Most Efficient Engine Operating Temperature?
 

Out at LOTO for the Shoot Out and starboard engine temp buzzer went off. Gauge showed 190. Shut down, changed impeller and found the belt was loose. Got her all fixed up but my buddy that owns the boat was concerned about possible engine damage due to overheating. I told him I don't think he has to worry about 190 and is fine until 210 or 220 or so. You can run a BBC in an automotive application at those temps with no issues.

I got thinking that you should have 180 to 190 as a normal temp in a car and you're probably not going to hammer it until it is fully wormed up. Why do most boats run lower temps like around 140? I know if you don't run a thermostat or a restrictor it it flow a lot of water and keep temps down.

What temp should the engines run and what are you all running?

Boats are run lower temps because enclosed engine compartment…think water cooled exaust and etc….

Good thing is this lets hoses/wires/ignition wires, etc last extremely long.

I find 100-140 really good for power. Oil temps 180-220 -240 (dep on tyoe of oil and how long at that temp and etc ) or so good for power and reiability

Boats typically run lower temperatures because they can with an unlimited supply of water. Lower temp can indirectly equal more power. In theory you can run more timing without detonation.

Technically anything below boiling is fine. But I think 180 is the universally understood "normal". I run a restrictor plate where the thermostat would be. My water temp gauges take forever to get past 100 but will go to 140 if I run 4000 for 15 minutes or more.

As SB mentioned, I am much more concerned with Oil temperature. Im slowing down if my Oil temps start creeping past 220(rare). All I have to do is back off a 1000rpms and the temps will quickly go back down.

John

So hitting 190 is nothing to worry about. Seems like all my boats have run around 140 or so.

I run around 165 to 170 in my Outlaw. Jumps up to around 180 when I’m running fast and long. I think 190 is a little high, but I’m no expert.

To make sure we are on same page….190 won’t hurt the engine unless it produced detonation/knock, but it is not where we want to be.

Most open cooled marine engines under a hatch are set up to run 140-160.

lol...your buddy must not understand engines at all...or ever looked at a car/truck coolant temp gauge. As noted above, oil temperature is much more critical than engine temp, 190 is a bit high but also keep in mind that the gauge may not be super accurate...but definitely not something to worry about. My first Baja with a carbureted 454 ran a 145 thermostat, the one I have now with a fuel injected 454 has a 165 thermostat...and the temps run right at that on the gauge.

Doesn't a higher working temperature mean better efficiency?
As early as WW II, glyckol was added to the RR, Allison, Packard, Jumo and Daimler-Benz engines cooling systems to raise the engine's operating temperature, power and efficiency.

Eng temps for best efficiency and safest for continuous high power will not be the same. Car engs since the early 70's have had to meet fed emission standards. A higher temp eng will burn more of the fuel creating less emissions and be more efficient. However, cars have detonation protection via knock sensor/s that pull timing reducing BMEP and thus detonation is prevented (and lowers power output). Most boats don't have this so dropping coolant temps gives more cushion against detonation. In other words, boat engs run much harder than car engs do so they need the extra detonation protection that lower engs temps provide.

None of my water temp gauges on any blower motor ever moved past 120*