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2001 Merc 15 4 Stroke Low Oil pressure

J

--JR--

New member
I'm working on a "new to me" 2001 Merc 15 four stroke. It seems to have oil pressure issues.

Symptoms:
  1. Runs fine from cold for about 30sec then oil pressure drops and oil pressure warning (ignition system goes into limp mode too)
  2. Idles fine
  3. Crank case seems to have a lot of blow by air pressure, doesn't blow out dipstick or anything (Not sure what's "normal" on these, I've heard everything from nothing --> there can be a fair bit)
  4. No exhaust oil smoke
  5. With oil filter removed, I can turn over the motor and oil pumps into the filter area.

Checked these already:
  1. New oil and filter today (10-30 conventional)
  2. Oil level @70% on the stick
  3. New oil pressure sensor
  4. Water thermostat opens properly at 60C
  5. Disconnect oil pressure switch from ignition module and runs normally

Not really sure where to go from here. I've heard there is an over pressure oil bypass value inside the case, but I can't find it. There also seems to be a case/leg gasket that seals a pressurized oil gallery. Wonder if that may have blown a hole into it.

It has been guested to attach an oil pressure gauge to measure the level. But I'm not sure how that's going to help. The oil pressure is so low the engine won't run properly. So why worry about measure how low is low.

I'm attaching photos of a block. Maybe someone can point out the oil bypass valve. I think it might be my next thing to check.

Other ideas?
IMG_2946.jpgIMG_2944.jpgIMG_2945.jpgIMG_2943.jpg
 
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Really starting to suspect the oil relief valve. I finally manage to figure out where the oil pressure relief valve is. It's the machined steel part in my attached image 1 located at the 8 o'clock position from the oil intake (suction) tube and near the center of the bottom face of the block. Can be removed with a 10mm wrench.

Ran the motor again, removed the oil fill plug and pulled out the dipstick at idle. There was an oil tornado coming from there. The crankshaft is not in the bottom of these engines but the relief valve is fairly close to the dip stick hole. Seems to be an excessive amount of oil spraying around the bottom side of the engine.

BTW - The relief valve doesn't show or list on the bottom end exploded parts view diagram on this web page's parts store.


Thoughts guys? Should I tear into the power head on this engine?
 
My guess after studying your post and photos is a stuck relief valve. I really doubt if it's a leak between the pressurized oil chamber and the crankcase. This stuck valve could have been caused by some debris. Perhaps the oil pickup screen is damaged, but more likely.....some crap got in at filter during some service/oil change work. That valve is protected....so something got in at filter.....my guess. Good post.
 
Right, there are other participants here with more experience than I on this particular motor. I'm just running on my general knowledge here. Most of my experience is with 4 strokes outside of outboard repair. Let's get this solved before you tear into this motor.
 
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I know that the only reason that it could be pumping the sump dry is if there is a restricted oil drain back passage but for the heck of it make sure the oil level is at full.
 
Thanks Swagonmaster, but the sump is still doing well when this issue is happening.

However, problem solved today!

Took the chance and pulled the power head off the leg. This issue was IMMEDIATELY obvious.

If you compare my first post image 4 (the top of the leg picture) to the leg top image attached here... Can you spot the problems?

There are two. Some backyard "Master Mechanic" must have had the power head off before. The gaskets are now discontinued by Mercury, WTF with that anyways, and are hard to find. So this guy found one that looked the same. Notice though that the oval gasket area in image 4 of the first post is missing from the image below. That's a pressurized oil gallery seal for the Merc engines. There was a large gap in the mating surfaces between the leg and the power head as a result. That caused my low oil pressure condition.

Problem two is that they threw out the oil baffle plate. Probably not the end of the world if the motor lives on a transom all it's life, but once this motor gets laid down it will get oil into places it shouldn't.

I also found a little "hairy" stuff on the oil suction intake screen. Looks like fiberglass insulation almost. Cleaned that up too.

I've prepped the mating surfaces and picking up new gaskets Monday. That should "git-er-done"!

Only thing that worries me now is... Why did they take off the power head before? Hmmmm

IMG_2951.jpgIMG_2952.jpg
 
Re: 2001 Merc 15 4 Stroke Low Oil pressure *Solved*

Great job. I ALWAYS LOOK FOR, "pecker tracks".......if somebody did something before me, it's often not done correctly. If I see a motor for sale on "Craig's List".....and it says " just recent tune up".....I always raise an eyebrow. Most home mechanics should stick to servicing their wives.
 
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