2005 Mercruiser 5.0 MPI overheating at idle only

[Ming15237]

Engine # 0w339318 Drive # 0w584139 Boat never operated in salt, total hours on engine are around 250, hour meter states 350 hrs but shop who replaced drive left key on for over a week and a half an killed both batteries and caused meter to count non running hours. History on boat, complete new SEI drive installed by dealer at end of last season due to upper gear failure. Took boat out one time this season all was well, ran for maybe 1 hour total. Last time out ran for 30 minutes parked for a couple hours went to restart and within 1 min heat alarm sounded and shut engine down and was towed back. Tried to run it on muffs and no flow to engine. Removed drive replaced a faulty impeller which had failed where the collar was bounded to the rubber impeller. (Note that impeller looked fine, just collar was no longer bounded to impeller. I also replaced thermostat with a 140 stat from West Marine as they did not have a 160 in stock. I inspected the hose near the gimbel housing, and found no kinks or damage.) Now, put new impeller I have flow to engine I back flushed hoses from T stat housing down to power steering oil cooler, and from oil cooler to outdrive, there was no debris in any of the hoses. I flushed drive while it was off and flow was good. Put boat on muffs and engine temp slowly starts to heat up at idle. I figured I am going to put in the water and test in real world environment. At idle engine slowly (within 5 min of idle speed 500 to 900 rpm no wake speed) begins to heat up 200 + degrees and alarm will sound , as soon as rpm's reach 1000 temp goes right back down to 150-160 as per the gauge. I ran boat from 1k rpm to 4800 rpm for 1hr + and temps never went higher than 165 degrees. (I did NOT IR temp test the T stat housing, but to the touch it is hot. Is it possible that the water pump (I believe the term is circulation pump) mounted to the front of the engine is not circulating enough volume of water to help coal the engine at idle? I searched multiple threads including Nauticool's lengthy post with a similar issue, but his issue seemed to revolve around an mismatched drive/engine combo. I am an ASE certified automotive tech so I have a sound understanding of engines, but this one is really stumping me! Any help you guys could offer would be greatly appreciated. I am getting ready to jump ship over this and buy a new Yamaha 242 Limited S and say "sayonara" to Mercruiser entirely, but my wallet really wants me to stay put

 

[alldodge]

Do you have the 7, 3 or single point drain system?

 

[Ming15237]

Do you have the 7, 3 or single point drain system?

I believe it is the 3 point system. I have a vertical blue knob to drain the system on the port side on the engine, a blue plastic drain plug on the t stat housing and one blue plastic drain plug on the lower port side on the engine.

 

[alldodge]

Here is your motor link for parts
http://www.mercruiserparts.com/5-0l-mpi-alpha-bravo-0w310000-thru-0w6

The single and 3 point systems are becoming more and more problems every year. In the pick below you there is a check valve which can cause a restriction, also the green arrows show the flow of incoming water. The issue is if the water flow to the manifolds is less restrictive then the motor, the exhaust gets more cooling. This is just for info right now.

Since you mentioned

faulty impeller which had failed where the collar was bounded to the rubber impeller

I'm wondering if there is also an issue with the impeller housing. I would start with adding a piece of clear hose before or after the power steering cooler (item 17. This way we can see if your drawing any air when its running. Installing it up front by the lower port side would be better but is harder to get at, depending on your boat design.

 

[Ming15237]

Any idea where I can obtain the clear hose.

 

[alldodge]

Any idea where I can obtain the clear hose.

About any hardware store, Lowes, Home Depot, ACE ... It should be 1 1/4 inch. Suggest measuring the hose to verify just incase its a different size.

Now if you do this and see no issue, were going to try other places like the exhaust feed hoses which are about 3/4

 

[Ming15237]

About any hardware store, Lowes, Home Depot, ACE ... It should be 1 1/4 inch. Suggest measuring the hose to verify just incase its a different size.

Now if you do this and see no issue, were going to try other places like the exhaust feed hoses which are about 3/4

Great, I'll get 3 feet of each.

 

[Ming15237]

I just returned from Lowes and purchased 4 feet of each size hose. Can this test be performed on the muffs, or do I need to drop the boat into the water? I also ordered one of those check valves as a precaution (#2 in the diagram).

 

[alldodge]

Drop in is better, due to less chance of air being introduced. Otherwise you need to make some assumptions.

 

[Fun Times]

Complete new SEI drive installed by dealer at end of last season due to upper gear failure. Took boat out one time this season all was well, ran for maybe 1 hour total.... Replaced a faulty impeller which had failed where the collar was bounded to the rubber impeller. (Note that impeller looked fine, just collar was no longer bounded to impeller.

There was a run of bad impellers where the collar became disengaged from the rubber. SEI uses sierra marine water pump impellers from new I've heard. Hopefully you let them know you had an issue.

I also replaced thermostat with a 140 stat from West Marine as they did not have a 160 in stock

When you reinstalled the new thermostat, what seal did you install into the housing first before setting in the thermostat? A rubber O-ring or cork gasket? What part number kit? did you buy?

Put boat on muffs and engine temp slowly starts to heat up at idle. I figured I am going to put in the water and test in real world environment. At idle engine slowly (within 5 min of idle speed 500 to 900 rpm no wake speed) begins to heat up 200 + degrees and alarm will sound , as soon as rpm's reach 1000 temp goes right back down to 150-160 as per the gauge.l

Since you know it's getting hot both at home and in the water, you should be able to do most of your testing at home for now until you believe you solved the issue....Then if possible, retest at the lake before going out for a big outing with family and friends to avoid possible disappointment.

