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Radiator cap never really gets super hot to touch? #4564445
11/05/17 01:49 AM
11/05/17 01:49 AM
Joined: Oct 2017
Posts: 81
Gatineau QC Canada
TheMidnightNarwh Offline OP
TheMidnightNarwh  Offline OP
Joined: Oct 2017
Posts: 81
Gatineau QC Canada
I noticed the other day the radiator cap never gets real hot to touch. I can feel some warmth to it but not burning hot. The upper rad hose does become hot to touch and the car doesn't overheat.

Is something wrong, should I be worried and check for something or it's fine?

Re: Radiator cap never really gets super hot to touch? [Re: TheMidnightNarwh] #4564459
11/05/17 03:42 AM
11/05/17 03:42 AM
Joined: Sep 2010
Posts: 7,485
S California
OneEyeJack Offline
OneEyeJack  Offline
Joined: Sep 2010
Posts: 7,485
S California
Does your cooling system need to be topped off?

Re: Radiator cap never really gets super hot to touch? [Re: TheMidnightNarwh] #4564467
11/05/17 04:24 AM
11/05/17 04:24 AM
Joined: Jan 2011
Posts: 2,826
N.Ohio
Lubener Offline
Lubener  Offline
Joined: Jan 2011
Posts: 2,826
N.Ohio
If the upper hose is hot, you don't overheat, if heater works good, you are fine. My radiator cap is never hot to the touch. I am assuming you do maintain proper level.

Last edited by Lubener; 11/05/17 04:25 AM.

The "thinking" man's friend.
Re: Radiator cap never really gets super hot to touch? [Re: OneEyeJack] #4564779
11/05/17 11:28 AM
11/05/17 11:28 AM
Joined: Oct 2017
Posts: 81
Gatineau QC Canada
TheMidnightNarwh Offline OP
TheMidnightNarwh  Offline OP
Joined: Oct 2017
Posts: 81
Gatineau QC Canada
Originally Posted By: OneEyeJack
Does your cooling system need to be topped off?


No I filled it up about 2 weeks ago, checked every day and then to make sure it was wasn't leaking and looks good. Always coolant to the top when I take it off in the morning.

Re: Radiator cap never really gets super hot to touch? [Re: TheMidnightNarwh] #4564788
11/05/17 11:35 AM
11/05/17 11:35 AM
Joined: Mar 2008
Posts: 6,133
Michigan
ZZman Offline
ZZman  Offline
Joined: Mar 2008
Posts: 6,133
Michigan
Is your cap on a plastic tank or a metal radiator?


2003 Mercury Grand Marquis. PP HM 5w-30 and Fram Ultra
2008 Sebring Hardtop convertible. PP HM 5w-30 and Fram Ultra
2006 Kawasaki Vulcan 900 LT. Motul 7100 10w-40 and K&N
Re: Radiator cap never really gets super hot to touch? [Re: ZZman] #4564824
11/05/17 12:10 PM
11/05/17 12:10 PM
Joined: Jun 2003
Posts: 33,560
ME
eljefino Offline
eljefino  Offline
Joined: Jun 2003
Posts: 33,560
ME
Originally Posted By: ZZman
Is your cap on a plastic tank or a metal radiator?


yeah this. How would your cap get hot? You have boiling water pushing on a rubber gasket under a metal disc under a spring under the part you put your hand on.

If you've ever noticed the handle on a wood stove, it's a spring, so it doesn't conduct heat very well.

Re: Radiator cap never really gets super hot to touch? [Re: eljefino] #4564900
11/05/17 01:27 PM
11/05/17 01:27 PM
Joined: Oct 2017
Posts: 81
Gatineau QC Canada
TheMidnightNarwh Offline OP
TheMidnightNarwh  Offline OP
Joined: Oct 2017
Posts: 81
Gatineau QC Canada
Originally Posted By: ZZman
Is your cap on a plastic tank or a metal radiator?


Originally Posted By: eljefino
Originally Posted By: ZZman
Is your cap on a plastic tank or a metal radiator?


yeah this. How would your cap get hot? You have boiling water pushing on a rubber gasket under a metal disc under a spring under the part you put your hand on.

If you've ever noticed the handle on a wood stove, it's a spring, so it doesn't conduct heat very well.


It's not on the overflow tank, it's on the rad itself.

So you're saying it's normal it doesn't get hot? All the videos I watch they say if your cap is hot don't open, even says so on the cap itself. But it's never really hot like that.

Re: Radiator cap never really gets super hot to touch? [Re: TheMidnightNarwh] #4565196
11/05/17 06:24 PM
11/05/17 06:24 PM
Joined: Jun 2003
Posts: 33,560
ME
eljefino Offline
eljefino  Offline
Joined: Jun 2003
Posts: 33,560
ME
Back 30 years ago with brass radiators the radiator tank would conduct heat to the cap fairly efficiently through the mounting boss.

And if you remove a cap holding back pressure it could cause instant explosive steam, no fun.

Grab the upper radiator hose to get a feel for temp, even with 1/4" of rubber they get pretty hot.

Re: Radiator cap never really gets super hot to touch? [Re: TheMidnightNarwh] #4566323
11/06/17 09:29 PM
11/06/17 09:29 PM
Joined: Jun 2011
Posts: 1,803
Crawfordville FL
SilverFusion2010 Offline
SilverFusion2010  Offline
Joined: Jun 2011
Posts: 1,803
Crawfordville FL
Probably some air trapped under the cap acting as an insulator. If you're brave you can burp the system. Take an old rag and very slightly start to remove the cap, just enough that you hear it hiss. When it gurgles tighten it back.

Or just wait until it's cold and top up the rad. I kinda like the hot purge though.


2010 Ford Fusion SE 3.0L V6, 181 miles M1 HM 10w-30
Re: Radiator cap never really gets super hot to touch? [Re: TheMidnightNarwh] #4567554
11/08/17 09:18 AM
11/08/17 09:18 AM
Joined: Sep 2004
Posts: 7,812
Marshfield , MA
andyd Offline
andyd  Offline
Joined: Sep 2004
Posts: 7,812
Marshfield , MA
Are the caps with a lever to release pressure still sold? Sounds to me like a warm cap would mean an air gap at the tank top. The 528e uses a pressure cap on the expansion tank. I once drove a '62 F250 with bad radiator. It was summer and we took it on a 200 mile trip to rescue my '62 Bug. We carried water jugs and stopped 5 times to add water. That was one of the bug's many good points. A shop fab'ed tow rig pinned to the front beam and they towed like they weren't even there grin2


'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2

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