Mercrusier Riser

[Raider316]

I have a 2000 Bayliner 2150 with a 5.0 Mercrusier in it.
It has been overheating at high revs and I believe a leaking riser is the problem. Seems to be leaking at the bottom at what appears to be a plug. (Rust)
I understand a dry joint riser is better to install.
My question is.. does the exhaust manifold also have to be changed to accommodate a new riser. Old own replaced the other riser a few years back

 

[alldodge]

Unless the riser is clogged up it would not be what is causing overheat. As for the leaking this could cause a motor issue if the water gets into the cylinders. Dry joint exhaust can be installed but you cannot use a dry joint with a prior version manifold

 

[Raider316]

I am going to change the thermostat also. The impeller was put in last year by previous owner. I would like to change it also but the tag with the serial number is unreadable

 

[alldodge]

It should be a Alpha Gen 2 so just look at kit up for it

 

[nickmo]

I chased a high speed overheat problem for 4 years on a Alpha 1 Gen 2. Narrowed it down to the impeller sucking air at higher rpms. There is a service bulletin from Mercruiser about this. I did the recommended fix. It would work for a while (2-3 hours) then start overheating again. Turns out the surface of the lower unit that the impeller housing bolts to is pitted and warped enough that the gasket continues to fail and allows air to enter even if permaseal is used.
Finally bought an SEI lower unit which solved the problem. I'm not saying this your problem as this is rare and there are many other reasons for an overheat, but it's something else to look at.