Rust on radiator cap?

[Intrepid]

I would like to add that I went by Advanced Auto Parts to look at their radiator caps, and they carry a vent cap. It's pretty nifty looking........it has this lever across the cap that you release to take off the cap. The salesman noticed my interest in the cap, and informed me the vent caps are superior than other pressurized caps. I'm not sure why, maybe because of the lever, but it costs a $1 more than the radiator cap I purchased at O'Reillys. Any input on this?

 

[Ray H]

You were boiling with the old cap because it was no longer within pressure specification (or the cap that you replaced really wasn't the OEM cap and some moron had substituted a lower opening pressure specification cap prior to your acquiring the car). Did you mix the G-05 to 50% or a higher water percentage - if the latter, you might not have sufficient corrosion protection. If the mix is verified to at least 50% working glycol concentration with an antifreeze hydrometer, then I'd be suspicious of either pre-existing corrosion that didn't get flushed, or an air pocket remained after refilling in which corrosion developed. (Some vehicles require loosening a special "burp" screw-plug after coolant changeout - check your owner's manual.)

The lever pressure-relief caps only offer a convenient, safer way to relieve the pressure (and lose coolant in the process if coolant oveflows the capacity of the overflow bottle - not hard to do in hot climates) prior to removing the cap. They offer no improvement in basic operation. If your engine has overheated, it's a safer and virtually coolant loss-free procedure to open/prop the hood wide open and wait 20 minutes before loosening the radiator cap. Standard caps' simplicity offers the advantage of one less thing to go wrong, too.)

 

[Intrepid]

Hey guys,

Let me start by explaining I know my question about a radiator cap does not pertain entirely to coolant, but I figured many of you members here are familiar not just with coolant, but with radiator caps.

So here we go. I drive a 99 Dodge Intrepid 2.7L w/ 72,000 miles. The car used to be a fleet vehicle, but I purchased the Intrepid a year ago and restored the engine. Some of you might be familiar with how hot these 2.7L Intrepids can get.

I noticed that when I turn off my car, I could hear a boiling sound in the coolant tank. I flushed the coolant and replaced with Zerex G-05/distilled water as this is recommended for my car on an Intrepid website. I could still hear the boiling sound coming from the coolant, so I replaced the radiator cap with a Murray Ultra cap from O'Reilly's for $4.32 back in January 2005........the boiling sound stopped!

My coolant has been great. My coolant needle never rises above the halfway mark. My car runs great. I'm using Mobil 1 oil with a Napa Gold filter so I'm very satisfied with the car.

However, I took out the radiator cap to inspect and make sure the coolant is at the proper level when I noticed there is burnt rust blotches forming on the inside of the cap. Why is this happening? I understand water tends to rust aluminum parts, but I figured there shouldn't be this burned looking rust on the inside of the cap.

Did I get what I paid for? Maybe I should try a different cap? Any suggestions on what to do or what I might come across in the future? Thanks!

 

[Big Jim]

I don't like the lever vent caps. They do offer just one more thing to go wrong with them. My experience has been that they don't last as long as conventional caps.

 

[Intrepid]

Good info! Thanks for pointing me in the right direction........stay away from the lever vent caps. I don't have a need for them as my car never overheats, so I have no use for the lever if it is to relieve pressure.

As for the 50% mix between Zerex G-05 & distilled water, I'm pretty sure I got an even mix after the radiator was flushed. I had no idea that it isn't good to have a 50% mix, but instead more Zerex? I guess it does make sense to have more Zerex to fight corrosion. I guess these kind of directions don't pop up because they don't want to confuse people into pouring more then they should, and it defeats the whole purpose.

I wonder if I should take my car back to FireStone to see what percentage of mix is in the coolant, as well check to see if an air pocket is present as I know for sure there is a special screw plug.

 

[Ray H]

No, no, no, no, no, no, no... I was referring to the possibility of too much water in the mix - which would result in less than a 50% glycol concentration. For goodness sake, get one of the Prestone or Victor pointer-type antifreeze testers and check your glycol concentration, and adjust as needed. I'm concerned about the corrosion at the radiator cap. Something's still wrong. If the coolant level isn't right up to the bottom ring of the radiator cap opening when cold, you have to find out where the coolant's going. If you're lucky enough to have a radiator cap on the radiator itself (I believe most ChryCorp products now have the pressure cap on the pressurized plastic overflow tank - someone correct me if that's wrong.) check the condition of the visible radiator core compenents - if there's scale present at the core tube openings you're able to view, you got corrosion problems whether your car's oveheating yet or not.

[ September 12, 2005, 11:42 AM: Message edited by: Ray H ]

 

[HerkyJim]

Lever caps are a gimmick. I just squeeze the upper radiator hose (lightly; it might be HOT!) and if its "tight as a tick" there's big pressure in there and don't even think about removing the radiator cap.