Why 160 Degree Thermostat

"Just curious; does anyone kno

"Just curious; does anyone know why Merc calls for 160 degree thermostats, and not 180 or 195 degree as used in cars and trucks?
Would not the higher temperatures be more fuel efficient and better for vaporizing condensation and sludge in the oil?
Rod"

"It might be better from that

"It might be better from that standpoint but they probably don't want the motors to run lean, either,"

You also have to remember that

You also have to remember that most marine engines are cooled with raw water instead of antifreeze which can take more heat. I've heard of a few guys with closed loop cooling (antifreeze in the block) actually run with a 180 t-stat.

the cooler temps with unpressu

the cooler temps with unpressureized raw water cooling systems keep water from boiling in the cylinder heads among other things.

Secondary to that... the higher temp t stats in passenger cars serve to optimize exhaust catylist efficiency and are primarily for emissions strategy. That's making a long story very short.

Hays

I'm not sure but I'd s

I'm not sure but I'd say if the auto makers could get away with running at a lower temperature they would.
I think Mr. Hays has it real close as far as the emissions goes as one reason for the higher auto temps.

But it also would suck to only have 160 degree heat at -30.

"He's right. The EPA and C

"He's right. The EPA and C.A.R.B. (California Air Research Board) mandate lower emissions and there's no really good way to burn efficiently at low engine temperatures. They have to hit the numbers and "Best lean burn" is the way they do it- get the best performance/emissions balance with the leanest fuel table in the ECM program. Indmar is using catalytic convertors and O2 sensors on some motors this year, too.

" But it also would suck to only have 160 degree heat at -30."

You mean that a 190° temperature differential isn't enough for you?"

"With a raw water system, ther

"With a raw water system, there's not enough pressure in the block to prevent steaming of the coolant (and local, severe overheating. Steam does not remove heat.)

In designing a low water pressure alarm system for my boat, I measured a mere 1 psig water pressure at idle (at the hose sending water into the exhaust manifold). At 2,500 rpms it was only up to 2 psig! That's not a lot of pressure to keep the water in the block from boiling. By contrast, in a closed system (like FWC or cars/ trucks) the pressure cap maintains up to 15 psig in the system to prevent boiling.

So, not to belabor the point, a raw water system MUST stay well below the boiling point of water or it will boil; and that's curtains for the block and heads. That's why most use 140 T-stats, like mine.

Jeff"

"well said, gents."

"well said, gents."