7.4MPI oil loss... wheres it all going?!?!?!

Not seeing anything in the water as far as a sheen or spots.

It's a 98 with 613 hours currently.

Cruising around 3800rpms roughly a qt an hour.

Didn't get pictures of the plugs but from years of running 2000hp race cars Im pretty good at looking at spark plugs. And I didn't see anything that had me worried. I do have 1 hole that's got too much fuel. But I'm going to switch out that injector
 
Not seeing anything in the water as far as a sheen or spots.

It's a 98 with 613 hours currently.

Cruising around 3800rpms roughly a qt an hour.

Didn't get pictures of the plugs but from years of running 2000hp race cars Im pretty good at looking at spark plugs. And I didn't see anything that had me worried. I do have 1 hole that's got too much fuel. But I'm going to switch out that injector


Okay...no plug pictures, compression is okay, oil cooler replaced, no oil in the bilge and it is still using a quart of oil an hour. The only thing left is the engine. I'm not sure you would see oil on the water at cruise. Oil pressure builds with rpms and the amount of oil under the valve covers dramatically increases which if the valve seals are the issue would explain why it doesn't show up at idle or no wake speed. That said....if it was the valve seals/guides.....there are usually tell tale deposits on the plugs. And if that wasn't enough...the valve seals would have to be almost completely ineffective to burn a quart an hour.

It just seems like we are missing something.
 
im going to try and get some free time this weekend to pull the 1 injector out of the hole thats running fat and put one of the older injectors in there to clean up the 1 hole thats running fat.

im going to try and borrow a friends small air compressor to do a leakdown on it also my compressor is just too big to drag out on the pier.

and i agree 100%... im missing something
 
I quart or oil in an hour.......
If you’re in the mid 3k rpm range, probably burning about 15gal/hr gasoline.

15 gallons of gas to 1 quart of oil is a 60:1 ratio. Is it possible that it is a relatively small amount of oil and can burn off without fouling the plugs or showing any signs of oil contamination?

I know losing 1 quart per hour is a lot and not knowing the source is frustrating.
 
1 qt / hour burning thru cylinders would result in visible blue smoke for sure . check the bilge twice and then check it again for an oil leak .

you would also have a severe blow by from dead cylinders . when you remove the oil filler cap with engine running - does it blow severy out of the oil filler cap ?

if not you are not burning this oil.
 
I had that kind of oil coming from a valve cover. It was "hidden" and I only found it when a put my hand on it to pick something up. So I would start looking in hidden spots. Good luck.
 
I had that kind of oil coming from a valve cover. It was "hidden" and I only found it when a put my hand on it to pick something up. So I would start looking in hidden spots. Good luck.
ive thought about degreasing the motor and seeing if anything pops up that i see

1 qt / hour burning thru cylinders would result in visible blue smoke for sure . check the bilge twice and then check it again for an oil leak .

you would also have a severe blow by from dead cylinders . when you remove the oil filler cap with engine running - does it blow severy out of the oil filler cap ?

if not you are not burning this oil.
never thought to run the motor with the cap off... but i'll check that thursday when im down there. i want to hose the bilge out and get everything cleaned up in there. i forgot to put a bucket under the raw water hose when i pumped all the sand out of the motor after hitting bottom. so i still gotta get all that out of it.

so far ive put right around 18qts in the motor in the last 3 weeks... feel like id see it in the bilge by now if it was there.
 
Worn Exhaust guides or valve seals will pass a lot of oil and you will not see it on the plugs.
Is this a new boat to you?
 
My engine is the same year and the manual states that the engine will use 1 qt. of oil in 1-5 hours of running at or near full throttle.
 
My engine is the same year and the manual states that the engine will use 1 qt. of oil in 1-5 hours of running at or near full throttle.

My 502/8.2 manual says the same, but did not read that it applies to the 7.4. It is stated that the forged pistons need greater ring clearance due to the heat of the high performance 8.2 resulting in oil use.

I recently put 10 hours on for a trip and used a quart in each. Just as a friend that has had his 8.2's since new told me I would, it was that way from the factory.

MM
 
the 7.4 mag has forged pistons . Just had my motor freshened up and the machine shop ordered oversized rings and file fit them, I do say I'm using quite a bit less oil than last year. Using half of what you just mentioned
 
Yup, 7.4's eat oil like candy. I cruise at 3300 (3400 sometimes) and go through a lot of oil. I gotta say, though, running 3800 seems pretty hot for 7.4's. I wouldn't run that hot.
 
this is a non MAG MPI.

ive heard these motors should go to 4800... so 3800 didnt seem that high. im going out saturday maybe i'll try running them a lil slower and see what happens
 
My 7.4s don't burn anywhere near that much oil. I cruise at about 3400 rpm/30mph and maybe add on quart to the port engine and none to the starboard engine over a roughly 50 hr operating season. I am at about 900 hrs on them.
 
this is a non MAG MPI.

ive heard these motors should go to 4800... so 3800 didnt seem that high. im going out saturday maybe i'll try running them a lil slower and see what happens
You still haven't said if this oil usage is new or has been existing.
 

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