Check out this oil cooler – time to replace?

[DWB]

Found residual oil in coolant overflow tank and inside the heat exchanger cap. Not much but it shouldn’t be there. Pulled the oil cooler at bottom of heat exchanger (1978 Detroit 671 natural)

See pic of the cooler- basic 8 fin design. Was positive that was the source of the oil as I was told by a longtime Detroit guy/family friend that a failed cooler or cooler gasket was about the only way oil can get into the coolant which, according to him, is much better than coolant getting into oil. (He’s 80 and in poor health so can’t turn a wrench any longer)

Oil samples of engines and gears were lab tested about 10 runtime hours ago and came back free of water or fuel in oil. Engine was also serviced with fluids/filters/coolant flush, heat exchanger inspection, zincs, etc. 10 runtime hours ago. Engine runs strong, smoke clears quickly after cold start, no sheen on water, no smoke under load, etc. 

Cooler sent out to shop in Seattle for cleanup and testing. Shop says cooler tested okay – no leak. 

Update the Detroit old timer. He says either the shop mucked up the pressure test and/or the leak was from a bad gasket. He told me to get a new cooler, flush the system, and run her hard and under no circumstances put the old cleaned up cooler back in as he wouldn’t trust it regardless of how it tested.

Just looking for some second opinions on whether or not his advice is sound as I really want to avoid putting it all back together only to have to take it apart again.  I’ve attached a photo of the removed cooler for you to review.

 

Topic

[DWB]

Follow up

New gear cooler was installed after engine was flushed four times to remove the last of oil residue in the system.

Engine running great with no sign of further gear oil intrusion into cooling system (so far – fingers crossed)

Got the bill though – 30+ hours total to diagnose, remove, clean coolant from bilge, install new gear oil cooler, flush once, twice, three times, four times etc. (I figure there was some travel time from the shop to the boat in the slip as part of that 30+ hours)

I was stunned.  I’ve had coolant flushes on big diesels before that took about a day for both engines. Granted, that’s a single flush but 30+ hours for four flushes!!???

At $155 per hour you do the math – this one gear cooler swap cost me about what I could pay for an entire running 671 take-out including shipping!!! 

Damn I love boating but not these kinds of bills.  If my back wasn’t so hinky I’d have crawled down there and did it myself.

Okay, ranting grumble is over.

And for future reference if any others have this same issue with oil getting into your freshwater cooling system on this era of Detroit 671 naturals (1970s/1980s) make sure you look to the gear cooler first. It was later explained to me that given the high oil pressure required by Twin Disc transmissions (300-400 psi) that its far more likely to be the gear cooler that is leaking vs the engine oil cooler. 

Then I would strongly recommend that after the new cooler is installed that YOU do the coolant flushing and save a sh*t ton of $$$$ on what is a relatively simple/straightforward (albeit time-consuming) repair.

[DWB]

Same guy who responded before corrected himself and said the photo I attached was in fact the gear cooler which is housed just below the HE. 

Glad to have cleared that up. 

Apparently both engine and gear coolers on the 671 N of that era are cooled via the freshwater system, not raw water. 

At any rate, will install new gear cooler this week, flush system, button her up, and (fingers crossed) hopefully that was the cause of the trace amounts of oil getting into the freshwater system. 

[Rob Schepis]

When I read our original post it seemed you knew it was an engine oil cooler even though you mislabeled the photo as gear oil cooler.  Seawater circuit components re easy to locate just start at the intake thru hull and keep following the seawater circuit…

[DWB]

I hear that.

Had a member of another forum tell me the pic was of the engine cooler not the transmission cooler. They said the transmission cooler was raw water cooled while the engine cooler was coolant cooled.

He did confirm the pic showed contamination.

At any rate I have a new cooler on order that should go in this week to eliminate that as the issue. Will then flush system and watch and wait and hopefully its fixed.

Now I have to figure out where that second cooler is located. . .

[Rob Schepis]

Well it all comes down to one or the other: Time vs. Money.  For everyone one is more precious than the other.  For starters, I would do my own pressure test and go from there.

[Author]

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