2006 5.0L MPI Over heating - changed everything!

JJB4

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Jul 17, 2017
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I have a 2006 Mercruiser 5.0L MPI Alpha 1 Gen 2 sea water cooled that is overheating. I have changed everything I can think of, and flushed everything I can see.
Idles at 1500rpm around 170 degrees, but risers too hot to hold after a few minutes. After acceleration to 3000+rpm, temp climbs to 200+.

Changed out:
Impeller / pump housing on the lower drive
Both manifolds and risers
Circulating pump on the engine
Thermostat

Flushed:
Took off upper unit, flushed unit and port at the bell housing going into the boat. Lots of water exiting at transom bell housing.
Took off hose inside at transom, flushed forward. Lots of water exiting at transom bell housing.
Ran a snake out the transom fitting to the back out the boat

See merc diagram at this URL:
http://www.mercruiserparts.com/bam/subassembly/31751/12840/200
Flushed at points 7, 8, 22, 23, 12, 5, 6

Removed elbows, both flappers present and functioning.

Removed lower water distribution housing, was completely clean. (Nothing inside this round housing - should there be any sort of flow controls?)

Removed check-valve between power steering cooler & fuel cooler, was clean and functioning

Removed Tee at #20, clean.


Not sure what else to do...
 

team shadow

Seaman
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Sep 5, 2009
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My friend had a new SEI replacement drive that had a piece of metal or cast probably from manufacturing floating around in the upper near where the unit passes the water through to the transom. It was fine at idle but once you got going the metal was blocking water flow.
 

JJB4

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Jul 17, 2017
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Thanks for the reply. I took off the upper unit and flushed it at the plastic tube outward. I would assume it was clear after that.
 

Fun Times

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Does it seem to get hot when using a garden hose at home or only on the lake?

Next time you're in there with the engine running either at home or on the water, see if you seem to be getting water flow coming out of the hose number 8 when removed from the distribution housing.

Water coming out of the transom ports when running on the water hose at home?

Water tube and seal are in good condition and in the correct areas of the upper housing allowing good water flow to flow, 14, 15, 17 in place ...http://www.mercruiserparts.com/bam/subassembly/30862/2686/120

When you removed the upper unit and flushed the port at the bell housing going into the boat...Did you start the engine and watch the temp?
 

team shadow

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I think he used a clear hose somewhere in the cooling system to verify water flow which he could then see it dropping and saw air bubbles when up on plane
 

kenny nunez

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This has the symptoms of a head gasket leak or a cracked head. Did the drive pump ever have to be hanged because it was burned up and the engine got really hot? If so that may be the cause . A combustion leak will displace water in the cooling system and turn to steam, the symton is always the same. "It stays cool at idle and low rpm then gets hot with a load",
 

Rick Stephens

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This has the symptoms of a head gasket leak or a cracked head. Did the drive pump ever have to be hanged because it was burned up and the engine got really hot? If so that may be the cause . A combustion leak will displace water in the cooling system and turn to steam, the symton is always the same. "It stays cool at idle and low rpm then gets hot with a load",

^ +1

- Good post.
 

JJB4

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Jul 17, 2017
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Fun Times, thanks for your reply.

This weekend I will disconnect the inlet from the transom #7, and hook up the garden hose to feed the engine and run it, to isolate the drive / sea water pump. I (think) I should be able to push the engine a bit with the garden hose attached to simulate being in the water. I should be able to touch the risers for 5-10 secs even at 2000+ rpm?

I would assume that there is water coming out at #8 when on the water or the temp would get crazy hot fast?

Yes, the water comes out the transom with the muffs on with garden hose. Water is hot indicating it is removing (some) heat from somewhere.

Yep, when I had the upper off to replace the pump, the tube, seal, and plastic filler were in place and seem to be in good shape. It's an SEI-116 drive

No I didn't run the engine with the upper off when I changed the pump. Only simple flush. Again I will try hose at #7 this weekend.


Kenny, thanks for your reply.

Unfortunately I don't know the complete history of the boat. How can I determine if there is a head leak of some sort? Will a compression check of all cylinders tell me? Not sure how to determine a crack / leak...
 

JJB4

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Kenny,

I did check the oil on the dipstick and it is clean, no milky residue, which I thought was an indicator of a leaking head gasket.
 

Rick Stephens

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Kenny,

I did check the oil on the dipstick and it is clean, no milky residue, which I thought was an indicator of a leaking head gasket.

Not necessarily. It is possible for the head gasket to leak only pressurized gases into water jacket. Also a dipstick often won't show water in the oil. Easiest way to make sure of no water is to use an oil change suction device and pull some oil off the bottom of the pan through the dipstick tube. I don't know how many times people find they can pull water up that was not visible on the dipstick.
 

JJB4

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Jul 17, 2017
Messages
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Rick, thanks for the information. I will buy an oil change pump and pull up a bit of oil to look at it. First up is the compression test this weekend.

