stuck thermostat?

[diymirage]

first time i got the duster out this year, and it was running hot

(reading about 240 on the stock gauge)

when i came home i hit the whole thing with a infra red thermometer
the bottom hose on the radiator was 170
the top hose, near the radiator was 220 and near the thermostat it read 240

when i squeezed the top hose, it felt solid, no give in the hose

and not admitting i did this, but if i were to have pulled the radiator cap of coolant would have shot up like a mentos in a two liter and hit the hood and the ceiling


so, long story short, does this sound like the thermostat is stuck closed, or should i look for some other issue?

 

[RustyRatRod]

Simple enough to find out.

 

[mjmayhem]

I would pull out the thermostat and look at it. Then test it in a pot of boiling water to see if it opens.

 

[Bewy]

Could be [ stuck] ....& only one way to find out

 

[diymirage]

Looks like I can rule out the thermostat



One interesting tidbit though, when I pried off the thermostat (after removing the upper radiator hose) I could hear it sucking in air, showing me there was a vacuum underneath the thermostat

Isn't there usually a bleed hole in those things ?


For now, I've installed the housing without a thermostat and after the silicone cures overnight

And then we'll see how it does

Any thoughts on that vacuum though?

 

[TT5.9mag]

When the block and coolant cool down they contract and create vacuum. Usually pulling coolant back in from the overflow. If you pinched off the upper hose I could see there being vacuum under the thermostat. Not all thermostats have bleed holes. But they should.

 

[diymirage]

When the block and coolant cool down they contract and create vacuum. Usually pulling coolant back in from the overflow. If you pinched off the upper hose I could see there being vacuum under the thermostat. Not all thermostats have bleed holes. But they should.

When this happened the upper hose was off, that'd why I thought it was so strange


You'd think it would have a bleed hole to allow for expansion and contraction as it heat cycles

 

[mopar head]

Drill a small hole in it, if theirs room.

 

[TrailBeast]

Looks like I can rule out the thermostat



One interesting tidbit though, when I pried off the thermostat (after removing the upper radiator hose) I could hear it sucking in air, showing me there was a vacuum underneath the thermostat

Isn't there usually a bleed hole in those things ?


For now, I've installed the housing without a thermostat and after the silicone cures overnight

And then we'll see how it does

Any thoughts on that vacuum though?

View attachment 1716114049

View attachment 1716114050

I would suspect the water pump impeller next.
Pull the top hose at the radiator while your thermostat is out and fire it up.
That’ll tell ya real quick.

I drill every thermostat if it doesn’t have a vent hole.
You don’t have to screw around with air bubbles when filling.

 

[TT5.9mag]

When this happened the upper hose was off, that'd why I thought it was so strange


You'd think it would have a bleed hole to allow for expansion and contraction as it heat cycles

There has to be a restriction somewhere to have vacuum. If the upper hose was off and the radiator was open to atmosphere then the rad is severely plugged.

 

[TT5.9mag]

You'd think it would have a bleed hole to allow for expansion and contraction as it heat cycles

They don’t HAVE to have a bleed hole. It just makes it easier to fill. The bypass hose keeps the system happy through heat and cool down cycles. And the hoses have some amount of expansion by nature of material.

 

[TT5.9mag]

I drill every thermostat if it doesn’t have a vent hole.

You and me both

 

[diymirage]

There has to be a restriction somewhere to have vacuum. If the upper hose was off and the radiator was open to atmosphere then the rad is severely plugged.

The cap was off, so yes, open to atmosphere

When I squish the bottom hose I can hear the coolant move in and out of the engine (I can hear it sloshing through the thermostat housing


I put in the radiator 6,7 years ago when I swapped in the 360

 

[mopar head]

Drain your coolant in a bucket and run a hose through rad. If it pours out the bottom outlet, the rad`s just fine. that will guide you elsewhere, but you know this.

 

[TT5.9mag]

The cap was off, so yes, open to atmosphere

When I squish the bottom hose I can hear the coolant move in and out of the engine (I can hear it sloshing through the thermostat housing


I put in the radiator 6,7 years ago when I swapped in the 360

Weird. I don’t get it.

