Risers running to hot, (350 Mag MPI 2003, raw water cooling, dry joint)

[Leijon]

Hade my engine, 350 Mag MPI (2003) with dry joint, sea water cooling, pulled during winter and manifolds, spacers, risers??all the way to the outdrive inspected. No problems.
Hade the entire impeller pump replaced and the flow is perfect.

However I have a riser heating problem and my mechanic has a hard time figuring it out:
The raisers gets really hot when running at cruising speed. Can?t hold my hands on them for more than four seconds.
On idle, or below 2000 rpm, the front 2/3 is quite cool and the aft 1/3 is hot but not burning hot.
The engine itself is not running hot, according to the gauge.
There are no leaks and we have tested by removing the thermostat, but in vain.
If my recollection is correct my former boats raisers, on a V8 350 Mag (260hp, 1991), didn?t get that hot. I believe I could hold my hands on them for about nine second.
Oh.. and for the record??by mistake the gasket with the restriction were placed on top of the spacer on the port side and on top of the manifold on the starboard side. The free flow gaskets were installed in the opposite manner. As I understand this cannot be the problem.

So??now to the Q?s:
How hot should raisers get?
Are mine to hot or is this considered normal?
If I measure with an IR temp meter, what readings would be ok?
Any ideas what could be the problem?

Thanks / Leijon

 

[alldodge]

Exhaust boots can handle 300 degrees, with you being able to put your hand on the exhaust and not being instantly burned, then I think your OK. You have a new pump so flow should not be an issue. One exhaust is always hotter then the other, this is just hydraulics, one gets a bit more then another.

Hope there are some others come in with their opinions

 

[Leijon]

No Title

Finally I saw that on idle the water pressure was ok but as soon as increased RPMs it almost stopped.
As I removed the tube from inside of the stern, leading to the impeller, I detected the inlet was almost completely clogged. See picture.
I guess that on idle, with low water flow speed, the tube leading from the lower unit could still stay opened. But as the amount of water flow increased with the RPMs an increasing low pressure caused the faulty tube to collapse.
I have now installed a separate pickup through the hull, blocked off the useless inlet, and the cooling of my risers? works like a charm. Below 100F even on cruising speed. Problem solved.

 

[alldodge]

Glad you found the issue, the hose clogging on bravo drives are starting to show up here more often. Still not in mass quantities but still showing up

 

[Leijon]

No Title

If anyone would like to check their own intake, here is a simple guide:
Look at the red markings in the pic. Remove the tube leading from the intake to the impeller pump. Unscrew the two screws (mark nr 6 in red box) The lower screw is REALLY hard to get at. Spent an hour on that one alone.