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Surge Tank Pressure Cap


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I went to the local dealership the other day to get a new pressure cap, some dexcool and pellets to change my coolant.

Asked for a cap for 1998 SLS and they gave me a cap rated at 18 psi. I told them that original equipment was 15psi. Their response was that this is what the new stock numbers show as the replacement for that cap.

I wasn't to happy with their answer, so they brought out one on the technicians who told me that this new 18 psi cap would be fine. It would only make the boiling temperature higher which was ok.

My question - are they telling me fact of fiction??? and is this 18 psi cap ok to use.


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For what it's worth, my '04 Deville has an 18 lb cap.

And they are telling the truth about the boiling point.


Drive your car.

Use your cell phone.


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All of this is true, but there is one thing that the 18 PSI cap WON'T help, and that is the tendencies for the blankety blank <_< plastic tanks on the radiator and heater cores to crack.


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Thanks Guru,

I haven't read the thread on the "surge tank vs. coolant recovery bottle". I will as soon as I post this reply.

I just have a problem with the plastic tanks cracking after about 150,000 miles. I know that is probably longer than the design criteria. But I have two 1959 Chevrolet trucks and a 1977 diesel suburban. All of them have the original cores and tanks. Yes, they have been to the radiator shop to have the cores cleaned and tank to header joints repaired. Probably more than once. But with good maintenance they have lasted.

Not so with the plastic tanks on the present day cars. My 1988 Seville, 1994 Seville and my 1996 Suburban have all had cracked plastic tanks. Admittedly, the tanks see a pressure temperature cycle once per engine start, but they lack the longevity of the old all metal radiators.

I would think that adding an 18 lb. cap to a plastic tank equipped vehicle that has already seen numerous pressure/temperature cycles would just shorten it's life further.

All of my plastic tank failures have been in the sides of the tanks. The tank ribs crack first ant then the constant flexing induced by the heat/pressure cycles eventually cause the tank to fail.

Possibly a thicker tank wall with the number of ribs doubled and the addition of an ozone resistant coating would cure or prolong the life of these tanks. But that adds costs (and a proce$$) to the construction of the tanks.

This is just an observation on my part. I opted to replace the radiators in the three vehicles rather than just change the tanks. The aluminum cores in the failed radiators were in excellant condition however.

Take Care

Thanks for your input to this board. It is a great asset to have someone with your background who will take the time to address the concerns of the board members.


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