 

[TT5.9mag]

Maybe it was just the weight of the column of water and the thermostat was that well sealed.

 

[barracudadave67]

I would drill a hole in the T-Stat, as mentioned. I drill a 1/8 inch hole in all of mine.

ole man Dave

 

[diymirage]

I would suspect the water pump impeller next.
Pull the top hose at the radiator while your thermostat is out and fire it up.
That’ll tell ya real quick.

I drill every thermostat if it doesn’t have a vent hole.
You don’t have to screw around with air bubbles when filling.

Not much of a test, but with the upper hose off and the belt off I can hear the impeller sloshing around as I move the water pump pulley


This is with the belt back on , sure seems to be flow in the coolant



For now I put it back without a thermostat
I should have time for a good shakedown tomorrow, see what it does

 

[mopar head]

see what it does

Probably over heat.
Hope I`m wrong...

 

[Bewy]

There is never any reason to drill a hole in a stat [ except on the rare occasions a race pump is used that has no bypass ] to let air burp. There is always a space around/in the stat that air can escape. Drill a hole if it makes you feel good....

 

[RustyRatRod]

The cap was off, so yes, open to atmosphere

When I squish the bottom hose I can hear the coolant move in and out of the engine (I can hear it sloshing through the thermostat housing


I put in the radiator 6,7 years ago when I swapped in the 360

What does the coolant do with the cap off and the thermostat open when you rev the engine?

 

[RustyRatRod]

Not much of a test, but with the upper hose off and the belt off I can hear the impeller sloshing around as I move the water pump pulley


This is with the belt back on , sure seems to be flow in the coolant



For now I put it back without a thermostat
I should have time for a good shakedown tomorrow, see what it does

If you have to remove a thermostat trying to get one to cool down, you have something WRONG.

 

[Ricks70Duster340]

Not much of a test, but with the upper hose off and the belt off I can hear the impeller sloshing around as I move the water pump pulley


This is with the belt back on , sure seems to be flow in the coolant



For now I put it back without a thermostat
I should have time for a good shakedown tomorrow, see what it does

Is the bottom hose soft? Is there a coiled wire in it? If not, then it may be collapsing under the suction from the water pump. When I bought my Duster, the bottom hose did not have a coiled wire so I put one in.

 

[TrailBeast]

Not much of a test, but with the upper hose off and the belt off I can hear the impeller sloshing around as I move the water pump pulley


This is with the belt back on , sure seems to be flow in the coolant



For now I put it back without a thermostat
I should have time for a good shakedown tomorrow, see what it does

It certainly appears to be circulating.
Hopefully you just had a stuck thermostat like you suspected in the first place.

 

[diymirage]

There is never any reason to drill a hole in a stat [ except on the rare occasions a race pump is used that has no bypass ] to let air burp. There is always a space around/in the stat that air can escape. Drill a hole if it makes you feel good....

under normal circumstances, i suppose you are correct, but in this particular case there was no space for air to either escape or sneak in

i dont know why, but when i pried the thermostat off i could feel it sucking in air

What does the coolant do with the cap off and the thermostat open when you rev the engine?

swells up like a river in the springs, it was moving real nice, with a little bit of foam on top

If you have to remove a thermostat trying to get one to cool down, you have something WRONG.

the point of removing the thermostat was not so much to fix the issue as it was to troubleshoot it

Is the bottom hose soft? Is there a coiled wire in it? If not, then it may be collapsing under the suction from the water pump. When I bought my Duster, the bottom hose did not have a coiled wire so I put one in.

no spring, but also not collapsing

It certainly appears to be circulating.
Hopefully you just had a stuck thermostat like you suspected in the first place.

sure looks that way, i took her out for about a half our spin today and all is well
i even put her through the most gruesome of cooling test...the burger king drive through


The first pic is after driving for about 15 minutes


The second pic is while idling for 7-8 minutes in the drive through

The last picture is about one minute after pulling out of the drive through