25 hp 4 stroke Tohatsu

[nrobideau]

Hello,
I have a 2007 25 hp 4 stroke that is getting gas in the oil. It still runs fine. I have changed oil and filter, tried it again and still get the same results. Any thoughts on what maybe causing this? Thank You Nelson Robideau

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

A blown diaphragm in the fuel pump could cause that. If so, you need 3H8040001M, FUEL PUMP, F25/30A F9.9/15/18, $60.46.

 

[nrobideau]

Re: 25 hp 4 stroke Tohatsu

Thanks for reply, I will order new fuel pump. Nelson Robideau

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

The Factory part is available from any dealer, including me.

 

[TOHATSU GURU]

Re: 25 hp 4 stroke Tohatsu

You might want to see if the diaphragm is blown BEFORE you order a new pump.

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

You might want to see if the diaphragm is blown BEFORE you order a new pump.

Indeed!

 

[nrobideau]

Re: 25 hp 4 stroke Tohatsu

Hello,
I replaced fuel pump,filter and oil. It is still getting gas in oil. Any thoughts on what to do next? Thanks Nelson Robideau

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

If the fuel pump diaphragm is not leaking into the crankcase, then the only other route for fuel into the motor is the carb. Are you running so rich that you are getting so much blow-by that the residue is landing in the oil? How much oil gain are you getting from the fuel?

 

[nrobideau]

Re: 25 hp 4 stroke Tohatsu

Hello,
Thanks for reply Paul, I have a efi motor. Could there be something wrong there? It runs fine,plugs do look a little wet.
Maybe a sensor or computer? Hope not, I am 62 years old and unfortunately not very up to date with new technology.
I purchased service manual and hope to fix this motor. 40 years ago this would not have intimated me. Nelson Robideau

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

The best thing to do for a 25B (EFI) motor would be to drop by a dealer who should have the diagnostic kit (for his laptop) available in order to do a better diagnosis than otherwise possible in the field. You could have a dribbling injector, for example.

 

[TOHATSU GURU]

Re: 25 hp 4 stroke Tohatsu

There isn't anything wrong with the engine. It's a case of running the engine too cool. That can be from the water/air temperature, running the wring oil or excessive idling.

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

Nelson,

Elvin may have hit it on the head! Especially if you are located in the cool North, and particularly if you idle a lot. Has this oil contamination occurred since the motor was new, or is this a recent thing? Have you started running a different oil?

Are you running FC-W rated, 10w-30, non-synthetic, oil? Is the crankcase filled to only half way on the dipstick? If you run heavier oil, or synthetic, or fill even a drop above full, you should expect to "gain" significant amounts of oil, due to unburned fuel residues and blow-by. Cold temperatures and lots of idling exacerbate that. Likewise, if the motor has never been run "hard" to seat the rings, you will be getting more blow-by, as the cylinder-to-ring seal technically hasn't been "broken in" -- even on a 5-year-old motor. If you only get a little blow-by gas in the oil, that's to be expected. But, if you are getting lots of gas, say a half pint or more, in a half hour or less, there is still a serious problem, and it is typically the diaphragm in the fuel pump, as that is the only point where liquid fuel can enter the crankcase directly.

If that is the case at this point, a dealer, with the diagnostic kit (can turn individual injectors and individual spark plugs on and off, can review any alarms, and can check the temperature sensor readings and any tachometer speeds that have been recorded in the ECU's memory) may be your best resource. If the motor is running perfectly, and there is no misfire, a dribbling injector isn't to be expected, but a complete checkout wouldn't hurt, especially if you have only one plug that seems unusually wet. Wouldn't hurt to check the compression... that can tell a lot about how well the rings are sealing.

 

[210bert]

Re: 25 hp 4 stroke Tohatsu

Darn. I have a 2002 3cyl. 4 stroke Nissan from new. I have been having problems with gas in the oil since 2004. I have email from some rep. from Nissan (from 2005) that attributes it to my oil or lack of the proper oil. And I have never been accused of to much idling. Of course it does have 3 carbs that I rebuilt last fall to see if the needle or seats were bad. Only now the problem with the gas in oil is worse now. I will just buy a fuel pump and change it then look if the diapram is bad also. I have the factory service manual and parts book. The reason I rebuilt the carbs is because I always unhook the gas when the boat is on the trailer but leave it hooked when on the water, but normally hook it up before I start it. Last year I started it up with out the hose off and it ran like on 2 cyl. which it was till I hooked up the hose and it smoothed it when the 3rd carb got fuel, so I figured a needle seat was not holding on 1 of the 3 carbs, so I rebuilt the carbs. I other words the needle/ seat problem was leaking the gas into the cylinder/piston area then into the crankcase. Now when I start it, when I first put it in to the water (with out the fuel line hooked up) it starts and idles fine. I figured that the gas in the oil was because of the needle/seat but now I think it maybe the fuel pump. OH CRAP. Of course it really may be was combo now. My gas in the oil was so bad I think it was an extra qt. which caused it to RUN out if you pulled the dipstick. I think the world of my Nissan engine. A bunch of my Buddies have Honda's which I deal with. I have the only Nissan/Tohatsu here in the La Crosse, WI area. I don't believe in the oil BS or temp thing.

