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Author Topic:   Mercury Optimax 150-HP Major Problems
ctoolman posted 07-16-2005 07:55 AM ET (US)   Profile for ctoolman   Send Email to ctoolman  
What kind of hours [of use] have anyone seen before major problems showed up on the 150-HP Optimax?

I just got my 23 OUTRAGE with twin 150-HP Mercury OptiMax engines that have 250-hours of use. All normal maintenance has been done at the dealer. Plugs. Foot. Oil. Water pumps. Owner kept good records.

Thank you for the help.

jimh posted 07-16-2005 10:20 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is a saga of a fellow on his fourth powerhead with a Mercury Optimax 150-HP. Several lasted only a few hours.

I hope your experience is better. Many have reported strong performance from this engine. The fundamental block is a strong performer and with carburetor or fuel-injection systems these same engines have outstanding records.

As you may know, Mercury was forced into a settlement of a class-action lawsuit against them brought by owners of OptiMax engines.

When they are running right they give good fuel economy and good performance.

prm1177 posted 07-16-2005 01:40 PM ET (US)     Profile for prm1177  Send Email to prm1177     
Much depends on how you treat the engine. How is it propped? Is it subject to over-revving? This engine block is very reliable. Most issues with the Optimax engines have been on the larger 225 HP motors. Here are my recommendations for a longer life:

1. Use Optimax DFI oil. Buy in bulk from a dealer in your own containers and it's reasonable.

2. Change water pump impeller, fuel filters, plugs, clean compressor filter, and change lower unit oil every season (no matter how few hours you use it).

3. Check all belts every season for wear and replace as needed.

4. Use only a 1000 MCA (800 CCA) starting or dual purpose battery. Change every 2 years.

5. Run Mercury Quick Kleen in your gas periodically to help in minimizing carbon buildup. I do it every 2 or 3 tankfulls (between 500-800 miles on the GPS).

I own the Opti 135 (twins) and have had the same engine on my last Whaler. I bought my newer boat with this engine because of my past experience. My contacts at mercury tell me they are extremely reliable with regular maitnenance.


dcritch posted 07-16-2005 02:07 PM ET (US)     Profile for dcritch  Send Email to dcritch     
prm 1177
I know this is a little off ctoolmans topic but I had a question about appropriate batteries to use with my 90 optimax. I recently added electric downrigger outlets and a battery switch to my 170. My manuel says "No deepcycle batteries" and the dealer who did the install said to use another cranking battery as my number two battery which the downriggers are hooked upto. I use the optimax as my trolling engine. Does this sound ok or would a dual purpose batterys be better?
jimh posted 07-17-2005 04:49 PM ET (US)     Profile for jimh  Send Email to jimh     
Dave--From what you wrote above I understand you to mean that the Owner's Manual for your Mercury OptiMax outboard explicitly states that use of deep cycle batteries is prohibited. If that is true, I don't think you get a pass if someone else recommends another battery. If it says you can't use deep cycle batteries then I would follow the recommendation.

I am a bit curious to know if it actually says that. The Mercury maintenance manual for the 150-HP Optimax c.2000 just says the following:

"Recommended Battery
A 12 volt marine battery with a minimum Cold Cranking amperage rating of 750 amperes or 1000 (minimum) Marine Cranking amperes should be used."

Perhaps they have changed their specifications.

A deep cycle battery with a rating of 1,000 MCA may be harder to find than a marine starting battery with that rating.

The general impression of the OptiMax engine is that below a fast idle speed, say 1,000-RPM, the engine is a net consumer of current. That is, it needs more current to run than it can generate from its charging circuit, therefore it is draining the battery at those speeds. It also appears that these engines are very sensitive to voltage, and if the supply voltage drops much at all below 12-volts, the engine will not run properly. This is probably why they specify such a huge starting battery for them. They need to have a stiff supply of 12-volts to get started and running and idle speeds.

The Optimax engine has a lot of electrical devices. It has electrical fuel injectors AND electrical air injectors. It has twice as many injectors as other fuel-injected or direct-injected engines. And it has an electrical fuel pump (which all fuel injected engines tend to have because they have a pressurized fuel rail).