Since it got hot, your exhaust water shutters may have fallen down inside the exhaust Y pipe and possibly clogging up the exhaust flow causing heat issues. Item number 7,http://www.mercruiserparts.com/bam/s...1851/11681/340

On the back of the circulating pump there is a stainless steel plate you could remove and inspect it (the pump impeller) for damage, debris, etc. if desired. While it's sort of on the rarer side for them stop circulating water through the engine for the marine side, they do eventually give out. On marine engines, they're more know to leak out the weep hole vs stop circulating. http://www.mercruiserparts.com/bam/subassembly/31851/11681/140

Being an auto tech, you can't just give up this easily...Overall, It's just a GM engine. Using the clear hose should help tell you something...Good luck.:encouragement:

 

[Ming15237]

Well i have a little egg on my face, what I thought was the Power steering cooler was actually the fuel cooler located underneath the port side of the engine it goes between hoses # 3 and 8. It would appear that the power steering cooler is located on the rear/transom side of the engine, correct?

 

[alldodge]

The cool fuel module is between 3 and 8, the power steering cooler (if one is installed) is between hose 1 and 7

See post 4 above

 

[Ming15237]

There was a run of bad impellers where the collar became disengaged from the rubber. SEI uses sierra marine water pump impellers from new I've heard. Hopefully you let them know you had an issue.

When you reinstalled the new thermostat, what seal did you install into the housing first before setting in the thermostat? A rubber O-ring or cork gasket? What part number kit? did you buy?

Too be honest I didn't see a seal inside the thermostat housing, and simply placed the stat in the housing,followed by the plastic diverter piece, followed by the housing gasket.

Since you know it's getting hot both at home and in the water, you should be able to do most of your testing at home for now until you believe you solved the issue....Then if possible, retest at the lake before going out for a big outing with family and friends to avoid possible disappointment.

Since it got hot, your exhaust water shutters may have fallen down inside the exhaust Y pipe and possibly clogging up the exhaust flow causing heat issues. Item number 7,http://www.mercruiserparts.com/bam/s...1851/11681/340

It was not hot for more than one minute max, is this enough to cause this to happen?


On the back of the circulating pump there is a stainless steel plate you could remove and inspect it (the pump impeller) for damage, debris, etc. if desired. While it's sort of on the rarer side for them stop circulating water through the engine for the marine side, they do eventually give out. On marine engines, they're more know to leak out the weep hole vs stop circulating. http://www.mercruiserparts.com/bam/s...1851/11681/140

Being an auto tech, you can't just give up this easily...Overall, It's just a GM engine. Using the clear hose should help tell you something...Good luck.:encouragement:

I really appreciate all of your help. The boating community on this site is second to none with regards to helping other members and the vast knowledge you guys possess. I owe you all a big THANK YOU for your continued help with this problem!

 

[Ming15237]

Here is your motor link for parts
http://www.mercruiserparts.com/5-0l-mpi-alpha-bravo-0w310000-thru-0w6

The single and 3 point systems are becoming more and more problems every year. In the pick below you there is a check valve which can cause a restriction, also the green arrows show the flow of incoming water. The issue is if the water flow to the manifolds is less restrictive then the motor, the exhaust gets more cooling. This is just for info right now.

Since you mentioned


I'm wondering if there is also an issue with the impeller housing. I would start with adding a piece of clear hose before or after the power steering cooler (item 17. This way we can see if your drawing any air when its running. Installing it up front by the lower port side would be better but is harder to get at, depending on your boat design.

Getting to the back of my motor due to its configuration is nearly impossible. Is there an alternative place to install the hose on the front side of the engine?

 

[alldodge]

Can you do it where the orange arrow is

 

[Ming15237]

Yes I can get to the area where the orange arrow is located.

 

[Ming15237]

I would really like to put the clear hose in more than one place as to avoid the 1 hour round trip to the water each time. I am going to place the 1 1/4 hose near the fuel cooler, and 3/4 hose between where and where?

 

[alldodge]

From the thermostat housing to the bottom of the exhaust manifolds.

Another spot to check is between 11 and 12, you want to see how much water/air is making it to the circulating pump

The drain on the low port side maybe letting air in

 

[Ming15237]

So I bypassed the ps cooler, and the check valve all the way to the water distribution housing on the muffs, I had zero flow! I then added water to the water distribution housing and had plenty of flow to exhaust manifolds, back flushed each manifold, and each flowed extremly well! It is clear now my issue lies in the outdrives, which is the new addition to my engine, as I never ever had a cooling issue before this drive was installed. I will tear it apart tomorrow, and report back. Thanks again for everyone's help, I cand say thank you enough!

 

[Ming15237]

Ok so I removed the complete drive again changed the impeller again, replaced the plastic tube and tube connection and all o rings. flushed drive from tom to bottom NO restrictions, flushed engine from gimbel housing through engine water POURS from exhaust ports on gimble housing plug exhaust ports and water pours from other area on the gimble housing area. So I am certain there are no restrictions. Last question before I drop it into the water today to test. Do I need to bleed the cooling system before it is put into the water? Or will the engine completely fill itself with the impeller water supply alone? On most modern auto engines we have to vacuum fill the cooling system to avoid air pockets.