Leaking fuel cooler?

[Diver Down]

I've got a full tank (300 gal) of fuel that looks like a strawberry milk shake. Took a sample to a fuel polisher working the VA Beach boat show last weekend and his reaction was "that's a train wreck". Looks like we may (probably) have a leaking fuel cooler. Ran the boat at idle for 30 minutes before I discovered the problem... hoping we did not do any permanent damage. Anyone have experience with this problem or wish to offer some comments?


17171

[Boatsb]

I've seen that 2 x lately.

1 time was bad fill o rings.

The other was suspected to be the coolers but they checked out. Never found the source of the water.

[petewentsailing]

Possible for sure, but I would have thought the fuel was at a higher pressure than the water and the fuel cooler would leak the other way. How about a leak at the deck fills?

[thoward]

I just replaced a bad fuel cooler. Lenco had one that fit perfectly. This was my first experience with a bad fuel cooler but.....The fuel pressure was high enough to overcome the raw water pressure so our symptom was fuel in the exhaust water. We had a minimal amount of water in the tank/filter.

[Cricket]

Had a leaking fuel cooler once too.
Since we put access plates for all 3 tanks we were able to let the tank settle so the water would separate from the diesel and then suck the water out from the bottom until gone. Then we rented a filtration set up with pump and ran that for a day, maybe had to change those filters twice. After the season we installed a Reverso filtration system with its own pickup and returns including a valve system so we can move the fuel around as needed.

[saltshaker]

Are you sure it's water? Wouldn't water seperate from the fuel and settle at the bottom of the bowls? That almost looks like the fuel is aerated. Might be bad or overtreated fuel. I had cloudy fuel once after a fill up. I was told it was overtreated fuel. Fuel was pretreated and I added a biocide when filling. I tried to filter it but nothing made a difference. Eventually burned it and never had that problem again.

[Boatsb]

Are you sure it's water? Wouldn't water seperate from the fuel and settle at the bottom of the bowls? That almost looks like the fuel is aerated. Might be bad or overtreated fuel. I had cloudy fuel once after a fill up. I was told it was overtreated fuel. Fuel was pretreated and I added a biocide when filling. I tried to filter it but nothing made a difference. Eventually burned it and never had that problem again.


Looks a bit emulsified.

[Diver Down]

Until recently, the fuel in this tank looked normal. The other tanks filled at the same time still look OK. This problem came on suddenly and in the fuel polisher's opinion, the emulsification likely came from mixing with saltwater. Don't really know but I'll be pulling both fuel coolers this week for pressure testing.

[Mike in S Fla]

Just replaced one of mine, found one at diesel pro in miami around 450.00

[JLR]

Please take what I say with an appropriate grain of salt as I am by no means an expert on this stuff. But, I thought the various operating pressures between the fuel system and the salt water cooler would have prevented any intrusion of salt water into the fuel. When I have seen leaking fuel coolers, they leak out fuel not in salt water and often leave a sheen at idle.

[Diver Down]

JLR, I'm no expert on this topic either, just listening to a couple of mechanics who expressed the same opinion about how this fuel may have been contaminated with saltwater. Took the coolers off last night and will pressure test today. If they have no leaks, I don't have a clue what we look at next.

[bobk]

JLR, I'm no expert on this topic either, just listening to a couple of mechanics who expressed the same opinion about how this fuel may have been contaminated with saltwater. Took the coolers off last night and will pressure test today. If they have no leaks, I don't have a clue what we look at next.

Mike, Have you confirmed it is salt water? If so, and it is in just one tank you may have a malicious prankster at work.

Good luck,

Bobk

[Fanfare]

Last year my fuel cooler was leaking. I kept finding water in one Racor, about a half cup per day. Then I noticed the sheen in that engine's exhaust water. I figure the fuel goes out when the engines are running and the fuel is under pressure but then a bit of cooling water flows back when engines are stopped. At that time any water in the raw water system, normally flowing past the fuel cooler, is now higher than the fuel tank in the keel. Gravity takes a bit down.

My Racor fuel filter kept any sea water from damaging my injectors by collecting the water in the filter bowl. My FloScan return may have been damaged by the water as it has not worked right since then. I will be investigating next week when I get to the boat.

[jrmccoy]

Gents I am following off an old thread as its the closest I could find to what I'm dealing with. I have sea water in my forward fuel tank, and I don't mean a 1/2 cup a day. I'm talking pulling STRAIGHT water out of the tank, and filling 2 x Racor 1000's FULL in about 3 mins at which point engine stalled. I had just changed filters and was testing...once the fuel I put in the bowls to prime was burnt, engine stalled and when I went to investigate I was horrified to find ONLY water (no fuel) in the bowls. It is verified as seawater.

