So, in replacing the thermostat yesterday, I found the one in the car that looked very old to be not only backwards, but off-center in the housing. I'm guessing the fact that it was off-center might have allowed a constant flow of coolant by with the thermo having no effect.

If there was no free flow-by, what is the effect of a thermostat being backwards?

Hi krytellan.
If the thermostat is in the upside-down position, one should believe that it should not open at all! But, that is not entirely true. Looking at the action of a thermostat, it is a temperature dependent expanding or contracting coil that moves the valve to open or shut for hot water. The fact that the coil is on on the incorrect side, usually doesn't make it stop working, it just takes a lot longer time before it reacts initially. The construction of the thermostat also dictates how difficult it is to open the valve against higher water pressure on one side. Once open, the coil itself is in the hot water stream, and should remain open without any problems for the cooling system.

Before fitting the new thermostat, you should reverse flush out the entire cooling system - including the heater circuit - with clean water; seeing how a previous owner treated the car should make you raise questions on all parts of servicing or repairs ever done to your car! Then refill it with a proper amount of antifreeze, which also acts as a lubricant for you water pump, and clean water. As this is a car you're going to keep for the rest of your life (no??), it is worth while to treat your cooling system to a flush and new fluid on a regular basis.

You should also drill a small hole (app.1/16") in the thermostat's flange before fitting it. That will prevent air from being trapped behind the thermostat, and it will make no difference to the thermostat's function.

Regearding the correct temp thermostat to use, I finish with a quote:
Olaf.

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Aspenized

Hey, thanks for the info! That was the most education I've had in thermostats in my life. It will serve me well.

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Aspenized

Olaf nailed it: When you reinstall that drilled thermostat, orientate the hole at 12:00 o’clock, or rather, the highest point in it's housing.

Bill

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

"Information" vs. "Verbiage". They are not the same. What you were given was not "education", it was verbiage -- a collection of assertions on the subject of thermostats, but not much accuracy to be found in them. He who made them does not seem to understand how cooling systems work.

The thermostat is not operated by an "expanding or contracting coil". It is opened by a piston extending from a cylinder filled with themosensitive wax which expands (to push the piston and open the thermostat) at a particular temperature. It is closed by a counterspring.

The thermostat is not responsive to water pressure, and there is no "higher watter pressure on one side".

You should not drill extra holes in your thermostat. What you should do is buy a good quality thermostat of the correct temperature rating (Stant SuperStat 45358 for 180°, 45359 for 195°; which temp to pick depends on the particulars of your application). A good quality thermostat has either a jiggle pin or a notch in the valve plate to allow air to escape. Drilling an extra hole just slows the rate at which your engine reaches full operating temperature (and wears out your drill bits; stainless steel is very hard to drill through).

Very good, very sound thermostat info and mythbusting here. My experience agrees with almost all of it, except for their preference for the old balanced-sleeve type thermostat. Those work fine, there's nothing wrong with them, but I like the Stant Superstat better. It's a theoretical question anyhow; the balanced-sleeve thermostat does not fit a slant-6 engine.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Da has spoken....enough said ...LOL...I do drill hole if air escape not pesent


keep on roddin'

How nice of Dan to present a vague but general description of the solid expansion thermostat, which is the most used thermostat type today. I can contribute a little extra information, even without asking Dan's permission.

While basically functioning the same way, but with different designs, there are three main types that are commonly used variations of

Solid Expansion Thermostats

1) The balanced sleeve thermostat
This type has all it's moving parts open to the flow of the pressurized coolant, and the construction equalizes the pressure above and below the thermostat's moving valve. The thermostat is "balanced", because the coolant exerts equal but opposite pressure on the sleeve, thus making the thermostat respond to temperature changes only. Several manufacturers use this design as a high-flow thermostat.

2) The reverse poppet thermostat
This thermostat type opens against the flow of coolant from the water pump, and uses the pressure from the water pump to assist in keeping the valve closed, thus reducing the possibility for leakage when cold. This type of thermostat is very sensitive to temperature changes, and is the most used type today. The disadvantage is that, depending on the design, it usually will stay closed when mounted upside-down. (Stant's reverse poppet thermostats won't open at all when mounted upside-down, according to Chris Hoffman of Stant Inc.)

3) The three-way thermostat
This is most often a poppet-style thermostat with two valves, used when there is a bypass passage under the thermostat. When the upper thermostat valve opens for flow to the radiator, the other valve mounted lower on the same stem, closes the bypass passage below. The valves may also be made to operate independently when used in a mixed-temperature application.

