5.0 Vortec Manifolds setting off alarm,

[ms3820]

Hello everyone. I have fuel injection 5.0 VP Vortec/XDP outdrive closed cooling. I replaced the manifolds and risers last year. I had a grounding on the surf which caused a major amount of sand being introduced to the system. I flushed the risers out but still get an intermittent overheat alarm causing the rpms to drop. I will run the engine for sometimes as long as 20 minutes before the issue arises. Engine temp stays constant at 150. Manifold riser temp has peaked at 136. The starboard manifold is consistently 8-15 degrees hotter than the port.

I opened up the flush plugs on manifolds, water is hot but they seem to get cooler. When I run the motor with external hose in the flush inlet the manifolds stay cool. Could there be sand in the manifolds? Why is it intermittent? Also I did not use any sealant on the new riser gaskets could there be air getting into the system? Thanks for any help.

[ms3820]

Update, I cleaned the manifold and risers, a little bit of sand did come out, but no real blockages. I checked the temp of risers they kicked the sensor off at 126 is this to low? The max temp got up to 136. I will launch this weekend to see how it runs. Also there was times when black smoke came out of the exhaust, intermittent, could this be related to the overheat? Thanks for any suggestions.

[Don S]

Need either serial numbers or full model numbers to even be able to look up any information. 5.0 VP Vortec/XDP doesn't tell us much.

[PS94]

When you're running it on the hose, the town water pressure is pushing water up into your motor...if you ate sand, could be (if you have one like my merc) the lift impeller got abraded and no longer works...so it's not lifting the water you need....

[ms3820]

I spoke with VP mechanic he feels that I have a sensor problem since the temp is to low to set it off (136) I was am wondering though if there is hot exhaust gas making actually hotter than the reading. I couldn't launch because of other non related boat problems.

[ms3820]

I put a new impeller in, the pump housing was replaced last year....I believe there are only two pumps, one is raw water that brings water to manifolds and heat exchanger, and motor water pump that cools internal motor with antifreeze/water mix. Thanks!

[Don S]

Might help if you would answer the questions I asked earlier.