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

Darn. I have a 2002 3cyl. 4 stroke Nissan from new. I have been having problems with gas in the oil since 2004. I have email from some rep. from Nissan (from 2005) that attributes it to my oil or lack of the proper oil. And I have never been accused of to much idling. Of course it does have 3 carbs that I rebuilt last fall to see if the needle or seats were bad. Only now the problem with the gas in oil is worse now. I will just buy a fuel pump and change it then look if the diapram is bad also. I have the factory service manual and parts book. The reason I rebuilt the carbs is because I always unhook the gas when the boat is on the trailer but leave it hooked when on the water, but normally hook it up before I start it. Last year I started it up with out the hose off and it ran like on 2 cyl. which it was till I hooked up the hose and it smoothed it when the 3rd carb got fuel, so I figured a needle seat was not holding on 1 of the 3 carbs, so I rebuilt the carbs. I other words the needle/ seat problem was leaking the gas into the cylinder/piston area then into the crankcase. Now when I start it, when I first put it in to the water (with out the fuel line hooked up) it starts and idles fine. I figured that the gas in the oil was because of the needle/seat but now I think it maybe the fuel pump. OH CRAP. Of course it really may be was combo now. My gas in the oil was so bad I think it was an extra qt. which caused it to RUN out if you pulled the dipstick. I think the world of my Nissan engine. A bunch of my Buddies have Honda's which I deal with. I have the only Nissan/Tohatsu here in the La Crosse, WI area. I don't believe in the oil BS or temp thing.

If you are getting large amounts of fuel contamination, definitely check the fuel pump. Pull it off the motor, and connect it to the gas line, then prime. If it's leaking, it will be obvious.

If you leave the fuel line connected when the motor is not running, heat/cool sun cycles will cause pressurization of the fuel system (the primer bulb will act like a pump, and a closed fuel tank can do the same), which can cause flooding, and oil contamination, even with good carbs. The needle valves were never intended to tolerate the kinds of pressures that can develop in the hot sun. So it is wise to disconnect the fuel line and run the carbs out at the end of the day, as you have recently been doing.

Since you seem to have had one carb that was emptier than the others, yes, that carb might have had more of a tendency to weep. But if you run them out, that will never be an issue.

The oil situation is not BS. You must run oil that is 10w-30 viscosity (or -40 is OK if in a really hot climate), NMMA rated for FC-W service (because of extra corrosion inhibitors compared with automotive oil), and it must not be synthetic (because the synthetic oil film strength doesn't let the rings seal/scavange quite as well, which contributes to blow-by). If you run car-grade straight SAE 30 synthetic, expect to make lots of oil. And yes, colder oil is more viscous, so idling, or short runs, and colder weather all do contribute to "making" oil in any 4-stroke OB from any manufacturer. See the FAQ on this board about making oil for more info.

 

[210bert]

Re: 25 hp 4 stroke Tohatsu

I took the pump off and primed it but it did not leak. The new pump is not here yet. I will install it then. I do unhook the gas line and NEVER shut the tank vent. I have never run the carbs out at the end of the day on any of my cars/trucks, snowmobiles, boats (outboard or I/O), ATV's, lawnmowers (push or rider), motorcycles (Harley's, Kawi or Honda), etc, etc. I may at the end of the year. I also do not shut the fuel off any of them. I also run premium fuel in everything except the automobile daily drivers to stay away from ethanol. I may agree somewhat on the FW-C oil for corrosion but my good friend has a Honda and has used auto oil (10-30 or 10-40) for years with no gas in the oil. We run the same sloughs with alot of others that have Hondas. Quite a few of them duck hunt and fish almost year round while trolling or running from one spot to the next. I was also told Tohatsu, Nissan, and Merc are the same except for paint. I had a 15hp Merc 4 stroke and never had an issue. I am just confused.

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

Bert,

In Tohatsu/Nissan land, there is no year designation of any significance for servicing; Model/serial is everything. Carbed 25 and 30 4-strokes would be A models; the B's are EFI.

