Chennai-Guruavayur express history is as below:[-
AFAIK, initially it used to be run as Nagercoil-Guruvayur overnight express
(inaugarated by then Railway MOSR Shri Rajagopal).
Then...
more... it got extended to Tirunelveli due to demand from Nagercoil-Tirunelveli office goers for morning and evening services.
Later it further got extended to Madurai due to inadeqaute terminal facilty at TEN then and was running as Madurai-Guruvayur express for many years.
After Chennai-Madurai MG to BG conversion erswthile MS-MDU day Koodal express was restored by merging with the Madurai -Guruvayur express to operate as present day Chennai Egmore- Guruvayur express.