Because you are using your OptiMax for trolling, you may be running it close to the point where its charging current and its electrical demand are about equal. It would be interesting to actually measure the charging current at your favorite trolling speed.

In any case, stick with a strong battery and you will avoid problems. The principal job of the battery on your boat is to start the engine, so I'd get a battery that was designed for that job as my primary battery.

It is possible to have two batteries of different type aboard, but you need to have some plan to charge and maintain them. I would use a voltage-sensitive relay (VSR) type charging combiner. That is a whole different topic. If you want to discuss VSR relay set ups, let's start a new thread, and let this discussion stay focused on the 150-HP Optimax as its TOPIC suggests.

Whalerider posted 07-18-2005 09:00 AM ET (US)     Profile for Whalerider  Send Email to Whalerider     
I use Cabelas group 24 "dual purpose" AGM batteries with my Opti 150. They say it has 1195 MCA and 945 CCA. I regularly sit for several hours with my GPS, depth finder and VHF running and I also troll at idle for hours at a time, NEVER had any problems with the engine starting right up. I have a two battery setup just incase one battery gives up but have never needed to switch to the other battery. I use the #1 battery on odd days and #2 on even days to keep them both exercised and charged.


prm1177 posted 07-18-2005 11:00 AM ET (US)     Profile for prm1177  Send Email to prm1177     
I user Interstate Batteries: Model 24M-XHD, 800CCA,1000MCA. It's listed as both cranking and dual purpose depending on the literature. Two batteries with switches for the dual Opti 135's. The Opti 135 and 150 both have 65 amp alternators which should supply enogh current for most loads. At cruise, my voltmeter shows the system at 14.1 VDC, and at idle (with all electronics on - Fishfinder, radar, VHS,& GPS) the charging voltage reads 13.7 VDC.
dcritch posted 07-18-2005 07:59 PM ET (US)     Profile for dcritch  Send Email to dcritch     
Sorry for getting a bit off topic however in answer to your question my manual for 75/90/115 Optimax says "Do not use deep cycle batteries. Engines must use a marine starting battery with 1000 MCA or 800 CCA." The manual then has an image of a warning sticker that needs to be placed on or near the battery box. The sticker says "DO NOT USE DEEP CYCLE BATTERIES". I don't have any stickers but I get the point.
Thanks for taking the time to explain some of the issues related to batteries and the optimax.

My 170 came with an interstate 24mxhd 800cca 1000 mca Marine rv cranking battery so if its listed elsewhere as a dual purpose battery it seems to make sense to use the same one as my second battery.

I wish we had Cabelas out here. I get the catalogs but its not the same as having a store nearby. Thanks for the information, I need to get a good book on marine electronics, probably one of those for Dummies books.

jimh posted 07-19-2005 02:06 AM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the information on the battery warning from the OptiMax owner's manual. Yes, I would say they are definitely emphatic about no deep cycle batteries.
Hristo posted 09-17-2006 03:48 PM ET (US)     Profile for Hristo  Send Email to Hristo     
Hi from Canary Islands,

I have a 2001 Mercury Optimax 150 Hp with 500 hours of use.
After having my boat in a garage for one week, I start it and remark that it stalls and coughs at idle speed,and stops running after less than a minute. That repeats over and over again. Once over 1200 rpm, the engine runs O.k.
We check and clean the 12 inyectors, we put 6 new candles and a new coil (all original), as well as a new fuel filter. Another checking discards fuel escapes and electric problems.But the problem remains the same, rpm are very ustable at idle speed. We take the engine to the local dealer for a computer-assisted diagnostic. apparently everything is ok for the computer. But the engine keeps running badly. We check the mechanical fuel pump (OK) and take the boat to the water. From 1200 rpm on it runs as if it was perfect, (til 5250 rpm) but after half an hour we notice that it makes it difficult to get over 4500 rpm. In any case, we don't observe any other anomaly running at high rpm.
We have also measured the fuel pressure (70 PSI) and the air pressure (60 PSI). We know that these results are under the normal parameters (over 80 PSI for fuel pressure) but we don't really know where the problem is, as the fuel pump (with less than 100 hours) apparently works good.
My local dealer doesn't dare to change it (maybe a lot of money for nothing) and have no idea about the problem root.

