why are marine t-stats temps so low?

[tfret]

I'm just wondering why marine thermostat tempuratures are so much lower than their automotive counterparts. Anyone know why?

 

[jtmarten]

Re: why are marine t-stats temps so low?

So your engine doesn't overheat and sieze. With raw water cooling you're using continuous cold water to cool in a zero-pressure system. Not ideal conditions to pick up and remove heat.

 

[Brentathon]

Re: why are marine t-stats temps so low?

Marine engines are designed to run at high rpm and very high torque (i.e. load) under normal conditions..........auto engines operate lower rpm's and much lower torque conditions.
Water boils at lower temps, when it's not pressurized and not mixed with a 50/50 antifreeze.
Other reasons, too,...

 

[JustJason]

Re: why are marine t-stats temps so low?

Salt will also start to crystalize inside of the engine when the temps get up there. And there's also the fact that the engine is sitting inside essentially a non-vented area. If it got to hot it would start to melt the boat around it.

 

[HT32BSX115]

Re: why are marine t-stats temps so low?

Salt will also start to crystalize inside of the engine when the temps get up there.

This is the main reason.

Closed cooled engine can run much hotter than raw-cooled engines.

 

[tfret]

Re: why are marine t-stats temps so low?

This is the main reason.

Closed cooled engine can run much hotter than raw-cooled engines.

What temp do closed systems typically run?

 

[Philster]

Re: why are marine t-stats temps so low?

Boat closed-cooling systems still are not equal to automobile closed-cooling systems.

Not all parts get the closed-cooling liquid in a boat that has closed cooling.

Can't have water boiling and salt/minerals crystalizing.... be it a closed-cooling system boat or a raw water setup.

In a car, you can run near boiling or even over. In a boat -- even closed cooling -- not so much... because some parts aren't being cooled by the closed-cooling system.

What kind of water or coolant are you running through your automobiles exhaust system?

 

[Lou C]

Re: why are marine t-stats temps so low?

I think the main reason is that the system is not pressurized so water will boil at 212* and maybe start boiling even sooner in hotter parts of the engine. Your car has a 15 lb pressure cap that in combination with 50/50 antifreeze/water raises the boiling point to 265* F which allows car engines to run anywhere from 195* to 230* without damage...
My 98 Jeep has run between 210* to 220* or so in hotter weather with no problems...but thats with a big viscous drive fan and a lot of airflow...neither of which a boat has..

With closed cooling you still have an engine with no airflow around it to remove heat...

 

[EddiePetty]

Re: why are marine t-stats temps so low?

.......
What kind of water or coolant are you running through your automobiles exhaust system?

EXCELLENT !!!! Just down right EXCELLENT (in addition to the salt thing)

 

[rodbolt]

Re: why are marine t-stats temps so low?

salts and various other minerals tend to scale at temps above about 150*,however with modern EFI,and a lot of modern carbed stuff,the Tstat is now 160 and typically operating temps are between 170 and 180*.
the hotter the operating temp the more efficeint the engine is.
up to the destruction point.
thats why cars years ago ran 160,then 170 and now anywhere from 195 to 205.
if the engine box was designed correctly and never modified the air vents will carry away engine box heat.
I am fighting a 2010 chris craft with twin 300 catalytic converter 5.7L volvos.
outside air temp at 85* the IAT reads intake air at 125* after a 2 mile run.
means the engine compartment venting needs attention.

 

[HT32BSX115]

Re: why are marine t-stats temps so low?

What temp do closed systems typically run?

Mine came with a 160* stat.

It typically runs at around 170-180 (on the gage)

LouC is right. There's little or no airflow around a marine engine and my engine compartment does get warmer than it used to since it is completely enclosed.

Since most pleasure runabout boats don't run continuous forward speeds, (pulling ski-ers, start, stop, idle, slow speed, etc) they don't get a lot of natural ventilation without electric blowers....
I run my bilge blowers pretty much all the time.


Not because I have had a problem......(vapor lock, etc) but because I want to PREVENT things like vapor lock or other heat related problems......

I'm not worried about salt build up because I don't operate in salt. And I have a FULL closed system. The block, heads, exhaust manifolds and 3" riser-extensions are in the closed circuit.

Only the elbows get raw water directly from the heat exchanger before it goes into the exhaust and overboard.


Regards,


Rick

 

[Aviator5]

Re: why are marine t-stats temps so low?

Actually, raw water cooling system is pressurized too.
That is one of the functions of the thermostat.

 

[SRC8778]

Re: why are marine t-stats temps so low?

A better question is why are automobile thermostats set so high and the answer is to lower emissions. Surely some of you are old enough to remember when thermostats in vehicles were quite a bit lower than they are today. Lower temps make more power and can extend engine life. Higher temps lose power but lower emissions.

 

[Robj]

Re: why are marine t-stats temps so low?

My closed cooling 4 banger Volvo runs at about 200 degrees F, maybe even 210, with a 5 lb cap. Nothing wrong with my cooling system, they are designed to run that hot.


Have a great day

Rob.

 

[Simoniz]

Re: why are marine t-stats temps so low?

My wifes Polo runs at around 90 deg C = 194F. Also it warms up in an amazingly short space of time, less than 1 mile of driving.

The only way it can do that is if the block and head is light weight and the cooling passages are designed to carry minimal amounts of water - all in the search of low emissions.

Ive got another car, an old Peugeot diesel which takes ages to warm up (T stat is good) and runs at 70 C = 158F (cooler than my boat, 175F)

I think the diesel takes a long time to warm as its more thermally efficient than a petrol engine bearing in mind too that the air into a diesel isn't throttled.