So today on the river my outboard started losing power and eventually quit. When I lifted the cover I found the oil cap laying off to the side but the engine still had oil and none was splashed out. There was hot burnt smelling smoke emitting from the motor.

So the question: Does the oil system for this 4 stroke operate OK without the oil cap off or does the cap keep the system pressurized? Am I likely SOL???? (Its a 15hp Suzuki 4-stroke).

I just had the outboard serviced a few weeks ago and I hadn't touched the oil cap.

Confused here. Motor still had oil and NONE was splashed out. So the oil level was FULL then because NONE splashed out. Right?

those missed beaver are going to cut into the profits now
did you touch the water discharge =was it hot
after re-reading your post....time for a back-up motor

Did you check the oil level when this happened? Could be who ever serviced it didn’t refill with oil if the cap was left off. Don’t think the system is pressurized. Was it peeing water good? Might had water pump go out and got motor hot. Did you check the filter on your fuel system? Might have got some watered down gas.

More questions, what was done on the motor. Maybe they overfilled the oil?

I also have a yah15 4 stroke on a 1448. Have it because of the regs on the waterbody. Anyway, I remember reading about guys saying they were having high oil pressure on other motors brands and hp. Had something to do with being overpropped. I don’t remember the exact theory but for over a decade ive used 3 different pitches depending on how much the boat was gonna push and the performance is great propping correctly. I run 9 10 and when im solo and light 11! Keep us informed on what you find out. Im intrigued

It was definitely used too much when it was new.

SO, I just had the outboard serviced at the Suzuki shop. Oil level was fine... I saw it myself. Oil level is still fine after the motor lost power but smoke emitted form motor and it smelled burnt. When motor was serviced a new impeller was installed and its been peeing just fine. I previously had an issue after it was serviced but it turned out that the tank and hose were the issue and it wasn't pulling gas right. New tank and hose so that's not it.

After the engine died I cranked it and it still cranked OK but I didn't want to start it for fear of possibly doing more harm.

So my question is does anybody know whether the oil cap has to be on tight to keep things pressurized? In other words was the oil circulating properly?

It might of overheated due to plugged intake or water pump out. Or... some gremlins put something in your oil and left the cap off.

What size engine is it ...... the larger ones hav a O2 sensor and if the oil cap is off the blow by coming out of there can be enough to confuse the ECU ..... had one with a tiny crack in the exhaust manifold that played up because of that. You could hardly see that crack but it was enough to get it to sulk.

It's a 15hp 4-stroke. I think it's an 2003 model year. The cap was off but no oil had blown out of the top.

I will be down there tomorrow if’s ya need a tow

Sounds like it over heated and it should have lost power first then quit. That is a safety feature. Wouldn't think the oil cap would be the issue as the oil on that end shouldn't be under pressure. You may have picked up something on the water intake or there could be an issue with the new impeller or something with the install on the new impeller. I hate to say it but I would first call the service dealer and explain what happened and if it is the first time you've run it since the service they would probably be seeing it again. I have a 16 200 Suzuki 4 stroke and I found the symptoms you are describing while I was trying to flush it and realized I didn't have enough flow. I have them change mine every 50 hours.

The loss of power was gradual over the course of about a mile going upstream. But I've probably put in about 35-40 hours on the water since it was serviced. I plan on taking it in tomorrow morning to see what can be found out. It's a drag 'cuz I've got traps out that I set on the 24th.

oil cap, is this to the crankcase or oil injection unit?

Water in the gas?

My Suzuki 25hp did the same thing to me awhile back. Except the system warning light and beeper came on indicating it was overheating. I shut it down and waited a bit and fired it back up, ran fine the rest of the day. I'm thinking, either ice blocked the the impeller or some junk plugged the water intake. Anyway, I doubt you can hurt the motor by running it. It's either OK or smoked. I'd run it and see what happens.

I believe your oil system is pressurized (some outboards had sumps) and the cap could prevent the oil from flowing and instead -cooked it from the engine heat.

Pull the dip stick on it and smell to see if the oil is burnt. The white smoke could be caused by water in the fuel system. A slow loss of power could be fuel line collapse or water in fuel system. There was a problem with fuel lines that were getting the inside ate up with ethanol gas. If you have a 55 gallon drum put it next to the transom, lower motor into it, fill the drum with water, and start it. If it puts out white smoke I would look at fuel issue. If it smokes blue that ain’t good. While in the drum you can check to see if it’s peein too.
We just got stranded on the river for 2 hours in my buddies boat with a 25 evinrude on it. It was a fuel issue.

I always run a remote Racor gas/water removal filter, to guard against fuel issues. Even if your tank and hose is newish, the internal lines may be failing from Ethanol, check all the internal fuel filters too.

I've seen "mechanics" that have installed new water pump impellers backwards, causing poor water flow, the (This word is unacceptable on Trapperman) is an ok indicator but not foolproof.

The oil cap is a screw on with an O ring, they don't come off by themselves, If the cap is needed "on", then the service guy forgot to screw it back on.

It's a small engine, I'd take it back and have them explain exactly what they did, and you explain your not happy and losing money.... good luck.

Just use your spare boat. Don't tell me..............

Carl, call me if you need to barrow my boat.

Western Wildlife Services

You're right, it's a screw on yellow cap. But I saw it on after the service job. Later it came off...somehow.

While it was gradually losing power, was it still running rather smoothly, or was it missing? If it was running smoothly, then I'd guess it was losing compression. Have you tried a doing a compression test? That would be my first go-to if all the other systems seem to be working; fuel, air, spark, etc..

It was smooth waggler....slowly losing compression.

SO the update:

Checking craigslist I found a Merc 20hp last night that I planned to go up and buy, but first I wanted the marine service center to check out my motor. Went over there first thing this morning at opening time and saw the sign that they're closed until the 2nd. At this point I was in contact with wws on here who graciously offered me use of his boat and motor, But I decided to first go try out the motor with the cap screwed back on and see if it would run.

And EUREKA! It did run, and at full compression! So I'm guessing the cap off lead to the oil system not functioning correctly. It does have a more hollow metallic sound at idle speed though now. I don't know if that is going to be an issue in the future but for now I'm OK.

Thanks for all on here with your valuable advice and best wishes. I truly appreciate it. And special thanks to wws who offered me his boat. Who does that anymore?

How much oil does it use since you have used it for some hours ?
I would still have a 2 hp back-up

Doesn't use oil. Well, after this latest incident I'll be checking frequently.

A 2hp wouldn't work on the waters I traverse. Plus, with a small Jon boat that 115 lb 15 horse is all I can carry.