Ideal Mercruiser 350 cu.in. running temperature?

[LAWRENCE Owen]

New 350 Chevy engine with about 400 HP. Running terrific but water temps seem to be too hot. Gauge reading 190º at, say, 3500 rpms. However with my hand-held LED thermometer I get readings of 125º-145º taken from the thermostat housing, the manifold, the engine block and the risers. Thermostat is 140º. The new crank-driven water pump is flowing a LOT of water. Also has new circulating pump system. Can a new gauge and sender be that far off ... what am I missing?

 

[Lou C]

While temps vary I found that the part of the engine closest to the dash gauge temp is the intake manifold right below the thermostat housing. I find that it reads approx 10-15*F cooler than the dash gauge. Try taking it there is still way off your sending unit & gauge may be mis matched or there may be too much resistance in the wiring.

 

[LAWRENCE Owen]

Thank you, Lou. Makes sense. I did find the temp at the intake manifold above and below the sender and thermostate housing to be consistent with the 128º to 145º range. Actually, the sender screws into the side of the new Mercruiser housing itself, and not into the intake manifold where it normally goes. I could lay my hands on top of the risers and they were warm, not hot when the gauge read 180º. I will trouble shoot the gauge/sender, which are matched.

 

[Scott Danforth]

140 degrees for carbureted and seawater cooled
160 degrees for carbureted and heat exchanged cooled or EFI and seawater cooled
180 degrees for EFI and heat exchanged cooled

make sure you have a good ground to the gauge sender

not sure how you got 400hp out of a 350 with a marine cam and without nitrous or a blower. a 383, yes, however not a 3.48" stroke SBC

 

[LAWRENCE Owen]

140 degrees for carbureted and seawater cooled
160 degrees for carbureted and heat exchanged cooled or EFI and seawater cooled
180 degrees for EFI and heat exchanged cooled

make sure you have a good ground to the gauge sender

not sure how you got 400hp out of a 350 with a marine cam and without nitrous or a blower. a 383, yes, however not a 3.48" stroke SBC

Thanks, Scott. Happy to learn about the 140º temp. Engine is 1987-vintage marine 5.7 rated at a dynoed 373 HP from manufacturer. The Vortec heads have been massaged and a higher lift non-marine roller cam swap, a marine Edlebrock intake and 670 CFM (Holley) carb and custom exhaust (sounds awesome) and I'm guessing about a 25 HP increase. BUT, I've been wrong many times! Idles smooth at 650 rpms and jumps out of the hole even with the current under sized prop. Full throttle reached a momentary 5300 just to test prop. I want to get it down to wide open at 4600 rpms. Does that sound reasonable?

 

[Scott Danforth]

I would have to see the cam card

 

[Rick Stephens]

Reason for being under 160ƒ with seawater cooled is that around 170ƒ plain water under atmospheric pressure will start to form bubbles on the walls of your cooling system. These bubbles significantly lower heat transfer from passage walls to coolant and the engine suffers spot overheat conditions.

Most efficient temperature for a gasoline powered motor is around 210ƒ. However you need over 12 pounds of additional pressure to reach that temperature without creating bubbles.

 

[LAWRENCE Owen]

I would have to see the cam card

As I confessed, mine is just a layman's guess. I don't have definitive cam specs. But it is somewhat more aggressive. Can't be radical since it idles and runs so smoothly. I can say that the power from this engine compared to the previous 300 HP Crusader is immeasurable. Whether it has 360 or 395 horsepower, I'm very happy with it. Just needs more prop.

 

[achris]

I wonder if the engine builder retarded the cam to increase top end power...??? That would give you a smooth idle, but still promote reversion if the lobe separation is too small.

Chris....