Dish detergent to clean oil sludge out of the cooling system?

Gasoline engines don't have oil coolers.
In an oil cooler the oil passes through a 'cooler' (which has coolant in it going the opposite direction), usually pretty thin material comparatively speaking (like a radiator but slightly thicker). Ruptures or gasket failures aren't uncommon.

 

Typically when an oil cooler leaks, oil shows in the water because the oil is under more pressure (roughly 30 -70 PSI) than the water (roughly 5- 15 PSI)
When water shows in the oil typically either a liner or gasket on a water passage (head, air compressor, water pump on some, etc) leaking into the crankcase because the water is under more pressure than the air in the crankcase.

Either way makes a disgusting curdled crapacino like snotty mess. if caught quickly little extra damage will be had. If missed or ignored, Big Bad news will be headed your way!!!
Now in the operating room some of your mothers favorite cleaning supplies and really hot water usually work better at cleaning up that MilkofNastyness better than anything from the parts store.

 

The soap is only for cleaning up oil. soap is not caustic enough to get rid of the normal cooling system residue. for that you need to use either a antifreeze flush product or CLR, Limeaway, type product. and not recommended on a tender radiator. And the reason I suggest using some type of bottled water for refill. Distilled would be best but not necessity. your Coolant and cooling system will last longer with a high quality antifreeze and good water (few or no minerals)
Sorry for the Long Ramble

 

I can't see the harm in it. I would be hesitant about leaving it in there too long because water has no corrosion inhibitors. Would definitely recommend re-checking the coolant strength after letting it circulate as you won't be able to drain out 100% of the water.

 

I've always used cascade, works great and dissolves any mineral deposits too..

 

Dawn is the best for cutting grease,and rinsing clean.
My buddy makes eyeglasses..Jim Jay..eyewear 20-20.
Dawn is the only product they use,for cleaning their optics.

 

I've used liquid Shout with great results as well for flushing cooling systems. CAT makes a cleaner designed to be left in for a couple days at a time but you're limited to using it above freezing obviously. Just remember to rinse several times when done and all the products mentioned above will do the job.

 

You will find engine oil coolers on gasoline engines but usually on 3/4 ton and above pickups set up for towing and even then, it's an air cooled unit mounted on the radiator.

 

Won't foam up either. We used to use it for cleaning out barrels.