Tired of junk thermostats. Going with NOS. Do I need to drill a hole in in?

[cruiser]

Hi all: I've had terrible luck with my recent thermostat purchases for my 1974 slant six Duster. They run too cold, erratically, or whatever. This includes NAPA Premium and Stant Super Stat brands. None of them seem to work right, regardless of the price. I bought a nice NOS one on e-Bay, p/n 3780112, which is the correct p/n according to the 1974 factory parts manual. The FSM shows this exact stat in the cooling section. I'm puzzled by one thing, however. The FSM says to install it with the "vent hole up". But the accompanying photo in the FSM shows no such vent hole in the 3780112 stat. So what gives? Should I drill a 8/32" hole in the rim of it before I install it with the aforementioned hole at the top? Whaddya think? Slant Six Dan, feel free to weigh in. Thanks!

 

[Cranky]

I've never drilled a hole in any of them but noticed some came with a small hole. Try a solid plate with say a 1/4" hole and see how it does.

 

[toolmanmike]

Hi all: I've had terrible luck with my recent thermostat purchases for my 1974 slant six Duster. They run too cold, erratically, or whatever. This includes NAPA Premium and Stant Super Stat brands. None of them seem to work right, regardless of the price. I bought a nice NOS one on e-Bay, p/n 3780112, which is the correct p/n according to the 1974 factory parts manual. The FSM shows this exact stat in the cooling section. I'm puzzled by one thing, however. The FSM says to install it with the "vent hole up". But the accompanying photo in the FSM shows no such vent hole in the 3780112 stat. So what gives? Should I drill a 8/32" hole in the rim of it before I install it with the aforementioned hole at the top? Whaddya think? Slant Six Dan, feel free to weigh in. Thanks!

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It just helps bleed the air out easier. I have never had an issue without.

 

[slantsixdan]

Photos in the FSM are not necessarily 100% representative of real-life parts. Look at your new thermostat carefully; sometimes there's a small hole on the flange plate, or sometimes there's a very small notch in the valve disc. Either of those features should go at the 12:00 position. If neither feature exists, install it anyway, without drilling holes.

If you insist on drilling a hole, "small" means SMALL. Like, 3/32" is plenty. 1/4" is way too big; that's known as a drill-to-order stuck-open thermostat.

 

[Killer6]

What Dan said, some of the 'V' notches are a bit too tiny, 1/16-3/32" is plenty.....I do this to EVERY 2.2/2.5L Mopar I own,.....IYKYK......

 

[cruiser]

Great - thanks all!

 

[RustyRatRod]

Get a quality thermostat from Stewart Components.

Home - Stewart Components

www.stewartcomponents.com

 

[4spdragtop]

Are you checking the stats function in a pot of boiling water?
Also its pretty easy to throw a $5 stat into an old Mopar box call it NOS and charge $$$.
As to your question, yes to hole, but 1/16 will do, I've done it.

 

[Desoto291hemi]

I usually drill a small vent hole in every thermostat I install ,,,just as a safety measure .
It lets the coolant flow through when you are filling up and you can completely fill it before startup .
You don’t have to,,,,but I like to know my coolant is full before I fire it for the first time .
Usually about a .060 thousandth hole,,,maybe up to .125 depending on the application .

Tommy

 

[slantsixdan]

Get a quality thermostat from Stewart Components.

1. Their thermostats are made by the same companies as thermostats available through all other channels; change my mind.

2. Who says they have one in the correct size to fit a Slant-6, anyway?

 

[cruiser]

Are you checking the stats function in a pot of boiling water?
Also its pretty easy to throw a $5 stat into an old Mopar box call it NOS and charge $$$.
As to your question, yes to hole, but 1/16 will do, I've done it.

Yeah, I will definitely check it on the stove before I install it.

 

[Bewy]

Temps vary. On some engines, the machined seat for the stat is quite deep. Then, when you add the gasket, that depth gets bigger......& more coolant gets past around the edge of the stat. So if the engine seems to be running colder & the stat is not regulating the flow properly, it might be because coolant is 'pumping' past the stat in the closed or near closed position.
To stop this happening, place three blobs of silicon at 120* on the edge of the stat to stop it moving & letting coolant pass.

 

[RustyRatRod]

1. Their thermostats are made by the same companies as thermostats available through all other channels; change my mind.

2. Who says they have one in the correct size to fit a Slant-6, anyway?

1. I cannot change your mind. We both know it's a steel trap. lol

2. My die grinder.

 

[harrisonm]

Get a quality thermostat from Stewart Components.

http://[URL]https://www.stewartcomponents.com/

[/URL]

You beat me to it.

Are you checking the stats function in a pot of boiling water?
Also its pretty easy to throw a $5 stat into an old Mopar box call it NOS and charge $$$.
As to your question, yes to hole, but 1/16 will do, I've done it.

Agree 100%. It takes 5 minutes to test one. I have found a few bad ones over the years. Remember that a 180* starts to open at 180*. A lot of people get confused on that. Plus, I agree with your NOS comment. A lot of NOS parts out there sat on a shelf for a good reason; it was returned as not fitting properly or defective 55 years ago and was not thrown away. it just sat on a shelf until NOS parts got popular. I am not saying that all NOS parts are bad, but I have been burned by a defective NOS part still in its box.

