Oil cooler put oil in coolant CAT 3408. Changed out cooler, cleaned out radiator with degreaser. There is still some oil left in block and heads, so what do you guys use to clean out the cooling system? Most have suggested washing up liquid and get the engine hot and flush it a few times. Another guy said no, use water soluble degreaser (not petroleum based). If I use washing up liquid or laundry liquid, how much would I use? Cooling system holds 65 litres / 17 US gal
Cleaning out oil in cooling system after oil cooler went south
Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Ozdriver, Feb 4, 2026.
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Here is another thread on subject
Oil in coolant resevoir after coolant change | TruckersReport.com Trucking Forum | #1 CDL Truck Driver Message BoardOzdriver, blairandgretchen and dosgatos Thank this. -
Welcome back, haven’t seen you on here for the longest time. Missed the your road train clips.
I remember seeing a guy many moons ago using Palmolive dish washing soap, and water. Ran the truck in Hi idle for a long time, flush and repeat. Did it twice. This was on a 12v71 Detroit. -
3408? Nice. Except for the fuel mileage I imagine. Dishwasher tabs soap is what I've also heard to use, even for routine flush between regular coolant change. I think I remember being told to run it for 1-2 hours. I've used flush from a shop-and not Cascade. Their directions were to run it for 5-10 hours. But I imagine just bringing up to temp for 1 hour would remove any oil. Any longer would be for hard water deposits, which wouldn't exist when using distilled water. I'd still use distilled water for the flush, and flush one more time with distilled water only to remove any soap left behind in the first flush.
Ozdriver Thanks this. -
See video starting at 7:35. Dawn dishwashing liquid is excellent. This is what they use on birds and other animals after oil spills.
Cat C15 and 3406 Oil Cooler Removal and Install. When Should You Replace an Oil Cooler? -
It's sure good to see you on here Ozdriver!Ozdriver, blairandgretchen and Diesel Dave Thank this.
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Too many suds with regular dish soap. Hard to rinse out. Dishwasher detergent is better. Cascade is probably the best. It has softener in it. “No more spots” lol. I always flushed a lot afterwards using regular garden hose. Then used distilled a time or two. It’s arguably overkill. Cheap insurance.
W923, D.Tibbitt, BoxCarKidd and 2 others Thank this. -
dish washer cascade is good distilled water lol never used that in my life garden hose past 50 years works just fine
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I'd plan on bringing the system back up to temperature when flushing a 2nd time, and maybe more depending on much oil is in the drain water. Hot water rinses out oil residue better than cold water. And I'd drain while the water is hot. When I have done it, I would drain at the bottom line between the radiator and water pump into 5 gallon buckets, which has a petcock valve pointed towards the ground.
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We use Fleetguard Restore Cooling System HD Cleaner
$35 a gallon.BoxCarKidd, D.Tibbitt, dosgatos and 2 others Thank this.
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