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

If/when the temperature ever gets to 350°F, you'd be replacing the heads and head gaskets.... abd maybe even the engine......
BOB RENTON
Thanks Bob..
That's my point. I had the Dakota Digital temperature gauge reading crazy high temps, but no other signs indicating high temps. I need that gauge to be reliable, or should I say the temp probe/sender...
 
Thanks Bob..
That's my point. I had the Dakota Digital temperature gauge reading crazy high temps, but no other signs indicating high temps. I need that gauge to be reliable, or should I say the temp probe/sender...

Out of curiosity,....what is the temperature probe? Its probably not hot enough for a thermocouple (2 dissimilar metals fused to generate a milli-voltage when heated, like a class J) to be accurate (at least I don't think) but likely its an RTD or resistive temperature detector (usually a 100 ohm platinum device...very accurate) or its a positive temperature coefficient Thremistor...not real accurate but inexpensive. Digital instruments like RTDs (usually) but it depends on the analog to digital circuitry that converts and displays the data. Digital stuff is nice, but sometimes, the old filled system, a pressure gauge calibrated to read temperature degrees F or C, based on increasing pressure due to temperature change. How accurate does the system need to be??? +/- 0.5 degrees or +/- 5.0 degrees and how fast is the reporting time.....just a rhetorical question.....
BOB RENTON
 
This has been an interesting thread (I just stumbled on it waiting for decaf to brew). Two things:

First, I think everyone is missing the reason temps spike when there is air in a system. It isn't the sending unit that sees the air (and "heat"); it's an air pocket at the thermostat, which keeps the thermostat from opening when it should. Thermostat coils don't operate in steam, and there needs to be a huge spike in temp for a "dry" thermostat to open. Once it does, coolant circulates and the temp plummets fast. (This is why I also drill a 1/8" hole in all my thermostats)

Second, I NEVER run a fresh cooling fill with the cap on, until it is about to geyser. Fill a fresh system, turn the heat on full, start the car with the cap off, and stand ready at the radiator with a gallon of coolant (to fill as the level drops when air is replaced with coolant), a rag, and the cap. Looking in the fill neck, you will easily see the progression - stagnant cold coolant while the thermostat is closed (perhaps a trickle of circulation if you have a 1/8" hole in your thermostat); levels that drop along with bubbles that appear as air is replaced with coolant (top off to keep the levels correct, as needed); faster visible flow and mixing of coolant as the thermostat opens; finally, level rising to the cap height indicating full circulation has been reached and temp is approaching full. At this point I will let it circulate until I see zero bubbles (constant bubbles indicate a head gasket leak), let it overflow just enough to make a bit of a mess, then I'll cap it.

This method, along with a hole in the thermostat, has kept me from having air pocket issues for as long as I've owned cars. An 1/8" hole isn't enough to cause operating temperature differences, all it does is allow coolant pressure to push the air through the hole, so the thermostat isn't "dry" after a fresh fill.

To the issue at hand for this thread, it seems to me to be a blockage of some sort in the radiator, if the problem is persisting. For my money, I would:

1. drill a hole in the new thermostat and install it
2. drain the system
3. remove the lower radiator hose from the radiator
4. put a garden hose in the radiator filler neck (cap off), turn it on about halfway, and allow it to flush the radiator. don't use full pressure, just a steady flow. It should exit the lower hose fitting as quickly as you are putting it in the top. If it doesn't...you have a blockage. I know - it's a "quality part". Even quality parts have defects sometimes. If you do see a blockage or flow issue, remove the radiator from the car, turn it upside down, and do the opposite - put the hose in the lower radiator hose fitting and let the water flow out the cap opening, as a back-flush to try and dislodge whatever is stuck. *note: make sure neither your radiator, nor your water pump, are notated as being "reverse-flow" units.
4a. if you want to rule them out, perform the hose-flow-test on the other two members of your cooling system- the engine itself (remove the thermostat, hose in the thermostat housing, water flows out the lower hose), and the heater core (connect the hose to your heater feed hose, disconnect the return hose, and monitor those flow capabilities as well - again, NOT at full pressure!). You have now flow-tested all three sections of your system - radiator, engine, heater - as well as all the connecting hoses.
5. Once component flow has been proven, reassemble everything (with a hole in the thermostat), fill the system, turn on the heat, start the engine, and run/bleed it as noted above.

