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

[biomedtechguy]

I installed a Wraptor serpentine belt and accessories system in my 440 6bbl 70 Roadrunner last year. Dakota Digital gauge system.
I had to install and remove my Cold Case radiator about 6 times because of a defective electric fan motor, and to fit the largest flex fan I could, as well as install 2 Spahl 10" fans, that finally work reliably w/out burning up.
Anyway, I recycled the antifreeze just about every time because it was new, like not even a day in use. My luck, once I had the combo of fans that worked, I developed a problem. Most often when I am first running the engine, it will spike the temp gauge, to impossible high numbers, sometimes as high as the max temp of 350° I have a Stant Premium thermostat, but I just removed it to take that variable out of the equation.
NOTE: I say "impossible" high temperature readings, but I'm concerned it could be STEAM that is making the temp gauge spike. Once the engine is revved up, either stationary or from driving, the temperature gauge quickly goes to a temperature I'd expect, 180 w/T stat installed, and around 145 with it removed.
So when I removed the thermostat, I also ran the heater, thinking I could get any trapped air out of the cooling system. The temperature went high again, I was squeezing the top radiator hose and the 2 heater hoses, to get air out, check for firmness via pressure, etc.
I turned the engine off. The top hose and top 1/2 of the radiator was hot, but the bottom half was only warm, barely, and I could hold my hand on it. I then heard a "gurgle" sound like an air pocket moved, and the bottom of the radiator immediately came to the same expected hot temperature and the gauge read in the expected range.
So, how can I fix this, and what do you suspect the problem is?

 

[440+6]

Sounds like you surely had an air pocket. keep pumping that top hose get the air out of that thing.
How do you know it went to 350, never heard of a gauge that wnt that high?

 

[Jeff Peterson]

I have one of these and it works awesome to purge air out, it seals to the radiator and the air burbs up into the funnel once the thermostat opens.

https://www.amazon.com/OEMTOOLS-870...ocphy=9018694&hvtargid=pla-493792710903&psc=1

 

[440+6]

I still drill a eight inch hole in all my tstats, it seems to work just fine for bleeding, been doing it for 40 years plus.......
Really wondering what you got going on.
Very interested in the outcome.
Please keep us posted.

 

[69Bee]

I still drill a eight inch hole in all my tstats, it seems to work just fine for bleeding, been doing it for 40 years plus.......
Really wondering what you got going on.
Very interested in the outcome.
Please keep us posted.

Holy crap, how big is that thing for an 8" hole??

 

[biomedtechguy]

First, thanks for all the replies, and yes, I will certainly post what I find and the solution.

How do you know it went to 350, never heard of a gauge that wnt that high?

Dakota Digital gauge system.

To add to the description of my gauge system being a Dakota Digital, it's the "new" RTX series, and it displays default and/or selected "alarm limits exceeded" data on the LED data info display. When my water temperature exceeds a set temperature, that displays on the screen at the 6 o'clock position of the gauge system.

I still drill a eight inch hole in all my tstats

I know what you meant, ⅛th " but I also thought something similar to

Holy crap, how big is that thing for an 8" hole??

because we all need a little chuckle, and have all fallen victim to auto-correct or fat fingers...

 

[diesel_lv]

I still drill a eight inch hole in all my tstats, it seems to work just fine for bleeding, been doing it for 40 years plus.......
Really wondering what you got going on.
Very interested in the outcome.
Please keep us posted.

That usually works very well w an 1/8" hole but he also said it does it w no t-stat.

OP, put front end up in the air on jackstands and run n burp cooling system. As for steam, if I'm not mistaken, the temp sensors will not read steam or air temps.

 

[biomedtechguy]

had a bad thermostat that acted that way

I removed the thermostat and the problem remained.
The most informative observations of the "remove thermostat" episode was:
¹Immediate water flow evident across the top chamber of the radiator, viewing with cap off.
²Water temperature gauge still spiked, even though the thermostat was out!
³I turned off the engine while it was still reading very hot, in the high 200s, like 270 or so. I let it sit 10 minutes, squeezed the top radiator hose which was somewhat firm with pressure. I turned the radiator cap a half turn, and then with firm downward pressure and a towel, I turned it the last bit and some coolant came out under pressure. I probably let 2 tablespoons of coolant come out, or less.
⁴ HERE IS THE MOST CURIOUS BIT: Engine still off, the top half of the radiator was hot, too hot to touch more than just a light touch and not linger, about what I'd expect at normal 180 degree or so. I could grab and squeeze the heater hoses and top radiator hose, they were hot, but not so hot that I couldn't squeeze or linger my contact time. BUT the bottom half of the radiator was barely warm, and I could have held my hand on it for as long as I wanted. After I opened the cap a bit for a second, and that bit of coolant came out, I sat in the car watching the gauge, thinking about starting the engine again, and I heard a "GLUG-GLUG" sound, so I am 100% certain there was a significant air pocket that was released or moved.
I started the engine and IMMEDIATELY after that, the temperature gauge dropped and I put my hand on the bottom of the previously barely warm radiator, and BAM it was just as hot as the rest, and everything was as it should be.

