it''s my 88 dl d/r spfi wagon , 197,000mi , no coolant in oil, or oil in coolant, does not over heat, runs fine , my question is what is the cause of the foamy in the over tank

Probably dirty coolant. Flush the system.

 

GD

right, after i made the post i was thinking about when was the last time i flushed it ,thanks

Jim:

You should flush it both ways to really clean things out. You'll need two flushing tees; one at each heater hose. I always use Prestone Super Flush to dissolve any buildup in the rad or heater core.

Once things are flowing freely again, you shouldn't have anything but bright green in your overflow tank. Don't forget to clean out the tank too as part of your coolant flush.

good luck, John