140 or 160 thermostat. Does 20 degrees make a difference?

[soulsalvation]

Running a 140 thermostat on 1975 233hp 351cu Ford mercruiser when the suggested thermostat is 160. I’ve not noticed anything wrong with the engine’s performance but after cruising the temperature goes passed 140 to 160 plus but goes back down quickly to 140 after slowing down. Is there anything to be concerned about here? All opinions welcomed. Thanks

 

[Scott06]

Ive used both temps in my engines in the past. thinking on the 140 is you will crystalize less salt out of brackish/salt water with a 140 vs a 160 if raw water cooled.

I suspect what you are seeing with the temp rise is either water pump impeller needs replacement, or thermostat isnt opening up or there is a restriction in exhaust manifolds and or elbows. 160 isnt going to mechancially hurt the engine but rather a sign somehting isnt right.

When was the last time the impeller was done ? Im assuming you have a MC-1 drive ?

 

[Lou C]

I don’t think it will cause any harm in fact Mercruiser for many years specified a 140 stat even in fresh water. They moved to the 160 it seems when they transitioned to electronic fuel injection. In fresh water you can use either in salt water the 140 is advised because at temps above 160 calcium starts to drop out of the salt water solution and can cause deposits to accumulate over time which may lead to overheating. I used to have a 160 in mine in salt water however I did not have that problem but when I found a 140 stat that would work in my engine I did switch to it. My running temps went from 160-175 to 140-150. When I had the heads off 4 years ago I didn’t really see evidence of built up deposits even after 15+ years of salt water use.
One scenario where I’d use a 160 is in a cold water region like Alaska because the engine might run too cool to burn off moisture in the oil.
In the final analysis I think this is why closed cooling is superior because the engine can run closer to the temps the manufacturer intended and internal corrosion and deposits are greatly reduced. In salt water engine life may be extended by a factor of two….

 

[Scott Danforth]

generally, 140 for carbed fresh water cooled, 160 for carbed HX cooled and EFI fresh water cooled, 180 for EFI HX cooled

 

[Rick Stephens]

Water temps that hit 170ƒ under ambient pressures will start to form gas bubbles on the walls of the jacket in the heads. This causes that spot to get hot as the bubbles don't transfer much heat. Hence the desire to keep temperatures far from that on open cooling systems.

 

[MarcelSydney]

I just put a 160F on my 1999 4.3L (was the part to use on the specs) and had the same query only becuaseI read it on a forum I came across. I run only in salt water, but figured since I flush it after each use, it probably wasn't a big deal and would be better for a slightly warmer engine?
No idea though