Merc 4.3 MPIs will not get past 100 degrees

[Jimmy Buoy]

This boat has become a project and a half. It is not consistently idling without stalling once the boat is run for about 10 minutes. At least part of the issue is that the temps don't get over 100 degrees ever and that's verified by an infrared heat gun at the thermostat and the exhaust risers. I'm thinking that the water flow on my engines are not correct.

I've taken both thermostat assemblies off the engine, they both appear to be the same, removed one of the thermostats (which both appear to be closed at room temps) and placed it in 170 degree water. It opened as it should and appears to be working just fine so a stuck thermostat isn't the issue.

I did find a water flow diagram that describes my situation...

In this diagram, tube #8 is raw water coming thru the fuel cooler which enters the Water Distribution Housing (one large open bowl with one inlet, two outlets, and a drain).

The pressurized water is forced up tube 19 which feeds the exhaust risers. OK.

The other outlet is tube 11, BUT the flow diagram shows water flowing INTO the Water Distribution Housing??? I'm really confused with this as it appears the Water Housing now has two inlets, one outlet and a drain...

In my case, both engines do NOT have tube 9 which seems to just give the ability to drain the block and lower exhaust manifolds via the Water Distribution Housing Drain. The previous owner had added brass valves to the two block drain hoses and there are blue plugs at the bottom of each exhaust manifold. I don't think tube 9 has any other purpose but could be wrong on this.

Tube 4 seems to pull engine water from the block down to the engine's circulation pump, but then tube 12 appears to avoid having its water pulled into the circulation pump and instead heads back to the Water Housing?? How does that happen?

Tubes 5 and 6 should only see water flowing to the bottom of the exhaust manifolds once the thermostat opens - correct? That is the only way water would travel from the lower portion of the thermostat housing to the top where these exhaust water tubes exit.

What am I not seeing here?? Any help would be greatly appreciated!

 

[scoflaw]

tubes 5&6 flow with t-stat open or closed

 

[Jimmy Buoy]

tubes 5&6 flow with t-stat open or closed

That’s what I would have thought, but upon close inspection with the t-stat removed I can see that tubes 5&6 are fed from the top part of the assembly which only is open to the top of the t-stat. There doesn’t appear to be any passageway for water from the underside of the t-stat to get up to those two ports without passi

tubes 5&6 flow with t-stat open or closed

I stand corrected! Thanks for your comment. I ran some water through that upper part above the stat and there is a passageway to the underside after all!

Any ideas on why the engine refuses to heat up?

I could suspect the engine's circulating pump has failed, but for one to go is rather rare. For both engines to fail at the same time is probably not a possibility. I did see a YouTube vid where the circulating pump failed causing the raw water to be forced up and into the t-stat housing, into the motor, and back out the circulating pump hose so the temp gauges would show a cold engine. Weird stuff.

 

[scoflaw]

Some how the water is able to bypass the stat. Is that plastic piece in t-stat housing oriented correctly?

 

[Jimmy Buoy]

Some how the water is able to bypass the stat. Is that plastic piece in t-stat housing oriented correctly?

Here's the one undisturbed (took the t-stat out of the other and broke the plastic ring to get it out). It looks to be correctly placed. (sorry - photo doesn't want to post)

 

[Jimmy Buoy]

 

[Jimmy Buoy]

Interesting video with the same type of setup as my MPI engine. This ended up being a failed circulation pump, but my temps NEVER seem to jump up, but the engine does slow down and stall coming back to idle. Sometimes quickly, sometimes it recovers for a while but it eventually will go below 500rpm and stall. It will however startup easily once stalled, then repeat the process. Temps never get into the triple digits.

Think I should remove/check both engine's circulating pumps based on this vid??

 

[Jimmy Buoy]

Here's part 2 of the video with the diagnosis and solution..

This is so similar to what I'm experiencing other than the engine temps have not gone over 100 with the gauge - just stays cool. The mechanic says, "first time he's seen this happen in 40yrs" which makes me doubt that's my issue with two engines at the same time.

For the sake of a couple of replacement gaskets, I'm thinking that I should check one of the circulation pumps out for issues. Then again, I was convinced that the problem was stuck "open" t-stats (even though both stuck open at the same time was doubtful). They operate nominally.

Trying not to get too frustrated. This is some basic physics in play. I should be easily diagnosed since it happens every time, all the time. Maybe I'm too close to the problem to see it.

 

[Jimmy Buoy]

New theory.

The previous owner like to reinvent to make things "better". Sometimes it does, but other times it can create more issues.

