That's an engine built with 12A RX7 R5 gas nitrided cast iron housings and '76-'78 RX4 rotor housings. I had a customer in AZ with a rotary beetle..... Years ago someone sold a kit to do the conversion.... Good luck with that - It should be lots of fun.
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'77 RPU
'75 RPU (V-6)
'76 Courier
Rotary Sprite (3 - 2 project)
'85 IT 7
EP '85 Rx7 (in progress)
'85 GSLSE (4)
C6 Corvette Roadster
i've cleaned many with all kinds of stuff. brake cleaner, simple green, soap and water, ATF, baking soda.....lots of high pressure water. never cleans it all out
take it to an ultrasonic cleaning shop. had a few coolers that rattled when shaking them after i cleaned them myself. sent it to these guys and no more rattling (they got it out). smells much better too and they vacuum seal the whole thing in clear plastic when they're done.
i have all mine done at:
Ultrasonic Cleaning
20730 Main St.
Carson, CA 90745 USA
Tel: 310/327-7103
It only costs $55 with a pressure test to boot. gets a report card too! many pro race shops send their oil coolers here. including penske. they do oil lines too.