If you do all these steps, including 4a, and you still have air pockets that appear after a proper bleeding, and you don't see any external fluid leaks...you have a compression issue somewhere, either a cracked block or a blown headgasket.
 
This has been an interesting thread (I just stumbled on it waiting for decaf to brew). Two things:

First, I think everyone is missing the reason temps spike when there is air in a system. It isn't the sending unit that sees the air (and "heat"); it's an air pocket at the thermostat, which keeps the thermostat from opening when it should. Thermostat coils don't operate in steam, and there needs to be a huge spike in temp for a "dry" thermostat to open. Once it does, coolant circulates and the temp plummets fast. (This is why I also drill a 1/8" hole in all my thermostats)

Second, I NEVER run a fresh cooling fill with the cap on, until it is about to geyser. Fill a fresh system, turn the heat on full, start the car with the cap off, and stand ready at the radiator with a gallon of coolant (to fill as the level drops when air is replaced with coolant), a rag, and the cap. Looking in the fill neck, you will easily see the progression - stagnant cold coolant while the thermostat is closed (perhaps a trickle of circulation if you have a 1/8" hole in your thermostat); levels that drop along with bubbles that appear as air is replaced with coolant (top off to keep the levels correct, as needed); faster visible flow and mixing of coolant as the thermostat opens; finally, level rising to the cap height indicating full circulation has been reached and temp is approaching full. At this point I will let it circulate until I see zero bubbles (constant bubbles indicate a head gasket leak), let it overflow just enough to make a bit of a mess, then I'll cap it.

This method, along with a hole in the thermostat, has kept me from having air pocket issues for as long as I've owned cars. An 1/8" hole isn't enough to cause operating temperature differences, all it does is allow coolant pressure to push the air through the hole, so the thermostat isn't "dry" after a fresh fill.

To the issue at hand for this thread, it seems to me to be a blockage of some sort in the radiator, if the problem is persisting. For my money, I would:

1. drill a hole in the new thermostat and install it
2. drain the system
3. remove the lower radiator hose from the radiator
4. put a garden hose in the radiator filler neck (cap off), turn it on about halfway, and allow it to flush the radiator. don't use full pressure, just a steady flow. It should exit the lower hose fitting as quickly as you are putting it in the top. If it doesn't...you have a blockage. I know - it's a "quality part". Even quality parts have defects sometimes. If you do see a blockage or flow issue, remove the radiator from the car, turn it upside down, and do the opposite - put the hose in the lower radiator hose fitting and let the water flow out the cap opening, as a back-flush to try and dislodge whatever is stuck. *note: make sure neither your radiator, nor your water pump, are notated as being "reverse-flow" units.
4a. if you want to rule them out, perform the hose-flow-test on the other two members of your cooling system- the engine itself (remove the thermostat, hose in the thermostat housing, water flows out the lower hose), and the heater core (connect the hose to your heater feed hose, disconnect the return hose, and monitor those flow capabilities as well - again, NOT at full pressure!). You have now flow-tested all three sections of your system - radiator, engine, heater - as well as all the connecting hoses.
5. Once component flow has been proven, reassemble everything (with a hole in the thermostat), fill the system, turn on the heat, start the engine, and run/bleed it as noted above.

If you do all these steps, including 4a, and you still have air pockets that appear after a proper bleeding, and you don't see any external fluid leaks...you have a compression issue somewhere, either a cracked block or a blown headgasket.

