Weird overheating problem

[carolynrose]

1988 5.7. This is very weird. The boat runs great and never goes over175F. Except if I have to take it out for maintenance or winter storage. I recently replaced the lower gear case and had it all apart so I know the pickup tube and seals are good and put in a new water pump. Had the bell housing off so I replaced the hose and cleared out the p/s cooler. Ever year or any time the boat comes out and then in it becomes air bound and the water won,t circulate and it overheats until I screw with hoses and manifolds by filling with water and running it several times. Then all of the sudden it works good and circulates and then it's good until I pull it again. It gets air bound. Any ideas.

 

[jerryjerry05]

I've heard and seen this before.
Not sure why it does what it does.
What can be done is install a fitting/ valve to release the air.
The one I saw was in the thermostat housing.
It was opened when it was starting for the first time and then after it started spouting water it was shut down and usually didn't need to be opened again.

 

[carolynrose]

Jerryjerry05, thanks for the reply. Makes sense as I've seen the bleeder in some cars. Never thought of that simple cure for the boat.

 

[Lou C]

No Title

If this is a Cobra drive, make sure that the little nipple on the impeller housing spits out water, (disconnect the small hose connected to it, and start the engine with the drive in the water). This nipple lets air out of the impeller housing, which lets the water get IN when you launch the boat.... in my pic, you can see the pic in the lower impeller, there is a nipple sticking out the lower right side, that has to be open and spray water out.

Also make sure the bypass is not blocked in the thermo housing. This allows water to go right out the manifolds when you start a cold engine. Then when the thermostat opens, it lets hot water out of the engine and that mixes with the cold incoming water that exits via the manifolds. This happened to me once and the manifolds got hot very fast. If you are in salt water, it might be a good idea to replace the thermo housing if its original. They do get corroded inside like manifolds and then flaking rust clogs passages.

 

[redneck joe]

I had a bleeder on all three motors (geset) on my last boat.

 

[carolynrose]

I forgot to mention that this is a heat exchange engine. I had heard about the bypass nipple and check it every year along with cleaning the P/S cooler and heat exchanger. I also replace the flappers every year. It's just weird that it only gets air locked when it first goes in the water. I'm definitely going to put in a bleeder and give that a try.