Twin Racor problem

LMBoat

LMBoat

Well-Known Member
Oct 4, 2006
753
Ft Lauderdale
Boat Info
1999 450 EB
Engines
Cummins 6CTA's
Hey Guys,

This is my first experience with twin racors on a diesel boat. My plan has been to run on one filter (I know this is counter to Frank's method). When that filter needs changing, I change it and switch the valve to the other filter, run on that one until the next change, and so on.

I just did this, but when I changed over to the other filter the engine stalled. Air was in the system and I had to bleed it. It it my understanding that switching fuel filters should not introduce air into the system.

Is my stragety wrong, or do I have a mechanical issue with my set up? This happened to both engines.

Thanks for the comments.
 
I cannot comment to how the filters will perform when subjected to 2x of intended fuel volume passing through them, but I suspect that you lost prime when switching to the new filter because of an airlock in the unused filter housing. If you know the fresh filter housing was purged of air (full of fuel) then somewhere in the new fuel circuit there is a bad seal. Its also possible that you are creating that bad seal by sucking air into the system due to the high 2x demands...or it could be something as simple as a bad or improperly installed o-ring at the fresh filter housing, allowing air in.

If your boat ran on the new filter at idle and slow speeds, but stalled out under high demand - you are looking at a leak somewhere. If it stalled out at idle, it was probably due to air at the fresh filter.

High pressure injection pumps on electronically fuel injected diesels DO NOT LIKE fuel starved or negative draw (vaccuum) situations. They live the longest having postive fuel pressure at their intake (the purpose of lift pumps at the tank) so they do not starve for fuel at high demands, and start pulling air out of suspension of the fuel. These bubbles can cause erratic fuel rail pressure readings, and are hard on injectors as they pass through at 20K#psi or better. (Think of a garden hose with spray nozzle, when air purges itself from the hose.)

My advice would be to follow your SeaRay service manual for the fuel system. I doubt that they show your 'one filter at a time' approach as anything more than an emergency 'get home' solution, with one plugged filter.

There are two filters (one for each tank and engine) for a reason. Operate the boat within the design spec - or you may clever yourself to an expensive set of new injector pumps.
 
Last edited:
He has dual 900MA Racors on each side, and they only flow 90gph no matter how many engines they feed. He was running a 60gph requirement on one 90 gph filter instead of 2- 90gph filters.

My guess is that you have one or more of the following problems, but never realized it because you had the filter off-line:

1. The Racor was not properly primed by filling the canister to over flowing. Fuel enters and leaves at the mid point, so a partially full canister can allow the engine to suck air as the fuel sloshes around in the canister.
2. The lid gasket is a square 0-ring. It is very easy to roll it 90 degrees when you install it in the groove in the lid. If that happens, it won't seal and the engine will suck air.
3. The red o-ring on the T-handle either wasn't changed or whoever changed it, cut the o-ring while sliding past the threads on the T-bolt.

If any of the above occur, the engine will suck air and will immediately die when it does.

I'm not much on I told you so's.....but you probably are seeing now that having 2X the filter capacity at sea makes some sense. If you are going to have a fuel filter leaking air, its much better to find out about it and to deal with it while you are tied to the dock.
 
According to the labels on my racors they flow 180 gph, or 90 for running on one filter. My flow is less then 20 gal for each engine set up. Under my plan all that needed to be done is switch the valve and keep going. If I had thr valve flipped to both, i would not have had an option.

Also, switching the valves from one to both makes no difference in the vaccum guage. My engines are not electronic, and this did happen at the dock. The problem is the oring gasket in the lid was leaking in air.
 
Don't get confused by the fact that you only burn 20 gph...........your engines are mechanical and they process between 2-3 times your actual consumption since the fuel gallery in the injectors has to stay charged with pressurized fuel. The unused fuel goes back to the tanks via the fuel return system. With your selector set on one filter, you have very little excess capacity.....i.e. you are processing 60± gallons of fuel thru a filter than can only flow 90 gala, when its perfectly clean.

So item # 2 above was the problem........and its worth mentioning again for others because that little square section o-ring is very easy to roll or twist. To check it, I wet a finger in fuel and rub the gasket all the way around to both lubricate it and to check it for a twist.

