Broken Thermostat already?

[otto in norway]

Hi there everybody!

Been a while since my last post here now.

This time i have a question about the external oil thermostat.

It seems like my thermostat does not open. I have cold pipes going to the front oil cooler, and really warm pipes on the "inside". (Pipes going to oil tank and engine pipe.) The temperature reading on the instument in the front of the car goes to about almost "10 o'clock". Also, I have replaced the temperature sender, because I suspected that first. So I know I have the right reading. The thermostat used to open at below "9 o'clock".

Look to this drawing for reference:



The thing is:
I have already opened the thermostat. (which is only two years old)

I checked for sliding resistance for the piston. The piston fell out when i tipped the housing over, so I guess that's fine.
When I tested the actuator inside the slider piston, by putting teh piston in boiling water, the actuator came out when the water was barely boiling. But, when I took it out of the boiling water, and pushed on the actuator with my finger, (wearing gloves), it felt quite easy to push in again. At the time, I just thought "It probably gets cold really fast, making it retract again".

So I assembled everything, and went for a test ride. The dial in the dash was at almost "ten o'clock" after ten minutes of driving. And the pipes going to the front oil cooler was still cold. In other words: No change to what I have seen before I checked the thermostat.

Any Ideas guys?
Is the actuator really supposed to be easy to push in after it has opened?
How likely is a faulty bi-metal actuator after only two years?

[Walt Fricke]

Otto

Nothing bimetalic about the thermostat. It works on wax!

That tiny piece which looks like a nail (round flat head, small shaft under it) is forced out of the wax filled capsule as the wax expands with heat. It seems impossible that wax pushing on such a small diameter rod would generate the needed force, but it does.

I have tested several of these units, some of which worked, and some of which did not. Those which did not didn't budge when tossed into boiling water. But I don't recall whether I tried to push the plunger piece back in, and if so, how hard it was to push.

I have been fortunate in having oil temperature gauges which have temperature markings on them, so I don't know just what 9 and 10 o'clock represent in degrees F or C (but lots of other 911 owners do know these things). The thermostat should open at about 90 degrees C or 180-190 degrees F. So first thing I'd want to do would be to assign temperatures to these gauge readings, lest it isn't as hot as you think and that's why the thermostat isn't opening.

But if the 10 o'clock angle puts the needle up in the upper red zone, I guess it is hot.

The next thing to consider is the condition of the piping and front cooler. If it is blocked (or a line squashed flat), not much hot oil will circulate.

I would agree that a new thermostat (or its innards) should work well for more than two years.

Walt

[johnsjmc]

Which stat have you tested? There is a stat on the scavenge side in the wheel well which directs oil to the front cooler. The pressure side has another stat which is located on the top of the engine cases. If you look at the temp guage you can sometmes see small numbers along the outer edge (look at a steep angle to see them.My 911 barely reachs 8 O' clock

[otto in norway]

Thanks for the input. Amazing that wax is used for this...

I guess I'll need to measure the oil temp exactly, but in my mind I'm pretty sure it's way hotter than normal.

I am talking about the external thermostat. It should open when oil going through it gets over 83 Celsius.

[dshepp806]

I'm kinda' with Walt on this,..I simply can't stand this "clock analogy"........drives me nuts.


Doyle

[burgermeister]

Have you checked the temperature of the oil line? You can get a cheapie IR thermometer for $20 ... my external thermostat barely works, but my car doesn't run above 220degF in normal use.

If your gauge is accurate and your car gets to 250degF in 10 minutes, it almost seems like the internal thermostat also isn't working. But the gauge could be faulty as well as the sender - or the sender could be wrong for the particular gauge.

I've checked a couple of external thermostat regulators. The plungers were very difficult to push back in, even after cooling them down for a bit. Dunno if that's normal, but that was my experience.

[johnsjmc]

I have thought a bit more about this and would point out that the original cooler set up was adequate by itself until about 1969 . Then S got the foreward cooler loop and it was made standard about 1977.The trombone cooler loop really doesn,t add that much cooling without a fin style cooler anyway. You really need to confirm with a thermometer into the oil tank if you have a problem. Touching a cooler tube is not really good enough and the electrical gauge is often inaccurate.

[otto in norway]

Thanks for your input guys.
I still have not made any more progress.

But I feel like I need to explain a few things for you.

"9 o'clock means straight out horizontally. (in the middle of the scale) And before my engine swap, it would open the loop for front cooler at "8 o'clock" I guess that means that 8 O'Clock means 85-90 Celsius. dunno about the figures above that, but probably 90-95 at 9 o'clock, 100-115 at 10 o'clock, or something like that.


