I have a 1989 E350 with a 7.3. At hwy speeds (55 or higher) I get blue smoke coming out the tail pipe. It will do it for a few minutes then clear up for a few minutes. I'm thinking valve guide seals, but don't know these diesels to well. Any body out there have any ideas?

 

Id check over in the pre-powerstroke forum on this site. Lots of IDI knowledge there.

Yes it could be valve seals, depends how bad its smoking and under what conditions. I know they start to smoke when injectors or pumps start to **** the bed