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Join Date: May 2005
Location: Detroit
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External Thermostat

Is there a way to test an external oil ine thermostat (the one in front of the right rear tire) while it is off the car to make sure that it is working properly?

Pot of boiling water?

Any ideas?

Thanks
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Millhaus
Old 05-19-2011, 08:24 AM
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Although I have never done it myself........

The t-stat should allow no front to rear flow when tested cold. If checked immediately after removing from boiling water, the unit should allow front to rear flow.
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Tom Butler
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Old 05-19-2011, 09:39 AM
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Hot water bath test.......

Quote:
Originally Posted by millhaus View Post
Is there a way to test an external oil ine thermostat (the one in front of the right rear tire) while it is off the car to make sure that it is working properly?

Pot of boiling water?

Any ideas?

Thanks

millhaus,

As earlier stated, the flow of oil goes straight back to the oil tank when the oil temperature is below 186F. For easy reference use 180F point for your test. Place the clean auxiliary thermostat in a heated water bath. Observe the valve slide opening/aperture as the temperature of the water increases to 180F. Once the water temp. approaches the opening temp., the slide valve will slowly and gradually move. This change in aperture opening will continue before the water gets to its boiling temp. (212F). By 200F, it should be fully opened.



Place the aux. thermostat in the water bath with the stamped number facing up. If you look closer, you'll see a section of the slide valve (temp.). The other valve (smaller) is the pressure relief valve. The movement of the slide valve is attributed to the expansion of the paraffin inside the valve. Keep us posted.

Tony
Old 05-19-2011, 10:33 AM
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Tony,

Thanks for the info and the photos. Before I saw your post I ran some tap water through the supply line of the thermostat closest to the oil tank. What happened was the water basically flowed from three of the four lines. The supply line from the thermostat to the oil cooler did not flow.

I stuck the entire thermostat in a pot of boiling water. When the water was a rolling boil I took it out and ran water through the same opening. This time it flowed out of all four openings.

So I can assume that the valve that opens to the oil cooler is working since water flowed here after heating. It only flowed for a short time. The tap water cooled it quickly and the valve shut again.

What is the other spring valve for? Pressure relief for what? Line pressure? How to check this spring function? Seems to always be open. When does it close?

Thanks

Tom
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Old 05-19-2011, 03:53 PM
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Tony (or anyone)

How do you open up the thermostat to replace the spring valves? Machine shop?

Thanks

Tom
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Old 05-19-2011, 03:55 PM
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Auxiliary thermostat......

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Originally Posted by millhaus View Post
Tony,

Thanks for the info and the photos. Before I saw your post I ran some tap water through the supply line of the thermostat closest to the oil tank. What happened was the water basically flowed from three of the four lines. The supply line from the thermostat to the oil cooler did not flow.

I stuck the entire thermostat in a pot of boiling water. When the water was a rolling boil I took it out and ran water through the same opening. This time it flowed out of all four openings.

So I can assume that the valve that opens to the oil cooler is working since water flowed here after heating. It only flowed for a short time. The tap water cooled it quickly and the valve shut again.

What is the other spring valve for? Pressure relief for what? Line pressure? How to check this spring function? Seems to always be open. When does it close?

Thanks

Tom

Tom,

I'm a little bit confused on your result. The line from the thermostat to the auxiliary cooler is always OPEN. It does not change. It is the return line from the cooler that is part of the control. When the engine oil is below 180F, all the warm oil from the engine circulates back to the oil tank. As the temp. builds up, the thermostat's valve starts to OPEN (return line from cooler).

The amount of opening (from cooler) corresponds to the amount of closing (going from engine to oil tank). So the cross-sectional flow area is kept the same. Here are some illustration:

Oil is below 180F.......orifice to oil tank = 100% open; orifice from cooler = 0%

Oil is above 186F.......orifice to oil tank = 100%-X% open;orifice from cooler = X%

As you can see, for every change (closing) a corresponding equal amount is opening. So the flow area is maintained the same at all time (cold or warm/hot).

