1976 Evinrude - Metal vs. plastic water pump housing?

[mct75]

Hi everyone. I have a 1976 Evinrude 35HP -- 35653G. The water pump housing is solid aluminum, but it looks like all the replacement pumps are plastic with a stainless steel insert. It also looks like the newer water pumps are smaller in diameter than the old metal one. Does anyone know the reason for this? Are the newer pumps better? I am just wondering if the newer style pump is an upgrade or it's better to keep the old aluminum one. I'd guess the smaller pump would have less volume but more pressure.

Also, does anyone know some of the lore behind the 1976 OMC motors? It looks like they had several revisions and 1976 motors are somewhat unique. Seems odd!

 

[F_R]

Well first, we had a lot of trouble with the cooling system on the 1976 35hp. motors. So much that they couldn't even be used in our Florida waters, The water intake would get blocked with weeds and fry the motor.

That being said, the plastic housing pumps were far better than the aluminum ones they replaced. This goes for all the applicable motors. There was a problem with electrolysis in the aluminum housings destroying the impellers when used in salt water. Yeah, I know, I didn't believe it either. But I became a believer after repairing or replacing so many burn't-up powerheads.

 

[mct75]

Well first, we had a lot of trouble with the cooling system on the 1976 35hp. motors. So much that they couldn't even be used in our Florida waters, The water intake would get blocked with weeds and fry the motor.

That being said, the plastic housing pumps were far better than the aluminum ones they replaced. This goes for all the applicable motors. There was a problem with electrolysis in the aluminum housings destroying the impellers when used in salt water. Yeah, I know, I didn't believe it either. But I became a believer after repairing or replacing so many burn't-up powerheads.

Thanks for that info! Yeah, the metal housings seem to be rare but I was curious if it was because they were trying to save money later on or because they had some flaw. The motor is new to me so I'm still learning about it. I replaced the impeller and took it out but actually had it clog with grass and start to overheat so I feel you on that regard. I may opt to get the newer plastic unit and see if that is any more reliable.

Aside from weak suction on the pump the engine makes good compression and seems in great shape so I'd like to "bulletproof" it as much as possible. Maybe the newer pump design is less prone to clogging!

 

[F_R]

Nah, the basic design problem was the water intake holes on the front edge of the gearcase. Weeds would wrap around them and cut off the flow. Later models had slots across the holes in an attempt to prevent totally blocking the flow. I guess it helped some, but not much. Not till the complete redesign of the gearcase with the water intakes on the sides was the problem solved. Then they had a great motor. I have one (a 1984) on my boat. I consider it the best motor I've ever personally owned.

 

[jimmbo]

In 1980, We bought a 35, the Dealer had both the 79 and 80 models in Stock, and was offering a better price on the 79, and my Dad was seriously considering taking it. I told him that the Water Intakes on the 79 would likely get clogged by the Weeds. He grumbled at me a bit, but after some thought he agreed, and got the 1980 model, which was when the Intakes were moved to the Side of the Housing.

 

[mct75]

Good info, thanks! The old style water pump is unobtanium and the new plastic/stainless unit is pretty pricey if it won't solve any issues.

I had some free time today and decided to drop the lower unit and check out how the water flows through the system, and y'all are right, the intakes are definitely right on the front leading edge of the lower unit. I looked into drilling some holes towards the rear to offer some relief in the event grass gets caught on it, but the exhaust pathway is in the way. It may be possible to fabricate some guards that open towards the rear that may help, but that's getting complicated. My motor didn't come with an overboard indicator so I decided to drill and tap the exhaust cover to install a hose. I think I'll run that to a pressure gauge on the dash which ought to offer an instant readout of water pump health.

Thanks so much for the pointers!

 

[TN-25]

I thought that OMC originally sold metal pump housings as "H.D. Chrome Water Pump" for silt-laden or salt water. I've got one new in the box for my 9½.


I am guessing the stock aluminum housing & the chrome version aren't the same thing. Mine looks cast & iridescent, not shiny like bumper chrome.

 

[F_R]

Yeah, the chrome pump housing was a whole different animal. t was cast bronze with had chrome plating to resist the abrasion caused by muddy waters. Surprisingly, I've only seen a couple of them, even here in Florida with our sand.

 

[racerone]

I think I have one in a box somewhere.-----The heavy duty chromed version V-4 model 75 HP