7.4L just purchased boat , water in oil. How to identify issue ?

First stop after the raw water pump is the cooler. Not much could get past that point (pretty small holes for the water to travel). But I guess anything's possible.
 
Update ... Put in new stat and ran up motor in slip. Seems to still run hot170-180 . 160f stat was installed , throttled up motor and was seeing 190f on gauge. At a loss of where to go now. Can only think that chunks are lodged in cooling system from impeller or water pump is failing. Any suggestions appreciated
 
Oh what should be optimum temp with a raw water 7.4l. I figure about 150-160
 
Had a small block Merc in an old Cruisers Inc. Always ran hot. Changed exhaust components and water pump - no help. Turned out to be the thermostat housing - water passages in there were occluded with corrosion.
 
jeffc said:
Oh what should be optimum temp with a raw water 7.4l. I figure about 150-160
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Mine runs about 160 quite steady actually, but I have a 140 thermostat installed, and I replaced the sending unit also. Before that it read 150 on the temp guage. I'm assuming the sending unit and gauge are showing slightly different with the new configuration, overall the engine feels the same as far as the risers being hotter or cooler.
 
I was just reviewing the cooling system diagrams and noticed there shows 3 oil coolers ... I only noticed and inspected the one on the front of motor by stat housing. I am looking for a blockage . Which oil cooler would be first inline from raw water pump
 
Jeff
Your best bet is to find the raw water pump and trace the hose to the first stop. According to the diagram, it's the engine oil cooler, which is the same setup on my old 7.4 (1989). Regarding the other two coolers - The one they show positioned vertically is the transmission fluid cooler - obviously a Bravo drive doesn't have a transmission. Not sure what the other horizontal one is? Fuel cooler?
 
Did a visual on the cooling system and from Raw water pump the hoses go around back of motor and through a power steering cooler first then up to the oil cooler on front of motor. Going to pull apart the power steering cooler tonight and look for blockage. It is difficult to get at down by motor mount.
I did run motor in slip for 20 mins at idle and the temp stayed at 170. I also ran a 2000 rpm for a bit and it held at 170....
 
Hi Jeff, both my power steering fluid and the engine oil pass through the same cooler you described that is down by the motor mount. Not sure about the newer models.
 
Jeff, curious. How's the oils since the hot cruise? Still milky?
 
Well good news and bad new. Pulled apart coolers and no blockages. Took boat out for a 30 min run and temp held well at 175-180max. Bad news after looking at dip stick its showing it is starting to milk up again.
To sum it all up.
1. Risers are cold no issues
2. Did compression test all good at 150-155
3. Inspected plugs all were the same color brown/black
4. Installed new raw water impeller
5. Flushed engine oil 3 times to clear orig milky color

Where to go from here ??
It brings me back to one of 3
1. Head Gasket/ cracked head
2. Intake gasket ,
3 Cracked block

I am note sure how I can isolate the above 3 without stripping down motor
Please assist if you can
 
scoflaw said:
Then you can't pressure test the system
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He might have been referring to a leak-down test, which can reveal issues that won't show on a compression test.
 
src said:
He might have been referring to a leak-down test, which can reveal issues that won't show on a compression test.
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People with no mechanical knowledge shouldn't even post, it's tough enough when the OP hasn't got a clue which end is up, if you don't know what your talking about, your just going to confuse him even more.
 
Just a thought ... a raw water system open would not generate much pressure vs the oil at 40-60psi .... when there is a transfer of fluids between the two it would only reason that the oil should be pushing into the cooling system mostly resulting in oily mixture exiting the prop ?. Just a notion
 
scoflaw said:
People with no mechanical knowledge shouldn't even post, it's tough enough when the OP hasn't got a clue which end is up, if you don't know what your talking about, your just going to confuse him even more.
Click to expand...

Who are you talking about?
 
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