Other types of thermostats are:

The bellows-type thermostat.
In the early days, before the pressurized cooling system came into use, the bellows-type thermostat was frequently used. Instead of todays thermal wax operated valve, it used a bellow made from thin metal, and filled with a fluid with low boiling point, mostly alcohol. The varying temperature caused the bellow to expand or contract, to open or close the valve. It went out of use because pressure in the cooling system made it inaccurate.

and

The bimetallic type thermostat.
This type of thermostat uses a coil made from two metals that are fused together. These metals expand at different rates when heated, and thus lengthens the coil to open the valve, and similarly contracts to shut the valve when cooling shortens the coil.
This type of thermostat is not much used today, if used anymore at all. The design is simple, but it is prone to corrosion, and inaccuracy over time because of weakening of the coil.

As this is the simplest thermostat to describe, I allowed myself to use it in my post above as an example of how a thermostat works.

Hi krytellan, sorry for being too general in my description of the thermostat and not 'writing a book' on a subject, as I frequently have done in many earlier posts. For once I thought I should keep it short and simple. My mistake.

As for balanced-sleeve thermostats not fitting the SL6: someone should tell Jegs, and Milodon, and Mr.Gasket about their mistake in designing and selling high-flow thermostats for Mopars! And ALL manufacturers of poppet type thermostats must have missed Dan's opinion about the lack of different pressures in a cooling system!

Dan, if you have decided to sit there on your mound,waiting, only to throw s h i t every time someone writes something not to your liking, without contributing yourself, that is just pathetic and does not deserve additional comments!

Olaf.

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Aspenized

A quick accurate description beats a long inaccurate one, in my opinion.

(snip a bunch of face-saving copy-and-paste including irrelevant antique thermostat info)
Nothin' wrong with short and simple as long as it's also accurate. Try not to take my response personally, Olaf. You posted wrong info in response to a query asked by a new guy who doesn't yet know enough to be able to discern wrong from right info. He was looking for an accurate answer to his question. Anybody could've provided it; I don't have a monopoly on correct info. It just happens I was the one to call you out this time for your incorrect advice. Try not to let it get under your skin. Next time it might well be someone else (or perhaps nobody will, and the next newbie who doesn't know any better than to take what you say as authoritative will learn for himself that you weren't quite as correct as you made yourself sound).
Read carefully: I didn't say balanced-sleeve thermostats don't fit Mopars. I said they don't fit slant-6s. I said it because they don't. The sleeve's too big in diameter. Go try it for yourself, if you have an aversion to believing me.

(Psst: no matter what brand and type of thermostat you specify, it's not the same physical size for Mopar V8s vs. Slant-6. But you knew that already, right?)
An imaginative assertion, but not one I'm inclined to spend any effort or time trying to decipher.

As for the value of my contributions, I think they stand on their own merits and I don't much care what you think of them. Sorry you feel wronged or attacked or whatever it is you feel.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

This paragraph was an attack Dan. This, and your propensity to quote identifiable individuals line by line while refuting their assertions is also, by my definition, an attack.

In effect you are inferring that various posters are wrong. Whether they are or not is irrelevant. The delivery is "Unkind."

Out making friends and influencing people again. Must be that time of year. You really need to get out of Toronto. It's making you peevish.

CJ

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Part of Tyrde-Browne Racing

Agreed

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Mancini Racing - Thermostats

Year One MP Thermostat P4876308

Mr. Gasket Thermostat 4367

Mr. Gasket Thermostat 4365

The 195° Mr. Gasket #4365 balanced-sleeve, copper/brass thermostat, is also listed for use with all Mopars in their latest catalog, as is the 4367.

The brass/copper thermostats can, if necessary, safely be drilled without ruining your normal drill bits. When drilling in stainless steel, it is common practice to use the correct drill bits for that material.

Seriously, are none of these thermostats fitting the SL6?

Olaf.

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Aspenized

My experience is the thermostat cavity on many slant six heads will not accept the larger diameter of the balanced sleeve thermostat. A little work on the head with a rotary file/carbide cutter and the balanced sleeve thermostats fit fine. Also, '77 and earlier small block V8s, and all big blocks use a larger diameter thermostat which does not fit a slant six.

Personally I like the balanced sleeve thermostat because they are not sensitive to the water pressure in the cylinder head created by the water pump. I don't feel it's a big deal on low speed street engines especially if one is using a Stant Super-Stat with it's larger wax pellet which has a greater opening force.

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Joshua

Thank you, Joshua.

I have a Mr.Gasket #4365 in my hand right now, I'll report back later to tell if it fits a '77 without modifications.

Olaf.

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Aspenized

I have to correct myself, the Mr.Gasket #4365 thermostat fits all SL6 and all V8 '79 - '89, the #4367 fits all V8 '51- '78.

Olaf.

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Aspenized