5.0 MPI overheats on muffs and stalls on idle when warm

[aerobat]

hey gents ! i have purchased a 2010 searay 240 with the 5.0 MPI . the boat has less than 100 hours and i know its history since new ( its my ex parents boat ) it has sit for 2 years ( block drained ) . i went forward and replaced the oil, plugs ,impeller and tstat even when the boat never made any problems.i fired it up on muffs and it started up right away. BUT - when it gets warm it stalls at idle. when i give it throttle it keeps running ( IAC valve??? ) when cold it dles fine.

further it oveheats on muffs , that with a brand new impeller and tstat. it got to 185 fahrenheit and the alarm went off , here i stopped the engine immediately. on the smartcraft i read about 0.06 bar waterpressure ( 1 psi ) . oil is clean, no water in oil ,water comes out the drive, both risers get warm. any ideas what is going on ?

thanks so much for any help !

 

[alldodge]

hey gents ! i have purchased a 2010 searay 240 with the 5.0 MPI . the boat has less than 100 hours and i know its history since new ( its my ex parents boat ) it has sit for 2 years ( block drained ) . i went forward and replaced the oil, plugs ,impeller and tstat even when the boat never made any problems.i fired it up on muffs and it started up right away. BUT - when it gets warm it stalls at idle. when i give it throttle it keeps running ( IAC valve??? ) when cold it dles fine.

further it oveheats on muffs , that with a brand new impeller and tstat. it got to 185 fahrenheit and the alarm went off , here i stopped the engine immediately. on the smartcraft i read about 0.06 bar waterpressure ( 1 psi ) . oil is clean, no water in oil ,water comes out the drive, both risers get warm. any ideas what is going on ?

thanks so much for any help !

My guess would be to remove and clean the IAC for the idle and dying problem first.

Just to clarify, you installed a new 160 thermostat which was designed for the engine (mercruiser or equivalent)?
Was the old impeller complete when removed, or all the pieces present when you change it?
Check and back flush the intake hose, maybe something has gotten in and built a home.

If you have an IR thermometer use it to verify the engine is getting hot.

 

[aerobat]

Just to clarify, you installed a new 160 thermostat which was designed for the engine (mercruiser or equivalent)?
Was the old impeller complete when removed, or all the pieces present when you change it?

hey ! yes, the tstat is a sierra marine 160 for this engine. the "Old" impeller looked like brandnew, there was for sure no need to change it but i nevertheless did it to be on the safe side . so any debries can be excluded. the supply hose to the pump looked also good but i will flush it.

i will clean the iac valve and look if it helps, when it comes to the overheat i just phoned with a mechanic and he told me to be careful with muffs on a V8 , esoacielly with a bravo three, since it may be as simple as my gardenhose and the muffs are not able to deliver a sufficient amount of water. it sounds odd but somebody ever heard this ?

problem is that watertesting the boat is not easy since the channel my harbour sits is a little bit away - and towing and launching it only to see it indeed overheats might be not funny.

 

[alldodge]

hey ! yes, the tstat is a sierra marine 160 for this engine. the "Old" impeller looked like brandnew, there was for sure no need to change it but i nevertheless did it to be on the safe side . so any debries can be excluded. the supply hose to the pump looked also good but i will flush it.

i will clean the iac valve and look if it helps, when it comes to the overheat i just phoned with a mechanic and he told me to be careful with muffs on a V8 , esoacielly with a bravo three, since it may be as simple as my gardenhose and the muffs are not able to deliver a sufficient amount of water. it sounds odd but somebody ever heard this ?

problem is that watertesting the boat is not easy since the channel my harbour sits is a little bit away - and towing and launching it only to see it indeed overheats might be not funny.

If your running on muffs only, and it overheated then it could be insufficient water being supplied by city water, agree with Mechanic. If you had it in the water and it overheated then it is something else.

 

[aerobat]

thanks much all dodge ! i did not had it in the water by now, only muffs so i cannot say . well, the logical way will be a watertest, but i,m sceptic the low watersupply by muffs will be the answer. i can only say this boat had never overheating issues before but i also never tried to run it on muffs for a longer time.

i see you have a 7.4 and 8.2 - did you ever had this big blocks for a longer time on muffs ?

 

[Fun Times]

If you had to guess, do you have good water pressure at the house? What size garden hose do you have? Is it heavy duty so it can't be sucked closed by the impeller? Also what design muffs are you using?

Quicksilver marine engine flushing kit would be the best choice to use. http://www.ebay.com/itm/like/120670669475?lpid=82


Did the water pump housing have any deep grooves/scores either inside the housing or on the back cover? If so you will have priming issues allowing air/cavitation into the system making it run hot. Did you have the engine RPM at 1300 RPM like recommended by Mercruiser.


Also is the new impeller Mercruiser OEM? If so, can still check the date on the paper packaging bag it came in? Sometime around 2012 Merc had an issue with the impeller being made to short which in turn made the engine run hot I believe the issue was.

 

[ktbarrentine]

Mercruiser service bulletin 99-9 gives the recommendations for using muffs on alphas and bravos. Easiest to find on a google search or via the adults only sticky. (I would upload mine but I am still trying to figure out ow to make that work with the new forum....maybe someone else can upload.

 

[OllieC]

Is there a sufficient amount of water exiting out? When on the muffs, do you notice it taking in the water from the muffs - suction?

I had an issue where there wasn't enough suction coming from the pump. I ended up purchasing a wear plate for the water pump for about $50. As I was installing the wear plate, I noticed my water-input hose wasn't connected properly which probably let air in and not enough water. (read Fun Times thread as well in regards tot the water pump housing - i had the same issue with grooves)

I do not have a water pressure gauge (wish I did) but I read somewhere that when you throttle up it can get up to 20psi

 

[aerobat]

hey gents ! well, its a normal gardenhose like you would use to waterspray your lawn . the waterflow is like you would expect from your sillcock in the kitchen or garden. no more no less. the pump looks brandnew, no wear on it. muffs are like this :

http://www.ebay.de/itm/like/2312095...MENTS_IN_HLP:true&hlpht=true&ops=true&viphx=1

impeller is sierra marine, surely the correct one, you have to bend the vanes solidly that it fits tightly in.

the engine sucks in the muffs even at idle, water is leaving the transom. i do not have an IR gauge but surely believe the engine instruments are true - e.g the risers get hot to touch when it warms up to 175-180. i removed the main supply hose and can blow in by mouth without any resistance. i removed the waterhoses to the risers and also can blow in without any resistance. either the 5.0 MPI needs more than a regular gardenhose can deliver or i have no clue what is happening.

i also pulled the IAC valve to look at my stalling problem but the valve looks like out of the store. no need to clean anything there , the only chance is all odds are against me and the coil has failed and the valve does not move by ECM command. i moved thhe valve several times by hand, and contact sprayed the connection.

i will fire up tomorrow to see if the idling problem still exists, if not i will watertest the boat.

i,m a little frustrated because i,m talking here a less than 100 hours engine and honestly epected to have no issues at all.