I am glad you found and rectified the problem at the dock. I won't debate the one vs. both filters, you make your own choices, but consider your plight had you been 45 miles out in the Atlantic 1/2 way to Bimini in a 6-8 ft sea. It really isn't fun working on Racors in a seaway over hot engines while you are bouncing around under the deck. I prefer to do it tied to the dock as a part of preventive maintenance. I may spend a little more on filter elements since I change them all every 100 hours, but the one time I had to change Racors while off-shore taught me to use the capacity I have.
 
I won't debate the one vs. both filters, you make your own choices, but consider your plight had you been 45 miles out in the Atlantic 1/2 way to Bimini in a 6-8 ft sea. It really isn't fun working on Racors in a seaway over hot engines while you are bouncing around under the deck. I prefer to do it tied to the dock as a part of preventive maintenance. I may spend a little more on filter elements since I change them all every 100 hours, but the one time I had to change Racors while off-shore taught me to use the capacity I have.
Click to expand...

Frank, Thanks for re-stating your thinking on "one v. both" for the last hour I've been searching old posts unsuccessfully to find your previous postings on the subject.

Thanks again for your invaluable contributions and insights.

Art
 
fwebster said:
Don't get confused by the fact that you only burn 20 gph...........your engines are mechanical and they process between 2-3 times your actual consumption since the fuel gallery in the injectors has to stay charged with pressurized fuel. The unused fuel goes back to the tanks via the fuel return system. With your selector set on one filter, you have very little excess capacity.....i.e. you are processing 60± gallons of fuel thru a filter than can only flow 90 gala, when its perfectly clean.
Click to expand...

Question for you Frank...would electronically controlled engines process (or require) a different flow rate than mechanical engines (2-3 times)? Because if a 6CTA is consuming 20 gph but the fuel gallery needs 2-3 times the volume-- or rate of flow actually-- not volume (possibly up to 60 gph), then I'm curious about whether or not it's the same for my motors. at WOT, I'm near 30gph and if the injectors need to see 2-3 times this amount as well, then I'm drawing near 90 gph, or at the max spec of a racor 900ma, and as you state, thats with clean filters. That seems like a poor design due to little or no margin for error... what am I not grasping here?
 
I don't have an answer............but I suspect that the precise metering that Cat's electronic injection provides means that the electronic engines probably don't require the flow that mechanical engines do. Caterpillar has an engine installation manual for each engine type and the raw fuel requirement is usually listed in it somewhere, if you want to run it down.

I have some experience with larger boats and I am surprised that Sea Ray only uses the 900MA filter for the 480DB. I looked at the parts manual to be sure (not that I doubted you!) and sure enough, they are 900MA's, so your concern is a valid one.
 
I'll pull the installation manuals out this weekend and see what they say for curiosity's sake. I don't mind being doubted, my wife reminds me all the time about how much I don't know.
 
FYI, from Searay:
"The idea behind the twin set up is to have a back up. Turn the valves so that only one Racor is in use.

Also, there is only one primary on the engine that will limit the flow no matter how the racors are set.
 
I also run with both filters on and have found that with proper fuel maintenance and periodic checking it all works.
I used to run with one on and when that engine shuts down it is never in a good place to crap out.Besides it startles the bigeebees out of you when it does and makes for a very uncomfortable situation.
 
Last edited:
I Run one also. When the seas are bad tossing your boat around its doing the same to the crap settled in your tanks.The Inlet back to port is even worse and sloppy than the sea. Often times very dangerous . This would be the very worst time in my opinion to have one or both engines go down because your filters are clogged.When you think about it its also the most probable time the filters will clog. So as your port fuel alarm goes off then stalls the port engine your screwed ... To restore your port engine you will have to change at least one filter. I go below switch to the back up filter or the both setting and in less than 30 seconds my port motor is going . Your only other option is trying to limp through the most dangerous conditions one one motor. screw that!!!!And screw trying to change it as you bounce and roll off the rocks any buoys while sea water crashes on you below. Run on both and you may just as well be running on one big filter that you cut in half and over complicated for no use full reason. I'll be at the dock with a beer below changing the filter that failed me while the coasties are pulling you and your crew off the jetties .
 
You must log in or register to reply here.

Forum statistics

Threads
113,186
Messages
1,428,156
Members
61,095
Latest member
380Thumper
Back
Top