My 00 vert's expansion tank needed to be replaced. I replaced it with no problem, but I was wondering if I should have bought a new cap with it? What does everyone else thinks? Before I locked it away in the garage for the winter. I was having a problem with the temps getting to around 225. The other fan would kick in and cool it down a bit. Thanks a million.

 

The cap is cheap enough, I bought one before putting mine away for the winter and it was about $12 from the dealer, so I'd go ahead and replace it if I was you. I have no idea if that's what's causing your car to run hot, though.

 

The fans don't turn on till you get to 225/6 degrees unless you have the HVAC turned on. They go to high speed when you get to 235 degrees. Sounds normal too me... unless your HVAC is turned on and the fans aren't running, then that would be a problem. To clarify, BOTH fans run when the fans are supposed to be on..not one fan.

 

I should have been a little more specific. During normal driving without the air on, The temps are at around 210. As soon as I stop at a light, that's when the temps get to 225. If I drive with the air on, I don't have that problem.

 

Normal, check this out:

C5 Cooling Fans Operation

The low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

In fact if you want to cool off the engine at low speed (while waiting at a light, drive through, etc.), just turn on the A/C.

To answer your original question, if you are seeing temps significantly over 212, than your cap is working. Unpressurized, water boils at 212 F. Another check, BUT BE CAREFUL, is to slightly, slowly turn your cap after it is running for a short time, to see if it releases pressure. DO NOT turn it off after car has been running a long time, steam could burn you. You could also feel the upper radiator hose after it has been running, it should be hard, if it is soft you are not pressurizing the system. The professional way would be to pressure test the cap, but that requires a special tool/fixture.

Last point, new caps will say 18 psi instead of old caps which say 15 psi, this is okay.

 

In addition to everything that Oldvetter mentioned, there's one more thing to watch for.

If you see a collapsed upper radiator hose, after the engine has cooled,
the surge tank cap should be replaced. The cap also has an internal vacuum relief valve, that may not be working.

 

Good catch Quicksilver Vert 01, I forgot to mention that !

 

It's hard to remember everything, but LOOK OUT when we all put our heads together!