 

[volaredon]

I recently bought a box of 10 (not in factory Mopar) boxes aftermarket NOS all US made t- stats from eBay. It came from Canada and "customs* seemingly had them forever. I have ordered parts from Canada before including from members of this site and before this one transaction I usually get stuff from Canada faster than I get stuff that originated within 3 hours of me .. the 79 and newer V8s take the same stat as every/6 I have ever had my hands on. So far I have used 1 and it's working fine. Not all were stant (at least as packaged, they might all be for all I know) some were packaged private label (I think a couple say "Texaco" on them as if sold by a gas station service center, etc) not looking at the box.... But when I did all individual ones said "made in USA" on them and all were definitely older stock. A thermostat isn't something that i'd be afraid of an old one from the shelf.

It helps that I put an aftermarket temp gauge in the vehicle that thermostat is in along with the original one... I have them both connected and working. I much prefer "mechanical" gauges when possible vs "electrical".

I've had vehicles on which for years and never had to change a thermostat even once, (or maybe ONLY once) and I've had others that I've had to replace them twice a year every year I owned them....

 

[toolmanmike]

I have got spanked with a few new t-stat's( I was going to say burned but hot water and "burned" isn't the right word LOL)
I spend more money buying one hoping for a better product and test each one in a pan of water on the stove with a thermometer to make sure it works properly. It's worth the extra effort.

 

[TylerW]

Makes me wonder if your temperature gauge is out of calibration. Mine in a '72 Valiant is and I saw another person on here complaining the that the engine ran too cool after repeated thermostat change-outs. That's what I thought mine was up to, but after changing the sending unit, testing the thermostat in water and running the engine with a candy thermometer in the radiator, it became evident that the engine was running right at 180 degrees instead of the 160 the gauge indicates. I'm not taking it apart to swap the gauge.

I think the folklore about thermostat quality is up there with motor oil. I'm using an NORS Stant I picked up from eBay. No hole. Works great.

 

[Bewy]

I tested some of the 'Robert Shaw' stats a few years back. The Chinese versions that have the s/steel bridge. I found they opened at the rated temp & did go the fully open position. All good. If the engine cooled down, they did not fully close at the rated temp, stayed open slightly. Temp had to drop further until it fully closed. I switched to the Stant Super Stat & opens/closes bang on the rating.

 

[RustyRatRod]

I've actually had good luck with the Edelbrock thermostats. They're high flow and stainless.

 

[318willrun]

I'm odd.... I grab a the basic stant, drill a small hole, fill er' up, and a way we go.... I laugh when folks say "that hole is a touch to big"... Like the small hole is enough flow to cool an engine without the stat opening... LOL If that's the case, then I will give you a thermostat block off plate and drill a small hole in the middle and your car should cool just fine...

 

[RustyRatRod]

I'm odd.... I grab a the basic stant, drill a small hole, fill er' up, and a way we go.... I laugh when folks say "that hole is a touch to big"... Like the small hole is enough flow to cool an engine without the stat opening... LOL If that's the case, then I will give you a thermostat block off plate and drill a small hole in the middle and your car should cool just fine...

Exactly. All it's for is to bleed out air. Nothing to do with water. It's a good practice.

 

[cruiser]

Yeah, I will definitely check it on the stove before I install it.

Well, the saga continues. Bought a NOS Mopar thermostat with the correct part number on the box one e-Bay. Lo and behold, when it gets here, it is, in fact, the correct box with the correct part number (according to my 1974 factory parts manual). Upon opening however, I discover a 1970 160 degree stat instead of a 1974 195 degree stat. Burned again by people who sell stuff on e-Bay and have no idea of what they're selling. Got my money back, though. Now I have a useless 160 degree stat. Returned the old faulty stat to NAPA. New NAPA unit seems to be working so far. The drilled hole trick seems to work out nicely, for what it's worth.

 

[toolmanmike]

I have a Lisle brand spill free funnel that you fill the system with, let it run and the air will bubble it's way out of the system. Also, not cheap, but there are cooling system vac's that pull all the air out and then the suction draws coolant in. No air in the system. The small hole in the stat and let it run with the cap off is the cheapest and works well. Like mentioned before. Test every t stat before installing it. Many/most new ones don't work, right out of the box.

 

[RustyRatRod]

I have a Lisle brand spill free funnel that you fill the system with, let it run and the air will bubble it's way out of the system. Also, not cheap, but there are cooling system vac's that pull all the air out and then the suction draws coolant in. No air in the system. The small hole in the stat and let it run with the cap off is the cheapest and works well. Like mentioned before. Test every t stat before installing it. Many/most new ones don't work, right out of the box.

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Those work well. I had one years ago, but somebody liked it more than I did. It sprouted legs. I've not had much trouble though on conventional systems with trapped air. Now where the radiator cap is the low spot in the system, that's a different story.

 

[TF360]

All this talk about drilling a hole. I have done many thermostat's (including several Slants) and never had a problem. Just did one about a week ago on my 360 and no issues???