2001 Mercury Saltwater 90HP 2 Stroke

[Blade]

Hi Raiders, 

I recently purchased a boat with powered by a  MERCURY 2001 90 Model number 1090412YY serial number OT277836

Since buying it I have spent far more than I could ever have imagined sorting out  things that haven't been attended to over the past few years and the costs are really building up.

One of the recent expenses was the replacement of the oil tank and sensor to get the low oil warning system working again, this was the advice I was given at the time. After having done some reading it seems the popular approach when the low oil warning system goes is to bypass the oil injection system and premix.

I have obviously already spent the money and had the work done on the oil tank and low oil level warning system, the thing that is now worrying me is the thought of the oil injection pump failing, there is no warning system linked to the oil pump so provided there is oil in the tank no alarm would sound and I would be none the wiser.

The mechanic says that oil pump failure on this model motor is very rare and I would have to be extremely unlucky to have this happen to me (the way the expenses have been coming through on this boat one could argue that my luck is not the best) does anyone have any experience or insights on the reliability on these oil injection systems.

Is there a way I could fit either an oil flow sensor or an oil pressure sensor (it runs at 2 PSI so would need to be able to trigger an alarm should the pressure drop below say 1.5PSI)

Or is the only option to bypass the oil injection system and pre mix and write off the money I have already spent to experience?

Looking forward to hearing from fellow raiders. 

 

 

[noelm]

There is a warning system, oil injection failures are rare, your mechanic is correct, most disconnect the  system on bad advice or because some "old time" back yard mechanic said so.

[Blade]

1 hour ago, noelm said:

There is a warning system, oil injection failures are rare, your mechanic is correct, most disconnect the  system on bad advice or because some "old time" back yard mechanic said so.

Can you clarify if there is a warning system for oil injection failure, my mechanic said my motor doesn't have one and he is not aware of an aftermarket option

[kingie chaser]

I'd be asking Mercury!

That way your getting the correct information.

[zmk1962]

@Blade ask Merc as KC says you may be lucky and get someone that’s interested in helping regarding an older motor worth a shot. More often they will just refer you to a local dealer. The other thing you can try is to locate a service manual PDF for your motor and read through the fuel system section. I was able to find one Free for my previous 1999 200efi On this site. Sorry I only have the link for the 200 but play around with the url and see If you can locate one for your 90. 
 

http://www.hedges-uk.com/boat/Merc/outboards/2-stroke/2-stroke/135-150-175-200-225/MODELS%20135-150-175-200-225%201992%20and%20Newer%20%96%20135-150-150-%20XR6-150%20Magnum%20III-150%20EFI-175-175%20EFI-200-200%20EFI-150-200-225%20Pro%20Max-150-200-225%20Super%20Magnum%20.pdf

Alternatively go look at a site that shows parts for your specific Year make model Motor and check the fuel system - see if there are any parts relating to oil sensor :

http://www.boats.net/parts/search/MercuryMarine/0g884040/3743/parts.html

Again this link is specific to my old Merc. Play with the url or the site once you open it.
cheers Zoran 

[Blade]

@zmk1962 I have checked the service manual for my motor. It just notes (models with oil pump warning module) as the service manual covers a number of models. I have had a look at the oil pump and there are no wires coming out of it or anywhere else on the oil injection system. The only wires I could find were on the oil tank itself. 

Would putting a flow sensor inline be an option, I would have to figure out how to connect it to an alarm or buzzer in the event that the oil flow stops.

 

[noelm]

Sorry, misunderstood what your meant, there is a low oil warning system, not a "no oil" the system is very reliable, I know of no aftermarket alarm setup.

Edited August 6, 2020 by noelm

[noelm]

The amount of oil used is quite low, I doubt there would be anything sensitive to reliably sense such a low flow.

[zmk1962]

Hi @Blade I will describe how I understood my 200efi to work (as that's where I have direct experience), you can cross reference with the service manual for your motor.  Look in the Fuel/Oil injection section of the manual there should be a verbal description of the oil injection system design/operation. 

On the 200, the oil injection pump was driven by a gear shaft running off the motor crank case. So if the motor was spinning, the oil pump was pumping as long as the oil gear shaft was intact or the gears were not stripped. The oil pump was crank case driven not electric motor driven. So assuming the gear and shaft were intact the only time you would not have oil flow when the motor was running would be if the oil tank was empty of oil - hence the empty tank oil sensor. Even if the tube exiting the oil pump broke, the oil tank would be quickly emptied and you'd have the alarm go off.