The normal power steering on the boat was completely removed including the pumps, lines, and cooler tube (yes including the water pressure sensor) and replaced with SeaStar hydraulic steering. With that removed, the normal water line coming from the raw water pump that went up the back of the engine to the now gone steering cooler tube was replaced and re-routed. He used wire wound sanitation hose (that won't collapse or easily crush) with 90 degree plastic connections to round the back underside of the motor and attach to the cool-fuel unit. He said how this would less restrictive and have a longer life than the OEM way.

He also abandoned the traditional water intake from the outdrive (capped it inside and outside) and installed a thru-hull for each engine to supply cooling water again using wire wound sanitation hose for longevity.

Theory as follows: Could it be that reducing the OEM's natural restrictions (numerous connections, bends, and passing through a cooler) has increased the gal/minute and pressure of the water flow to the cooling system that it is muscling out the engine's circulation pump's ability to dominate and thereby allowing the flow of water through the engine to be reversed??

I did have a brand new water distribution housing fail at the seam while operating the engine at 4500rpm. Was it a defective part or was there too much pressure applied by the water pump for the plastic housing to handle. Here's a photo of the part that split on the heat welded seam.

and it in the boat at idle after finding it split (was running over 4G minutes earlier - quite the water spray)

Before launching the boat I did run in on the hard. The thru hulls were closed, but a Graco "Crash Pump" fitting was removed between the shut off and the engine's raw water pump. A hose with a Graco Crash Pump adaptor was put in its place which supply water directly to the intake hose. Instead of chancing just hooking up a garden hose directly I used a 5 gal pail with a spigot installed at the bottom and attached the hose to supply the engine. The pail was filled with a garden hose and the engine started while the hose was running fully. Either engine just at idle would pull more water out of the bucket than the garden hose could supply. The pail was drained completely and sucking air within about 4 minutes. Does that seem like a reasonable flow rate for a Merc pump? I really don't know what is normal for these pumps. Keep in mind that the pail was above the top of the engines so the water didn't have to travel upwards, but gravity fed downwards.

Maybe I need to add some kind of restriction in the water supply hose to compensate for the lack of natural restrictions in the OEM setup?

Opinions?? Thoughts??

 

[scoflaw]

The go fast guys use a pressure relief valve. What is the actual pressure?
When did this problem start? Does the guy you bought it from have any ideas?

 

[Wayward Sun]

New theory.

The previous owner like to reinvent to make things "better". Sometimes it does, but other times it can create more issues.

The normal power steering on the boat was completely removed including the pumps, lines, and cooler tube (yes including the water pressure sensor) and replaced with SeaStar hydraulic steering. With that removed, the normal water line coming from the raw water pump that went up the back of the engine to the now gone steering cooler tube was replaced and re-routed. He used wire wound sanitation hose (that won't collapse or easily crush) with 90 degree plastic connections to round the back underside of the motor and attach to the cool-fuel unit. He said how this would less restrictive and have a longer life than the OEM way.

He also abandoned the traditional water intake from the outdrive (capped it inside and outside) and installed a thru-hull for each engine to supply cooling water again using wire wound sanitation hose for longevity.

Theory as follows: Could it be that reducing the OEM's natural restrictions (numerous connections, bends, and passing through a cooler) has increased the gal/minute and pressure of the water flow to the cooling system that it is muscling out the engine's circulation pump's ability to dominate and thereby allowing the flow of water through the engine to be reversed??

I did have a brand new water distribution housing fail at the seam while operating the engine at 4500rpm. Was it a defective part or was there too much pressure applied by the water pump for the plastic housing to handle. Here's a photo of the part that split on the heat welded seam.
View attachment 129969

and it in the boat at idle after finding it split (was running over 4G minutes earlier - quite the water spray)
View attachment 129970


Before launching the boat I did run in on the hard. The thru hulls were closed, but a Graco "Crash Pump" fitting was removed between the shut off and the engine's raw water pump. A hose with a Graco Crash Pump adaptor was put in its place which supply water directly to the intake hose. Instead of chancing just hooking up a garden hose directly I used a 5 gal pail with a spigot installed at the bottom and attached the hose to supply the engine. The pail was filled with a garden hose and the engine started while the hose was running fully. Either engine just at idle would pull more water out of the bucket than the garden hose could supply. The pail was drained completely and sucking air within about 4 minutes. Does that seem like a reasonable flow rate for a Merc pump? I really don't know what is normal for these pumps. Keep in mind that the pail was above the top of the engines so the water didn't have to travel upwards, but gravity fed downwards.

