Servicing info on 3.0lt 135 merc

Mark RSA2AU

Mark RSA2AU

New Member
Sep 21, 2009
62
Melbourne
Boat Info
Sea Ray 180
Wakeboard tower
Engines
3.0lt Mercruiser
Hi Guys

I am new to the site and thank you for all the previous post's which I have poured over for the last few weeks!

I have just bought my first mercrusier powered boat. A '99 Sea Ray 180 bow rider with a 135 hp merc and Alpha 1 drive. I am running a 4 blade 18 pitch prop.
I know this is an underpowerd rig by comparison but great for my family. This week end I filled up the tank with 95 unleaded fuel ( Australian ) which should be better for the boat, but it felt worse. Previous tank was old fuel of unknown octane rating.
There was little or no difference felt in power from half throttle to full throttle pull off (hole shot).
The motor also ran on after the key was removed.
I was planning to have it professionaly serviced untill I found out the cost!!!! Quoted price AU$95 an hour, 3 hours for the motor and 3 hrs for the Leg excluding parts.

So can anyone advise me on where to find a service manual for this motor and what to look out for to solve the above.

Thanks
 
You can order the factory manuals from Mercruiser. Their site asks you for serial numbers to get the correct manual so have those numbers handy if you decide to order from them. I would also stop running the 95 fuel as that engine shouldn't need it and the extra octane just retards your combustion and doesn't give you any extra power unless you've modified your motor and chipped or adjusted your ignition to match the new setup. Poor performance and engine dieseling could be a simple timing issue but you need to put the proper fuel in there before you diagnose for the fault.
 
Thanks mate, pity about the fuel. I will probably need to throw 80lt of fuel. I can't use it cause I drive a diesel!

Appreciate the help!
 
You shouldn't have to dump the fuel but you will need to factor in the timing difference required for the different octane. When you get your next batch of fuel, you'll need to adjust your timing again. Running the higher octane in your engine won't do catastrophic damage but it can adversely affect the performance which is what you are trying to resolve. You can continue to burn it off and fill the tank with the correct grade and the octane level will eventually level off to the norm. You could also siphon the 95 off into a container and mix it in with the new fuel when you fill up. You might go 75% fresh fuel and 25% of the 95 to get you to a tank octane rating that is within a margin of error for you engine setup. As for the performance and dieseling issue, could you give more history of the vessel? Did the previous owner offer up any maintenance information/records for the boat and drive system? When you say there was 'old' fuel in the tank before you filled it up, is that a simple reference to the fact that it was there when you purchased it or did you get information that the fuel had been in that tank for a long stretch of time because of non-usage of the vessel?
 
I have the same boat and engine set up but in the 2001 model. Engine run on after shutting off the ignition is common on this model. Usually it occurs after running hard and shutting off very soon after. If you let the engine run at slow speed for a couple of minutes after running at high for some time it usually solves the problem.

The higher octane fuel you used should have actually helped the problem. Strange. Mercruiser actually published a service bulletin on the subject but I don't have it handy. If I recall, it invoved retarding the ignition timing a few degrees and run the correct octane fuel.

As for not much more power with half vs full throttle from a dead start, mine is similar until you get over about 3,000 rpms then it takes off well. I would try a couple of props with lower pitch and I think you would be surprised. I recommend a Mercury high five 19 pitch (yes I know that is a higher pitch than your 18 but they tend to perform at a lower pitch) or a high five 17 pitch and see if the performance improves
 
Below is some info I found on the running on issue. One easy thing I forgot to mention is to try slowing down the idle speed. If the engine idles too fast, it makes the problem much worse.