The only place that I am aware of on the DD's 8V71-T's where fuel and water meet is in the fuel cooler tube, and if breached they can mix and return water back to the tank. I understand the whole concept of the fuel pressure being higher than the water pressure and it should be leaking in the opposite direction, but that's not what I'm seeing.

So my question...is anyone aware of any other way that seawater (a LOT...don't even know how much yet) could enter into the forward fuel tank? I'm not talking stuff like hull breach or vandalism or anything like that...this boat is tight and bottom is inspected once a month by diver...I'm talking something technical.

[bobk]

Not to hijack this thread, but what do you do to prevent leaking coolers, or how do you detect them at an early stage? Can they be opened and re-soldered like the old copper radiators for preventive maintenance? I don't see any zincs on mine on 6V92 TAs.

Bobk

[krush]

Anybody ever experiment and see if the fuel cooler is even needed at all?

Detoits re-circ a lot more fuel, but Tony Athens says yank them on the cummins B and C.

Not sure if 2strokes had coolers on trucks or not....though trucks did have big metal tanks out in the air.

[racclarkson@gmail.com]

Boats have bigger tanks in the shade and they need a cooler. Coolers are also heaters in colder climes. Fuel temp is important in that hot fuel ignites earlier in the compression cycle. That's commonly referred to as knocking. Modern motors can more easily handle this through electronic injection control. Older mechanical fuel injection can't. Coolant temp has the greatest impact on early ignition. A hard running motor in hot weather needs cool fuel. Cooler fuel also helps keep cool heads helping to keep ignition on time.

[Fanfare]

IF YOUR FUEL COOLER LEAKS DO NOT TRY TO REBUILD IT, JUST REPLACE IT!

In viewing these posts I can't believe I have been screwing with my fuel coolers since 2005. What a waste of time and money!

The cooler on an 8-71 and a 6-92 are the fat round jobbies surrounding the raw water line as the last thing on the engine before this raw water is injected into the exhaust line at the showerhead. The 6V92TA cooler cools two things, first the returned fuel (about 2/3 of the fuel sent from the fuel pump to the injectors is used to cool the injector rather than being burned, then this hot fuel is cooled and returned to the tank.) Behind the fuel cooler portion of this jobbie is the transmission cooler which takes the high pressure oil from the transmission and does the same thing. Both coolers are a distinct series of horizontal small pipes looking like a honeycomb through which all the hot raw water of your engine passes on its way out of the boat. My fuel pressure is about 60 psi going to the injectors, probably a lot less returning to the tank. My transmission pressure is zero in neutral, but 250 psi in gear. I didn't think water could get into these fluids against these pressures, but I was wrong. When my "new" engines were sea trialed in 1993 the raw water pressure varied from 10.5 psi at 2300 rpm down to 5 psi at 1200. No measurement at idle, but even at low rpm the raw water pump seems to be pushing a lot of water. There is bound to be some pressure there, and it can both push water where it should not go and suck oil or fuel out through the exhaust.

So way back in the day I had my stbd. fuel cooler rebuilt. Fixed that problem. Last year, in the Exumas, I was doing my daily pre-start engine fluid check and found nothing at all showing on the stbd. transmission oil dipstick. Added a gallon or two of engine oil, started engine, no apparent leaks, nothing in the bilge. Went through 10 gallons of oil getting back to the US. Sent cooler out again for a rebuild. First shop said it was fine, but I learned they only could test it to 60 psi. Second shop found it leaking at 250 psi, allegedly rebuilt the cooler. With new oil boat went about two miles each way to get bottom painted and new zincs. Two days later I arrived to go to the Ocean Reef Vintage Weekend. Checking the stbd. transmission I found it was filled to the top with a white goo, with the emulsified consistency of toothpaste. My first thought was #@%&*##@, followed by, "Well, there goes Ocean Reef." By replacing the 23 year old cooler (air freight) and flushing much lube oil through the transmission until it came out clear we got to the show only three days late. Ran fine coming and going.

My conclusion is that water can pass from the raw water line into the cooler, small amounts into the lower-pressure fuel, probably larger into the transmission because this can have zero pressure in neutral. Hot sea water erodes the cooler's little tubes and once this starts happening the best thing to do is replace it. The cooler does not look like it comes apart. The paint looked intact so I don't know how it was rebuilt. I am hoping it did not ruin my transmission. Twin Disc recommended removal and complete rebuilding of the transmission. Since the water was only in a few days I will see what happens this spring. One marine engineer recommends replacing all the clutch plates in the forward and reverse linkages as he says the material will begin delaminating by next year, clogging the tiny directional orifices which can prevent shifting out of gear. Does anyone have any suggestions on this?