I have replaced my stock engine. (It's now a 3,2 lier) But before I replaced it, I upgraded the cooling system with a front mounted cooler. This worked great with my 3 liter engine. As I just explained, it would open the thermostat at the right temperature. The thermostat front loop has not been opened while the engine swap has been done.
After I put in the 3,2 liter engine, things seemed strange. Immediately I dismissed my readings on the temp Gage to be a wrong configuration of sensor/Gage. So I ordered a temp sensor for my car. And still, with the right sensor mounted, no difference to my initial high-temp readings.

I know that a touch on the oil lines will ultimately be subjective to individual interpretations, but I'm pretty sure it's way hot, as my readings suggest. That said, I need to check my subjective opinion with a thermometer, to verify this.

To be continued...

[jimbauman]

I've never disassembled one of those thermostats, but I'd like to. If you remove the internal working parts, does that allow free flow of oil at all temps through the external cooler? If the answer is yes, you could run the car in that mode and see what the temperature gauge reads.

JB

[Walt Fricke]

Failure mode, for both the thermostat in the engine, and the external one, is closed. Which means oil doesn't go to the cooler - either of them, depending on which thermostat.

The operating part - the capsule which encloses the wax - is the same for each one. However, the external thermostat also has a pressure relief valve included in it. The large round "nut" is for the thermostat part, the smaller one for the pressure relief.

In addition, at least as to the external thermostat, it is designed to allow cold oil to pass up to the front of the car, and back. I think it does this by being basically open in each direction: to the cooler, and also back to the oil tank. When the oil is cool, it will preferentially flow back to the tank, as the line resistance is much lower in that direction. Because it is a lot shorter.

That way, when the thermostat closes off the more direct path back to the tank, the pressure doesn't go way up trying to push sludgy cold oil all the way through the long lines to the front, through a cooler, and all the way back.

I think the same thing happens with the thermostat on the engine which directs oil through the engine mounted cooler or not. Though I am not entirely sure of this.

So, no - removing the thermostat internals means as little cooling as possible, I think.

[Walt Fricke]

Otto

If someone doesn't take pity on you, use the search function for "marking oil temperature gauge" or some like terms. Plenty of folks have figured out how to assign temperatures to gauges without the markings, and have discussed how to do this. In this discussion someone mentioned peeking at the rim of the inner gauge plate, where there are small markings. But you need to know what those stand for.

One way to solve this all is to purchase a gauge with the markings.

Gauges and senders have to be matched, but I deduce your car was a 3.0, so a '78-83 SC?
The senders were the same from '77 through '89 (in the US, anyway). While the combined gauge changed some in that period, that was because of changes on the oil pressure side (specifically, one was the switch from a 10 bar gauge and sensor to the 5 bar setup).

My experience has been that the gauges are pretty long lived, the sensors less so (though my oil temp sensors have been stable over 25 years - it is the oil pressure gauge which has moving parts inside and thus fails sooner).

Like you, I wonder why an external thermostat which had been working faithfully for many years would pack up and quit just because you replaced the engine. As to the one on the engine, you might swap back in the one from your 3.0 (if you still have that engine).

But first, do the feel test on the engine oil cooler. You can get a hand on enough of the bottom of the fins to get an idea if it is hot or not.

[ossiblue]

IMO, you have one, possibly two, failed thermostats. Regardless of the on-engine thermostat failure (assuming it may be in failure mode), if the external thermostat is working you will feel hot lines running to the cooler and this will not be subjective--the line to the cooler (inside line) will be extremely hot to the touch, especially if the temps you report are accurate.

Burgermeister posted his observations on the plunger and there's a possible clue. JB posted a test--try a drive without the internals--to see if the lines will heat, and they will if there is no obstruction within them or the cooler itself. (You do have a pressure relief valve on the external thermostat but you may wish to run the engine a bit before removing the internals to insure you don't blow out the cooler.)

[DW SD]

I bought a brand-new factory external thermostat for my 3.6 conversion. I also bought an instrument grade digital thermometer that is about 12" long. I can drop it into the oil tank and accurately measure oil tank temps. Though they are not exactly the same as temps in the engine, they correllate.

Further, I calibrated my on-engine, factory oil temp sender and gauge by using boiling water and it is accurate. My car has two front oil coolers. In most conditions, the car runs right at 210 F, which I'd call 8:30 on the gauge (my gauge has numerical temperature markings. I was concerned, initially, as others seem to have thermostats which open at a lower temp as cited by Walt F. In checking with Chuck from Elephant Racing, who sold me the lines and thermostat, that things were indeed working normally. I've seen as hot as about 220F, last weekend on track with about 78F to 80F ambient. What this data says to me, is the thermostat opens at 210, where I have reserve cooling capacity in most conditions from the two coolers. Eventually, the thermostat would pipe all of the hot oil to the coolers and temps will creep up when cooling capacity (heat transfer from the coolers) is maxed out. Remember, temperature differential drives heat transfer.