A convenient way to open the auxiliary thermostat is using an impact wrench. One zap and you have the cover off in a second.

Tony

Last edited by boyt911sc; 05-19-2011 at 05:49 PM..
Old 05-19-2011, 05:28 PM
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The proper way to open the thermostat is with a special tool. It is a sort of big screw driver blade (but short) with a ring around it. The ring fits over the round screw in cap, and keeps the screw driver part from slipping off. You'd need two sizes for complete disassembly. Plus, for the older cars, another size for your engine oil pressure spring caps.

I've often wondered who invented this system, and what its advantages might have been thought to be.

The most common way of removing these is with a pipe wrench. Yes, its teeth will bite into the cap. Whadayya want, tuna with good taste or tuna that tastes good?

With the large cap removed you can pull the working part - the wax filled cylinder with the improbably small nail like thing protruding. Put it in the freezer, then toss it into a pot of boiling water. Than back to the fridge. If it opens and closes, it is OK. If you don't get any movement, then the wax is tired out.

At one time, anyway, you could get replacements for these. Not sure if PET shows an individual part #. It is said to be the same element as is found in the engine oil thermostat, but that housing, I think, is not easy to disassemble.

I believe that there is always, by design, some slight flow through the front cooler lines/radiator, even when things are cold. That way you don't get a bolus of cold oil in the way of smooth operation when the oil temp warms up, but you don't impede oil warm-up either.
Old 05-20-2011, 07:55 PM
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Auxiliary thermostat......

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Originally Posted by Walt Fricke View Post
The proper way to open the thermostat is with a special tool. It is a sort of big screw driver blade (but short) with a ring around it. The ring fits over the round screw in cap, and keeps the screw driver part from slipping off. You'd need two sizes for complete disassembly. Plus, for the older cars, another size for your engine oil pressure spring caps.

I've often wondered who invented this system, and what its advantages might have been thought to be.

The most common way of removing these is with a pipe wrench. Yes, its teeth will bite into the cap. Whadayya want, tuna with good taste or tuna that tastes good?

With the large cap removed you can pull the working part - the wax filled cylinder with the improbably small nail like thing protruding. Put it in the freezer, then toss it into a pot of boiling water. Than back to the fridge. If it opens and closes, it is OK. If you don't get any movement, then the wax is tired out.

At one time, anyway, you could get replacements for these. Not sure if PET shows an individual part #. It is said to be the same element as is found in the engine oil thermostat, but that housing, I think, is not easy to disassemble.

I believe that there is always, by design, some slight flow through the front cooler lines/radiator, even when things are cold. That way you don't get a bolus of cold oil in the way of smooth operation when the oil temp warms up, but you don't impede oil warm-up either.


Walt,

When you get a chance to inspect an auxiliary thermostat, you'll find that the line to the auxiliary cooler is permanently OPEN. The return line from the cooler is closed when cold. The warm oil from the engine circulates back to the oil tank. Once the oil temperature gets closer to 186F (180F plus), the thermostat valve will start to open (return line from cooler) and at the same time a similar closing (cross-sectional area) is also happening to the main return line to the oil tank.

The opening/closing of the slide valve is kept equal for the by-passed oil to the cooler to keep the oil pressure/flow stable.

Tony
Old 05-24-2011, 04:47 PM
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I have had these apart, but my focus was on checking function (i.e., the canister). It is a complicated appearing system of holes and slots, all controlled by that improbably small nail headed piece.

Perhaps this blending as it heats up is what was mistakenly thought to be a permanent minimum flow?

The two aren't entirely incompatible if the closed phase isn't 100%, which it would not need to be. But your description sounds like an ideal design. Next time I look at one perhaps I will be able to understand the passageways better.
Old 05-25-2011, 09:44 AM
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Old 05-25-2011, 09:44 AM
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