5.7 overheats over 3500 rpm

[oldseaox]

My 2453 Bayliner has a 5.7 replacement engine, last year. With approx 65hrs on new eng it has 2 venturi carb. alpha 1 gen2 leg. when rpm is sustained over 3500 it heats to over 185 and alarms, this started at about 50hrs. Normal is about 145 to160. Seawater impeller was replaced but changed nothing, with boat on the hardstand and ears on the water flow appears very good. replaced thermostat and again no change. What am I missing?

 

[Bt Doctur]

did you use sealer on the water pump gaskets? water pocket cover leaking, transom hose kniked internally, manifold and/or riser restriction.
plug and play motor or did you rebuild it?

 

[oldseaox]

Plug and play, installed by marine mech with a good rep but he is now 700 miles away.

 

[oldseaox]

One more thing. A friend has the same rig on the same type boat, side by side on the hardstand they "appear" to flow equal.

 

[Bt Doctur]

cant tell nothing on muffs, got to be under a load. sometimes a pump sucks in hot exaust because at planning speed the pump body is above water.
that's why you want sealant on the gaskets. what shape are the manifolds and risers in?
a quick test is to drop the lower, put the muffs on the lower and see is the pump body leaks water.

 

[alldodge]

My 2453 Bayliner has a 5.7 replacement engine, last year. With approx 65hrs on new eng it has 2 venturi carb. alpha 1 gen2 leg. when rpm is sustained over 3500 it heats to over 185 and alarms, this started at about 50hrs. Normal is about 145 to160. Seawater impeller was replaced but changed nothing, with boat on the hardstand and ears on the water flow appears very good. replaced thermostat and again no change. What am I missing?

Why was the engine replaced? Were the exhaust manifolds and elbows inspected? Was there ever a time the prior engine overheated and the impeller was the issue?

 

[oldseaox]

Found it!!! Purchased a remote temp gage, IR unit, and it indicated the starboard riser was 70 degrees hotter the port side. Removed riser and found red sealant was used with gasket and had filled and blocked some of the holes. I replaced the gaskets and cleaned out the red sealant, it no longer overheats.

 

[NHGuy]

Good for you, and thank you for letting us know what solved the problem.

 

[Volphin]

Very good diagnostics! Glad you found the issue.