1996 Mercury 90hp running cool

[chrisczub]

Have a wierd one. I'm getting the boat back from the mechanic on thursday for a sea trial on saturday. 2 carbs were rebuilt and one was replaced, rebuilt fuel pump, new fuel filter. Got the engine running good on the muffs but he noticed it was running cool. Did a thermo reading and engine was about 100 degrees. He though the thermostat was bad so cheked it and it was good(replaced it cause he ripped the gasket). Poppet also looks good. Oil pump is pumping oil and is not putting out too much oil either. He says I should keep an eye on this. <br /><br />Any opinions or things to look for?

 

[Laddies]

Re: 1996 Mercury 90hp running cool

It's posiable that the muffs are pushing to much pressure and blowing the popit valve open

 

[chrisczub]

Re: 1996 Mercury 90hp running cool

Thanks Laddies! The mechanic said to keep an ey on it out in the water. Can this cause a problem? I'm new to boats. What is the purpose of the popit valve? What do you look for to see if this is the case?<br /><br />Thanks

 

[Laddies]

Re: 1996 Mercury 90hp running cool

At higher RPMs the water pressure increaces and the poppit opens to allow more water to cool the engine

 

[chrisczub]

Re: 1996 Mercury 90hp running cool

Thanks Laddies. I'm actually launching the boat today after I pick it up to see how it runs. IF she is running cool can that cause any problems??<br />I don't want to take her out an blow her up or anything!

 

[andy6374]

Re: 1996 Mercury 90hp running cool

running cool won't blow it up. Just may run poorly in cold conditions or take a while to warm up

 

[chrisczub]

Re: 1996 Mercury 90hp running cool

thanks andy.. weather is kinda threatening so don't know if I'll get out today. The mechanic said I have to keep an eye on it so I don't wear out the motor.

 

[chrisczub]

Re: 1996 Mercury 90hp running cool

Here's some background on what's been done then I'll get into what happened yesterday:<br /><br />1996 Mercury 90HP 3cyl<br /><br />Top and Bottom carb rebuilt<br />Middle Carb replace<br />Rebuilt fuel pump<br />New Thermostat and fuel filter<br />De-Carbed<br />New Plugs<br />Compression=125 all 3 cyl<br /><br />At idle she sounds a little rough to me. WHen I put her in yesterday in low forward gear she would be REALLY rough and sometimes died. However, if I advanced her to about 1/4 throttle she runs good and stays good through WOT which is only 4800RPM which I know is a low. If I back her down from WOT to even a little under 1/4 throttle she is fine. She is running very cool.<br /><br />3 questions:<br />1. Does this sound like a carb mixture issue?<br />2. Doe it sound like I need to replace the popit valve?<br />3. Is there anything else I should look for?<br /><br />In idle not in gear I'm bouncing between 600-800RPM.<br /><br />Thanks for any advice, I'll be trying it out again tomorrow!

 

[andy6374]

Re: 1996 Mercury 90hp running cool

don't need to replace the poppit unless you are overheating at idle (i.e. the poppit is stuck open), which you arent.<br /><br />My guess is that the throttle shutters in the carb throat are not fully closed at idle. Put the engine in neutral, take off the air silencer box and look at the carb throats. Make sure the throttle shutters are closed and adjust them if need be.

 

[chrisczub]

Re: 1996 Mercury 90hp running cool

Boat ran great! Found that the mechanic never re-conected the linkage to the bottom carb!LOL.. Had to adjust the mixture screw again to bring down RPM at WOT but she ran great until I brought her home then the tach went.. It's always something...<br /><br />Thanks for all the help!