88' Sea Ray 5.7L Merc

[Erawk]

Hello, I have a 21' runabout i/o and I am wondering about which thermostat I should use. When I search I find a 142 and a 160 degree thermo listed as compatible with my boat's engine. I assume that you can run either one and people have preferences between the two for certain reasons. Would someone please shed some light on this for me? Oh, and if I should post this somewhere else to get more responses, please direct me there. I'm new here. Thank you in advance

 

[Matt89GT]

Hello, I have a 21' runabout i/o and I am wondering about which thermostat I should use. When I search I find a 142 and a 160 degree thermo listed as compatible with my boat's engine. I assume that you can run either one and people have preferences between the two for certain reasons. Would someone please shed some light on this for me? Oh, and if I should post this somewhere else to get more responses, please direct me there. I'm new here. Thank you in advance

I would go with the 142º T-stat that you found, 1st a cooler engine will produce more power, and 2nd you dont wanna overheat the engine and start melting all the rubber hoses and exhaust boots, and also start blowing head gaskets, ALWAYS keep an eye on your guages, just sayin

 

[Nehalennia]

Well it depends. Do you have Fresh water cooling (a closed cooling system)?
If so, the 160 is the way to go as warmer engine run more efficiently.
If not and you are raw water cooled, you'll want the lower temp. The main reason is that If you are raw cooled and in salt water (which I doubt if you're in Vegas) the saltwater crystalizes at the higher temps so the idea is the keep it cooler.

In Vegas I would still go with the warmer thermometer since you're in fresh water regardless if you're FWC or not.

 

[JVM225]

160 for fresh water cooled.
140 for raw water cooled.

 

[Iprof]

Interesting we have people that have told you to go with both. While I won't tell you which to go with I can tell you that my 1988 raw water cooled 5.7's came with the 142. Because of an over heating problem in one motor that turned out to be a flapper that fell off I had removed the starboard thermostat. We ran the boat for the first time this past weekend in 65 degree water and both motors ran at 125 degrees. I will be putting the 140 back in next week.

Ken

 

[1956olds]

from manual #9 all 5.7L mercs use 143f degree thermostat .i think all 5.7 1987 to 1992 were the same.My twins run 143 and while cruising are in the 145-155 range ,they cool to 135 when idoling ,the starboard is a bit cooler i believe because it has the water heater manifold and hoses on it.hope this helps.there is no mention of different t stats for closed cooling in the manual which was from 1987.

 

[stevea661]

160 for fresh water cooled.
140 for raw water cooled.

What he said

 

[Erawk]

Thank you. I think The 140 is the way to go. I use the boat pretty much exclusively at Lake Mead (freshwater)and it is an open cooling system.

 

[Erawk]

Thank you

 

[Erawk]

Thanks for the quick responses, sorry I took a bit to get back.

The problem I am having with the boat is that it runs cool at speed, but will overheat if idling or running at no-wake speed for too long.

I'm planning to replace the thermostat and check the floats and springs in the Thermostat housing.

I'm thinking that we'll need to replace the impeller in the outdrive as well just because I don't know when it was done last.

Does anyone know what would cause the boat to run hot at idle but not at faster traveling speeds?

 

[Spookeay]

I'm thinking that we'll need to replace the impeller in the outdrive as well just because I don't know when it was done last.

Does anyone know what would cause the boat to run hot at idle but not at faster traveling speeds?

Your impeller is bad...... High RPM's produce more volume from the raw water pickup. You impeller is going bad. it cant produce volume at low rpm........

Easy fix.... Most often a thermostat will show it's self at high RPM as will a engine circulatory pump. "The car looking water pump."

 

[Erawk]

Thank you, Spookeay.

I'm searching google to find prices for the proper kit, but there are many different options. How can I tell which kit is correct for my boat?

I need to have an idea of what is a fair price because some of the shops around here like to gouge noobs like me. One guy tried to sell us a used return hose for $50 and it wasn't even the correct hose.

The serial number on the outboard is 0B880383. Thank you for the help.

 

[Spookeay]

I think this is what you need.
http://www.go2marine.com/product.do?no=155974F

 

[Erawk]

Thanks again, Spookeay. I went to another shop here in town and they sold me a Mercury Water Pump Upper Repair Kit 46-96148T 8 $56 w/ tax.

The box says it fits all Mercruiser I/R/MR/Alpha One outdrives (s/n 2495186-0D469858)

My serial is 0B880383

Do you know if it is necessary to pull the entire drive to replace the impeller? Or should I only need to pull the lower half?

Thank you =)

 

[Spookeay]

Hold on I thought you had a Bravo? But that is the right kit for the Alpha-1.

No you do not need to pull the entire drive,,,,
How ever, if you have never done this before I advise you to pull it.

Make sure your shifter is in forward gear.. this is important...... See Photo 1 and 2.

The reason you want it in forward is becasue of the way the shift mechanism works. When in forward The part in photo one mates in photo 2... this allows you to pull it off. If you did not have it in gear this tung and slot would be 45 DEG to the left not allowing you to get it to slide apart.
Photo 1 and 2



Then pull the 6 bolts from your upper and lower unit "Photo 3"
also, take loose the trim cylinders , Rock it till it comes off.


In photo 4 It shows the Kit you should have.

Photo 5 shots the housing removed. Install the new housing as you saw it come apart. Just grease or oil the impeller before you put it in....

When you attach the upper to the lower unit,, Turn the shift rod to the center/neutral. Rotate it left and right and you will feel the 3 points. Get it in center and mate the 2 making sure the tong in the upper unit is center and inline. Mate the 2 and reinstall. Make sure the upper unit gaskets are still good. bolt it up, put her on the muffs and see how it does.

 

[Iprof]

Thanks again, Spookeay. I went to another shop here in town and they sold me a Mercury Water Pump Upper Repair Kit 46-96148T 8 $56 w/ tax.

The box says it fits all Mercruiser I/R/MR/Alpha One outdrives (s/n 2495186-0D469858)

My serial is 0B880383

Do you know if it is necessary to pull the entire drive to replace the impeller? Or should I only need to pull the lower half?

Thank you =)

You only need to take the lower half off on an Alpha. Your over heating sounds just like my old problem and it was the flapper causing the problem.

Ken

 

[Matt89GT]

The drive should be pulled at least once a year to grease U joints and for inspection as well as checking alignment.

 

[andyr]

Thanks for the quick responses, sorry I took a bit to get back.

The problem I am having with the boat is that it runs cool at speed, but will overheat if idling or running at no-wake speed for too long.

I'm planning to replace the thermostat and check the floats and springs in the Thermostat housing.

My money is on the springs. There are other posts on this. Look at the ball seats too to see if water is leaking past them. Replace or temporary fix, stretch the springs.

 

[SCORPIO]

FYI for anyone with Alpha drives, I had a low rpm heating issue last year. Turned out to be the hose from the drive to the transom had a kink in it and was restricting flow at low rpm. At higher rpm the pump could force water thru the kink and it cooled but a low speed, it would heat. I replaced the hose with 3/4" marine wet exhaust hose (reincorced hose) and the problem is solved. Somebody on here mentioned that the stock Merc hose was about a half linch too long and caused the kink, which I believe to be true, mine looked like they were too long so I shortened up my new hose about .5 inch.

 

[Erawk]

it was the flapper causing the problem.

Ken

Thanks Iprof. What exactly do you mean when you say the flapper?