since.
I replace the impeller kit every 3 seasons.
And everyone I know has:
A VHF radio (I have 2, a hard mount & a portable back up, radios do go bad eventually)
Towing insurance…a must! Don’t want to break down in the middle of Long Island Sound!
It’s just plain foolish to boat here without them!

 

[Reactivity]

With the Cobra pump mounted in the upper gear housing there are only a few things that can cause low water flow & wear on the impeller:
Clogged plastic water inlet screen
Bad water tube gaskets
Water tube has a hole rotted in it
Aftermarket impeller kits sometimes don’t pump right
Clogged water nipple might not allow the impeller to prime easily
On mine I had an issue with barnacles growing on that screen, even when painting it with anti foul paint. Common on boats moored in salt water. This caused low water output and warm running but not overheating. I removed that screen about 9 years ago and no problems since.
I replace the impeller kit every 3 seasons.
And everyone I know has:
A VHF radio (I have 2, a hard mount & a portable back up, radios do go bad eventually)
Towing insurance…a must! Don’t want to break down in the middle of Long Island Sound!
It’s just plain foolish to boat here without them!

I removed my intake screen as well after reading your post about it in another thread. I also inspected/ cleaned all the water inlets when I had the outdrive off. I suspect it's either the after market pump or the pump adapter plate still not being aligned somehow. The drive is pitted in places so I'm sure the adapter plate is not perfectly flush. I concur one should never put to sea without the right equipment, and towing insurance is a great thing to have, but I've heard a lot of people over the VHF calling a tow only to end up in the rocks waiting for the coast guard or Boat US. I'm operating out of San Diego so it goes without saying you should never leave the dock without backups for backups. The cliffs and currents here are unforgiving and take very capable vessels and captains every year. I really cringe at the thought of not being able to fix something at sea, certainly something as important as engine cooling.

 

[Reactivity]

a $27 water pressure gauge would tell you if you lost water pressure 30 seconds before an overheat.

True, but then what? I've had the pump work great for me at the dock, but fail when starting the engine at sea. Knowing it doesn't work before it's wiped out is great, but it still leaves you with few options about what to do next when at sea. You can keep trying to idle or rev the throttle slightly as I've seen people do to aid in prime, but you're still running the pump dry the entire time it isn't primed. If it had some sort of redundant pump or was mounted in the engine bay I'd have kept the original, but it's in the outdrive. You also have no access to the suction lines, only discharge, which means you can't really aid in priming in any way if/when it doesn't work. You are just kind of stuck hoping you lose cooling in a safe area or never have an issue with it. Sounds like wishful thinking to me. In my experience, if it's going to fail, it will fail at the worst time in the worst place.

 

[Lou C]

There is a company up in Canada, that specializes in OMCs and sells an improved plate for mounting the impeller, that might help. Here's what I've always done when changing an impeller:
remove housing
install muffs on lower unit
turn on hose full blast and watch for a good stream of water coming from one of the water passages in that mounting plate (this tells you the lower unit water intakes are not blocked, water tube gaskets/tube probably OK)
next, disconnect the raw water intake hose at the thermo housing, then stick a garden hose in it, turn on the water, water should come out the other water passage in the plate. This tests for a blockage in the P/S cooler.
When I install the new impeller I make sure that small thin water passage on the plate is open, (OMC called this the plate relief slot) and use all OE parts. Also make sure the water nipple isn't clogged.
Doing this, I have not had an impeller failure really ever. The only cooling problem I had was when the hose on the PS cooler popped off about 8 years ago (that shows how much flow these impellers can put out) and overheated the engine.
When I start up the first time of the season, one trick is that after I hook up the muffs & turn on the water but before firing the engine, I disconnect the raw water intake hose at the thermo housing, and fill it with water. This puts water right in the impeller housing so the impeller doesn't start dry.
If you are boating in rocky coastal regions (as am I) you should have enough line and a good anchor that will keep you off the rocks till help arrives.

if your problem is that the pump won't prime check that thin straight passage on the plate (it can get gummed up with sealer) and the water nipple in the housing.
My normal operating temps with the 160 stat are 160-175 and the 175 is only after coming off plane for a few min, then it cools back down.
In salt water you should be checking and probably changing your exhaust elbows every 5 seasons, they will clog after that long.

 

[Grub54891]

In most cases people forget to drop anchor if getting close to shore. I know in some area’s you simply can’t. I’m on the Great Lakes and it can get nasty out here to. I carry two anchors and a lot of rode.

 

[Scott Danforth]

True, but then what? I've had the pump work great for me at the dock, but fail when starting the engine at sea. Knowing it doesn't work before it's wiped out is great, but it still leaves you with few options about what to do next when at sea. You can keep trying to idle or rev the throttle slightly as I've seen people do to aid in prime, but you're still running the pump dry the entire time it isn't primed. If it had some sort of redundant pump or was mounted in the engine bay I'd have kept the original, but it's in the outdrive. You also have no access to the suction lines, only discharge, which means you can't really aid in priming in any way if/when it doesn't work. You are just kind of stuck hoping you lose cooling in a safe area or never have an issue with it. Sounds like wishful thinking to me. In my experience, if it's going to fail, it will fail at the worst time in the worst place.

stock pump is submerged when the boat sits, this primes the pump. all impeller pumps are designed this way. OMC, Mercruiser, Volvo Penta, Indmar, Ilmor, PCM. all have the rubber impeller pump at the crank centerline or below to self prime when sitting. when underway, the forward motion of the water entering into the strainer inlet forces water to the pump.

now run the outdrive into muck at low tide, and you will plug the water passages. no amount of adding pumps or valves will cure that. however when you are watching your gauges, you see water pressure go to 0, you key off, toss the anchor, call Tow Boat and drink beers for the hour it takes for him to get there.