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GM has changed the part number for the radiator surge tank cap on vehicles that came from the factory with Dex-Cool. The new cap is 18 PSI (RC87 - part number 25713160), the old one for many vehicles was 15 PSI (RC75 - part number 10296465).

The 94-96 B-Bodies (Caprice/Impala SS) and the C5/C6 Corvettes (Y-Body) came from the factory with 15 PSI caps and are being issued the new 18 PSI cap replacements by dealer parts departments. Is this likely to cause any problems?

GM does a lot of strange things to save a buck. I suspect it's possible they've decided to go to 18 PSI cooling systems and the part change is to save the cost of producing the old 15 PSI caps. Can anybody confirm / deny?

Update

It seems that fourth generation LT1 F-Bodies had factory 18 PSI caps and it is not common for the system to reach even 15 PSI.

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The main thing the higher pressure cap will do is to increase the boiling point of the coolant slightly. 3psi isn't going to make a huge difference, but it will make some difference.

If your cooling system is in good shape, the higher pressure unlikely to cause problems. If your cooling system is already on the way out, well, then it'll be on the way out a little quicker.

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    As a rule of thumb, yes. Antifreeze can also increase the boiling point somewhat so it might not be an exact 9 degrees. But it's a little more.
    – Timo Geusch
    Commented Oct 23, 2012 at 0:49
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I can't speak for GM, but one reason they may be doing it is that they have a reputation for overheating under heavy use (heavy towing on the trucks and track days for the cars) amongst motorsports enthusiasts. Bumping it up a few psi is relatively safe for the cars and may well be enough to help keep the overheating under control.

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