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8v71N oil in coolant

R

Rolfe

New member
Hi, 8v71N marine has a small amount of black oil in coolant resevoir. I have dismantled and pressure tested the oil cooler and hydraulic cooler all ok. No water in oil that I can detect, engine runs as good as it has ever done. Starts after a couple of winds, usual cloud of white smoke then complete combustion. Idles when warm at 20PSI and runs at 50PSI oil pressure. Oil changed regularly. Not a problem at the moment but it would be good to know where it is coming from so when down time arrives I can look at repairing it. Any help appreciated.
 
The usual suspects besides the oil cooler and hydraulic cooler are the injector tubes, cylinder head seals and, rarely, the water pump oil seal.

It is also possible that a cylinder head is cracked or there is a crack in the block but the soft areas such as the seals and coppers are much more likely. Finding a small leak like this can be difficult but if you are due for a tune up and compression check then I'll put my money on you finding the injector tube that is leaking.
 
jgmo said:
The usual suspects besides the oil cooler and hydraulic cooler are the injector tubes, cylinder head seals and, rarely, the water pump oil seal.

It is also possible that a cylinder head is cracked or there is a crack in the block but the soft areas such as the seals and coppers are much more likely. Finding a small leak like this can be difficult but if you are due for a tune up and compression check then I'll put my money on you finding the injector tube that is leaking.
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Thanks, I will keep monitoring it and when I get a chance I will get the injector tubes looked at that then work from there.
 
In many cases, you can locate a bad tube seal by removing the valve covers and pressurizing the cooling system then watch for bubbles after spraying a little soap solution around each injector. Or, you might notice coolant spilling down the slope of the head. While it can seem cheaper and easier to replace just the leaking copper, it is usually wise to do them all or, at least all the ones in that head.

Good luck.
 
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