Manifold conversion for Mercruiser 255

[ct4sberg]

I have replaced may old log style exhaust manifolds on my Mercruiser 255 hp small block engines with barr marine conversion kits to a center riser manifolds. Engines run really well with an increase in rpm's. They don't however come up to proper temp. They seem to run at about 105 instead of the 142 previous to replacement. I have replaced thermostats and gaskets with no change. Anybody have any suggestions

 

[Haut Medoc]

Re: Manifold conversion for Mercruiser 255

Welcome to iboats.....
This is a Ford 351?......
You should ask this on the i/o forum....
Anyway, is this a closed system or a raw water?....
What kind of resricter plates/gaskets are you using?....​

 

[SpinnerBait_Nut]

Re: Manifold conversion for Mercruiser 255

Mercruiser/Volvo/OMC I/O and Inboard troubles and repairs.

 

[MikDee]

Re: Manifold conversion for Mercruiser 255

IMO the circulation is so much better with those manifolds compared to the log type, that is why. I would guess that at the point of your engine where the thermostat is, it is reaching enough temp to open your thermostat, but the exterior surrounding parts are cooling it down below that. You should find under load, and, or, in hotter weather it will level out around 140 degrees on your gauge.

 

[ct4sberg]

Re: Manifold conversion for Mercruiser 255

These engines are small block GM 350's and 255 HP in a 1978 Sea Ray Weekender inboard. They are are raw water cooled. I have considered trying a higher temp. thermostat, say a 160 degree. What do you think?