All information on this subject will be very welcome.

thank you in advance for your effort

Angel Hernández Suárez

VI Jamie 22 posted 09-17-2006 06:12 PM ET (US)     Profile for VI Jamie 22  Send Email to VI Jamie 22     
Hristo, The low numbers are from a worn air compressor, replace it. Also, It sounds like the valve/diaphram that balances the fuel/air pressure is leaking. I forgot the name of this green diaghram, but it is located on the starboard fuel rail about halfway down and is secured with four bolts. After relieving fuel and air pressure, remove the four bolts, remove the valve and carefully inspect it while holding up to a bright light, you probably will find a defect. good luck.
Hristo posted 09-18-2006 06:43 AM ET (US)     Profile for Hristo  Send Email to Hristo     
Thanks a lot.
I have already checked that valve/diaphragm and it seems to be ok. I forgot to mention in my former post that fuel pressure when the engine is not running (just loading the pumps) is between 20-40 PSI. I am more and more afraid that the fuel pumps are involved in the problem. But which one shoud I check? the mechanical or the electric one? Is there any other way to check it than the DDT? Any other alternative?

Thank you again for your help

VI Jamie 22 posted 09-18-2006 06:42 PM ET (US)     Profile for VI Jamie 22  Send Email to VI Jamie 22     
Do you have the service manual?? If not buy it. If you want to check all the fuel pumps, leave the guage on and run the engine. If either the lift pump or high pressure pump are not working, after a few minutes, the guage will drop because of lack of fuel. Unfortunately, I do not know the numbers that you should be reading.
Hristo posted 09-19-2006 06:11 AM ET (US)     Profile for Hristo  Send Email to Hristo     
Thank you again VI Jamie 22,

One more thing, what do you mean by "guage"? Are you referring to the device which is used to measure pressure?
I have the service manual, and according to it I shoud be reading 87 +-2 PSI as fuel pressure, with a difference of 10 PSI in comparison to air pressure (which should be then 77 +-2 PSI). When the engine is running, pressure keeps the same all the time(70 PSI for fuel pressure, 60 PSI for air pressure),it doesn't fall down, but it doesn't reach the optimal levels. Does it suggest too a pump problem?
I don't want to bother too much , but I'm really interested in knowing your opinion on that.

Thanks, thanks, thanks...

VI Jamie 22 posted 09-19-2006 10:07 PM ET (US)     Profile for VI Jamie 22  Send Email to VI Jamie 22     
I have been told that the fuel pressure is linked to the air pressure. In other words, no matter what the air pressure,, the fuel pressure will be ten pounds different. If that is true, your consistent low readings are caused by your air compressor. I am surprised that the readings don't go up or down when you go for a ride.

I am sorry about my misspelling guage. I am refering to your tool that reads your pressures.

Hristo posted 09-22-2006 04:56 PM ET (US)     Profile for Hristo  Send Email to Hristo     
Sorry for not asking before Jamie, this engine is driving me crazy...
As you told me, we checked the air compressor and it seems to be ok (working at 90 PSI), but a general checking of the fuel pumps has showed that the low pressure electric fuel pump is working at an unnormal operating amperage. It fact, it is working at 0 amperes. In any case, we are not sure that means that the pump is broken. Could there be any other reason to explain such an unnormal operating amperage?
By the way, do you know any reliable shop in USA that ships these pumps to Europe? Here these parts are quite difficult to find and are really expensives.
Thank you a lot for your help, I hope I'm not disturbing too much.