Engine ‘Dieseling’ or ‘Running-On’
Models
MCM 4 Cylinder, V6 and V8 with Carburetors.
Situation
Under certain conditions, carbureted engines may ‘run-on’ when the ignition key is turned off. Normally, it
will take a combination of several of the following conditions to make the engine ‘run on’. These conditions
include but are not limited to:
1. Type and formulation of gasoline available in the area.
2. Type of boat and its engine compartment ventilation system.
3. Outside air, inside engine compartment air and engine coolant temperatures.
4. How quickly the engine is shut off after running at cruising or higher RPMs.
5. How the boat and engine are operated.
6. Engine idle rpm set too high.
7. Wrong heat range spark plugs or spark plugs with deposits on them.
8. Deposits in combustion chamber.
Carbureted engines, unlike EFI, do not shut off the fuel supply to the engine when the ignition key is turned
off. As the engine is coasting to a stop, air is still flowing through the carburetor into the manifold. This air
flow can still draw fuel from the carburetor, through the intake manifold and into the combustion chamber.
A hot spot in the combustion chamber will cause this fuel/air mixture to burn. The engine now ‘diesels’ or
‘runs on’ although the ignition system is not firing. EFI engines do not have this problem because the injectors
do not inject fuel once the ignition key is turned off.

Suggestion to Minimize ‘Run On’
Items number 1 ,2 and 3 can correct or reduce most of these ‘run on’ problems. Letting any engine idle a
minute or two before shutting it off is desirable. This helps the engine to normalize at idle rpm before being
shut down.
1. Be sure engine idle mixture, idle rpm and ignition timing are correct. On 4 cylinder and V6 or V8 engines
with Thunderbolt IV ignition, setting idle rpm as low as possible can help stop ‘run on’.
2. Adjust throttle cable barrel so that the carburetor’s throttle lever returns against the idle speed stop
screw every time the remote control throttle lever is returned to neutral, idle.
3. Idle engine 1 to 1-1/2 minutes before turning key off after running at cruise or higher engine rpm.
4. Try a different brand of regular fuel or try some premium fuel.
5. Increase idle mixture by 1/8 turn ‘richer’.
6. Go to next colder heat range spark plugs.
7. V6 and V8 only: Install a 140 °F(60 °C) thermostat.
 
Hey Guys

Great advice! I was told by the previous owner that the boat was serviced every year by a Merc Dealer and that the fuel was left over from last season. The boat and motor seem to be in exelent condition with all the oils looking fresh. I do not know what grade of fuel it was.
I have since been recommended a local boat mechanic who is going to service it and benchmark it againt other 3.0 lt he services.

I will forward him this info as well.

Thanks again!
 
Mark, your hole shot (which is from 0MPH) should actually be quite tremendous with that prop. Stock prop would have been a 21" or 23" 3-blade. Unless you're saying this is a new situation, I would venture a guess that most of your problem is due to the prop. I could be misreading what you wrote, though.

Higher octane should resist run-on, shouldn't it?
 
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Higher octane only slows down the burn process, it doesn't prohibit it altogether so you still have ignition. If they use ethanol to boost the octane rating (alcohol burns slower than petroleum, also has less energy per unit), that still shouldn't affect the ignition temperature as there is still a lot of petroleum fumes to ignite and start the process. For clarification, when I read the suggestion about trying a different fuel formula, I read that as 'try a different station', preferably a different brand, that gets its supply from a different refinery and has different additives as that is more likely to affect your engine than getting a different octane from the same pump.
 
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Thanks Dennis, I assumed that the higher octaine would improve performance and reduce the run on but as I have been informed, the '99 carb motor does not have electronic ignition, so it cannot adjust its self for the higher octain and needs to have the timing reset to make best use of higher octane.

The prop is a 4 blade 18 pitch and although the hole shot is ok it is not what I expected. I will see what the mechannic says about the motor, maybe my expectations are too high. I have also been recommended the ProPulse Prop which is a composite (light) prop which has an easily adjustable pitch from 15 to 21.
So if the performance improves after the service then great, if not then I will prop down. I might even have to shed a few kilogrammes from the gut..... maybe Ill just prop down.

Cheers
Mark
 
Mark, I'll let Biff give the specifics as it seems he is much more versed than I am in regards to octane. But, the way I understand it is that higher octane doesn't do anything for performance when talking about a normal compression engine. And the reason a higher compression engine needs the octane is to avoid pre-detonation. But again, I'll digress to Biff on this.

I ran a 4 blade 18" on my '00 180 and was extremely impressed with the hole shot. Are you comparing to a real ski boat? In that case, no it's certainly not as quick.
 
