1987 VP 290 cooling problem

[Andy Spidal]

I have a 1987 Sunrunner cuddy cab with a VP 290 outdrive. I got the boat with a Mercruiser 305 engine with a cracked block. I am replacing the engine with a Chevy 350. It has the water pickup pump on the front of the engine. I started the engine with the outdrive in a tub of water covering the intake over 6” after a few minutes the exhaust manifold was getting hot so I shut it off. I put muffs on the intake clamped tight with a extra spring clamp same problem. I pulled water pump impeller out and turned hose on very little water flow. I pulled the water pickup hose at the outdrive turned on water on no flow coming from fitting on top of outdrive. I put externa hose on outdrive water pickup water flows good out of water pickup, I noticed a large hole in bottom of outdrive water pickup should I try to find a plug for this when using muffs? I ran water through the hose to the water pump, good water flow. I put everything back together not much water flowing to the pump housing. I will try to find a plug for the hole in the bottom of the outdrive and try again. Do I need to pull hoses off exhaust manifold to allow air out when I first run after changing water pump impeller?

 

[kenny nunez]

Try plugging the hole first. Also check the area where the lower unit mates to the suspension fork. There is a “O” ring at that joint that will get air if the “O” ring is worn. This causes overheating when the boat is planing.

 

[Scott Danforth]

The fitting at the top is the suspension fork is a common failure point. That little white metal beauty rots in fresh water within 3-5 years. It's an annual maintenance thing in salt water

 

[Andy Spidal]

Try plugging the hole first. Also check the area where the lower unit mates to the suspension fork. There is a “O” ring at that joint that will get air if the “O” ring is worn. This causes overheating when the boat is planing.

I plugged the hole still no water. I disconnected the hose at the back of the boat again with muffs on and the drain hole plugged no water flows out of the fitting on top of the outdrive. I back flushed the drive and the hose going into the boat, water flowing good. Connected muffs again with drain hole plugged and still no water flowing out of the fitting on top of outdrive. Water pressure from muffs up 1 foot should flow? is there a check valve in the outdrive in backwards? next thing to try drop lower part of outdrive to check, it looks like it should be a strait tube up from lower unit to fitting on top of outdrive/

 

[kenny nunez]

In the lower the water cavity should be open. The stainless tube in the suspension fork is hollow. Unless it is packed with mud I cannot imagine what could cause water not to flow.
Keep us informed what you find.

 

[Scott Danforth]

There is no check valve

The fitting sits on a hollow shaft that has a rubber seal at top, and O-rings at the bottom and the lower casting

You could have debris or growth in the cavity