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Old 08-13-2015, 05:39 PM   #1
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How to backflush an FL 135

One of the jobs on my must do list that I developed after buying our boat was to flush the stb engine and add coolant - there wasn`t any in it and the water had a hint of brown rust.

So, I want to back flush the engine to clean it out before I add new coolant. Any suggestions as to how? I also intend to do the anodes and probably rod the heat exchanger when I drain the system.
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Old 08-13-2015, 06:12 PM   #2
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Hey George,
I would think you would want to secure a shop vac and a 5 gallon bucket or two. You will also want to get a thermostat, gasket and cap from American Diesel. Does it have a pan beneath the engine? If so I would remove the cap and locate the drain located on the side of the block and loosen/ remove. Let old coolant drain and use shop vac to remove from pan and pour into bucket. Remove the thermostat and put T housing back on (no need for a new gasket yet) and I suggest you fill and drain the block a few times to get as much of the contaminated coolant out that you can.
Put the drain back in, install the necessary amount of your favorite engine cooling system flush and fill with clean water. Cap on. Start engine and run till hot at least (Ski may have some suggestions how best to achieve this), drain and flush again. Note, if you fill it to the top- expansion will probably push some of your flush/ water mix into the recovery tank (if you have one installed). New thermostat/ coolant and cap and you are done! Occasionally a new thermostat will hang up closed initially- then open and drop the temp to where it should be. You may see the temp spike to 200-210 then level back to around 185. After once- it's fine.
Good Luck!&


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Old 08-13-2015, 08:09 PM   #3
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I bought a proprietary radiator/cooling system flush (from Supercheap Auto, I think it was a rebranded Nulon product), needing 2 bottles for the volume, with the intention of DIY. but then got a mechanic to do it. Another mechanic had confirmed it as ok to use such a product. Not sure about L135s, but L120s get a build up of crud affecting no. 6 cylinder. It was successful, resolved the overheating, (though I now know my gauge reads +20C). Multiple flushing as Steve advises is good. My mechanic did an extra flush when the alternator belt failed taking out the front hose during a WOT test run I found out about afterwards. Good luck with it, your instincts to do it are right on.
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Old 08-13-2015, 08:59 PM   #4
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Take a good look in the expansion tank. I've found them before thickly coated on the bottom with sludge that you can't get out with simple flushing.

Don't bother rodding out the heat exchanger. Acid flush the entire raw water cooling system all at once.
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Old 08-13-2015, 10:59 PM   #5
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Why not just flush flush.

I mean double flush. I just did that. My engine is quite new (10yrs) but I've not flushed her yet and she'd been sitting for 2.5 yrs.
Since the engine is fairly new I used 1/2 of the flush in the bottle on the first flush and then flushed again. Then I did a 3rd flush w one quart of AF (to hedge against boiling) and distilled water. Actually I used distilled water and a little AF on the first two flushes for the same reasons.

I threw away the drain plug and installed in it's place a little ball valve for future draining and plan on changing coolant once a year. Distilled water and long life coolant.
I used an oil extractor w a hose attached to the new drain valve to extract the coolant. Works very well.
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Old 08-14-2015, 03:31 AM   #6
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I had a crack at the flushing today - Got a little cunning and used the off take to the domestic hot water heater - disconnected it from the service and held it into a bucket whilst running the engine - I had a hose running into the header tank. First three or four buckets were mud, but after about six it started to get clear. I now intend to run some flushing compound through it then lock it up and add the proper coolant.

I did the pencil at the same time - both engines actually as I had the spanner out of the box - both good BUT both were bone dry - I thought they would have been immersed in coolant and I was expecting to loose some when I took them out. Is this right?

George
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Old 08-14-2015, 07:56 AM   #7
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The zincs are in the raw water side of the cooling system. Not the fresh water side.

This is pretty basic. If you don't under how the cooling system works I suggest you get a book on basic marine diesel engine systems to get a good understanding of how your engine systems work.
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