marlinspike

My car, when it had its factory 3.8 liter engine, came with a 1.2bar radiator cap (~17psi). Later, when I bought a replacement cap, they had moved all cars to a 1.4 bar cap (~20psi). This last time I ordered a replacement cap I forgot that the cap for my old engine was not the same as used with the new 5.6 liter engine, and apparently they have gone back to making 2 caps. So here I have a 1.2bar cap. Does it matter given that the normal operating temp of the engine is 82C (~180F) and it never gets to 212F?

If it matters, some of the cooling system parts are same as original to the 3.8 liter (radiator, hoses - which are the same for all engines) and the water pump is for the 5.6 liter.

Fabrik8

The higher pressure cap just allows higher coolant temp (and therefore higher pressure) before it bypasses. Either one should work fine, and it's probably a case of making the lower pressure cap again because people were getting confused about the new one. If the engine is newer than the one in there before, it might need the higher pressure cap to give a little more headroom if it operates a slightly higher temp.

marlinspike

But if it never has seen more than ~92C, it doesn't matter, right? I'm thinking maybe they went to the 1.4 bar just because the engine isn't considered as overheating until 120C? (but it never actually gets near there)

ILLEGAL

cap? You dont need a cap. I run capless

marlinspike

Actually, looking into it, it looks like even this newer 5.6 liter was leaving the factory with a 1.2 bar, they went to the 1.4 bar later, and now they sell both. I guess they wanted to simplify parts (because the new cars run at over 100C and need the 1.4 bar cap) but, like you suggested, decided it was confusing people.

marlinspike

Any reason for that? This isn't actually a radiator cap per se, but an expansion tank cap (there is no radiator cap). The only time I go capless is when trying to get an air bubble out after changing the coolant.

ILLEGAL

I was joking. Like saying oil filters are for pussies.

Fabrik8

Yeah, I think it's probably just some extra headroom if the newer engines run slightly hotter.

marlinspike

LOL. Well, running without a cap with the heater turned on works great for getting the air bubbles out after changing the coolant (in fact, the service manual says to do this, though it's talking about idling), but I think things are different today with cars running such higher coolant temps.

ILLEGAL

thats how you do it, but you dont drive like that, which is what my joke was about. Not running a cap at all.....ever.