Hmm.. After seeing that there was a bit of grease residue in the radiator of an A I just purchased, I decided to drain the coolant and fill it up with 1/2 Super Purple Degreaser, 1/2 water, run the motor to operating temp and then block off the airflow to get it really good and hot.. Worked like a dream! The radiator was all shiny inside and cooled so much better..
The Mistake? Using a Soap Based Cleaner.. Apparently Lawrence Welk used the same mixture in his bubble machine in the 50-70's

.. I thought it was very well flushed out, running a hose into the top and then draining it out at the same time while the motor was running should have given the block and radiator a very good rinsing.. Well, it didn't
I filled her up with new 50/50 antifreeze and being well pleased with myself, noticed that it indeed ran much cooler.. Well, took her up a 6% pass not too far away and once I got the motor turning really well and generating the heat, the temp started to climb - a lot. Apparently the ghost of that super purple degreaser came to visit me.. The radiator fill started to foam like an overworked racehorse from beneath my motormeter and spew all over the windshield with great gobs of lovely foam. I'm sure it was quite a sight from the outside, but could not tell from the inside as my radiator had pretty well foamed over my windshield before I could get stopped..
Well, I opened the cap while she was running and got a stream of foam about 3 ft tall to eject right out of the top of the radiator, and then the engine seemed to cool down a bit.. It seems that there was anough soap in the degreaser that it seemed to soak into the block and come out once the motor got good and hot.. also the prestone seemed to be encouraging the foam. The waterpump likely got cavitating, and with a pile of foam rather than coolant to work on, caused the waterflow to cease until the engine started to pump the fliud out of it due to the heat expansion, and when the hot water got up under the foam and finally into the impeller of the pump, the ejection of the foam was quite energetic.
Once she was through frothing I poured about a gallon of fresh water into her and proceeded home, sitll foaming, but a bit less. My wife had a good sense of humor, even refering to the car as 'Cujo' for the remainder of the outing..
We got home, rinsed more and even after adding fresh 50/50 still got foam, but a bit less, so this summer, she will be out and about with water and a bit of antirust and pump lube in the mix. Drained after each run and refilled again before the next run.. The head and gasket all check out and there are no noticable bubbles with the water mixture in place.
Moral of the story.. Use Simple Green or another non-foaming degreaser to rid your radiator of grease next time.
- Dave