Out of curiosity, you mentioned static circulation with the thermostat closed, save for the proposed 1/8" diameter hole in the t-stat's valve plate, if so, how does the thermostat bypass hole, in the casting below the thermostat, in B/ RB engines and the 1/2" diameter bypass hose, connecting the intake manifold's water passage to the water pump housing affect the overall circulation? Until the t-stat opens, the coolant is vigorously recirculated, thru these passages, to bring the coolant to operating temps quickly as possible and allow for heater/defroster operation (assuming the heater is plumbed into the system) and to minimise thermal stresses in the block and heads.
Many thermostat manufacturers, provide a small notch or hole in the valve plate to provide an air bleed to allow air to escape during the innitial fill....does the proposed 1/8" hole in the t-stat valve plate help? I'm just trying to understand what's going on......
BOB RENTON
 
Thanks Bob..
That's my point. I had the Dakota Digital temperature gauge reading crazy high temps, but no other signs indicating high temps. I need that gauge to be reliable, or should I say the temp probe/sender...
Reading through this whole thread, I was thinkin wiring short the entire time. Quite possibly the sender & easy/inexpensive to try. After replacement if that gauge still finds 350 degrees, something is wrong deeper in the electrical components or wiring. I have no expierience with Dakota, but am fairly confident that number is inacurate as you & others have indicated. Any spot you could temporarily add a cheep mechanical gauge to confirm?
I dont think your issues revolve around the thermostat. I can see a spike the first few heat cycles till the stat opens & purges air but not ongoing. Sure there could be cylinder/compression leaking in & causing air but that still wouldn't explain the high readings and surely would create other issues..
Just my thaughts. Good luck & keep us updated.
 
Out of curiosity, you mentioned static circulation with the thermostat closed, save for the proposed 1/8" diameter hole in the t-stat's valve plate, if so, how does the thermostat bypass hole, in the casting below the thermostat, in B/ RB engines and the 1/2" diameter bypass hose, connecting the intake manifold's water passage to the water pump housing affect the overall circulation? Until the t-stat opens, the coolant is vigorously recirculated, thru these passages, to bring the coolant to operating temps quickly as possible and allow for heater/defroster operation (assuming the heater is plumbed into the system) and to minimise thermal stresses in the block and heads.
Many thermostat manufacturers, provide a small notch or hole in the valve plate to provide an air bleed to allow air to escape during the innitial fill....does the proposed 1/8" hole in the t-stat valve plate help? I'm just trying to understand what's going on......
BOB RENTON

The 1/8" hole does just like the "V" notch or the floating rivet some put in. I've put a 1/8" hole in every thermostat as well. Chevy, Ford, Mopar etc... it allows a natural "burping" of the cooling system. It has never seemed to reduce any of my engines ability to reach operating temps.
 
Thanks for ALL replies, and from THIS ONE on too, as some time has passed.
Unfortunately at this moment I can't even take the time to read all the 3 or 4 posts. Yes, it may well have been an electrical problem all along that got progressively worse, I'm not sure.
I thank all of youand when the situationis resolved, problem(s) confirmed I will post, if I don't drop dead of stress in the meantime.
This has been an interesting thread (I just stumbled on it waiting for decaf to brew). Two things:

First, I think everyone is missing the reason temps spike when there is air in a system. It isn't the sending unit that sees the air (and "heat"); it's an air pocket at the thermostat, which keeps the thermostat from opening when it should. Thermostat coils don't operate in steam, and there needs to be a huge spike in temp for a "dry" thermostat to open. Once it does, coolant circulates and the temp plummets fast. (This is why I also drill a 1/8" hole in all my thermostats)

Second, I NEVER run a fresh cooling fill with the cap on, until it is about to geyser. Fill a fresh system, turn the heat on full, start the car with the cap off, and stand ready at the radiator with a gallon of coolant (to fill as the level drops when air is replaced with coolant), a rag, and the cap. Looking in the fill neck, you will easily see the progression - stagnant cold coolant while the thermostat is closed (perhaps a trickle of circulation if you have a 1/8" hole in your thermostat); levels that drop along with bubbles that appear as air is replaced with coolant (top off to keep the levels correct, as needed); faster visible flow and mixing of coolant as the thermostat opens; finally, level rising to the cap height indicating full circulation has been reached and temp is approaching full. At this point I will let it circulate until I see zero bubbles (constant bubbles indicate a head gasket leak), let it overflow just enough to make a bit of a mess, then I'll cap it.