Maybe I need to add some kind of restriction in the water supply hose to compensate for the lack of natural restrictions in the OEM setup?

Opinions?? Thoughts??

Near as I can tell my stuff is completely stock. And you already know I'm having the same problem. I'm amazed that with the circulation pump's impeller being cracked like that the engine doesn't overheat consistently.

 

[Jimmy Buoy]

Thanks Scofflaw,

I just bought the boat last fall as is, knowing the work that he'd put into it but also knowing that I'd have a few projects. Definitely more than I expected - surprise surprise!

I don't know if the Rinda Pro shows water pressure on the 4.3mpi. If it does, I didn't notice. The Rinda does show some garbage info though like the coolant temps before starting being 32F - not likely, or another parameter showing the air temps at 425F - nope.

I did install Vessel View Mobile and it does give the option for coolant pressure, just not sure what that measures. Sounds like engine coolant in a closed system, but I don't think I ever clicked on it to see.

This is the first time I've actually used the boat in the water more than just taking from the launch to the dock (less than 5 minutes running) other than the first run with all the beeping. I thought either the temp gauges were shot (the previous owner sent me a new pair that he had purchased) or the sensor wasn't grounded since no temps were showing on the dash. Then again, they don't register until 100 degrees and the engines haven't hit that mark.

My first run this year of any length was when the water distribution housing split. Something I just remembered that might be a clue was that while the engine was idling and spilling water into the ER (as in the photo) the engine temps climbed to 150F. I kept my eye on the temp since most of the water being supplied by the raw water pump was spewing out, I was concerned of starving the engine of cooling water. Even with much of the water spewing out, the temps stayed at 150 then began to slowly climb. When it hit 158F I decided to shut it down since I didn't have my laser temp gun and wasn't confident in the info from VV Mobile and shut off the seacock. With the engine off, water continued to drain out of the broken plastic part and it began to steam as it poured out - showing me that it did indeed increase beyond its normal 90F running state.

That reinforces my theory that the pump is providing too much water volume or pressure, or both. I guess I wasn't too worried about see what the PSI reading was from the old water sensors installed anyway since they were at least making the damn beeping alarm stop. VV Mobile also would have told me if the pressure was too low OR too high. Just glad that the installed sensors cleared the fault.

As for contacting the previous owner, I told him of the engines quitting at idle last fall. He said that the gas was 3yrs old, non-ethenol and treated, but still 3yrs old and that must be the issue. This spring, I drained most of the 1/8 tank (as much storage as I had) and filled the tank to 3/4 full with new fuel. Not the fuel. It starts and idles fine when cold, but after it gets to its 80-90F running temps is when the stalling at idle business starts.
I'm thinking that when I get the thermostats back in the boat I'll try shutting the thru-hull water supply valves to reduce the flow of water by half (simulating the OEM restrictions) and see if the temps go up to normal.
Also, the previous owner left a new IAC unit on the boat which I installed on the port engine. I'll see if that makes a difference with both the stalling and the Rinda IAC test results. Last time I did the Rinda IAC tests, I could not get either engine's idle to increase, but I could get them to decrease and stall using the Rinda. I'll retest the new IAC and see if there is a difference before investing in a replacement IAC for the stb engine.

This boat is keeping me busy - VERY busy...

 

[Jimmy Buoy]

Near as I can tell my stuff is completely stock. And you already know I'm having the same problem. I'm amazed that with the circulation pump's impeller being cracked like that the engine doesn't overheat consistently.

You must be referring to the video off YouTube? You have to remember that the engine's impeller wasn't doing anything, but the raw water pump then had no resistance to push raw water through the hoses, right up to the thermostat housing and directly into the engine (bypassing the thermostat entirely). That water was then going thru the engine block and heads in the reverse direction of what is normal and back out through the circulation pump's stationary impeller. That's not going to cause an overheat but an overcool situation.

I can see maybe one engine's circulation pump failing, but not both. Something else is happening here.

 

[Wayward Sun]

You must be referring to the video off YouTube? You have to remember that the engine's impeller wasn't doing anything, but the raw water pump then had no resistance to push raw water through the hoses, right up to the thermostat housing and directly into the engine (bypassing the thermostat entirely). That water was then going thru the engine block and heads in the reverse direction of what is normal and back out through the circulation pump's stationary impeller. That's not going to cause an overheat but an overcool situation.

I can see maybe one engine's circulation pump failing, but not both. Something else is happening here.

