Mercury Optimax 150 loss of water PSI

[Capt.Will]

Engine: 2008 Mercury Optimax 150hp

Issue: Beginning at 4000 RPM engine begins a gradual loss of water PSI and then my Smartcraft gauge throws an alarm and begins guardian mode for few seconds. It also says that it's overheating. I notice that the temp reaches 150 degrees then at idle it lowers back down and guardian mode is lifted.

At 3000 RPM everything is A-OK. PSI reads 9.5 to 10 PSI. As I excellerate past 3500 RPM and closer to 4000 RPM I see the PSI lower down to 8.0 then eventually 6.0 PSI and then the alarm hits.

Recent service includes: New water pump/housing/impeller. Lower unit complete seal job.

Any help with this is greatly appreciated.

 

[Strypes]

What's the alarm? Water in fuel?

 

[Capt.Will]

What's the alarm? Water in fuel?

The SmartCraft gauge says it's ever heating and I believe it because yesterday after coming off plane there was an incredible amount of steam emitting from the exhaust until it cooled down at idle speed.

Like I said also the water PSI dropped considerably until the engine put it in guardian mode briefly.

 

[blaster]

Check the poppet valve and thermostat. Have they ever been replaced?

 

[Jus Cruisin]

Do you have a water stream? It's so cold up here could it be as simple as an impeller that needs replacing? Water temps in the 40's.

 

[Capt.Will]

Check the poppet valve and thermostat. Have they ever been replaced?

I pulled both thermostats and the poppet valve yesterday. They all are original. They appear to be ok. I ordered the parts anyway since I have it apart.

Question on the Poppet valve. I assume that the spring and diaphragm are the only working parts on this valve that could really fail. The black plastic piece that Mercury calls the Poppet Valve really is just a piece of plastic that the diaphragm screws into. Pressure opens it and allows more flow of water into engine between 4 and 9 PSI. Correct?

 

[Capt.Will]

Do you have a water stream? It's so cold up here could it be as simple as an impeller that needs replacing? Water temps in the 40's.

Yes. Very good "tell tale" stream. Across the spectrum as far as I can see.

 

[blaster]

I pulled both thermostats and the poppet valve yesterday. They all are original. They appear to be ok. I ordered the parts anyway since I have it apart.

Question on the Poppet valve. I assume that the spring and diaphragm are the only working parts on this valve that could really fail. The black plastic piece that Mercury calls the Poppet Valve really is just a piece of plastic that the diaphragm screws into. Pressure opens it and allows more flow of water into engine between 4 and 9 PSI. Correct?

Yes that’s my understanding of how a poppet opens. They open up at higher RPMS and increase the flow of cooling water. That’s why I thought the poppet isn’t opening based on your description of events. You should be 12-15 PSI wide open.

 

[Capt.Will]

Yes that’s my understanding of how a poppet opens. They open up at higher RPMS and increase the flow of cooling water. That’s why I thought the poppet isn’t opening based on your description of events. You should be 12-15 PSI wide open.

After inspection of the poppet/spring. The function seems to be OK. Nothing jammed and the spring seems to be OK, but I am going to replace it anyway. Wasn't easy pulling everything off to get to it.

 

[JimG]

Is this an original setup? Could it not be deep enough in the water for good pickup at the higher RPM's?

 

[Capt.Will]

Is this an original setup? Could it not be deep enough in the water for good pickup at the higher RPM's?

I have a Bob's Machine Jack Plate installed but the set up at lowest portion is waterline above the water pick ups and just below the cavitation plate. Right where it should be.

 

[blaster]

I hope that fixes it. Something seems off with your issue. No corrosion or obstruction? Salt or freshwater?

 

[Capt.Will]

I hope that fixes it. Something seems off with your issue. No corrosion or obstruction? Salt or freshwater?

I purchased the boat from original owner in Louisiana. It only had 150 hours on it when I bought it and the signs of any salt water use are very minimal. So far after removing the parts I described above I do not see any excess corrosion. I have only used it in Fresh water since I have owned it.

 

[blaster]

Check through this online service manual I just found. Perhaps that will help you narrow down the issue.

https://www.manualslib.com/manual/905576/Mariner-135-Optimax.html?page=282#manual

 

[Capt.Will]

Check through this online service manual I just found. Perhaps that will help you narrow down the issue.

https://www.manualslib.com/manual/905576/Mariner-135-Optimax.html?page=282#manual

Thanks. I have that manual on my computer and have been glued to it for days.

Odd thing is, that manual shows a strainer screen that leads a water line to the compressor. My engine does not have any water line to the compressor. I am assuming Mercury changed this by 2008? Little befuddled by this. How is the compressor not cooled then?

The manual says that blockage in that strainer screen could cause the issue I am having, but my engine does not have that to the compressor. Strange.

 

[blaster]

Make sure the water tube is fitted properly and not leaking. Perhaps a real tech will chime in with first hand knowledge. You may need to buy an exact year service manual for your answer.

It looks like the tell tale runs from the compressor. If the strainer was clogged then you would have a weak or no tell tale. I’d start with going through the water pump again to make sure nothing was missed. It may be it is not making enough pressure to open the poppet valve.

 

[Capt.Will]

Make sure the water tube is fitted properly and not leaking. Perhaps a real tech will chime in with first hand knowledge. You may need to buy an exact year service manual for your answer.

It looks like the tell tale runs from the compressor. If the strainer was clogged then you would have a weak or no tell tale. I’d start with going through the water pump again to make sure nothing was missed. It may be it is not making enough pressure to open the poppet valve.

I have searched online for an exact downloadable service manual for this with no luck. I am definite need of some answers since the season is almost underway here and I am itching to get out on the lake.

I concur the tell tale does come from the compressor. Just stumped on where the input is coming from. I have been brainstorming about the water pump because that is usually the source of many things but it really checks out as far as I can see.

 

[blaster]

I would double check the water pump methodically before tearing into everything any further to completely rule that out. The t-stats and poppet were 14 years old so consider that maintenance. Any leak in the pump and it can lose pressure when you need it.

 

[Capt.Will]

I would double check the water pump methodically before tearing into everything any further to completely rule that out. The t-stats and poppet were 14 years old so consider that maintenance. Any leak in the pump and it can loose pressure when you need it.

I completely agree with you on this. Given the age I have no issues with replacing those parts.

The lower unit was professionally resealed and and new impeller kit installed over the winter but that still has me concerned with the impeller performance. As stated, I did remove the impeller pump again and I believe it looks solid but I am further concerned about it.

 

[Capt.Will]

I just took these photos of the water line from the very bottom keel and with the trim all the way down as well as the Jack Plate at the lowest setting. I am just finding it hard to believe that the water inlets are sucking air. Any thoughts?