Thermostat has been replaced (six months ago) and the problem persisted before/after, so the thermostat has been ruled out. Anyway, it basically costs you nothing to test the cap, and next to nothing to replace it, so might as well! Maybe then Jane will burp too. Sometimes the aluminum cap fittings get worn out too the steel caps are much harder than the aluminum flange. Once in a while I've seen aftermarket radiators with poorly-made cap fittings that prevent good sealing. The only things I've seen go wrong with radiator caps are degradation/hardening of the rubber seals, getting the valves all gunked up, and corrosion. Hissing is a bit odd my Mustangs both burp and occasionally groan, but I suppose each car finds its own voice Coolant and vapor flowing through those valves normally makes noise. It's normal for a radiator cap to make some noise it's a two way valve that allows vapor and coolant out if the radiator pressure exceeds the cap rating, and allows air (or coolant if you have a recovery tank on your overflow hose) back in when the pressure drops below atmospheric (ie when the engine cools down after driving). Instead it's done by pressurizing the cooling system.Īs to Kelly's question: if Jane's radiator cap wasn't holding enough pressure your radiator would be boiling over. This can be accomplished by using a different cooling fluid, but water-based coolant is much cheaper and easier to handle than the alternatives. To get the heat transfer advantages of a higher coolant temperature the boiling point of the coolant must be increased. This is what happens when your radiator boils over it's a vicious circle. This causes the engine to heat more, causing more boiling and more vapor. But once the coolant starts to boil it forms pockets of vapor, which don't transfer heat as well. The larger the temperature difference between the air and the coolant, the more effective the cooling system will be (up to a point). That's the whole reason automotive cooling systems are pressurized. well, it's Jane, and Jane does weird things and that does not even rank on the list of top "weird things Jane does".Ĭlick to expand.Close but backwards boiling point increases with pressure. So here's the question: Does that sound like a radiator cap issue, and how can I test the cap? What should I be looking for in a new cap? I don't know why it's never occurred to me that this is strange before, but. I didn't let it do that long term (ran the heater and ran RPMs up to keep it to 220*F), but when I did let it go that's where it sat. Again, same thing - didn't continue getting hotter and hotter, just seemed to want to get to that temperature and sit there. Last year I did have to deal with one "major issue" day when we sat at a near-standstill in 110*F ambient temps in the sun, surrounded by semi trucks, for 3 hours, and then the motor seemed to want to hang out at 230-240*F. In past warmer days in traffic, she has gotten up to 210-215*F pretty fast but does not continue getting hotter after reaching whatever equilibrium she seems to prefer. At idle, I was looking at 195*F (normal temp). Yesterday it was 80*F out and on the highway she was running at 185*F with a 192*F thermostat in (below operating temp). Never bothered to see if the seal was placed the same or anything.Ĭar doesn't overheat, but does tend to fluctuate in temps with ambient temp / speed more than she used to before installing this radiator. Not sure if it would be an issue with the cap going bad, or if maybe the Northern radiator wants a certain type of cap - when I first put it in a couple years ago, it came with a cap but I just stuffed my old one on because I liked the way it looked better. This has led me to wonder if the radiator cap is maybe not holding pressure the way that it should. I've always been able to pull the cap off pretty reasonably without any kind of drama when the engine is hot - that is, I can let a little bit of pressure bleed off for about 10 seconds and then remove the cap without it trying to go flying into outer space. Coolant levels aren't dropping at all, and yesterday I put 450 miles on the car at pretty rigorous speeds so if it was going to lose any coolant I would have noticed by now. No coolant coming out and there's no evidence of exhaust gasses in the coolant (in the form of visible bubbles in the radiator), so I don't think it's an issue with pressurizing from a leaky head gasket or anything. It also sounds a little bubbly almost, like it is digesting I guess. Whenever the engine has been run for enough to build up a bit of heat (not even to temperature, just to something above "stone cold"), you can hear the radiator cap hissing after you turn the car off. After yesterday's drive and being around some other peoples' cars for a change, it occurred to me that Jane's radiator cap is unnaturally.
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