This method, along with a hole in the thermostat, has kept me from having air pocket issues for as long as I've owned cars. An 1/8" hole isn't enough to cause operating temperature differences, all it does is allow coolant pressure to push the air through the hole, so the thermostat isn't "dry" after a fresh fill.

To the issue at hand for this thread, it seems to me to be a blockage of some sort in the radiator, if the problem is persisting. For my money, I would:

1. drill a hole in the new thermostat and install it
2. drain the system
3. remove the lower radiator hose from the radiator
4. put a garden hose in the radiator filler neck (cap off), turn it on about halfway, and allow it to flush the radiator. don't use full pressure, just a steady flow. It should exit the lower hose fitting as quickly as you are putting it in the top. If it doesn't...you have a blockage. I know - it's a "quality part". Even quality parts have defects sometimes. If you do see a blockage or flow issue, remove the radiator from the car, turn it upside down, and do the opposite - put the hose in the lower radiator hose fitting and let the water flow out the cap opening, as a back-flush to try and dislodge whatever is stuck. *note: make sure neither your radiator, nor your water pump, are notated as being "reverse-flow" units.
4a. if you want to rule them out, perform the hose-flow-test on the other two members of your cooling system- the engine itself (remove the thermostat, hose in the thermostat housing, water flows out the lower hose), and the heater core (connect the hose to your heater feed hose, disconnect the return hose, and monitor those flow capabilities as well - again, NOT at full pressure!). You have now flow-tested all three sections of your system - radiator, engine, heater - as well as all the connecting hoses.
5. Once component flow has been proven, reassemble everything (with a hole in the thermostat), fill the system, turn on the heat, start the engine, and run/bleed it as noted above.

If you do all these steps, including 4a, and you still have air pockets that appear after a proper bleeding, and you don't see any external fluid leaks...you have a compression issue somewhere, either a cracked block or a blown headgasket.
 
This has been an interesting thread (I just stumbled on it waiting for decaf to brew). Two things:

First, I think everyone is missing the reason temps spike when there is air in a system. It isn't the sending unit that sees the air (and "heat"); it's an air pocket at the thermostat, which keeps the thermostat from opening when it should. Thermostat coils don't operate in steam, and there needs to be a huge spike in temp for a "dry" thermostat to open. Once it does, coolant circulates and the temp plummets fast. (This is why I also drill a 1/8" hole in all my thermostats)

Second, I NEVER run a fresh cooling fill with the cap on, until it is about to geyser. Fill a fresh system, turn the heat on full, start the car with the cap off, and stand ready at the radiator with a gallon of coolant (to fill as the level drops when air is replaced with coolant), a rag, and the cap. Looking in the fill neck, you will easily see the progression - stagnant cold coolant while the thermostat is closed (perhaps a trickle of circulation if you have a 1/8" hole in your thermostat); levels that drop along with bubbles that appear as air is replaced with coolant (top off to keep the levels correct, as needed); faster visible flow and mixing of coolant as the thermostat opens; finally, level rising to the cap height indicating full circulation has been reached and temp is approaching full. At this point I will let it circulate until I see zero bubbles (constant bubbles indicate a head gasket leak), let it overflow just enough to make a bit of a mess, then I'll cap it.

This method, along with a hole in the thermostat, has kept me from having air pocket issues for as long as I've owned cars. An 1/8" hole isn't enough to cause operating temperature differences, all it does is allow coolant pressure to push the air through the hole, so the thermostat isn't "dry" after a fresh fill.

