Water temperature gauge spikes to impossible high #s then goes quickly to 180°

[Mark Barnes]

" I believe the gauge is reading an accurate temperature."
I believe you are seeing the difference between an extremely accurate digital gauge and the "not so accurate" analog gauge that we're all familiar with.
As long as you've eliminated the air in the system, you should be good, unless there's a rolling **** crumb in the radiator blocking a portion of the core.

 

[biomedtechguy]

Have you tried a different gauge?

No. The gauges on the Dakota Digital are all one unit.
EDIT: If trying to remove any air pockets doesn’t work, I can try a mechanical water temperature gauge as a stand alone and see what happens.

 

[biomedtechguy]

unless there's a rolling **** crumb in the radiator blocking a portion of the core.

...a rolling **** crumb...

 

[Ironbuilt]

No. The gauges on the Dakota Digital are all one unit.

I have Autometer digital gauges in my pickup and they can be finicky.

 

[Ironbuilt]

No. The gauges on the Dakota Digital are all one unit.
EDIT: If trying to remove any air pockets doesn’t work, I can try a mechanical water temperature gauge as a stand alone and see what happens.

Gauges in my pickup, all digital.

 

[440+6]

you said the whole radiator was reading the same temperature, the bottom half should be a lot cooler than the top half, are you reading this with a digital temperature gauge? how are you determining this?

 

[biomedtechguy]

you said the whole radiator was reading the same temperature, the bottom half should be a lot cooler than the top half, are you reading this with a digital temperature gauge? how are you determining this?

the bottom half should be a lot cooler than the top half,

Can you please tell me why that is?
Actually I said the bottom half was a lot cooler that the top half, or bottom 1/3rd cooler than the top 2/3rds. That was my observation when I had:
¹Started the cold motor after I had removed the thermostat.
²Found the temperature gauge was spiking hot.
³After 10 minutes, I unscrewed the radiator cap 1/2 turn, no change, then held pressure against the cap coming off and opened it for a second, allowing a couple of teaspoons of coolant to come out the top of the radiator filler neck.
⁴I recapped it and got in the car to turn power on and see what the temperature read. It was still higher than it should be. Then I heard "GLUG-GLUG" as though some significant sized pocket of air had risen in the radiator or engine, and I checked the radiator with my hand and found that it was uniform to the touch in how hot it was. BIG difference. I started the engine and the temperature gauge was reading the expected normal operating temperature.
YES, I have a laser thermometer gun, but I think the reflective nature of the aluminum radiator may give false readings vs the black hoses.
I have NEVER detected the kind of high temperature the gauge indicates during these high spike events.

 

[diesel_lv]

you said the whole radiator was reading the same temperature, the bottom half should be a lot cooler than the top half, are you reading this with a digital temperature gauge? how are you determining this?

I've never found the bottom of the radiator, in any of my cars/trucks, more than 20° cooler than the top once thermostat is open n flowing. You can't take a reading from the bottom while driving and while sitting still there is not the amount of airflow you need to create "a lot cooler" on the bottom.

 

[khryslerkid]

Are you waiting for the engine to reach operating temperature before placing the radiator cap on? (This can be another debate)

Is this a cross flow radiator?

 

[biomedtechguy]

Are you waiting for the engine to reach operating temperature before placing the radiator cap on? (This can be another debate)
Is this a cross flow radiator?

I'm not sure, but I believe it flows the same as factory. The hose nipples are in the same general location.
Well, I usually DO wait for the thermostat to open and then see the coolant circulate, and if I have any room for topping off, I do fill the radiator completely full-NO air space. I figure if that's too much it will go into my overflow bottle....
BUT since this occasion I'm focused on describing is after taking out the thermostat, NO, I didn't wait this time.
I did partly remove the cap for a couple of teaspoons of coolant to come out, and within a minute heard the "GLUG-GLUG" sound and that is when the radiator suddenly became uniform in temperature and the gauge read where I expected it to.

 

[Don Frelier]

350 degree steam requires over 100 PSI.
I'm thinking you are not chasing a good reading.

 

[Ironbuilt]

Hey @biomedtechguy I think that you are chasing a ghost and it all may be in your digital gauge. Like I said before, I have digital gauges and they can act funny. I go through similar things every now and then. Try hooking up a mechanical temp gauge to your sending unit and compare readings. It's simple to do and you may find that the gauge isn't calibrated properly.
I don't care how "expensive, sexy, good looking, etc" they are, they are finicky. My AotuMeter digital gauges are very expensive, but I think that I may go back to mechanical.
PS Mine are sexy too.

