Vented vs. Non-vented

I went to buy a new Radiator Cap for my 2001 S-10 Blazer 4.3L and the counter guy at Checker asked me if I needed a Vented or Non-vented Cap. I asked if he meant one with a lever or without a lever, he said the Vented and Non-Vented both come in either style. I asked if vented means there is flow in and out of the overflow jug and he said both types do that, and that vented caps go on vented systems. O.K. I'm stumped.

So, the big question is what is a Vented vs. Non-Vented Rad cap?

Never heard of such a thing. I would be like you and think it would mean if it would allow flow into the overflow or not.

Vented has the lever to relieve system pressure into the overflow tank. Otherwise, they're the same in operation.

Vented has the lever to relieve system pressure into the overflow tank. Otherwise, they're the same in operation.

Yes, I have one of these, but if you read his post the salesperson said that is not what he was refering too. I really think that the salesperson did not quite know what he was talking about on this one.

I agree....

the one with the lever lets you relieve the pressure in your cooling system.

IMO the best cap for an 01 Blazer would be a Stant 11230 (normal cap) or 11330 (cap with pressure release lever). I use a 11330, it functions just like a normal cap, but allows you to manually release the pressure if you need to sevice the system.

I found this online, it explains the difference between vented and non vented better than I can, because I've never noticed the difference:
Most caps these days are "vented" to a recirculating tank. This means that they have a one-way valve on the bottom of the plunger that closes when there is pressure in the radiator and opens when there is a vacuum in there. In the case of a 16# cap, when the pressure in the rad goes over 16#, it pushes the plunger up and releases the pressure into the little tube sticking out the side of the cap holder. Any steam/water under pressure blows out this little tube. If you have a hose between the little tube and the recirculating tank the steam and water go into the tank (it usually enters from the bottom and is vented at the top). When everything cools down, the radiator now has a vacuum in there and the little one-way valve on a "vented" cap opens and permits the liquid held in the recirculating tank to return into the radiator, because the vacuum from the cooled-down rad now sucks the water from the bottom of the recirculating tank back into the radiator. Old sytle rad caps don't have that little one-way valve in there.

Older cars used to run much cooler and normally didn't require a recovery tank, because they seldom "boiled over", unless there was some kind of problem - therefore a non-vented rad cap was the norm, with a vent hose exiting to the street, just in case. Modern day engines are designed to run at higher temps and in many instances dump water into a recovery tank from the expansion of the extra heat, to be "recovered" later, when the engine cools down.

Older cars used to run much cooler and normally didn't require a recovery tank, because they seldom "boiled over", unless there was some kind of problem -

Older cars that didn't have a recovery tank typically had oversized radiators, and you would only fill the radiator to about 2" below the cap. They ran just as hot, and the coolant expanded into the air space in the top of the radiator.

Older cars that didn't have a recovery tank typically had oversized radiators, and you would only fill the radiator to about 2" below the cap. They ran just as hot, and the coolant expanded into the air space in the top of the radiator.
It's true that they were filled below the neck, and the coolant expanded into the air space, but they did in fact run cooler. Cars today are designed to run hotter to reduce pollution.

Yes, thermostats have definitely become higher temp in the last 30 years or so.

The stant vented cap is the best way to go with Dex Cool and always fill the tank to the Hot line when the Blazer is cold to ensure NO air gets into the cooling system cause Dex Cool will then sludge up and deposit in the heater core, trash the water pump, and then the intake manifold gasket goes. Never leave Dex cool in for the 5 years/100k miles or you will be sorry. Chevy has redesigned their radiator caps several times cause the Dex Cool deposits shut the venting action OFF.

It might have to do with the different methods of intergrating the overflow into the cooling system. On the Blazer and my old Camaro, the overflow is connected by a smallish hose from just under the radiator cap and had just a lightweight plastic cap on it. In my BMW the overflow tank is actually a pressurized part of the cooling system. My BMW doesn't even have a cap on the radiator, but the cap on the overflow is a heavy duty one meant to hold pressure. The radiator has a ~3/4" hose leading to the overflow, and the overflow has another ~3/4" hose leading back to the engine. I'm not positive, but the GM method seems to be a vented system while the BMW/MB is non-vented...

Thanks to Blazee for the internet post, (Good Info) and to everyone that replied.

As usual, I bought a Non-vented cap, which sounds like I should have bought the Vented cap. PIA, PIA, PIA. The part that pisses me off is that I asked if the Vented cap was for a closed coolant recovery type sysem, and was told No. Obviously the counter help wasn't too smart.

Since the original (Garbage) Delco Cap seems to be of the vented variety, Shouldn't I replace the cap with a Vented Type? Maybe it is just preference, but I kinda like the idea of the overflow jug and returning the coolant to the Radiator.

Well, with any luck this post will help keep someone from buying the wrong cap, or at least understand the difference when they go to buy a new cap.

Rick