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There is a common misconception (mostly among young 'ricers') that the octane rating equates to a 'power rating'. This is false. The engines that run the higher octane fuel produces more power by burning more fuel, not because the fuel itself contains more energy. They do this because they are generally higher compression motors with more valves per cylinder to allow a larger charge to be drawn in (or pushed in if you prefer) per stroke for combustion. This is why a Honda 1.6 DOHC motor has a higher horsepower rating than the 1.6 SOHC. It is the same with a FoMoCo 5.0 LX versus the 5.0 H.O. You will note that the DOHC and the H.O. motors have a lower MPG rating. This is because they burn more fuel per stroke than their single cam'd siblings with fewer valves per cylinder and lower compression. As Dennis stated, the higher octane is used in the higher compression engines to avoid pre-detonation (explanation of octane rating). Higher octane has also been promoted, at times, as a remedy for engine knock. Most modern engines have knock sensors now so that use is of dubious value except for older non-computerized and ill-tuned motors. I've not heard of octane as a remedy for dieseling but that is not to say it hasn't been offered as such. It could work for a certain fuel formula, I guess, as there is no one defined method for raising octane, as the wiki alludes to. But, if you want 'more power', simply putting a higher octane fuel in your tank is not going to accomplish that. While I'm at it, 'water injection' isn't going to do it either as water has less energy in it than alcohol AND it doesn't burn when heated and compressed. Heated, it changes state and becomes steam (doesn't burn) but doesn't break down into its base elements of Hydrogen and Oxygen (will burn). What water injection can do is cool the incoming air/fuel mixture (like Nitrous) so that you get a denser (more petrol) charge for combustion. Putting a blower on the intake is also another means of getting more air and fuel into the cylinders. Water injection, done incorrectly, can boost your mileage as it takes up the space where petrol would have gone thus you burn less fuel per stroke...but you loose power because you are basically running lean.
 
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BiffStroganoffsky said:
I've not heard of octane as a remedy for dieseling but that is not to say it hasn't been offered as such.
Click to expand...

Biff, the only thing I can offer is that, from experience, I know it can help. For whatever reason, the 4.3L is prone to run-on (more-so than other engines), especially late in the season when gas companies (especially on-road) change their gas formulation that they carry. I have found over the years that uping the octane and/or running the blower all the time (to evacuate more heat) can both help in reducing run-on (also idling a bit before shutting off). I've always believed the run-on, in the case of the V-6, to be at least partly due to heat and if it's "right on the edge" of run-on, then I thought the higher octane could stop that. Am I on the right track? Maybe it can help in other engines as well?

Thanks for your in-depth explanations, too!
 
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If using a higher octane fuel remedies a run-on/dieseling issue, I don't see a problem doing so. Just keep in mind that it may well be the different formulation of the fuel and not the octane rating that reduces/eliminates the engine dieseling. I know it is splitting hairs somewhat (kind of like the slight differences in ignition/combustion/detonation) but I'm just trying to steer people away from the concept that 'octane' is the magic potion for higher performance/anti-knock/dieseling. I would rather include higher octane fuels as one of the options included in the 'try a different fuel formula' but after 'a different vendor/refinery of the same octane'. This seems to offer the benefits of lower fuel costs and not needing to re-tune the engine to the appropriate octane.
 
