Mercury Magnum 8.2 Magnum Operating Specifications - Erratic

Michael T

I'm having a heck of a time with two areas of the operating specifications for my 2014 twin Mercury 8.2 Magnums. Because the gauges are Vessel View I trust them more than analogue so I think the gauge readings are accurate - the senders well that's another story.

A while back I had two issues. My engines were showing quite different temperatures when fully warmed-up: Starboard 171F Port 163F. That seemed a HUGE difference to me for highly managed ECT engines. I was told 170 was normal and not to worry. They still show that difference and I am still concerned.

Second issue: At 3400 rpm the Starboard engine was showing water pressure of 24 psi while the Port engine was showing 14psi..... At 1200rpm  the Starboard engine was showing 14ps while the Port engine was showing 5 psi. It was determined that the Port coolant pressure was too low. The Port water impeller was replaced. No change. THEN it was decided that the Port coolant pressure was okay after all and the Starboard water pressure was too high. It was determined to change the Starboard water impeller.

Thinking that the Starboard water pressure was too high in the first place I suggested we replace the Starboard engine's water pressure sender. We did . It showed 14 pounds which we were told "should" be normal at 3400 rpm.

Returning to my marina the other day I got a RED screen (not good) on my vessel view. It stated critical low water pressure Port engine. I shut it off to clear a possible code fault (there are sometimes "ghosts" of past faults in the Mercury codes). I then re-started the Port engine. The engine temperature and oil pressure were normal. Then the low water pressure came on again. This time it showed just enough pressure to limp into my slip.

So I'm guessing that either the water pressure sender on the Port engine is now erratic or the water impeller that we did not have to install on the Port engine is bad.

On top of all of this I still have an 8 degree F difference in my engine operating temperatures which seems nuts! So I'm guessing that there may be a faulty temperature sensor on the Starboard engine too?

New engines <100 hours, babied - PITA

Any thoughts? Thanks!

MarkB

MT, I replaced my impeller in the spring of this year just as regular maintenance (ie, the old temps were fine, pressure fine, just good practice to change it every 2 years).

I noticed 2 things that changed when we did this. 1) The water pressure was lower and 2) the engine ran cooler.  My pressure was about 9 psi at 4000 rpm and my temp was 160F. At idle my temp was like 155F.  So I went and changed the T Stat. The old one actually looked good. Anyhow, after changing it, same. 155F at idle, 160F under load. Pressure a little high at around 11 psi at 4000 rpm.

My conclusion is that there is lower back pressure on the system, and the water flow is higher.  So over-heating is not a concern.  Running too cool (rich) is a concern. But given it still is within spec (I believe above 150F is still okay), I haven't bothered myself too much with it.

I'm assuming you had low water pressure, but the temp was still okay? Obviously the concern is low water pressure, meaning low water flow, meaning not enough cooling.  So as long as the engine temp is fine, it can't be low water flow. The only other condition that can cause low pressure, is insufficient back pressure and in that case you get high flow, more cooling than normal.

Not sure if anyone else can chime in, if there's any insight as to what (other than the T-stat) would reduce back pressure on the system).

LaRea

MT - My water pressures are around 5 psi at 1200 rpm, and 20-22 psi at 3800 rpm.  I'm not saying that's necessarily "normal," but it's consistent for my boat.  

High water pressure doesn't indicate a faulty impeller ... it indicates a possible blockage downstream from the pump, like maybe in one of the heat exchanger tubes.  I would't lose a lot of sleep about 24 psi on the stbd side.  You could try opening the heat exchanger and blowing the tubes out with compressed air.  

I'd be more worried about the port showing only 14 psi at cruise speed.  To me, that seems low, which would indicate either a faulty impeller, scored pump housing, or blockage in the supply leading to the pump.  

But it's odd that the port engine is the cooler of the two.  That could only be a faulty thermostat or a faulty sensor, right?

Dream_Inn

Well, if it helps at all, mine both run around 19 or 20psi at 3800rpm.  At idle they are around 5psi.

& thermostat is the only thing I can think of that would cause back pressure as well.  maybe you could swap the sensors between the engines and see if it follows.  Heck, you could swap the entire pump between them if you really want to see if there is a difference, but sensor would be an easier one to start with.

LaRea

Oh, wait - you're saying the stbd reading went from 24 to 14 when you replaced the SENDER ... so now they're both pushing 14 psi at 3400 rpm? 