VI Jamie 22 posted 09-22-2006 10:48 PM ET (US)     Profile for VI Jamie 22  Send Email to VI Jamie 22     
Some of what you are telling me doesn't fit with your previous posts. Tomorrow I will grab the service manual and answer your questions more accurately.
Hristo posted 09-23-2006 04:46 PM ET (US)     Profile for Hristo  Send Email to Hristo     
Sorry if I am not very coherent, but every day we find out new things about this motor. I have taken a look at the service manual, but I haven't been able to find any answer to my former questions.
I'm looking forward to hearing from you.
bsmotril posted 09-24-2006 03:43 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
There are Schraeder valves at the top of the Air and Fuel rails for measuring pressure. The balance valve maintains fuel pressure at 10 PSI above air pressure. I wish I could tell you the nominal pressure values, but a buddy borrowed my book.
Hristo posted 09-24-2006 04:36 PM ET (US)     Profile for Hristo  Send Email to Hristo     
Thanks, Fortunately I know the nominal pressure values: 87 +-2 PSI for fuel pressure and ten less PSI for air pressure, according to the service manual.

TRAFFICLAWYER posted 09-24-2006 07:18 PM ET (US)     Profile for TRAFFICLAWYER    
[Suggested that this discussion terminate and be moved to other websites.]
Tates posted 09-28-2006 10:46 AM ET (US)     Profile for Tates  Send Email to Tates     
You might also want to check the gas primer bulb in your fuel line, pump it prior to starting and check that it maintains pressure, Old gas bulbs can also be a source of problems.
Hristo posted 09-29-2006 07:25 PM ET (US)     Profile for Hristo  Send Email to Hristo     
Yes, I had already checked the primer bulb, and it maintains pressure. One less suspicious thing...

Thank you

quatz posted 10-12-2006 10:28 AM ET (US)     Profile for quatz  Send Email to quatz     
I have a 2001 Optimax 175. It will surge about 300 RPM at idle sometimes. Has anyone had an [problems] with throttle position sensors?
vistav85 posted 05-09-2007 09:16 PM ET (US)     Profile for vistav85  Send Email to vistav85     
I have a 1998 150 optimax I have problems with it surging. It acts like it is running out of gas. Sometimes it will die. Sometimes after running it for a while it won't start, but motor cranks over ok. BUT I can put the battery on a charger for a while and it...will start. But it still has the surge problem. ANY help would be great.
jimh posted 05-10-2007 01:09 AM ET (US)     Profile for jimh  Send Email to jimh     
The Mercury OptiMax motor is known to be sensitive to the voltage supplied during start cranking. Even though the battery can supply enough current to crank over the starter motor, the Mercury OptiMax will not start if the voltage during cranking falls below a threshold (which I am sorry to say I do not know precisely what voltage that happens to be). The electronic controls of the engine appear to suppress ignition if the voltage is too low.

You report your motor not starting but cranking, then following charging of the battery being able to start. This behavior fits perfectly with the situation I describe above regarding the somewhat sensitive nature of the Mercury OptiMax to voltage during starting. This accounts for the recommendation of Mercury that the OptiMax motor should be used with a battery that has a marine cranking ampere rating of 1,000-MCA or more. This information should be in the owner's manual for your motor.

lurkynot posted 05-10-2007 08:24 PM ET (US)     Profile for lurkynot  Send Email to lurkynot     
I have the 135 Optimax 01' model. While underway I was using the trim to adjust the ride and the engine starting missing pretty bad. Powered down and checked the battery connections and wala the wing nuts were loose and to make things worse the connections were pretty well oxidized to say the least. I used a knife to temporarily scrape the face of the connectors and reafed on the wing nuts as much as I could. Started her up and did'nt have another problem that day. Cleaned them up the next day the proper way and added lock nuts.
fourdfish posted 05-10-2007 10:55 PM ET (US)     Profile for fourdfish  Send Email to fourdfish     
Mercury says in The Opti Manual that the required battery for that engine is one rated at 1000MCA or 800cca. From what I gather the battery voltage should not fall below 11.2 volts.
ivansfo posted 05-14-2007 02:17 PM ET (US)     Profile for ivansfo  Send Email to ivansfo     
I concur with others that the Optimax is very sensitive to weak batteries. My first pair of Interstate 24M-XHD completely died after 3 years. However, prior to that the batteries were showing signs of weakness. This is when I started having problems on my 135 Optimax. I would get erroneous alarms and other odd problems on the Smartcraft gauges such as:

