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thermostat temp

There are several misnomers around the term FWC -vs- Raw Water cooled -vs- Closed Systems.
Aslo a few misnomers around stat temps re; closed cooling -vs- open systems -vs- river/lake -vs- ocean boats.
If FWC to you means Closed Cooling system..... then we're on the same page, although I wish the entire industry would call this Closed Cooling.
(there's nothing fresh about Ethylene Glycol. Ya can't drink it, ya can't brush your teeth with it, ya can't brew coffee with it! )

The 140-ish temp stats are intended for raw water cooled engines that run in salt water.
Salt crystallizes at/near 143*, I believe.

For engines equipped with Closed Cooling systems, you'll want the 160* stat and hope that it produces at/near 170*/180* coolant temps.
Same can apply for raw water cooled engines running in clean lake/river water.


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Last edited:
michigander said:
I always wondered why the colder t-stat in a raw water cooled motor, now I know. Thanks!
Click to expand...
Yep, and there are quite few seasoned Marine mechanics that still don't understand the difference.
Some of these guys will throw the cooler stat in a river/lake boat RWC engine without giving it any thought.
 
Rick:

Turns out that the cyrstalization (precipitation) you refers to is distributed over a pretty wide temperature band. Yes, it does increase with higher temps. Turns out the 142 deg F and 160 deg F represent 'optimal' conditions for nominal operation (while maintaining performance under the warranty window) in 'salt' water for raw and closed systems.

Both The OEM Engineering depts and the HX Engineer will tell you that an unqualified "fresh water" application can still cause issues if the T-stat is changed....just means make sure you know what you are doing and why before the start.
 
.."I always wondered why the colder t-stat in a raw water cooled motor, now I know. Thanks!"

THis is a commonly held and WRONG idea! THe only reason for lower RWC t-stats is to prevent water--that is not pressurized in RWCooled motors--from boiling in the heads. Steam is a lousy coolant. FWCooled motors run higher pressure, with their pressure caps, which causes water to boil at a higher temperature (allowing hotter t-stats).

Jeff
 
It'n not WRONG, it is INCOMPLETE...talk to the tech department at any of the OEM HX/MARINERIZER shops. Every one will tell you there are MANY factors that are considered in selecting a thermostat. the final values are a compromise.
 
Can anybody answer this? Considering the carb's job is to try and deliver the proper air to fuel ratio 14.7:1, and given that several factors affect it's ability to deliver that ratio; one very important one being temperature, if one were to switch the cooling system from a hotter running FWC system to a cooler RWC system or vise versa on the same engine, would a carb mod/adjustment need to be made now that the engine would be running 10s of degrees cooler or hotter?
 
Nope, probably even it it has been custom tuned. The exhaust crossover runs under the carb.

The factory jets the carb the same independent of the cooling system configuration at the time of ordering. Doesn't make it optimal but sure makes the logistics simple.
 
Never heard of an adjustment needing to be made but why the spec on some stats indicating they are for apps with a particular carb? What would the carb have to do with it other than temp? can't be mounting, that's dependent on the intake.
 
Technically Jeff is correct regarding just plain ole lake/river water and the boiling point. However, ideally we're not having over-temp issues and this raw water "coolant" is exchanging itself adequately and with plenty of flow.
But I certainly understand the principle.

My thoughts are that Ethylene Glycol and distilled H2O will always be a more efficient way to cool our engines.

BTW, Mercury Marine is where I got the 145* ish Crystallization info. Merc apparently wants their salt water engines using this stat temp.

Woodie, I too have always understood that we want the coolest possible f/a that we can shove down her throat......., but at the same time these engines seem to do better at/near the 160*/170* mark.
I suppose that if we to squeak this down to the finest specs, carburetor recalibration might help for the different temperatures. But then again there's the exhaust cross-over on the pre-vortec sbc engines and any other engine with the cross-over.
 
The temp/carb relationship was an interesting thought that had me pondering for a while when I was going through this thread. I guess the ability to make adjustments to fuel delivery on the fly based on external and internal conditions is what gives EFI an advantage.

Sorry for hijacking your thread a bit here 87chriscraft. Just had to throw that thought out there while we were on the topic of temps
 
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