Are the 525 and 500 EFI serpentine belts the same? They have a different part number but some times that mean nothing.

The accessories are different, I don't know for sure, but I think the belts have to be different.

i am speaking theoretically, i.e. no specific knowledge of the two belts you refer to, but the part number usually includes the discrete codeing that describes the belt... i.e. the number of ribs and the length will be the last part of the number... for instance a 5 rib that is 100 inches long might end w/ 5100... i would suggest that if you have two dif numbers , then you have two dif lengths. when i did my 502's w/ serp belts, i took the power steering off 1 motor and changed the accessories around a bit and needed a dif belt... i simply measured the one i had which identified the code for me and then called napa w/ my new " part number" the same code w/ a dif length code in it.... and it was on the shelf. i can't remember if it was inches or cm, but thats how it worked.

The reason for asking is I have a spare belt from my 500's and I now have 525's. I always like carrying a spare with me for just in case. If they are not the same does anyone have a cross reference number for a non HIGH DOLLAR Mercury belt?