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

S

SrtThis

Member
Feb 20, 2019
74
Maryland
Boat Info
270 SE sundancer
Engines
7.4 MPI w/bravo III
made a trip about 3 hours south last weekend, ran flawless down there crusing around 36-3800rpm all the way.

next day went out for a nice cruise and noticed the oil pressure starting to drop. go back to the dock and checked the oil level and she was about off the bottom of the dip stick (~5-6Qt)

filled it back up and made a trip 2 hours south of that and back and noticed the same thing with the oil pressure dropping down when we got back near the house we were staying (again cruising 3600 for a few hours with out issue) got back to the dock and checked the level again and again at the bottom of the dip stick. filled it back up again (another 6qt, so 12 total)

2 days later took it to go get fuel to fill up for the ride home, was about a 45 minute ride. checked it again and it was maybe 1qt low. topped it off again and stocked up with oil on board for the ride home. so total of 13qt in the boat in the 8-9 hours we were cruising at that point. ride back lost roughly 3 more. but still running flawlessly on plane for 3 hours at 3400-3600 rpm

my thoughts on this is it is leaking out of the oil cooler while its warm or while its under high oil pressure (cruise around 50-65). once it cools down the crack seals back up and doesnt leak. having a hard time believing its burning that much oil with out fouling the plugs out based on how its running, but im going to pull the plugs once the cooler comes in and do a compression test to know 100%. was going to pressure test the OE oil cooler but after finding the fittings to pressure test it, it was a few bucks more to just buy a new cooler from www.mrcool.us

anyone else have any thoughts to where the hell all this oil is going? bilge is oil free...
 
Your going in right direction. You'd see the oil cloud if it's going out the exhaust
 
thats been my thoughts... that and the temp thing would explain why i dont see it at idle in the water
 
Is there a sheen or spots of oil at the exhaust? Pull your hose off that oil cooler if it’s leaking that much you will see and feel it.
Older boats with side exhaust, you will have a black mess on the hull by the water line.
What is the hours on the engine?
My guess is valve guides and seals.
 
Rusted Nut said:
Is there a sheen or spots of oil at the exhaust? Pull your hose off that oil cooler if it’s leaking that much you will see and feel it.
Older boats with side exhaust, you will have a black mess on the hull by the water line.
What is the hours on the engine?
My guess is valve guides and seals.
Click to expand...

just over 600 hours on it. dont see any thing in the water, which is leading me to the heat/pressure theory

if a compression test doesnt show anything i guess i'll pull it out of the water and do a leak down.
 
SrtThis said:
if a compression test doesnt show anything i guess i'll pull it out of the water and do a leak down.
Click to expand...

like said above the engine would smoke like hell burning that amounts . you are loosing oil somewhere.
 
aerobat77 said:
like said above the engine would smoke like hell burning that amounts . you are loosing oil somewhere.
Click to expand...
thats been my biggest hang up is the lack of smoke and how well its running

hopefully the oil cooler is the issue, the new one will be here today. only other thing i can think of is a head gasket leaking between the water passage and an oil drain back hole. but i feel id see water in the oil at that point. if its not that i have no where else i know to look
 
Oil doesn't pass through the head gasket, only water. Was also thinking that if it was going out your underwater exhaust may be it wouldn't smoke.
 
scoflaw said:
Oil doesn't pass through the head gasket, only water. Was also thinking that if it was going out your underwater exhaust may be it wouldn't smoke.
Click to expand...
how does the oil drain back from the heads down to the block? every motor short of a dry sump set up has oil passages that drain back from the head to the block
 
All oil drains directly into the lifter valley, has nothing in the head gasket for oil
 
Have to read all the plugs? They must show oil on them or the oil is being pumped out of the oil cooler.
 
Well plugs show no oil... 1 hole is running a bit fat
All holes pump 140-150psi

New oil cooler is in and oil topped off. Going out this weekend so I'll report back
 
This was cruising back Saturday night
 

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Do you have any photos of the plugs?

If it isn't the oil cooler and the bilge isn't filled with oil.....the engine is pushing it out the exhaust.

I have seen dipstick tubes and senders come loose and will easily pump the oil into a part of the bilge that is difficult to see.
 
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