Intermittent smoke, loss of power 25 4st

[hwindle]

I had posted in the prop forum about my 16ft Sundance skiff with a 15 hp 4 stroke, which wouldn't plane. I traded it in for a 2001 25 HP big foot 4 stroke, which looks almost brand new, inside and out. The dealer changed all the oils, and even took the carb apart to clean it.
Took it out for the 1st time yesterday, and it now gets the boat up on plane nicely. However, after running about 45 minutes and stopping, when I took back off and gave it the gas, it revved up to around 4K, and then loss power. Oil smoke poured from the engine, and there was a little oil slick in the water. It never quit running or started missing, it just lost power. I checked the pee water and it wasn't hot.
After idling a minute the smoke cleared, and we took back off again. It did this one more time, and both were when taking off from idle initially, not after it was planeing already. Both times it didn't kill the motor, just loss of power and visible smoke, which all went away in a minute or so.
I searched this forum for similar symptoms, and couldn't find any. I looked at the motor this morning, and the oil level is in the center of the marks, and still very clear. There was some oil residue under the carb on the side of the motor, and a little in the bottom of the housing, but nothing major. the only thing that I can think of that could do this is a PCV valve that is sticking, but I don't know how that would suck oil into the carb. The smoke was definitely oil, and not gas.
Other then this problem, the motor runs perfect, but it did cut our day short. After the last episode, we headed back and it ran perfect the whole way. It always started back up immediately when I turned it off. I was so happy with this motor, and was telling my friend with me that a motor like this would last me until I died.
I am not feeling that bad yet. Any ideas?

 

[Swinerton]

Re: Intermittent smoke, loss of power 25 4st

Oil in clearly getting into the combustion chambers. Either through the carb(s) <----doubtful, or the PCV, or piston rings.

Maybe the dealer overfilled the crankcase in the beginning? I have seen more motor problems AFTER dealers/marinas played/fixed them, then when they were running fine, and never so called "serviced"... There is nothing "special" with Marine products. It's just another engine. I would keep an eye on it, keep the fluid topped off, and run it.

Run without the PCV hose into the intake, and see if it never smokes again.

 

[hwindle]

Re: Intermittent smoke, loss of power 25 4st

I checked the oil before I left, and it was at the top of the range, but not overfilled. I have seen some motors that don't like the top, and use it till it gets to about the middle. Now it is in the middle.

If I take off the PCV hose, do I just zip tie it to something, and plug the hole in the maifold? I guess I need to clean the valve anyway, and look for fresh oil in it. I can't see anywhere else oil could get into the carb, since there are no oil lines it looks like close to it. Head gaskets don't leak, heal themselves, break, and then heal themselves again. I ran about 1-1/2 hours and a gallon of gas, and it only did this twice. The rest of the time it ran perfect, and always started with just a twist of the key.

I take it you tilt the motor to where the bottom case is level, before checking the oil? I need to find a manual next also.

 

[Swinerton]

Re: Intermittent smoke, loss of power 25 4st

Just let the hose hang in a place where it won't coat anything with oil if there's indeed an issue. Motor should be close to level as possible. (Veritcal position)

 

[sschefer]

Re: Intermittent smoke, loss of power 25 4st

It could be making oil. This is a symptom that can occur when fuel gets past the rings or valves and into the oil. Check your oil and see if it's slightly muddy colored, over time it'll get mudier looking. You will experience a loss of power due to the excess oil in the crankcase.

It could also have shot valve seals and is leaking oil into the cylinders. That'll clear pretty quick but will cause a temporary loss of power also.

 

[DonHof]

Re: Intermittent smoke, loss of power 25 4st

I have a 30 hp 4 stoke (new). I pulled the boat and motor home put it in the garage. Next morning there was oil all over the floor.
Took it back to the dealer, he changed oil and filter. Dumped in two quarts of oil! Wrong!! It takes a 1.9 quarts. Check the oil level.

Don

 

[Swinerton]

Re: Intermittent smoke, loss of power 25 4st

Yeah, watch out for when laying the motor down also. It can only be laid down on its back, upright, or on the tiller side (left is non-tiller model)

 

[hwindle]

Re: Intermittent smoke, loss of power 25 4st

The oil level is now in the middle of the range, and still looks like the motor has never been run. I checked the oil before I had gone out, and it was at the top of the range, so it doesn't appear that over filling was a problem.

I pulled the PCV valve out, and found some drops of fresh oil on and inside it, as well as inside the intake where it plugs in. So that is where the oil came from. I will put a loose baggie around it, to let out any air, and hopefully catch any more oil that comes out. I also spoke to the dealer, who told me there was a service bulletin on these around 2003. At high RPM some of these 25's spit oil, and the cure was replacing two gaskets where the power head connected to the lower unit. The new gaskets either went from 2 holes to 3, or vice versa. My problem didn't come at high RPM, and with the motor being a 2001, I can't believe it has been doing this for 11 years without the PO doing this modification. The dealer agreed with Swinerton, and said to run it, keep a watch on the oil level, and it wouldn't hurt to take the PCV out. The PCV also seems to be built in to the hose, and looked new and clean-except for a little oil.
Now that I know where the oil is coming from, I am not nearly as worried as I was out on the water watching smoke pour out of it. On my bike, the breather hose is removed from the carb, and a small K&N filter or catch can attached to the end of it- to try to improve performance. I shouldn't need a filter, since the carb doesn't even have one, and there probably isn't room for a catch can, so a baggie is my best idea right now. I expect it not to be a problem in the future. This motor looks like it is one month old, not 11 years.

Does anyone know where to find the service bulletin the dealer spoke about? I searched this forum before posting, and never saw anyone talking about this, so it can't be a very big problem.

 

[Star]

Re: Intermittent smoke, loss of power 25 4st

I will bet that you have a gasket problem. Oil is leaking directly into the cylinders after shutdown. If it was going into the carb it wouldn't be as black because the fuel mix will delute it quite a bit. I have already replaced the head gasket on my 05 15 4 stroke with 100 hours on it. The heads on these motors have been known to warp. 300 grit wet sandpaper on a thick galss table will flatten any warpage. You will see if it is flat right away.

 

[hwindle]

Re: Intermittent smoke, loss of power 25 4st

I took it out yesterday, with the breather hose unplugged from the manifold and a baggie zip tied around the end. Motor ran great, with no issues. When I got back I checked the baggie, and it had about 1/4 cup of oil in it, but the engine oil still was near the middle of the range, and still looks like it was just changed. The oil in the baggie was a little darker.

Why would it blow oil through the breather hose? I thought there was a PCV valve on the end of the hose, but in the parts diagram it just calls it the breather hose. With the motor idling, it is push/pulling air back and forth. Is this normal?

 

[hwindle]

Re: Intermittent smoke, loss of power 25 4st

I took it out again last weekend with a new baggie, and only had a couple of drops of oil in it when we got back. I guess the dipstick is showing more oil than the motor likes. It is just a little below half way on the operating range. I will put the breather hose back in the manifold and see what happens next time.

 

[oldman570]

Re: Intermittent smoke, loss of power 25 4st

On some motors the dip stick is marked so as to show that the motor is realy over filled on oil. They forgot that oil expands as it gets hot from the motor heating up and will cause a overfill that has to go thru the PC valve and into the carb and is burnt in the motor untill the excess oil is gone. This is more than likely what is happening to the motor you have. As long as the oil level on the dipstick stays in the center of the range , there should be no problem. The loss of power can be because the crank and rods are splaching the extra oil in the crankcase and slowing them down.This is also why LU oil is made so that it dose not expand with heat and blow out the LU seals. JMO
Oldman570