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After cooler raw water leak
d_meister
Posted: Monday, April 19, 2010 6:57 PM
Joined: 02/03/2010
Posts: 7


My 3406 Cats have a recurring raw water leak at the after cooler inlet port from the raw water pump. The mechanic replaces the "O" rings and has replaced hard parts in the past, but after a couple of months, the tiniest drip of very brown water begins again. The previous owner left a supply of the correct sized "O" rings on the boat without explanation, so it seems to be an ongoing issue. Although not presently traveling, the engines are run every two weeks to prevent depleted oxygen corrosion (amongst other reasons). Any one else experience this?
junior
Posted: Monday, April 19, 2010 7:53 PM
Joined: 14/01/2009
Posts: 1026


I don't have a Cat. but Ive experienced a similar "O" ring weep. For an "O" ring to work it must have even surface contact and pressure applied along its entire 360 degree inside, outside, diameter . . Check that the two component mating surfaces are aligned correctly , are true and clean and that the correct torque is applied when clamping the joint.. If you carefully examine the shape of the Old "O"ring for distortion and the "O" ring seat for different shades in metallic colour, you might be able to spot possible misalignment .. Its very unlikely that an "O" ring would leak evenly along its entire 360 degrees of surface contact. Many times its worth while to consult the shop manual for your particular equipment. My MTU shop manual goes into great detail when describing correct reassembly procedures.
d_meister
Posted: Monday, April 19, 2010 10:40 PM
Joined: 02/03/2010
Posts: 7


Thanks for the response, Junior. In this case, the local professionals are dealing with it. They keep re-doing it for free, so they're sufficiently motivated to effect some real healing. The curious thing, is that they never leak when running, although there must be some pressure in the circuit. They get "fixed", and then two months later the weeping begins in between periods of engine running at the dock. Since it happens to both engines the same exact way, I'm thinking that it's a known product problem. Incidentally, the boat is well bonded, and the pencil zincs are checked every 30 days, but I think the salt water circuit in that area on the engines would make a very good battery. It goes from the raw water pump where there's a pencil zinc at the outlet, into a bronze tube that's isolated by "O" rings at either end, into a bronze sleeve mounted in "O" rings in an aluminum housing, and then mates inside a stainless steel heat exchanger.
junior
Posted: Tuesday, April 20, 2010 12:08 AM
Joined: 14/01/2009
Posts: 1026


Cat makes good gear. Id suspect that its an assembly problem. Never trust subcontractors to trouble shoot a problem. Subs are simply solving problem "A" on the work order....they very seldom spend the brainpower to assess the true cause of a problem. In my leaking "O" ring case, the cause of the problem was a non MTU water pump gasket that I manufactured on the engine room workbench . The gasket stock I had on hand at the time was the same quality, but was thicker than specs and this threw the whole alignment sequence out. Put your thinking cap on. Are all the dissimilar metal fittings you describe Cat. spec ? or has a past modification to suite locally available marine store materials been made. Electrolysis and metal pitting are easy to spot. If you had an electrolysis problem a competent Sub contractor would easily identify it. What they cant spot is non standard installation materials . By the way, take a voltmeter and prove that your engine is electrically neutral. Dissimilar metals are a very small source of metal erosion...stray DC electricity from alternator , starter motor brush filings and engine sensors are engine killers. Your engine and yacht must be completely free of any DC current. And Once again...never trust the sub contractors. This winter I had the Injectors out for service so I thought...what the heck , might as well have MTU adjust the valve clearances. Since the starter motor was off to view the TDC marks I took it as an opportunity to grease the Ring gear. Ive never been told exactly what type of grease is best for flywheel starter motor ring gears , so I asked the MTU engineer and his reply was..... WHAT ? why are you greasing the ring gear ? Well...errr emmm, because the MTU service manual states that it must be greased at this service interval!!! I never found out what the proper grade of grease was.............
Anonymous
Posted: Tuesday, April 20, 2010 8:16 PM
We had a similar problem on board w/ a 3516, it turned out that the "cat" oring was pretty inferior. We changed it out on warranty but decided to put a non cat (better made) oring in & haven't had a problem since. Are you using the orings that were left behind? Metric imperial issues? We were suprised by the lack of quality in the cat oring. Good luck
Anonymous
Posted: Tuesday, April 20, 2010 8:49 PM
Add to blog - 3406 sometimes the impeller on the water pump loosens because a bolt holds it on a shaft - spot weld solves that - you will knowest a slow rise in temp over months from the impeller slowly loosing. 3512 or others if the diff pressure is bouncing it is the pressure regulater in the fuel pump - very hard to find, it is not the regulator on the engine fuel return. Yes use better Orings and clean all surfaces very smooth and seal, a setting cold CAT is very much a problem at start-up, so pay the price and keep them warm. GOD Speed to all
kapt_mark
Posted: Tuesday, April 20, 2010 9:35 PM
Joined: 30/06/2008
Posts: 82


