cooling system surge tank cap
Thread Starter
Instructor
Joined: Apr 2004
Posts: 133
Likes: 7
From: Wenatchee WA
cooling system surge tank cap
I have a 98 A4 coupe and recently have had an issue with coolant pushing out past the cap when the engine is shut off and the coolant temp is 220 degress or higher. since I was not having any other issues I decided to start by replacing the cap. I picked one up today and when I got home realized that the new cap has a 18 psi rating but the old cap has a 15 psi rating.
any one out there know why they changed to the 18 psi cap? the 15 has worked fine for the 5 years I have owned the car.
any one out there know why they changed to the 18 psi cap? the 15 has worked fine for the 5 years I have owned the car.
Melting Slicks
Joined: Mar 2002
Posts: 2,203
Likes: 63
From: Staten Island NY
The RC87 cap (18 psi) is used on the later years C5s. Its one less part the dealer has to stock (the 15 lb cap) as the newer cap is backwards compatible with the 97 to 99s.
Cant say exactly why GM changed the spec, but the extra 2 pounds of pressure will allow a higher water temp before boil-over.
The newer cap also cant be over tightened by a garage monkey - it will ratchet like the gas cap once it tight enough on the plastic overflow tank.
Cant say exactly why GM changed the spec, but the extra 2 pounds of pressure will allow a higher water temp before boil-over.
The newer cap also cant be over tightened by a garage monkey - it will ratchet like the gas cap once it tight enough on the plastic overflow tank.
Last edited by warren s; Aug 30, 2008 at 08:57 PM.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The RC87 cap (18 psi) is used on the later years C5s. Its one less part the dealer has to stock (the 15 lb cap) as the newer cap is backwards compatible with the 97 to 99s.
Cant say exactly why GM changed the spec, but the extra 2 pounds of pressure will allow a higher water temp before boil-over.
The newer cap also cant be over tightened by a garage monkey - it will ratchet like the gas cap once it tight enough on the plastic overflow tank.
Cant say exactly why GM changed the spec, but the extra 2 pounds of pressure will allow a higher water temp before boil-over.
The newer cap also cant be over tightened by a garage monkey - it will ratchet like the gas cap once it tight enough on the plastic overflow tank.
EXCELLENT DATA!!!
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