Michael T

Thanks for the info Mark. Good thoughts and suggestions! I was relieved when I re-started the Port engine and the oil pressure and water temperature were normal. At that point I suspected a faulty water pressure sensor because if there was REALLY a water pressure problem surely the engine temp would be higher? BUT and this is a very big BUT .....my engine guardian system can reduce my available engine HP to 5%. The problem is that (as far as I know) the Guardian System relies on sensor data SO if a sensor is erratic it can shut my engine(s) down without real cause. On the day this happened there were 25 kph cross winds at my marina and I was worried that I would not have enough power to enter the marina safely. I aslo have to find out why my Starboard engine is reading 163 F  - I guess that could be thermostat or sender!

before we do any work on the Port engine low water pressure issue we are going to check the vessel view log to see if there any  "code ghosts" that need to be deleted and if there is any corrective software that needs to be up-loaded. My money is still on a faulty port water pressure sensor and either a faulty Starboard engine thermostat and/or temp. sender.

Michael T

La Rea - are you ready for this????? Yes they WERE both reading 14 psi at 3400 rpm - WERE!!!!

Here's how it went - After much discussion with the guys on the Merc techs' hot line (the one for the pros not we consumers) they told my tech (his phone was on speaker, so I heard it all) that 5 psi at idle was correct and 14 psi at 3400 was correct. At that point (8 days ago) both engines were at 5psi +/- a bit at  idle and 14 psi +/- a bit at  3400......after we changed the Port water impeller (for no reason, it now seems) and the Starboard water pressure sender.

I thought the water pressure issues were solved and was getting ready to address the different engine temperature issues.....NOT

NOW the Port engine is throwing critical low water pressure codes and showing 1.3 psi at idle and 5psi or so at 3400 AND this was the engine that just had its impeller replaced (unnecessarily it appears) as part of the previous trouble shooting!!!!!

On top of all of this my Starboard engine is showing 163F and the Port is showing 171F!!!!

The coup de gras is that the engine guardian can be tricked by either bad code or faulty senders into limiting my power to 5% - real nice if I'm heading into a lock or slip in a cross wind. Got to get this fixed!

Geez! I am not having fun with this BUT I'm sure glad it's still on warranty!

MarkB

MT, you and I have similar issues (comparing to your port). I still think there is high flow through the system, or the temperature would be through the roof. Something is not providing the necessary back pressure.

Michael T

I agree Mark, in my case, it would either be something allowing too much free flow or a cr*ppy sensor sending out erroneous data - like the one we replaced a week ago on the Starboard engine. If the sensor arrives by Tuesday the tech will bring it to the my marina and swap it out. I'll post what happens. Then it's on to the temperature reading from the Starboard engine!

MarkB

So, I just got off the phone with Mercruiser support. For the MAG 350 MPI with B3, they indicated at WOT typical water pressure is 11 psi!!!  So he said the fact that I'm getting 9 - 11 psi at 4000 rpm is just fine. He wasn't concerned about the temperature at all being at 158F under load.

He is pretty sure the lower pressure is related to the new impeller, but he indicates my engine is running fine.

I have to add, I've never had any alarms on my boat and I've gone on some nice runs for a few hours under load with 9 people on board.

Michael T

Great news Mark!  Merc tech support said I should be getting 3+ psi at idle and 14- psi at 3400 to WOT.  After replacing the Starboard sensor (a week ago) that's about what that engine is now showing. The Port engine, which - a week ago - showed the correct psi's of 3+ psi at idle and about 14- psi at 3400 to WOT is NOW showing 1+ psi at idle to about 7 psi at 3400 which is too low and hopefully a faulty sensor. My marina tech said they have had 4 of the water pressure sensors fail in the last few weeks - nice!

Mercury makes great equipment but IMO these new EPA mandated catalyst engines have gotten so complicated that they are driving the techs crazy. That and cr*ppy - unreliable parts form abroad!

LaRea

So, if the 350 runs at 11 psi, and the 8.2 runs at 14, I wonder what the design pressure is for my 496s.  They run great at 20 psi, but is this the Merc equivalent of high blood pressure?  Or do I have two faulty sensors?

Michael T

I think your 496s might just be meant to run at 20 psi. I'm pretty sure that was what the non-marinized 496s ran at. I assume they are both reading close to 20 psi? If that's the case I'd rest easy. Also I have not seen you post any issues with them re overheating etc. So again, imo, you're fine.

LaRea

Yes, both at 20, stable and consistent, and the temps are rock-solid.  

Dream_Inn

LaRea, as I've said, my 496's run at ~20psi as well for the 4 years I've had the boat, never an issue.  I think we're ok.

MarkB

I suppose we also need to specify whether the raw water pump is pumping directly into the block or whether it goes to a closed cooled heat exchanger. I'd expect the heat exchanger to require a higher raw water pump pressure. 

Dream_Inn

I'd think most of us are talking about a heat exchanger, that is what I have.

Michael T

Heat exchangers here.

MarkB

Mine is raw water cooled block, no HTX, as I'm in clean fresh water. That probably explains why my pressure is lower at 10 or so psi.  A heat exchanger requires more surface area to do the cooling (like a radiator) and the flow needs to go through a bunch of tiny pipes. That requires more pressure to get through all that, so I'm not suprised your systems are working at a higher pressure than mine.