Is This Normal [cooling System]?

[01Y87]

Tonight the car was parked for 5 hours, and then I drove home about 10 minutes, probably 6 - 8 miles, and the outside temp was about 60. When I got home and shut down I looked under the hood just to check around listening to something else and I felt the radiator.

The radiator cap was COOL- I mean it was "room temperature". I put my hand around the upper radiator hose and it was hot but I was able to keep my hand on the hose without getting burned or being uncomfortably hot. Maybe just a few degrees lower than what it would take to hurt my skin. The lower hose was even a bit less hot than the upper! My coolant level was not exactly full in the overflow container but it was ok. Also, the temp gauge on the dash was in its normal spot just below the halfway mark and there was heat from the vents, though maybe not burning hot heat.

Shouldn't the upper hose be HOT? Shouldn't the coolant be scalding hot? Also, shouldn't the radiator cap be at least warm? Do you think this is a sign that my thermostat is not fully opening? Or maybe I'm just crazy and it takes more than 10 minutes of driving to get it burning hot??

[96Camaro]

Sounds like a thermostat to me man dude. But if not maybe the cap itself??

[01Y87]

I have reason to suspect the thermostat. Last winter it took so long to get HOT air out of the vents on those single-digit nights. Eventually it was hot. But also, I always thought that the radiator cap on a fully-warmed up system should feel hot to the touch as well as the hose..especially the upper hose, that should be way hotter than the lower hose right? Since the hot water coming out of the engine flows to the radiator thru the upper hose and the cooler (well, relatively speaking) liquid goes back to the engine thru the lower.

[01Y87]

Is the radiator supposed to be full up to the neck when cold??

I would guess that it should be??? I noticed that mine was somewhat low, I could see the little pipes inside the radiator when looking in the cap hole. Or does much of the coolant inside the radiator get sucked into the engine by the water pump where it stays until the thermostat opens? This was the first time in a couple years that I opened the cap although I've checked the level in the jug from time to time. I also noticed a lot of light colored "sludge" - thats the best I could describe it. I dont think that is normal?

[Injuneer]

The radiator should always be completely full - hot or cold. That's the purpose of the pressure/vacuum cap and the overflow reservoir. When the coolant heats up, it expands, builds up pressure to the radiator cap rating, then the cap allows small amounts to escape to maintain the pressure, while keeping the system full.

As the radiator cools down and the coolant contracts, the radiator pulls a small vacuum and the vacuum side of the cap opens to allow the coolant in the reservoir to flow back into the radiator to keep it full.

If the hose that runs from the radiator fill neck to the reservoir is cracked, or the cap is defective, or you have a leak in the coolant system, the system won't work because it can't pull a vacuum on the hose to pull the coolant out of the reservoir and into the radiator.