I have one of these and it works awesome to purge air out, it seals to the radiator and the air burbs up into the funnel once the thermostat opens.

Thanks. I looked at it and I'm going to get that one or another, whatever one looks to be the best for getting air out of the system.
I'm convinced that's the problem.
I'm going to find a different thermostat, one that has the hole in it and has a good rep.
I'm also going to put the factory fan shroud back on, and see if that helps the flex fan work more effectively.

 

[biomedtechguy]

put front end up in the air on jackstands and run n burp cooling system

Good idea. Thanks

 

[diesel_lv]

I'm also going to put the factory fan shroud back on, and see if that helps the flex fan work more effectively.

Definitely put the shroud back on!! Is extremely important at idle. Also make sure that radiator, once system is burped and car sitting level, coolant level is between 1 and 1-1/4" below the bottom of the filler neck. Our old top/bottom tank radiators use that area as the "expansion" area.

 

[chtampa]

Thermostat keeps the water out of the engine long enough for the radiator to cool what is in it. "No thermostat" does not allow the engine to cool off after an overheating problem.

 

[biomedtechguy]

Thermostat keeps the water out of the engine long enough for the radiator to cool what is in it. "No thermostat" does not allow the engine to cool off after an overheating problem.

I appreciate the reply, and I understand the importance of a thermostat or "flow restriction" at least, as I've seen some use. I also know that I can check the Tstat in a pot of water heated up.
I am surprised that this particular Tstat doesn't have the factory drilled tiny hole in it, unless I'm missing seeing it, given that Stant thinks highly of it.
It's CHEAP, and that was a concern, but MAN they make it sound really good

I am NOT putting it back in, even though I know it's not the cause of the problem.
Check this description out:
Help your ride run more efficiently with Stant SuperStat thermostats. SuperStats feature a patented V-notch, non-linear valve design, which reduces cycling, bringing your vehicle to its proper operating temperature more quickly. This unique V-notch provides a small initial flow of coolant at start-up and, as your engine heats up, the V-notch opens wider to meter the proper amount of coolant into your vehicle's system. Other features include a high-flow venturi, a patented Weir valve, a larger actuator piston, a heavy-duty spring, and a thicker, high-strength burnished stainless steel flange. Stant SuperStat thermostats offer reduced oil consumption and emissions, improved fuel economy, and a prolonged engine life for your vehicle.

 

[Ironbuilt]

Thermostat keeps the water out of the engine long enough for the radiator to cool what is in it. "No thermostat" does not allow the engine to cool off after an overheating problem.

A thermostats purpose is to allow the engine to reach operating temperature, at which point it opens to allow coolant in. A thermostat doesn't close to cool the coolant after overheating. Flowing through the radiator and fresh air cools the water.

 

[diesel_lv]

A thermostats purpose is to allow the engine to reach operating temperature, at which point it opens to allow coolant in. A thermostat doesn't close to cool the coolant after overheating. Flowing through the radiator and fresh air cools the water.

And on that note, those who think the longer the coolant stays in the radiator, the cooler the engine will be are incorrect also. As the longer the collant is in the radiator, the longer the coolant is in the engine getting hotter. The only way it works like that is to keep the same flow rate, but increase volume of radiator. ie.. larger radiator.

 

[440+6]

Holy crap, how big is that thing for an 8" hole??

Ok typo.....very funny ha ha

 

[chtampa]

As to not start a big debate, do a quick search on why not to remove the thermostat. Allowing coolant in or keeping coolant from leaving are different views of the same result.

 

[biomedtechguy]

As to not start a big debate

Yes, please, let's NOT...
Let's not debate the relative functions of a thermostat.
Does anyone have a Mopar 180° thermostat that is the BEST and why?
I'm most interested in highest quality materials and DESIGNED TO HELP PREVENT AIR POCKETS.
I'm going to be cooling THIS, and aluminum heads, and I absolutely do NOT want to overheat!

 

[66chargerpat]

Does this repeat after it cools off ?

 

[biomedtechguy]

Does this repeat after it cools off ?

Yes, it has been. But I've seen it do this at the end of a ride, like parked running while I open the garage door, that may take a minute.
It is fairly consistent that when the engine is cool and is started up, and comes up to operating temperature, which was 180° with the Tstat in, about 145° after it was removed, this "spike" is most often at cold idle speed or less RPMs, and seems to go to the "correct" reading with an increase in RPMs, like it "moves the air pocket away" from the temperature probe, or "mixes up the coolant" so as to get the temperature of the system rather than what seems to be an impossibly high temperature pocket or isolated tiny amount.
If my coolant temperature was 285° to 350° throughout the system, I'd have **** blowing up, off, apart, swelling, etc.
That's the KEY, I believe the gauge is reading an accurate temperature, but the "what" is it sampling in that moment that's that extremely hot is a very small amount (of whatever, steam is what I suspect) because as soon as the hot spot starts moving, the temperature gauge rapidly drops to what I'd expect under normal proper conditions.

 

[65Fury440]

I had the exact same problem you are having when I plugged the mixing hole under the thermostat.
Apparently that little bit of coolant flashes hot for a a couple seconds while the thermostat reacts.