Have you tried using sealant/ gasket maker in conjunction with the o- ring? Is anything else leaking, as this could be a symptom of excessive vibration.

abouis
Posted: Wednesday, April 21, 2010 12:00 AM
Joined: 05/09/2008
Posts: 22


Before using something as permanent as sealant, try 100% Silicone Grease, for example "GLY", I use it on all my o-rings and it works wonders!!  All O-rings benefit from a coating of silicone, including the ones on water filters, raw water strainers, dive gear, etc.  This stuff also works wonders on the leaky hatch gaskets!!


d_meister
Posted: Wednesday, April 21, 2010 1:30 PM
Joined: 02/03/2010
Posts: 7


Thank you all for the responses and suggestions, you all made good points. Regarding competency of installation: The mechanics working on this are good guys. I was a dealership line mechanic for 15 years, and a factory service rep (Volvo) for 5. When it comes to supervising, I'm pretty good, if I do say so myself. The mechanic says that the "O" rings themselves are the issue, adding that there is significant variety in manufacture, and that he "cherry picks" the ones he installs. Again, all is well for two months or so, and then the oozing begins anew. The vibration is minimal, since the boat hasn't traveled, and the engines are only run in the slip. When we did travel, the staining appeared, but there was never an "active" leak. The mechanic lubes up the "O" rings nicely, but the container was unmarked, if I recall. Incidentally, the mechanic (Cummins factory trained), supplies new stock Cat "O" rings. It raises the question of whether the goop he uses eats the "O" rings, but they look good and maintain their bright yellow color upon removal. Since they're still on the hook for this repair, I might get out the old calipers and measure everything nicely while it's apart, cover the lube substance issue, and place an order with oringsinc.com. If you guys haven't used them, you can get any material, any dimension , with no minimum. Thanks for all the tips!
junior
Posted: Thursday, April 22, 2010 3:28 PM
Joined: 14/01/2009
Posts: 1026


Plenty of O ring knowledge on this site.....http://www.marcorubber.com/orings.htm And Perhaps you have a design defect ? I have a cummins diesel generator with a seal design defect. This cummins has the box type "push on" engine mounted fuel filter. This compact filter assembly is hard plumbed and uses rubber sleeves over the steel fuel pipes, in conjuction with compression nuts, to form a tight joint while allowing expansion contraction movement along one axis at the joint . Aside from the fact that access is poor, its almost impossible to service and torque the compression nuts correctly, I believe that when the engine runs hot multiaxial , expansion , contraction, of the "hard to hard " metallic plumbing joint " compression sets " the rubber sleeve seals and forms the leak. This monster can only operate perhaps 50hours before a slight fuel leak on the pressure side develops. It drives me crazy. Ive been on this yacht 16 years, fixed this fuel line joint 20 times, have a box of spare rubber sleeves for the fuel line compression nut joint assembly and have never been able to solve it. I CAN SMELL DIESEL FUEL RIGHT NOW !!!!!!!!!!!!! Arrrrrrrrrrrr......... Perhaps your problem is due to thermal expansion contraction of the joint, causing compression set to the O ring ? For assembly paste I have been using "Tef Gel" to bed O rings. Its non metalic and very very sticky, so it holds the O ring or gasket in position for assembly. Seems to work well and adds a bit of extra corrosion protection to the joint face on equipment like BOWMAN alloy oil coolers. .
d_meister
Posted: Friday, April 23, 2010 5:46 PM
Joined: 02/03/2010
Posts: 7


I went to the mechanics shop today and gave him the news about the re-appearance of the leak. He wasn't cheered to hear about it. I gave him the serial numbers and build specs, so he's going to Cat direct to find out what the deal is. I'm beginning to think that it's a design issue as you say, Junior. The pipe from water pump to intercooler can't be installed without some off-centering stresses. My Volvo turbo oil return pipe is similar, and they "normally" leak oil. I added a second square cross section "O" ring and forced the fit. Presto! Normal oil leak healed! We'll see what they come up with, I guess. About your diesel leak, Junior. I'm sure you've considered modifying the installation to a spin on rig. Northern Lights fuel filters are a spin-on affair that is a bracket mounted to the engine and plumbed with external piping. It might take a creative machinist to make adapters for what you have to go to pipe (tube). I think I know which secondary filters you have. Are they like the glass ones that Onan used?
 
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