I agree with what @noelm said about reliability of the system. My system was very reliable over the 21 years I had my Merc.

The 200 merc had an external 10L oil reservoir, feeding the smaller oil tank situated on top of the motor. The only problem I ever had with the oil system was when the cap for the oil tank on top of the motor cracked and was no longer air tight. The "system" recognised this as a low oil indicator in the top tank and continued to pump oil from the external reservoir. I had oil everywhere. It looked like a major issue but a new top cap solved it. The root cause was most probably an inexperienced me over-tightening the cap because I read somewhere that it had to be kept air-tight !!!!!!!! 

Also I'm also pretty sure if the system detects a NO oil situation the motor goes into a limp mode preventing you going above certain RPM. Again check your manual - I no longer have mine.

3 hours ago, Blade said:

Would putting a flow sensor inline be an option, I would have to figure out how to connect it to an alarm or buzzer in the event that the oil flow stops.

Again I agree with what @noelm said. I'd also add, that if you eventually figure out how to place an inline flow sensor between the pump and the motor, you are also adding another failure point. Most of the flow sensors have some type of impeller mechanism, if that jammed or failed, it could restrict oil flow (below the calibrated rate of the pump) and you would probably do more damage to the engine as you'd be running for a much longer period of time with lower oil content then you would if it went into limp mode.

Just my thoughts on the topic.

Cheers Zoran.

 

[noelm]

The very early Mercs had a plastic gear that gave a bit of trouble (not much, but some) it was later changed to a metal gear, and from them on, it was very reliable system, the bigger HP used a pressured system to transfer oil from the boat tank, to the motor mounted tank, this works well as long as everything is "serviced" and not left to just fall to bits.

[noelm]

Just to add, I THINK the EFI and Optimax systems had both low oil and no oil supplied alarms, because they operate differently to a "normal" carby setup, the Optimax should never have the oil injection disconnected, even if mixing oil with the fuel, same goes for e-tecs and Yamaha HPDI.

[Blade]

Called Mercury waiting for a call back- based on the feedback thus far it seems to be a reliable system that I should not worry about. I think that my motor has the plastic gear but I will ask Mercury to confirm.

Boat is still at the mechanic and they have suggested a carb strip down and rebuild, not knowing when last this was done it seems to make sense.

Is this something best left to the professionals? The labor costs are more than the parts hence me thinking perhaps I should give it a bash- any advice on this?

I also asked them to do a compression test and a leak down test, they reported that the compression is around 90PSI per cylinder. And the leak down test was within the expected range. The mechanic says that in his opinion the motor is healthy (he has water tested the motor)

Does 90PSI sound about right for this type and age of motor (350 hours on the clock)?

[noelm]

Carbs are easy enough to do, but, they need to be done properly, just washing them, or spraying them with cleaner is not doing it properly, all passages need to be clear, and small parts replaced, it does take time, hence the labour charge, an ultra sonic cleaner is best. Compression numbers need to be reasonably even, the numbers can vary from gauge to gauge, but they need to be close to even. I think your motor might have the metal gear, but you will need to parts book to know for sure. The oil system is reliable, even the plastic gear drive gave little trouble.

Edited August 7, 2020 by noelm

[Blade]

On 8/7/2020 at 5:37 PM, Blade said:

Called Mercury waiting for a call back- based on the feedback thus far it seems to be a reliable system that I should not worry about. I think that my motor has the plastic gear but I will ask Mercury to confirm.

Boat is still at the mechanic and they have suggested a carb strip down and rebuild, not knowing when last this was done it seems to make sense.

Is this something best left to the professionals? The labor costs are more than the parts hence me thinking perhaps I should give it a bash- any advice on this?

I also asked them to do a compression test and a leak down test, they reported that the compression is around 90PSI per cylinder. And the leak down test was within the expected range. The mechanic says that in his opinion the motor is healthy (he has water tested the motor)

Does 90PSI sound about right for this type and age of motor (350 hours on the clock)?

Thanks to everyone who has contributed so far, I have been searching high and low online for more information around the compression. 

In the service manual it refers to 120 PSI being acceptable, I asked the workshop to test using a different compression tester to eliminate the potential of the compression tester being faulty , the result was the same 90PSI across all 3 cylinders.