 

[biomedtechguy]

I'm thinking you are not chasing a good reading.

Ok, I understand the first part about steam, pressure, and temperature.
I don't understand "I'm thinking you are not chasing a good reading"
Do you mean the gauge is not reading anything that is actually present, so my gauge or temperature probe/sender are bad or something along those lines?
If it's the gauge, the RTX series, which is brand new and just became available late last year is a one piece housing and possibly integrated into one circuit board. I can't just swap out the gauge.
If it's the probe/sender, that is much easier, or the wiring isn't even that bad, unless I have to check for a wiring fault, but even that shouldn't be too bad the way the system, modules, and new power and ground point were established.
Still, it's very strange the way it manifests itself.
GEESH!!

 

[Don Frelier]

Sorry that was poorly phrased:
I don't believe the actual temperature at the sensor is 350 F from the water jacket even with steam in there.

My thermostat stuck on the Charger last September I knew it but I was in traffic and before I could get off the road and shut it off it climbed to 240 then the lower hose blew apart.
The only other thing that could cause that high of a reading would be exhaust gas hitting it.

 

[khryslerkid]

A IR temp reader can be your friend

 

[biomedtechguy]

A IR temp reader can be your friend

I have one! I never got readings that high.
I really need to either get my friend to commit to a weekend on his lift and some help to see if I can get my RXT McLeod dual disc clutch and/or hydraulic throwout bearing working so it doesn't "drag" and cause the input shaft to spin, so I can get to the track and try out my HitMaster launch control, and all the other stuff I've had done.
BUT first, I have to resolve this problem.

 

[Ironbuilt]

I have one! I never got readings that high.
I really need to either get my friend to commit to a weekend on his lift and some help to see if I can get my RXT McLeod dual disc clutch and/or hydraulic throwout bearing working so it doesn't "drag" and cause the input shaft to spin, so I can get to the track and try out my HitMaster launch control, and all the other stuff I've had done.
BUT first, I have to resolve this problem.

You don't really want help Steve, you want attention.

 

[dodgeboy440]

ByTheWay...
This Dilemma Is Most Intriguing.......Not to Demean , Just To Help!........................Been A Gearhead & Hot Rodder Since The 70's.
I Remember Helping A Friend With A BrandX Build A While Back & He Had The Most Perplexing Situation With His New Hot Rod Build. He Put On A Serpentine Setup On Too On An Early SmallBlock. It Made Us Crazy Too Cuzzzzzzzzzzzzz All This Stuff Was NEW & SHINY !! You Would Think The Setup Would Be SO COOL>>>>>>>>>>>Literally. NOT>>>>
But The Car Would Overheat & Puke All Over , You Couldn't Hardly Drive The Dang Thing!
GUESS WHAT!........... We Discovered The Water Pump Was Being Driven BACKWARDS!!!! By The New Serpentine Setup..........
DUH............
When We Changed Out The Pump For The Correct Rotation Style.............Easy Peasy Lemon Squezzy............COOL>>>>>>>>>>>>>

For Testing & Evaluation...............
I May Be Inclined To Load Up The Cooling System With Bottled Drinking Water . Not Distilled . You Know Distilled Has No Mineral Content & Promotes Electrolysis , Wrong PH too . Fire Up That Big Beautimus Hunnka Mopar Mettle & Let It Idle With The Radiator Cap OFF , Have An
Led Hand Held Thermometer In Hand & Start The Exam! Measure The Temp On Every Cylinder & All Cooling Components & Verify Temps You're Looking At On Those Moogly Googly Gauges. They May Be Off Too!
You Know A Water Temp Probe Wont Measure Air Temp......Ask Me How I Found Out................Ouch...........$$$$$.
Bet You'll Find Out ........

WHASSSAAAPPPPPPP In A Few Minutes!
Let Your Fellow MoPar Maniacs Know Bro!
Best Wishes!
John

 

[biomedtechguy]

You don't really want help Steve, you want attention.

Just for that comment, I won't post again until I actually do something.
Thanks buddy.

 

[Kern Dog]

The only times that I have had problems with a gauge swinging around is when the system wasn't full of coolant.