No water to cooling system from outdrive

[Chuckd91]

im almost finished with a full rebuild/repower of my excel 20sl and cant get raw water into the cooling system from the outdrive. The engine is a 4.3 mercruiser setup with an alpha one gen 2 outdrive. Ive removed the engine and outdrive multiple times to fix issues along the way and cant seem to fix this one! The system has no restrictions from the copper tube in the foot to the thermostat housing and to the block. It was flow tested with water. The impeller in the foot is new and has been removed and checked multiple times. The pump impeller and cover is slid down the drove shaft as the shaft is turned clockwise. There seemed to be corrosion around the sealing area under the pump base plate at the thin aluminum rib the seperates the water inlet from the exhaust and was sealed up to be sure that want the issue. The copper tube and all o rings from the pump to the upper section of the outdrive seem to be fine and the o rings are new. The intake screen and passage to the pump and clear. Ive tried submerging the lower unit in a large comtainer and the water hose with muffs with no water coming in still. I need to do the break in on the engine i built and the overheating is not good! Lol
im not one to throw parts at something but im on the verge of finding another lower unit. Any ideas?

 

[Grub54891]

Have you started the motor? The water won't flow till you start it, if you have, is the ps cooler clear of debris. Remove the pickup hose from the thermostat housing, start for a short period of time, you should get a pretty good food from the hose. If not the issue is somewhere between there and the drive.

 

[Chuckd91]

Ive ran the engine way too much as it is with no water. Ive had the inlet to the thernostat housing off many times and no water is flowing in. The cooler is clear. And water will flow from the water inlet above the water pump(in the outdeive) up to the thernostat housing using a water hose and the lower unit removed. So that waluld eliminate all plimbing issues from the water pump outlet in the outdrive all the way to the thermostat housing, correct?

 

[Bt Doctur]

If you tried in a tub first, you most likely destroyed the impeller because water must be ABOVE the cavitation plate by about 2 inches. Remove the drive as a unit and put a cut hose from a washing machine in it and run the motor . You WILL NOT be able to break it in under no load.

 

[Chuckd91]

It was submerged alteast 2” above that. And the impeller has been removed and inspected multiple times since then. Im aware of the engine break in requirements but cannot tune or load the engine without the lack of cooling water being corrected. I cant seem to find the reason its not moving water into the engine

 

[kenny nunez]

The only thing I can think of is if the base plate lower gasket is reversed may be the problem.

 

[harringtondav]

Reassembling the lower gear case onto the upper can be tricky. Possibly you didn't make the connection with the water pump coupling and the copper feed tube. Maybe recheck this.

 

[Grub54891]

Ive ran the engine way too much as it is with no water. Ive had the inlet to the thernostat housing off many times and no water is flowing in. The cooler is clear. And water will flow from the water inlet above the water pump(in the outdeive) up to the thernostat housing using a water hose and the lower unit removed. So that waluld eliminate all plimbing issues from the water pump outlet in the outdrive all the way to the thermostat housing, correct?

Yup you are correct. The issue must be in the drive. As stated above, make sure the gaskets are properly aligned, and the tube is in correctly.

 

[Chuckd91]

In reference to the base plate lower gasket, how would that be upside down and not be obvious as i installed it? All of the bolt holes line up properly and the housing/plate/and gaskets seem to fit together smoothly. I keep seeing people say to grease the impeller and other saying dont. Ive tried both as well with no luck

 

[Lou C]

im almost finished with a full rebuild/repower of my excel 20sl and cant get raw water into the cooling system from the outdrive. The engine is a 4.3 mercruiser setup with an alpha one gen 2 outdrive. Ive removed the engine and outdrive multiple times to fix issues along the way and cant seem to fix this one! The system has no restrictions from the copper tube in the foot to the thermostat housing and to the block. It was flow tested with water. The impeller in the foot is new and has been removed and checked multiple times. The pump impeller and cover is slid down the drove shaft as the shaft is turned clockwise. There seemed to be corrosion around the sealing area under the pump base plate at the thin aluminum rib the seperates the water inlet from the exhaust and was sealed up to be sure that want the issue. The copper tube and all o rings from the pump to the upper section of the outdrive seem to be fine and the o rings are new. The intake screen and passage to the pump and clear. Ive tried submerging the lower unit in a large comtainer and the water hose with muffs with no water coming in still. I need to do the break in on the engine i built and the overheating is not good! Lol
im not one to throw parts at something but im on the verge of finding another lower unit. Any ideas?

I recall reading someone posted about the fact that if that aluminum rib is corroded that area will not seal even if a repair is attempted and the only permanent fix is a new or good used lower unit.

 

[kenny nunez]

With the lower unit gear housing removed try submerging it to where the water is just below the pump base, with some vise grips turn the shaft to see if water comes up through the pump discharge. It will take some help to hold the housing in place. This will let you know that the pump is assembled correctly.

 

[Lewis1111]

I would agree it sounds like your issue is in the lower unit, very possibly the mounting plate being back-wards or possibly the water tube from the pump housing is not sitting correctly into the upper unit. Pull the complete drive off the boat and carefully split the half and look at the water tube positioning.

 

[QBhoy]

Have you tried cracking open the other internal water pump or priming it. Quite rare, but can get airlocked saw it happen this week for the first time. Spitting air and exhaust...held a finger over it (had the piped fittings for a hot water system) and woosh. Away it went.

 

[andrewterri]

piggybacking on what QBhoy said, if you think it might be an air lock I would think you could pour water down the thermostat inlet hose to prime the system. Just like you would antifreeze but use water. Just a thought

 

[QBhoy]

There is a square headed or Allen key headed plug on the top or side (near top), you can crack open and either bleed or prime. Worth a try.

 

[Bt Doctur]

There is a square headed or Allen key headed plug on the top or side (near top), you can crack open and either bleed or prime. Worth a try.

There is no uses access plug on a Alpha. The only plug is where the case was drilled for a cooling channel and then plugged. There is a welch plug sealing this area because the shift cable rides inside it

 

[QBhoy]

There is no uses access plug on a Alpha. The only plug is where the case was drilled for a cooling channel and then plugged. There is a welch plug sealing this area because the shift cable rides inside it

I’m meaning on the mechanical engine driven pump BT. I’m almost positive my old 4.3 and alpha drive set up had it. It certainly had a fitting on it for hot water feed to the domestic hot water tank. That could be used to bleed it too.

 

[QBhoy]

Around here.

 

[Bt Doctur]

Best bet is to remove the raw water inlet hose and backfill . If the water just runs right down and out the outdrive you found the problem. A correctly assembled impeller be it a Alpha 1 or a GEN II will slowly drain .

 

[QBhoy]

Best bet is to remove the raw water inlet hose and backfill . If the water just runs right down and out the outdrive you found the problem. A correctly assembled impeller be it a Alpha 1 or a GEN II will slowly drain .

Agree completely but I think he said he was sure the path from the drive to the t stat was clear.
Thats why I’m thinking either the circ pump is air locked (saw this only this week on a VP 570). Or the exhaust shutters are blocking the exits.
I would definitely be priming or bleeding that circ pump.