If you tested the pump and it didn't leak, it is probably not your problem. A blown diaphragm will dump tons of fuel into the crankcase.

It was always a good idea to run the carbs dry, but today, on modern carbs, it's pretty critical.

The newer OB motors are EPA rated. That means super-low emissions. That means super lean. Too lean, IMO. To accomplish that, the air/fuel mix needs to be very very very very emulsified. That's accomplished by longer, narrower passages in the carbs. Couple that with the US fuels that are dirtier than they were years ago, and you have a lot more varnishing problems than we had 10 or 15 years ago. So... the reasoning for running the carbs dry is to eliminate fuel reserve in the carbs that will evaporate and leave varnishing in the carbs. Older technology carbs have larger passages, which are not as succeptible to varnishing. EFI motors seal off the fuel when not running, so are not succeptible to evaporation, hence not affected by varnishing, though the gas will still spoil after a month or so.

Most US pump gas, even higher octanes, are E-10 blends. In NY State, the only way to get non-E gas is to use off-road fuels. Some marinas have that here. But E is not really the issue in the case of oil dilution, unless the water content in the E gas has corroded some areas of the carbs.

If you have a little gas in the oil, it is likely from blow-by. That will be reduced by running SAE 10w-30 viscosity, by using non-synthetics, and by reducing cold and/or idling operation. Another contributor is having the fuel line over-pressurized by solar "pumping" of the primer, causing carb flooding while the motor is not running, which leads to fuel contaminating the oil.

Yes, Tohatsu makes all Nissans. Also all Mercury motors 30 and under, as well as the 2012 Evinrudes 15 and under. In pure production numbers, Tohatsu is by far the largest OB engine manufacturer.

 

[210bert]

Re: 25 hp 4 stroke Tohatsu

First of all thanks for the help and I will replace the pump just to rule it out. By dirty fuel do you mean because of the detergents now compared to the 60's and 70's? I also run only premium so there is no ethanol. There should also be more energy/ gal. And the way I understand it reg. has more energy than premium but is needed for higher comp. engines due to knock/detonation. Anyway I don't want the ethanol. I also like the notes on "A and B" and the 2012 Ole E. engines. I may have used 10-40 which is for the bikes and been out of the 10-30. Why are my buddies with Honda's not having this problem when they duck/geese hunt and fish (trolling) fall, winter and spring? I am allready pricing a New 25 efi. I do not like the center tiller on the Honda's and don't think they offer tilt/trim o the short shaft. Once you have tilt/trim you'll never go back. Great getting the motor all the way in for take off then raising it till just shy of bouncing. Then going with the wind and turning around and adjusting for against it. Plus not having to change pins when your load changes. Gas mileage is also alot better. THANKS again for the help. I will be trying it again with the new pump, carbs rechecked and fresh 10-30. Kind of a pain for this many years but I sure like having the only Nissan around.

 

[pvanv]

Re: 25 hp 4 stroke Tohatsu

There are more impurities in today's US gas. And most US premium gas blends do have E, unless marketed for off-road use. But higher octane US fuels typically are cleaner, and have better detergents, so they are not bad. Running higher octane than needed will not change output of the motor (unless it is a complex O2 sensor setup on an EFI, and can adjust fuel ratios and timing based on temperatures and O2 in the exhaust). The 25B does not have that exotic a setup. Higher octane burns slower, which allows higher compression ratios. Modern cam profiles for car motors have more overlap, allowing lower octanes than what would have required premium on earlier motors. Still, premium is better gas overall (cleaner), so unless you run through several tanks a week, the price difference is insignificant... so it is not a bad thing to run premium. Just a little more expensive at the pump... for a little cleaner fuel.

The harder you run, the less dilution you will get. Ditto for running in warm water. Cold/idle is the most fuel-oil-diluting condition.

 

[210bert]

I believe I have found the long term problem. It is that the thermostat is stuck open and the engine never gets warm enough to evaporate fuel that gets into the crankcase. I talked to a guy finally, that that has had a 25 Nissan for years and has had no problem with fuel increasing the oil level. I went home and did more research and discovered that if the t-stat is bad and held open the engine will never get warm enough to vaporize any fuel in the crankcase oil. I measured the t-stat (thermostat) housing when warmed and it read about 130 deg. F. I then replaced the t-stat and after warmed up it read 155-160 at the housing on the side of the engine. I also noticed that the old t-stat that I removed was stuck open about 1/8th to 3/16th of an inch and the brand new one I installed was completely closed. I hope this helps anyone out there with this problem because this has been haunting me for years. CHEERS.

 

[GA_Boater]

Glad it's fixed after hijacking the OP's thread 4 years ago.

In the library for future use.

Closed.