Engine overheats above idle

[Rob1]

E

ngine was originally GM 305 cu in small block, replaced with GM 350 cu in small block.
​

Runs well at idle, but overheats above that.
New impeller in outdrive (Alpha One).
Exhaust manifolds are clear (Aqua Power 5700 Center Riser). Original manifolds were log style with risers all the way back.
Thermostat housing is 1978 style with six hose connections, two of which are capped (lower front ones) to accommodate center riser exhaust manifolds (it is the housing for an 898).
I suspect the out drive water flow is low b/c flow stays constant when I rev up the engine (disconnected water hose from outdrive before oil cooler and watched flow).
Although impeller is new, mechanic said he didn't check water tubes in drive b/c old impeller vanes were intact.

My questions are:
Shouldn't the water flow from the outdrive increase dramatically as rpm's increase?
Are the Aqua Power center riser manifolds compatible with the 1978 Thermostat housing?

 

[Bt Doctur]

Thinking the flow is wrong using that T housing

 

[Rob1]

Thinking the flow is wrong using that T housing

I agree. That and may be a blockage in the outdrive water tubes.​

 

[Rob1]

I am not sure which T housing to get to replace the old style 898 that is there now.

 

[Docksidemarineservices]

New impeller in outdrive (Alpha One).

Did you just change the impeller or did you replace the whole pump as a unit, upper and lower?

Did you buy oem or try and save money with an aftermarket?

 

[Rob1]

Did you just change the impeller or did you replace the whole pump as a unit, upper and lower?

Did you buy oem or try and save money with an aftermarket?

Boat was in shop to replace u-joint seal. Mechanic replaced impeller at that time (two weeks ago); did not replace entire pump. He did use OEM impeller.

 

[Docksidemarineservices]

Question?....What type of shop would only change an impeller on a Merc Pressure pump?

Answer.....One you don't use.

Start with replacing the complete pump and make sure the impeller has a fiberglass hub.

 

[Rob1]

Question?....What type of shop would only change an impeller on a Merc Pressure pump?

Answer.....One you don't use.

Start with replacing the complete pump and make sure the impeller has a fiberglass hub.

In defense of the shop, boat was there for a different reason. Anyway, I will replace entire pump as you suggest.
Thank you.

 

[Docksidemarineservices]

In defense of the shop, boat was there for a different reason. Anyway, I will replace entire pump as you suggest.
Thank you.

A lot of boats come to me for different reasons and end up getting a cooling system service. If I worked on a pump in a first gen Alpha, I would not just change the impeller.....No excuse.