To the issue at hand for this thread, it seems to me to be a blockage of some sort in the radiator, if the problem is persisting. For my money, I would:

1. drill a hole in the new thermostat and install it
2. drain the system
3. remove the lower radiator hose from the radiator
4. put a garden hose in the radiator filler neck (cap off), turn it on about halfway, and allow it to flush the radiator. don't use full pressure, just a steady flow. It should exit the lower hose fitting as quickly as you are putting it in the top. If it doesn't...you have a blockage. I know - it's a "quality part". Even quality parts have defects sometimes. If you do see a blockage or flow issue, remove the radiator from the car, turn it upside down, and do the opposite - put the hose in the lower radiator hose fitting and let the water flow out the cap opening, as a back-flush to try and dislodge whatever is stuck. *note: make sure neither your radiator, nor your water pump, are notated as being "reverse-flow" units.
4a. if you want to rule them out, perform the hose-flow-test on the other two members of your cooling system- the engine itself (remove the thermostat, hose in the thermostat housing, water flows out the lower hose), and the heater core (connect the hose to your heater feed hose, disconnect the return hose, and monitor those flow capabilities as well - again, NOT at full pressure!). You have now flow-tested all three sections of your system - radiator, engine, heater - as well as all the connecting hoses.
5. Once component flow has been proven, reassemble everything (with a hole in the thermostat), fill the system, turn on the heat, start the engine, and run/bleed it as noted above.

If you do all these steps, including 4a, and you still have air pockets that appear after a proper bleeding, and you don't see any external fluid leaks...you have a compression issue somewhere, either a cracked block or a blown headgasket.

Great explanation, thanks for taking the time to spell it out in black and white. It's exactly my findings from working on cars all my life also.

Tempature sending units won't work in an air pocket either. They need coolant contact to operate. Don't ask me why but I discovered this many years ago. Maybe Professor Bob @RJRENTON could elaborate.

I hear it all the time about people placing the cap on the radiator before the t-stat opens and coolant is circulating. Good way to blow a hose off and get scalded.
 
Great explanation, thanks for taking the time to spell it out in black and white. It's exactly my findings from working on cars all my life also.

Tempature sending units won't work in an air pocket either. They need coolant contact to operate. Don't ask me why but I discovered this many years ago. Maybe Professor Bob @RJRENTON could elaborate.

I hear it all the time about people placing the cap on the radiator before the t-stat opens and coolant is circulating. Good way to blow a hose off and get scalded.

The subject is complex ...... but simplified, this may help....exerpted ftom an article about improving temperature measurement.

The two main approaches to measuring temperature electronically are: resistance (resistance temperature detector [RTD] and thermistor) and voltage (thermocouple). In both situations the value indicated is the temperature of the sensor, which may or may not be exactly equal to the process media temperature. Getting an accurate measurement depends on bringing the sensing element to the same temperature as the process media. While this may sound like a simple problem to solve, in actual application it can be difficult.
It basically comes down to accuracy and response time you (the owner) wants or needs. The liquid immersion provides the fastest response but it also depends on the sensing element type, as RTDs are faster than resistive devices (Thermistors or temperature dependent resistors). This is the type typically used due to low-cost. RTDs are typically multi wire devices.
Refer to: https://www.google.com/url?sa=t&sou...FjANegQIJhAC&usg=AOvVaw1usyQVqZXidRrrFyC6v-ZA
the link for a detailed explanation.....if interested.
BOB RENTON
 
people placing the cap on the radiator before the t-stat opens and coolant is circulating.
I don't recall having made that mistake. It's an interesting process (kinda) watching the coolant sit there, then the first hints of motion, soon followed by a torrent of activity. One of the interesting parts of that is the "Whack-A-Mole" way the coolant pops up and down in the filler neck, then gradually climbs up and out.
I have a factory repop fan shroud to install, and I'm going to use a TALL funnel that "seals" to the cap that comes with the funnel in a kit. That design and the added height should help get any air out.
I have to check the temperature sender wiring first, once tech support gives me instructions on the procedure.
 
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