5.7L Mercruiser - Temperature Issue

Hello All, I have a 1997 Sea Ray 215 Express cruiser with a 5.7L Mercruiser 2 Barrel Carb engine. I believe it is rated in the 220 to 230 range It is RWC, running in Fresh Water with water temp being around 70. It currently runs around 170 at 3600RPM occasionally a bit higher. Top Speed is about 32-33 MPH Can anyone tell me 2 things: What is the correct running temperature for this engine? I don't know if this is ideal or to hot. 2.) What should the top speed of this boat be? I believe it has a 3 Blade aluminum 19 pitch prop. Thanks for your time and assistance

running a 165 thermostat, its sounds normal. Alpha impellers are changed every 2 years no matter what. GEN II `s can go a bit longer.
With no slip from the prop , 3600 x 19 = 68,700 inches per minute

I replaced the thermostat today. 160 Degree as the Serial Number parts Diagram indicates. I now runs closer to 180 and the temperature fuluctuates greatly. I am conserned it may be overheating. Is this a symptom of a bad Impeller. The thermostat I took out was 140. That doesn't seem right from what I have been told. Should I put a 140 back in? It still ran at 170 prior to the change.

Temperature fluctuated the same before I change therms.

The engine year calls for a 160 F. T'stat. Was the T'stat hsg. full of rust? It may have water passages blocked. Per Bt Dr.

Alpha impellers are changed every 2 years no matter what.

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After you do that and it still runs above 170F. then check the water inlet coupler in the transom for blockage. Pull off the water hose inside the transom and check it...corrosion likes to grow there. Also check the OD water hose for a kink.

I got the Boat this season. I am unsure when the impeller was changed I will try that first. Sounds like the entire Transom would need to come of to check hose and inlet coupler? The thermostat housing was rusty but didn't appear to have blockages.

Sounds like the entire Transom would need to come of to check hose and inlet coupler?

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No...It is part of the bell hsg. Pull the hose off and look at the opening..it is a pipe.

Got the impeller fixed, Complete tune up. No more Temperature Fluctuactions. Put the Temp gun on it and it runs at about 145 - 150 Idle, 160 Running 3200 RPM. Temperature gauge reads aprox 20 - 25Degrees higher. Thanks for your help, sounds like the gauge isn't very accurate. Should I start with the Sending unit or just get a new gauge? The alarm sending unit was tested and works properly. Any help would be appreciated

Need to know what type of thermostat housing you have.

How many hoses are going to it? 4 or 6

Is the sending unit screwed into the housing itself? If it is it needs a solid ground path. That path is thru the housing itself thru the base gasket.

You said you replaced the thermostat, did you replace the base gasket on the thermostat housing? The proper base gasket should have 4 brass rivets that make the ground path to the intake manifold and the threads of the sending unit (Threads must be clean with no Teflon tape or anything on the threads) must be clean to make the ground continuity.

Answer these questions and confirm what I describe...........

If all of the above is as I said it should be then it is a weak connection in the wire harness may be the issue.........I have seen a multi pin connector under the dash where the connection is weak. The main wire harness comes from the motor and has a multi pin connector (installed by boat manufacturer) so look for that if nothing else seems to work. A weak connection will cause a over or under reading on the gauge.

Gauge can be the issue but typically is last in the chain....

WHat is typically done is to have a "shop" gauge to confirm what the boat gauge reads..........

It is a 4 hose housing. I replaced both the inner and Base gasket that had the rivits. I sanded everything to ensure good ground. I think the Gauge read high prior to thermostat change so I would assume that isn,t the issue. The Sendin units are screwed into the Thermostat housing Starboard is temp, port is Temperature warning buzzer. I have not taken out the sending unit but perhaps I need to clean the threads on it to ensure a good ground? Can you use anything to seal the connection? Will it leak if you don't? I will trace the wires to harness and guage.

Bills32 said:

Hello All,..... 2.) What should the top speed of this boat be? I believe it has a 3 Blade aluminum 19 pitch prop. Thanks for your time and assistance

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Since things seem to be moving along on your first question.... If you look at the top of the flame arrestor ( where the air cleaner would be on a car) there is usually some engine info. If not, find the engine S/N ( it starts with a 0W where 0 is the number zero) and go online and find the engine specs. The number(s) you are looking for is the RPM range... for example, my 2BBL Carbed 5.7 states 4200 to 4600 max RPMS. Your engine when wide open, with a half to full tank of fuel with your "normal" passenger load should rev up between these two numbers. If it is outside this range ( assuming engine is in good tune, bottom clean, prop ok...etc) you have the wrong prop for your "application".
If it revs up to within this range, whatever top speed you get is what you get. I should warn you that running an engine at MAX RPMS often or for prolonged periods of time greatly shortens engine life. "Normal" continuous operation RPMS should be limited to 80% of your actual maximum Wide OPEN RPMS is ( assuming its within the spec'd range).

I only run my engine up to max RPMs for no more that 5 seconds at a time a couple of times a year. Once after launch, once mid season, and once just before haul out. Running it up to full once in a while for 30 seconds or a min a couple of times a season "for fun", is OK... but continuous operation at Wide Open will drop engine life to the range of tens of hours, total.