Operating Temperature?....Closed Cooling vs Raw Water Cooled

[davefin]

Can anyone tell me what thermostat should be used in a closed cooling Mercruiser 5.7 MPI? I repowered recently and converted to a closed system in both engines. The gauges are showing a running temperature of about 170 degrees for both engines. The original requirement was a 165 degree thermostat. I have heard discussions that the closed systems need a "hotter" thermostat like a 180 degree. True?

Also my 2001 310DA has 220 degree gauges. Should I change these to 240 degree along with engine sensors for a 240 degree range? OR will a 220 degree sensor work in the engine so that the gauges can be retained.

I hope I am making sense here. This has issue has been annoying my for weeks.

 

[fwebster]

Generally, later fuel injected engines run cleaner and burn fuel more thoroughly with warmer operating temps. I think which thermostat is a question for Mercruiser and you can probably find that out by looking up the current replacement part for your engines.

As to the temp gauges, keep what you have. You don't need to know any temperature over 220 degrees because you should have your engine shut down and be looking for the cause of overheating when they exceed 212 degrees anyway.

 

[Lazy Daze]

If you're running at a constant 170* (or even a needle width or two over), you're good to go. I wouldn't change anything. Being a 2001, you probably have an EFI system, which is a little simpler than an MPI, as well. EFI has 2 injectors sitting on top of the throttle body, by the way.

But, I'm basing what I said on what "feels" right. If you can't quickly find what you're looking for online, give a quick call to your local parts department and ask them.

As far as the closed cooling thing goes, I would think that IF ANYTHING, it would require a lower stat - although I don't think it does. But, the rationale is that you really can't beat the cooling power of an open system -- constantly sucking in a fresh supply of 70* water, rather than using that 70* water to pull the heat off the hot antifreeze.

And, I agree with Frank - no need to change your gauge (or sensors), regardless of what you do with stats. Temperature is temperature.

 

[scoflaw]

Are you aware that a closed cooled motor has a different ECM than an open cooled one?

 

[hottoddie]

The general rule in a raw water cooled motor running in salt water is you should run the 140-145* thermostat. With closed cooling the thermostat is usually the 165*. The reason for the lower temp in the raw water cooled motor is to prevent the salt from crystallizing in the water passages, manifolds and risers which it start to do at about 180*. With the closed cooling the salt water only comes in contact at the riser and sometimes the manifolds as well so the engine block is protected. Never seen a 180* or higher thermostat run in a marine engine. If the raw water cooled motor is run in fresh water you may be able to run the 165* thermostat but I would ask Mercruiser first as the ECM may need changing.

 

[Fun Times]

This would depend on what engine model, exhaust system (dry joint?), type of ECM/PCM, (OEM) closed cooled system you have.

With mercruiser, anything after 1998 the year really does not mean a whole lot, the only way to know for sure is by using the serial number.

We would need your engine serial number to help with this type of question.

 

[Vince_nj1]

FYI. My closed cooled engines engines run at a constant 163 degrees.

 

[spfortjohn]

The 6.2's in our 2002 Formula runs at 170 raw water cooled. My 2009 350 Mag runs at 155 in my sea ray.

 

[davefin]

Thanks all for the quick replys. My knowledge base grows daily via Clubsearay's Forum.

 

[villain style]

Mine run steady at 170-171 degrees.... I use the 160 T-Stats.

 

[edsmax]

Mine run steady at 170-171 degrees.... I use the 160 T-Stats.

Same here - according to the gauge I am running 170-175 and I have a 160 degree therm. This is on a raw water cooled carbed motor.

Ed

 

[Richt]

I have twin 8.1s and have had some overheating issues on my port engine. It seems to run at about 175 all the time while starboard runs at about 160 but at close to WOT it will overheat. I have had mechanic go through all the issues including putting on a new water pump, cleaning the heat exchangers, new thermostat (160 degree), even a haul out to make sure raw water intake was clear. Since heat exchangers were pretty crappy but fairly new and I do all boating in salt water I am thinking of fresh water flush kits for both engines. Anyone use those?