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Old 10-22-2018, 12:35 AM
Bartnich Bartnich is offline
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Boat: 1995 Prostar 205 5.7L
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New Boat- WOT speed, RPM and water temp questions

Hi all,

I just bought my first Mastercraft (YEA!!), a 1995 Prostar 205 with the standard 5.7 engine. It's in quite good condition but I have one slight concern about it. When we took it out for the water test at a lake at 2000 feet, WOT speed was 39mph (GPS) and the tach was showing about 3900. So today I took it out to our closest lake (6100 ft) and the numbers were pretty much exactly the same.

It seems like they should have been higher at the 2000ft level due to the power loss at altitude. In both cases the temp gauge never got above 130. I haven't had a chance to check if the thermostat is toast, or the sender isn't working or the gauge is dead. I'll check that tomorrow if I have time. Both lakes also had cold water, probably mid 50's.

I'm pretty sure it has the original OJ 13x13 prop. It starts up immediately when cold, never hesitates or studders when accelerating and is very smooth and surprisingly quiet. It also starts right back up when "hot".

So when browsing the owners manual the other night I see where it appears that the EFI will not go past a certain RPM until the engine temp gets above a certain point. At 140 degrees you supposedly have full RPM range. Could that potentially be the issue? There seemed to be minimal additional rpm over the final 1/3 of the throttle throw.

I'm going to do a compression test over the next day or two just for giggles and to get a baseline for the boat going forward but given the symptoms, I doubt its a compression issue (at least I really hope it isn't).

Any thoughts or ideas???
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  #2  
Old 10-22-2018, 02:28 AM
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Rico-X Rico-X is offline
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Congrats Bartnich on your new acquisition! Woohoo! Someone will correct me if I am wrong, but you should be getting about 160 deg water temp. Your WOT RPM and speed isn't too far off I'd say. This may be comparing apples and oranges here, but with my older prostar 351 I am getting 39 MPH @ 3900 RPM with an Acme 543. However, I have FAE also, which I believe slows the thing down 3 or 4 MPH and a few hundred RPMs. So I am not sure if the lower temp will slow you down a bit, what with a 350 w/EFI, since I have no experience with EFI marine engines (yet)
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Old 10-22-2018, 10:06 AM
SkiDad SkiDad is offline
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It might be the limitation of that prop on your boat. if compression checks out I would consider trying the ACME 541
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Old 10-22-2018, 11:03 AM
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etduc etduc is offline
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If your wide open throttle (WTO) rpm, is 3900 rpm. Then, you have a problem. ([email protected] is about right. But you should have about 600 rpm left, to WTO)

According to the owner's manual, max rpm is 4500! My 94 205 would easily do 43mph, at about 590 elev. (Acme 451 prop)

Not a big difference in performance, with stock set-up, at 2000ft. 6000ft, is a different matter.
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Formally, 1994 RED Mastercraft 205, Chevy 5.7 TBI.
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  #5  
Old 10-23-2018, 12:18 AM
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mikeg205 mikeg205 is offline
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1995 takes takes 143 stat.. above that on hot days heat soak can cause hard hit starts

Sent from my SM-G955U using Tapatalk
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...A bad day water skiing still beats a good day at work...1995 Pro Star 205....
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Old 10-23-2018, 11:59 AM
Bartnich Bartnich is offline
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Quote:
Originally Posted by mikeg205 View Post
1995 takes takes 143 stat.. above that on hot days heat soak can cause hard hit starts

Sent from my SM-G955U using Tapatalk
But shouldn't the temp get above 130 anyway? Even after 30 minutes of continuous running, it never climbed above that. Not sure that is the root of the speed/rpm problem, but I'm curious as to whats going on with the temp issue. I'm going to compression test this morning and then pull the thermostat to see what it looks like and to test if it still works......
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Old 10-23-2018, 02:37 PM
Bartnich Bartnich is offline
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Boat: 1995 Prostar 205 5.7L
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So here is what I found. Compression test

143
145
150
145
140
150
137

Nothing major there, right? I took out the thermostat and it was clearly the original one as the bolts were still painted on and the stat itself was pretty rusty. Not sure how these are supposed to work as I put it in hot water and nothing seemed to move....

Can someone please explain to me how to check if the water temp sensor is working? I pulled it, put it in very hot water, turned the key and got nothing at the gauge. Maybe I'm doing it wrong. Also, what are those two sensors at the front of the engine? The one right behind the thermostat and the bigger one back and to the left of it (looking to the back of the boat).

Thanks
Bart
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  #8  
Old 10-23-2018, 03:23 PM
88 PS190 88 PS190 is offline
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Sounds like a bad stat.

Thermostats have a spring that expands as it warms and contracts as it cools, they tend to fail stuck open. When cold they close down which causes the water to bypass the block and exit to the exhaust manifolds, but if they fail they'll just stay fully open which means all that cold water goes through your block and heads cooling the engine way down.

As mike mentioned the 143 stat is a bit cooler, it basically opens at 143. I prefer the slightly hotter ones but I do ensure that I idle after we ski before I turn off the engine to let it dump heat and avoid heat soak. I feel it improves the fuel burn/less smokey pulls on restart.
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Old 10-23-2018, 04:19 PM
Bartnich Bartnich is offline
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Boat: 1995 Prostar 205 5.7L
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Quote:
Originally Posted by 88 PS190 View Post
Sounds like a bad stat.

Thermostats have a spring that expands as it warms and contracts as it cools, they tend to fail stuck open. When cold they close down which causes the water to bypass the block and exit to the exhaust manifolds, but if they fail they'll just stay fully open which means all that cold water goes through your block and heads cooling the engine way down.

As mike mentioned the 143 stat is a bit cooler, it basically opens at 143. I prefer the slightly hotter ones but I do ensure that I idle after we ski before I turn off the engine to let it dump heat and avoid heat soak. I feel it improves the fuel burn/less smokey pulls on restart.
Thanks! Any idea how to easily check the temp sensor?
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Old 10-23-2018, 05:14 PM
Bartnich Bartnich is offline
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Boat: 1995 Prostar 205 5.7L
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I think I figured out the temp sensor. It probably works and the thermostat was just stuck open. Ordering a new one, but still don't think I have figured out why the RPM and speed are so low at WOT....
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