- Erratic speedometer. Speedometer jumps around when I'm running

- False Alarms like "Check Paddlewheel"

- False Alarms like "Check Pitot"

All these problems completely disappeared after putting in a fresh pair of batteries. Now I replace them every 2 years with the same Interstate models. This time I'm going to see if I can squeeze in a pair of Interstate 27M-XHDs

msl posted 05-17-2007 07:34 AM ET (US)     Profile for msl  Send Email to msl     
I bought my boat 2 years ago with twin 1999 150 opti max's. The motors when bought had 180 hours. When I hit 380 hours I had the port motor foul an oil check valve. At this piont we changed impeller, spark plugs, all filters, and fluids. The batteries were replaced at around 250 hours, and are do to be changed very soon again. It is starting to look like I will change my batteries every 250 to 300 hours. I'm still running on the original belts, tech as said they look fine every time. When have most of you had to replace your belt or has any one broken a belt on an Opti Max? I just had a power trim relay switch go on the port, easy fix, the motors have around 800 hours to this day. I average around 300 plus hours a year, we fish from March til January, alot of trailer in the DELMARVA region.
vistav85 posted 05-20-2007 07:07 PM ET (US)     Profile for vistav85  Send Email to vistav85     
THANKS for all the help with my 150 optimax.Surging was caused by a bad fuel pump.But the problem with not starting was a weak battery. Again, THANKS
strike_zone posted 05-29-2007 08:42 PM ET (US)     Profile for strike_zone  Send Email to strike_zone     
I'm hoping that one of you knowledgeable gents can help me out. I've got a 2000 Merucry OptiMax 150-HP, Have had it since 2002, and not a hiccup. Other than not starting so well in cold damp weather, it's been pretty good and very dependable. I just took it in for service: plugs, filter, and water pump impeller. The service department called me this afternoon and is dumbfounded in that they claim that there is no spark in either the lower left or upper cylinders, and only a minimal intermittent spark in the centre left cylinder. The diagnostics are coming back with no problem found. Other than that, the engine seems in great shape, but they cannot figure out this electronics glitch.

I recall seeing something like this in an older Evinrude engine. The problem was something called a power pack, but generally when these failed, there was no spark to any cylinder, not just some but not others. I just don't know enough about these newer electronic-based engines to know where to start. (And obviously am concerned that a service department is baffled on this one. My doubting side is wondering whether someone has connected something up incorrectly and damaged something, and they're now looking for a way out at my expense.)

Anyone got any ideas, or know what might be causing this?

Many thanks

jimh posted 05-29-2007 11:10 PM ET (US)     Profile for jimh  Send Email to jimh     
The Mercury OptiMax is probably like most modern outboard motors in that each of its spark plugs has its own circuitry which is more or less independent of the other spark plugs. There is usually a separate high-voltage coil (actually a transformer) for each individual plug. And the low voltage drive to the coil is developed independently for each cylinder, although sometimes in a V6 there might be some shared low voltage circuitry if two cylinders fire at the same time.

I am somewhat familiar with OMC ignition systems and their power pack, and it is possible that there can be a failure in a power pack which affects only one cylinder. I just went through half a boating season chasing an intermittent spark problem in just one cylinder of my engine, eventually curing it with a new power pack.

In older Mercury engines I have heard the term "switch box" used to refer to the ignition electronics which generate the low-voltage drive signal for the spark coils. I don't know the exact configuration used in an OptiMax, but it seems reasonable that there could be failure on an individual cylinder basis. There are some sharp professional Mercury mechanics that prowl here, so perhaps one of them can jump in with further explanation of the details of the ignition system on the OptiMax.

ggoodwin posted 07-11-2007 09:40 PM ET (US)     Profile for ggoodwin  Send Email to ggoodwin     
I have ready your replies and it sounds similiar to the trouble that I am having. I have a 1998 150 HP Optimax with 225 hours on it. It is idling rough and cutting off. I also have lost the top end RPMs above 4500. I have replaced the spark plugs, both TPI, fuel filter. My mechanic has tested it with the DDT, both static and running and it comes up good. Does anyone have any thoughts to help me. I have pulled all my hair out.