Is it possible there was a bad run with a batch of the circulating pumps? Maybe there was an overheat condition and that heat caused the brass impeller to prematurely fail? Sorry - spit balling here. I do get where you're coming from. Then you add my situation on top of yours and it just seems so unlikely when you start playing the percentages in your head

So... If I'm understanding you correctly the raw water pump is acting like the raw water pump AND the circulation pump? Do I have that right?

 

[Jimmy Buoy]

Is it possible there was a bad run with a batch of the circulating pumps? Maybe there was an overheat condition and that heat caused the brass impeller to prematurely fail? Sorry - spit balling here. I do get where you're coming from. Then you add my situation on top of yours and it just seems so unlikely when you start playing the percentages in your head

So... If I'm understanding you correctly the raw water pump is acting like the raw water pump AND the circulation pump? Do I have that right?

Bad batch of pumps - possible, but that was almost 20yrs ago. I would think it would be common knowledge by now if so.

Correct on the dual action raw water pump. At least that's what happened to the boat owner in the video (which was 2yrs ago). It's not surprising that he had been to 4 shops with nothing to show for it other than 4 bills for work that solved nothing. This was his 5th shop trying to get his boat fixed and they were the only ones who took the time to figure out what was going on which finally solved the issue. They didn't just throw parts at it like the others hoping it would work.

Maybe I'll buy some lengths of 1" clear hose to see what's going on while operating the boat if I can't seem to solve it.

In your case, your raw water pump is in the Alpha Drive itself and it does not have the pumping volume of the belt driven Bravo pumps so I doubt there is a pressure issue. Also, yours is stock so even less chance of that being the issue.

 

[scoflaw]

With the t-stat closed the block should be a sealed unit. Why would the circulating pump have anything to do with it? Raw water is getting in somehow

 

[Fill Ess]

Yes if you runs the odds of the same thing happening on both engines at the same time ... it's unlikely but not impossible. You could have both circ pump go at the same time.

 

[Jimmy Buoy]

With the t-stat closed the block should be a sealed unit. Why would the circulating pump have anything to do with it? Raw water is getting in somehow

Here's how I understand the water flowing so far - feel free to let me know if I'm "all wet" on my assumptions...

It would be a sealed unit with its water going round and round - pulled into the block by the circulating pump from hose 4, then pushed out the exit on top of the intake, through the t-stat housing flowing in the large channel below the t-stat (if the t-stat is closed), and out through hose 4 to be pulled into the block again by the circulating pump.

This continues until the water becomes hot enough to open the t-stat and some of the hot water is diverted up through the t-stat into hose 5&6 headed for the bottom of the exhaust manifolds.

That water needs to be replaced from somewhere - which can only be provided by hose 12 (the only raw water hose connected to the engine cooling system), but the diagram shown at the beginning of this post shows hose 12 with hot water flowing away from hose 4.

It must provide Raw water at some point to the engine as it is losing cooling water every time the t-stat opens. While the engine is running at temp there is a constant loss of hot water from the engine exiting via the exhaust.

Also, Raw water must constantly being introduced to the t-stat housing since additional raw water needs to always be flowing out of the housing via hose 5&6 or else the exhaust manifolds would not have any cooling. The system doesn't allow water starvation to the manifolds though, again telling me that hose 12 must provide raw water to hose 4 to some degree constantly. The way the diagram arrows are shown, I don't see the block getting ANY raw water supply other than from the hose 4/12 junction.

Is the diagram wrong?

Here's a thought, maybe the diagram is NOT showing operational water flow, but how the system drains itself from the water distribution housing!!

Thoughts?

 

[Wayward Sun]

J.B. - As far as both circ pumps going bad at the same time...... I'm not entirely sure that is necessarily the case for either of us. Could it be possible whatever the root cause of the problem is it failed on one engine and the PO didn't notice it, then the second engine failed in the same way but at a later date? Then we become the new owners and we notice both engines are running cool. I'm a gauge watcher. So I notice things pretty much right away. Not all owners are that way.

Is it also possible that our engines didn't get winterized correctly at some point and the circulation pumps were damaged where the brass impellers are spinning on the shaft?

 

[Jimmy Buoy]

J.B. - As far as both circ pumps going bad at the same time...... I'm not entirely sure that is necessarily the case for either of us. Could it be possible whatever the root cause of the problem is it failed on one engine and the PO didn't notice it, then the second engine failed in the same way but at a later date? Then we become the new owners and we notice both engines are running cool. I'm a gauge watcher. So I notice things pretty much right away. Not all owners are that way.

Is it also possible that our engines didn't get winterized correctly at some point and the circulation pumps were damaged where the brass impellers are spinning on the shaft?

Agreed. When I get a chance, I'll remove one of them and inspect and post my findings.