When I mentioned to the mechanic that the service manual noted 120PSI he said it is unusual for a manufacturer to list the PSI and that I am overthinking the PSI reading in his professional opinion provided the compression is not very low the most important thing to look for is the balance between the cylinders and that the motor revs up to the maximum WOT RPMS without issue and can maintain the WOT RPMS and then come back down to idle smoothly.  The fact that they also did a leak down test that showed no cause for concern is confirmation of the engines health.

I dont doubt his experience or credentials, however before I spend more money on this motor (which will mean that I would have done the following on the motor should I go ahead with the carb and fuel pump rebuild -new impeller and gaskets, new gear case oil and seals, new spark plugs, new thermostat and gasket, new oil tank and oil level sensor, inline fuel filter, fuel water separating filter, carburetor strip down and rebuild, fuel pump strip down and rebuild, new steering cable) I want to make sure that mechanically the motor is sound and that spending the money is really just getting the maintenance up to date and for peace of mind not knowing what was done on the motor and when.

Should I be concerned about the 90PSI or is it nothing to worry about.

[dunc333]

lower reading i would think if engine cold run engine to operating temp and test again if worried ,as said before as long as there all within a few psi all good ..when a cylinder is gone psi usually reads way below other cylinders ,hope this helps cheers dunc333

[noelm]

I wouldn't worry about the compression numbers, unless the motor is giving trouble, I personally wouldn't rebuild the fuel pump and carbs (it certainly won't hurt anything) the water pump and gear oil, plugs etc for sure.

[Blade]

1 minute ago, noelm said:

I wouldn't worry about the compression numbers, unless the motor is giving trouble, I personally wouldn't rebuild the fuel pump and carbs (it certainly won't hurt anything) the water pump and gear oil, plugs etc for sure.

The workshop is saying the fuel pump rebuild should be done annually, also because the motor is 20 years old the and I dont know when the carbs were last serviced they recon it is worth doing and then I dont have to worry about it again.

Do you think it is a waste? What benefit would I get from doing it vs the risk of not doing it?

[noelm]

The benefit is, you know they're clean, and low risk of running lean (and possible engine damage) as long as they are done properly! downside is cost.

[JonD]

I had a 2003 model which I believe was the same engine. I simply took note on how many hours it took for the reservoir to get low and topped it up before it got to the alarm stage. Pretty much every third or fourth outing of around 40-50km each trip I topped it up.

Mine like yours ended up costing me a fair amount in repairs. The powertrim unit leaked and needed replacing at $1600, then $700 for the electrics because I had the ignition in the on position when I turned on the battery isolation switch, the list kept on and on. When I got to $4000 I said enough was enough and bought a new motor!!!!!...sold it for $2000 and no doubt someone has had years of reliable use out of it since !!!!

[kingie chaser]

The fact that the 3 cylinders are all identical pressure would indicate to me that they are all wearing evenly & not one is failing over the other.

Still does not nessacarily mean that everthing thing 100% but shows even wear on the rings etc.

 

If your manual is correct & states 120psi is ideal & +-15% then 102psi then your under the factory specs, rings do wear & can cause engine failure.....fact! 

 

Why would a manual not show the recommended PSI, stange comment imo??

 

Will it do it tomorrow, no, next week, maybe?

In the end you trust the mech's opinion or not!

 

If buying a second hand boat/motor I would think it normal & sensible if the owner cant produce servicing doc's to do these basic's minimum, water pump, fuel filter, gear oil, spark plugs, grease all moving parts & any other items that can visibly be noticed which could include carb service, thermostat.

My mate just had his similar era 60Hp Merc serviced & just doing the basics was $800.

Wasnt cheap but & dont think its unreasoanble either & at least gives you the confidence when you head out.

Edited August 9, 2020 by kingie chaser

[dunc333]

blade with a motor of that vintage get the basics fixed and enjoy it ,dont over read it 1, replace servicable parts run some carbi clean and enjoy .if still playing up come back here and help will be here  on fr cheers dunc333

[Blade]

Thanks to everyone who offered advice. After a few days of Googling and reading up I had a conversation with the mechanic and sent him a copy of the service manuals reference to the 120psi.

He advised that they had done a boreoscope to visually inspect for damage or wear and they could not find any. This plus the leak down test plus the fact the motor runs to the Max rpm without issue makes me believe the compression numbers are probably due to a compression tester that is not calibrated properly and is reading low. 

I am going to get this final bit of work done and then just enjoy the boat and motor. 

Cheers 

[kingie chaser]

If it's had the tick of approval then get out & enjoy it 

Edited August 10, 2020 by kingie chaser