Any assistance would be greatly appreciated.

Royboy posted 07-12-2007 10:33 PM ET (US)     Profile for Royboy  Send Email to Royboy     
Do you typically use any fuel additives? What did your plugs look like?


ggoodwin posted 07-13-2007 12:49 PM ET (US)     Profile for ggoodwin  Send Email to ggoodwin     
I have put in Quicksilver injector cleaner and I have replaced the spark plugs as well. New gas etc. I now have the check engine light on. The mechanic and I played around with it for a while and now it runs better. It will now crank up and idle almost smoothly, runs great but still does not have top end like it use to. I am not worried about top end as I just want it to crank and be able to pull the kids tubing.

Now that the check engine light is on, it could be a bad (weak)coil, sensor, etc.

What are your thoughts?


Liteamorn posted 07-13-2007 06:27 PM ET (US)     Profile for Liteamorn  Send Email to Liteamorn     
Before I bought my 2005 Optimax 150 (new in 2007)I read a lot about them here. I found a few threads addressing the aforementioned problems and at least a few of them were solved by using Optimax DFI oil. My dealer STRONGLY suggested I use Optimax DFI oil. He was adament about it and he knew he would never sell me a gallon of it due to the fact that he is 100 miles away.
dolfin posted 07-03-2008 09:47 AM ET (US)     Profile for dolfin  Send Email to dolfin     
[Changed the topic of discussion from the general reliability of the OptiMax to an inquiry focused on diagnosis of a particular problem with a specific motor. In general it is not a good idea to revive discussions that have been dormant for many months or years only to change the topic of discussion to something new. I will spend a few minutes creating a new discussion on this new topic for this author--jimh]
fruchick posted 08-29-2008 02:31 PM ET (US)     Profile for fruchick  Send Email to fruchick     
I'm having similar problems with my 2000 150 optimax from those discussed earlier. Rough Idle, stahls after a minute or two. My service tech tells me it's the diaphram that regulates the air/fuel. However, merc is telling him (I also verified this) that I can only replace the entire fuel rail, for a cost of $1078!! Can anyone tell me where I can get just the diaphram??
jross036 posted 04-19-2009 03:01 AM ET (US)     Profile for jross036  Send Email to jross036     
[This discussion was revived and its topic changed. The new topic has been separated into its own thread. The revival of the discussion elicted this reply:]

I'll throw my two cents in.Optimax engines are real sensitive to low voltage and bad fuel. Bad fuel meaning old ethanol. If it sits too long then it messes with the two fuel pumps which are on and in the vst. It seems to be worse here in the tropics. I've had to replace both of these pumps more than once in 150's.The ddt tool didn't catch these problems, or at least the tech. who worked on them couldn't catch it. We purchased the diagnostic program from CDI and went at it ourselves. Very good thing to have. Live, on board dash with a laptop. Easy to use. With this and the factory manual these engines are much easier and cheaper to fix than say a Yam. 150 HPDI.Another must on these motors is to keep the thermostats changed every season along with the water pump. Lots of sensors which feed info to the ecm and all the electrical values must be within spec. for it to run at its peak. Lastly, the need for the good strong batteries, yes two blue optimas hooked in parallel work fine. Opti's need to have 90 psi+- on the fuel side and 80 psi air. If you don't see that at those shrader valves then look deeper. Most of the problems we've found have been linked to the two electrical pumps. Aloha

jimh posted 04-21-2009 02:58 PM ET (US)     Profile for jimh  Send Email to jimh     
[Please note: this discussion began five years ago. It is not realistic to direct inquires to participants who were involved five years ago.--jimh]
jimh posted 05-04-2009 10:30 PM ET (US)     Profile for jimh  Send Email to jimh     
For some reason there is an irresistible urge for people to revive this discussion which began five years ago. I am tired of moving threads out of here into their own new thread, so I am closing this discussion to prevent more revivals.

Thread closed.

jimh posted 05-05-2009 07:21 AM ET (US)     Profile for jimh  Send Email to jimh     
[Moved to REPAIRS/MODS.]

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