Just for Dennis, not because I'm trying to pick on you or your idea but because you've shown great civility and a certain amount of curiosity and desire to understand in your responses. Consider a scenario wherein two people in a neighborhood have car problems. One car is a 'sports' car with a high compression motor that is 'sluggish' and possibly knocking a bit. The other car is an econobox sedan that is dieseling after the ignition is turned off. There are various gas stations about but only three refineries that supply all the stations. Each refinery will have different 'formulas' for the petrol they sell, possibly because they each source their crude from different places. Suppose we find out that the 'sports' car owner had not read his manual and was pumping 87 into his tank because he didn't understand that 'premium' meant 91 octane and that the lower octane gas was completing its burn cycle before the cylinder got past TDC (pre-combustion). If that person switched to 91 octane from any of the local stations, his knock will stop because the engine can complete the compression stroke before the detonation is complete. So long as the refineries validate the octane ratings of their petrol correctly and the stations don't dope their tanks, this will always be a valid solution. The person with the dieseling motor has a different situation as a heat source is igniting the mixture even after the spark is shut off. In this case, it is the ignition point of the fuel that is causing the engine to run-on. Usually, there is excessive carbon buildup on one of the components in the cylinder that causes it to store more heat than usual but poor cooling of the block (bad coolant or poor bay ventilation) can also be a factor. In any case, this increase in temperature in the cylinder is enough to ignite the compressed mixture which allows the engine to run without spark. Introducing the concept of octane here doesn't negate the ignition of the fuel as it has to do with the duration of the detonation process and not the ignition point. However, the chemical makeup of the crude that is processed and the refinery and the refining process itself along with any additives or doping agents they introduce can affect the ignition point of the mixture. Thus you can have instances wherein a vehicle will have odd odors coming from the tailpipe when it is filled up at one station but no such problem at the others. The same can happen with the ignition point. You may have an instance where one refinery's octane process can alter the ignition point of the mixture and you can 'fix' the dieseling by buying the higher octane gas from the same pump. But, there is a chance that if you get 91 from a different station that buys from a different refinery which uses a different refining process which doesn't affect the ignition point in the same way that the dieseling won't be fixed or will return. In the case of our econobox sedan, by telling that person to 'fix' the run-on by running higher octane, you are implying that if 91 from one station stops the dieseling then it is certain that premium from any of the station will work also, which isn't necessarily true for the basic fact that the octane number isn't a guarantee of a mixture's ignition point but a scale of its detonation process. You could have an instance wherein 87 from a different station and refinery will cure the run-on which would invalidate the higher octane solution. What a windbag, eh? Sorry but I just thought that was the best illustration I could offer for why I don't consider 'higher octane' as a blanket solution for dieseling but would consider it as part of the 'try a different formula' suggestion. Yeah, splitting hairs. :p
 
I have a 95 with that motor and it deiseled quite a bit when I first got it. I am pretty sure it was due to old fuel in there that had started to go bad. Since then I have run only premium 93 Octane fuel through and it has never done it again. I know this motor will run on regular 87 Octane, but I figure that since it is as fuel efficient as it is I can spring a couple bucks for better gasoline. I also pretty much leave it running now. I use to turn it off everytime I stopped. This was before I knew I could have a 4-5 hour outing on 10 gallons of gas. So I usually only turn it off when I trailer it and I have no problems.

Also, make sure you use fuel stabilizer if you are using the newer gasoline with ethanol and not MTBE added to it. Ethanol naturally absorbs water vapor and can ruin a boat motor if it sits up for months and has a change to collect in the fuel tank.
 
I played with my motor over the weekend and by lowering the idle speed slightly and adjusting the idle mixture approx. 1/2 turn richer my problem went away. I use 88 octane fuel. I have only had the "run on" sympton when I shut down immediately after a hard run or pulling a tube etc. If I let the engine idle for a couple of minutes, it never would run on.

The idle speed is very easy to adjust and is a "stop screw" in the carb directly under the throttle cable. Turn it counter clockwise until you get the slowest stable idle speed. The Mixture screw is a T-handle screw on the bottom middle of the carb on the Port side. Turning is counter clockwise will richen the idle mixture slightly. If you turn it too far, the engine RPM will drop. This needs to be adjusted to match the altitude you operate at if your location altitude varies much.
 
Back on track I don't think the poster had an issue with run on. He was just wondering why his higher fuel didn't run better. It's not going to it just burns cleaner and stops some of the internal deposits. Run the boat on the recommended 87 or close that it's tuned for and once in a while run higher to clean out the carbon and other deposits in the combustion chamber. Yes from experiance on car engines the higher octane can assist in engine run on, but as was stated before run at lower RPM for a short while before shutting off the motor should solve that issue. It just needs to burn off the excess fuel.

I searched merc's website and found the recomended maintance. Oil/ Filter change, Gear lube change, Tilt trim fluid change ect...
 
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