How hot is too hot

[LuckyPenny]

Before I start, this has not happen to me, yet! <br />I have a 1984 Mercruiser I/O 5.7L RWC system. pushing an Alfa. The therostate is the standard 142F<br /><br />I know from reading other postings that poster have posed questions about cooling system since time began, but my question is how hot can a RWC get before an overheat condition exist? The reason for the question is I was talking to a buddy of mine and he tells me that his boat (same engine) rwc, usually get up to about 155-160 and planing speed. I rarely get over 130-135F I also know that a closed system get to 190F and folk indicate that the closer to this temp is better for the engine.<br />So why do RWC engines have such a low temp Therostate?

 

[tommays]

Re: How hot is too hot

you can have a 15 to 20 deg drift in the temp guage on on any give boat there not calbrated.<br /><br />Your stat could be stuck open ?<br /><br />tommays

 

[LuckyPenny]

Re: How hot is too hot

My stat is not stuck, it was replaced about 3 months ago as part of routine annual maintanence. I am still courious as to what the normal operating range should be.

 

[TilliamWe]

Re: How hot is too hot

So why do RWC engines have such a low temp Therostate?

To keep the engine compartment heat below 200 degrees is one reason. Supposedly the Coast Guard likes it that way.<br />The reason, well, that's just the way they have always been! I ain't saying it';s right, but that's how it is.<br />As far as how hot til you have an overheat, well, the answer is over 200 degrees might be time to get concerned. Just like you pointed out, closed cooled engines run at 190 all day. It takes a lot of heat to break a small block chevy, especially one of the 1984 vintage.

 

[Don S]

Re: How hot is too hot

The reason for the lower temp thermostat on raw water cooled engine is to prevent salt build up if the boat was used in salt and the increased corrosion. Since the manufacturers don't know if the boat will be used in salt water or not, they just install the lower temperature thermostat in all the engines.

 

[Reel Poor]

Re: How hot is too hot

Any thing over 160/165 in raw water cooled engine and you should suspect something needs servicing. <br /><br />Don S is correct. Lower temps reduce salt buildup and corrosion.

 

[Tail_Gunner]

Re: How hot is too hot

This is quite intresting, 160/165 dergree's in a 4 cylinder motor would normally mean very poor preformance,a normal operating range is 185-195 is generally where a engine is @ its peak effeincy (generalizing a bit)<br /><br /> Have marine engines been built specifically to run at these temps................. Or is there a issue of having very cold fresh water coming into a relativley warm block and its complication's?

 

[goinhungry]

Re: How hot is too hot

so could using a different thermostat if our RW cooled I/O's are totally freshwater boats increase performance while at the same time not negatively impacting the engine?

 

[LuckyPenny]

Re: How hot is too hot

Now I am confused. I higher temps would desolve more of the salt, actually flushing any that has built up out of the system. Additionally, whether salt or fresh water, at the end of a trip most of use usually are at lower speeds, approaching, docking and such before shutting down so the engine would be a bit cooler at shut down lowering the build up (i think)<br /><br />ok, thats my dime. I was just very courious about the cooling condition difference between two like boats running about the same, under nearly the same conditions

 

[mmainelli]

Re: How hot is too hot

RWC'd engines are supposed to run at 165 degrees or less, specifically to not boil salt out of salt water in the engine block. And although you might have 165 at the thermostat, there are numerous "hot spots" in the block casting (they don't flush as robustly as main cooling channels. Sea water will evaporate, leaving salt deposits (which, in turn , get the spot hotter). Also, a chloride solution (read salt water) becomes more corrosive as its temperature rises. The chloride radicals break away from the hydrogen and bond with the block's iron, creating ferric chloride (the black stuff). The creation of ferric chloride means less engine block iron. And while a FWC engine is more efficient internally at 180+ degrees (more complete combustion and less chamber carbon), the manifolds/risers and heat exchanger are being eaten up by 180+ salt water at a faster rate than a 165 degree RWC engine. Remember, only the block has FW going through it.You can't win.

 

[Haut Medoc]

Re: How hot is too hot

My manifolds are part of the closed system....JK