Even if one side of the heads in the V8 is cracked / leaking, could that cause both risers to be hot at idle? I can see the engine running hot at high speed, but I still can't get my head wrapped around both risers being hot at low speeds. Thanks.
 

maicoman

Seaman
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Nov 10, 2010
Messages
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Here is your solution to this problem.Get rid of the single point drain system.The extra hoses and bi-directional water paths make this system useless.I had the system on my Sea Ray and changed to 7 point and its 160 all day,On your PDF it says single point and 3 point ,go to 3 point and compare and study the water flow.It is very easy to discard the unnecessary parts.Look at the bottom of the water pump,how can water have 2 paths there nonscence.Its not expensive and you will love your motor again ,trust me or you will be flushing forever.You must buy a new Thermostat housing and a few hoses but nothing too expensive.The moderators of this site should warn all single point owners to scrap the system it is too troublesome.
 
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JoLin

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I think he used a clear hose somewhere in the cooling system to verify water flow which he could then see it dropping and saw air bubbles when up on plane

Google 'Mercruiser Service Bulletin 95-13'. You'll be able to open it as a .PDF. Describes the test and correction for the high-speed Gen 2 overheat condition you described.

Connect a clear plastic hose from the thermostat housing to the bottom of the exhaust manifold
on the starboard side of the engine. Take the boat out and water test it. Watch the clear hose for
air bubbles at around 3000 rpm and above. If the hose starts to fill with air bubbles, observe it until
it is about two thirds air bubbles and one third water. Watch the temperature gauge. It should begin
to show an increase in temperature.


Merc says you're sucking air into the engine through the water pump. I know you changed all that, but if you didn't seal the gaskets properly and USE ALIGNMENT PINS during the reassembly it may be your problem. Th bulletin tells you exactly what to do (try?). Anyway, read through it.

PS- you need 1" clear hose and it's a tight fit. They don't tell you that.

My .02
 
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khe

Petty Officer 1st Class
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Dec 7, 2012
Messages
225
Google 'Mercruiser Service Bulletin 95-13'. You'll be able to open it as a .PDF. Describes the test and correction for the high-speed Gen 2 overheat condition you described.

Connect a clear plastic hose from the thermostat housing to the bottom of the exhaust manifold
on the starboard side of the engine. Take the boat out and water test it. Watch the clear hose for
air bubbles at around 3000 rpm and above. If the hose starts to fill with air bubbles, observe it until
it is about two thirds air bubbles and one third water. Watch the temperature gauge. It should begin
to show an increase in temperature.


Merc says you're sucking air into the engine through the water pump. I know you changed all that, but if you didn't seal the gaskets properly and USE ALIGNMENT PINS during the reassembly it may be your problem. Th bulletin tells you exactly what to do (try?). Anyway, read through it.

PS- you need 1" clear hose and it's a tight fit. They don't tell you that.

My .02

If he is using the latest generation waterpump housing, the alignment pins are not needed. There is an on-size hole, an on-size slot, and two oversized holes in the new housing. Use the bolts in the on-size hole and on-size slot first, then install the two holes in the oversized holes.

The one piece gasket is a problem with the newer Mercruiser engines - they went back to the three piece gasket set for that reason. When I did my waterpump impeller replacement ('97 Alpha gen 2) last winter, I contacted Mercruiser technical support (very nice, helpful people!) and they explained all of this to me.
 
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JJB4

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Jul 17, 2017
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Maicoman, thanks for your input. Yes, I'm a bit confused with the water flow path of the single point drain system. Looks like the water 'should' flow in through the water pump, then out through the thermostat, to the manifolds and to the water pump again. I'm a bit disturbed that the stock system can't work though. It should work - not sure if merc is still producing the single point drain systems.

If all else fails, I think I will take your advice and convert to the thermostat housing that has a single water in, and single flow out to the water pump. Looks like merc part# 864592T1. Thanks!
 

JJB4

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Jul 17, 2017
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JoLin, Thanks for this. It is on my to-do list after I check out a few things first this weekend (clean out passages in thermostat housing, check compression of all cylinders, run engine on garden hose at transom input).

I did use the quicksilver OEM pump kit which comes with the 3-piece gasket which can only go on 1 way, and I was very careful when I installed it.
Thanks for the info on the clear hose size - will pick some up at Home Depot.
 

JJB4

Cadet
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Jul 17, 2017
Messages
11
Update from today. I did a compression test on all 8 cylinders to rule out a head leak of any kind - all 8 checked out very well, range of 150 - 175 psi, so I don't believe there is a leak of any kind. Engine only has about 220 hrs on it.

Removed the thermostat housing, clean as a whistle. No flow issues inside whatsoever (unfortunately).

Ran the engine on the garden hose - disconnected hose at the transom inlet, put garden hose to feed the engine, ran a separate hose out the back for the drive water. Engine definitely ran cooler with the garden hose attached. Even though I only ran it ~1000rpm, it never went above 165 degrees. Starboard riser cool, port riser a bit warm, but still ok. Then connected back up the drive hose to the system and ran it. Ran hotter, but I can't say how much because it started to rain & I had to cut the test short, and also I think after I shut the engine down for a while to switch water supplies, the risers started to heat up since they didn't have any water flow. Engine temp went above 170, but then I had to shut down the operation due to very bad weather. I need to go back and try this again with drive as the water source and report back.

I think at this point it is leading towards a supply problem, but I'm not sure what it can be. I have changed the drive impeller / housing twice now. SE 116 (alpha 1 gen 2) drive. I have a pic attached of what the drive pump is putting out (clear hose on the right) when I ran the engine on the garden hose. Seems ok to me...
 

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Fun Times

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Did this issue just start out of the blue or only after installing the SE drive?

How old is the drive?
 
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