I am also replacing the port cooler as it is probably not far behind in wear. A small amount of good news--the new coolers have their protective zincs on the bottom of the cooler assembly. The old ones were on the top. When not running the water level in the cooler dropped, leaving only the tip of the top zinc in the fluid. The bottom of the zinc would be used up while the top portion appeared like new. This is what probably doomed my coolers. Now the protection should be better.

I have had better days.

[Pascal]

On a Detroit I don't think fuel pressure is high, is it? That's probably why raw water pressure can exceed fuel pressure resulting in water the fuel.

I ve had two cooler failures over the years... one was a Hynautic power steering cooler which resulted in loosing all th fluid, but no contamination. The other one was a fuel cooler on a cat 3412E but the hole was in the outside shell and becsusr the cooler was on the intake side of the raw water pump it never leaked. I noticed something was off because the gear was running a little hotter than normal, as there was air in the water flow. Eventually while troublieshooting I shut down the engine from the engine room and heard the sucking sound from the hole.

[brico]

IF YOUR FUEL COOLER LEAKS DO NOT TRY TO REBUILD IT, JUST REPLACE IT!

In viewing these posts I can't believe I have been screwing with my fuel coolers since 2005. What a waste of time and money.

The cooler on an 8-71 and a 6-92 are the fat round jobbies surrounding the raw water line as the last thing on the engine before this raw water is injected into the exhaust line at the showerhead. The 6V92TA cooler cools two things, first the returned fuel (about 2/3 of the fuel sent from the fuel pump to the injectors is used to cool the injector rather than being burned, then this hot fuel is cooled and returned to the tank.) Behind the fuel cooler portion of this jobbie is the transmission cooler which takes the high pressure oil from the transmission and does the same thing. Both coolers are a distinct series of horizontal small pipes looking like a honeycomb through which all the hot raw water of your engine passes on its way out of the boat. My fuel pressure is about 60 psi going to the injectors, probably a lot less returning to the tank. My transmission pressure is zero in neutral, but 250 psi in gear. I didn't think water could get into these fluids against these pressures, but I was wrong. When my "new" engines were sea trialed in 1993 the raw water pressure varied from 10.5 psi at 2300 rpm down to 5 psi at 1200. No measurement at idle, but even at low rpm the raw water pump seems to be pushing a lot of water. There is bound to be some pressure there.

So way back when I had my stbd. fuel cooler rebuilt. Fixed that problem. Last year, in the Exumas, I was doing my daily pre-start engine fluid check and find nothing showing on the stbd. transmission oil dipstick. Added a gallon or two of engine oil, started engine, no apparent leaks, nothing in the bilge. Went through 10 gallons of oil getting back to the US. Sent cooler out again for a rebuild. First shop said it was fine, but I learned they only could test it to 60 psi. Second shop found it leaking at 250 psi, allegedly rebuilt the cooler. With new oil boat went about two miles each way to get bottom painted and new zincs. Two days later I arrived to go to the Ocean Reef Vintage Weekend. Checking the stbd. transmission I found it was white, with the emulsified consistency of toothpaste. My first thought was #@%&*##@, followed by, "Well, there goes Ocean Reef." By replacing the 23 year old cooler (air freight) and flushing much lube oil through the transmission until it came out clear we got to the show only three days late.

My conclusion is that water can pass from the raw water line into the cooler, small amounts into the fuel, probably larger into the transmission because this can have zero pressure in neutral. Hot sea water erodes the cooler's little tubes and once this starts happening the best thing to do is replace it. The cooler does not look like it comes apart. The paint looked intact so I don't know how it was rebuilt. I am hoping it did not ruin my transmission. Twin Disc recommends removal and complete rebuilding. Since the water was only in a few days I will see what happens this spring. One marine engineer recommends replacing all the clutch plates in the forward and reverse linkages as he says the material will begin delaminating by next year.

I have had better days.

On my 6-71 naturally aspirated engines fuel coolers are just after the raw water pump discharge so it is pretty much always cool water that goes through it. guess seeing oil sheen on the water while engine running may be an indication of the cooler leaking and fuel carry over through the exhaust pipe overboard.

[doc g]

what if there were a raw water restriction downstream of the cooler that raised the water pressure above the fuel pressure in the fuel cooler ?? Don't know if that's possible but.......Pat

[jim rosenthal]

Mike, Tony Athens at Seaboard Marine usually has some fuel coolers around; they are takeoffs from Cummins diesels. (new) At least he used to. They might fit your application, if you have to replace yours.

[Hat52MY]

My fuel pressure on my 8v92 reads 60 psi at idle. Not sure how raw water would be able to infiltrate back into the fuel. I would think it would be more having fuel in the exhaust??? Unless if back flows into the fuel line when the engines are shut off???

[krush]

Fuel cooler is on fuel return back to tank on Detroit, right? Isn't it low pressure back to the tank (orifice in the head)