I paid about $40 for the digital thermometer. It might be worth the investment for you. Boiling water should be free. I used some extra wires with alligator clips to extend the temp sender out of the car so as to drop into a pot of boiling water. Keep in mind, you have to ground the body of the sender, where the ground usually comes from being threaded into the engine case.

Doug

[burgermeister]

Without the regulator the oil will not go to the front cooler.
There really are only 3 failure modes for the external oil cooler.
1 - the cooler / lines are plugged up
2 - the pressure relief piston is stuck open for some reason
3 - the regulator is not functioning

250 degF oil ought to make water sizzle when it hits the lines, BTW ...

[boyt911sc]

Originally Posted by otto in norway

Hi there everybody!

Been a while since my last post here now.

This time i have a question about the external oil thermostat.

It seems like my thermostat does not open. I have cold pipes going to the front oil cooler, and really warm pipes on the "inside". (Pipes going to oil tank and engine pipe.) The temperature reading on the instument in the front of the car goes to about almost "10 o'clock". Also, I have replaced the temperature sender, because I suspected that first. So I know I have the right reading. The thermostat used to open at below "9 o'clock".

Look to this drawing for reference:



The thing is:
I have already opened the thermostat. (which is only two years old)

I checked for sliding resistance for the piston. The piston fell out when i tipped the housing over, so I guess that's fine.
When I tested the actuator inside the slider piston, by putting teh piston in boiling water, the actuator came out when the water was barely boiling. But, when I took it out of the boiling water, and pushed on the actuator with my finger, (wearing gloves), it felt quite easy to push in again. At the time, I just thought "It probably gets cold really fast, making it retract again".

So I assembled everything, and went for a test ride. The dial in the dash was at almost "ten o'clock" after ten minutes of driving. And the pipes going to the front oil cooler was still cold. In other words: No change to what I have seen before I checked the thermostat.

Any Ideas guys?
Is the actuator really supposed to be easy to push in after it has opened?
How likely is a faulty bi-metal actuator after only two years?

Otto,

You have to test the auxiliary thermostat (assembled) in boiling water. Your above test did not show if the slide valve actually opened or not. With the spring acting on the valve, the auxiliary thermostat only come into play when the oil temperature gets to around 180°F plus. Some reference manual says 186°F.

This is how the auxiliary thermostat operates:
1). Warm engine oil is delivered to the auxiliary thermostat. It does two things. Oil under pressure goes to the tank and to the cooler. Since the auxiliary thermostat does not into play until 180°F, warm oil is continually circulated back to the oil tank.
2). The line to the cooler from the thermostat is permanently OPEN (fixed). The oil fills the line to the cooler, the cooler is filled, and the return line from the cooler is also filled. And the oil (under 180°F) stops here. The return line still closed at this point. All the oil is continously circulated back to the tank.
3). Once the warm/hot oil reaches the operating temperature, the slide valve comes into action. As the opening to the oil tank closes, the return line from the cooler also opens. The cross-sectional area of the opening and closing remains the same or constant to prevent pressure build-up.
4).Valve opening examples:
From engine to oil tank: 90%-------75%-------50%-------60%............
From cooler to oil tank: 10%-------25%-------50%-------40%............
At any given temperature, the total cross-sectional areas or valve opening is maintained the same by designed.
5). Lastly, there is no 'wax' like device anywhere in a 911 auxiliary thermostat as previously mentioned. Photo of a dismantled auxiliary thermostat shown below. The temperature (thermostat) valve on the left side and the pressure relief valve on the right of the thermostat body.
6). The pressure relief valve works like most common pressure valve using a spring loaded valve to release excess pressure build up.



I have a feeling that your auxiliary thermostat's valve does not work based from your test description. Keep us posted.

Tony

[uwanna]

Originally Posted by boyt911sc

Otto,

5). Lastly, there is no 'wax' like device anywhere in a 911 auxiliary thermostat as previously mentioned. Photo of a dismantled auxiliary thermostat shown below. The temperature (thermostat) valve on the left side and the pressure relief valve on the right of the thermostat body.




Tony

Walt Frike is correct about the wax in the thermostat. The actual thermostat valve on the left side of your picture has a housing within it filled with a special wax that liquifies when heated and expands, exerting pressure against the spring tension and opening a poppet valve.

Thermostat design has been virtually the same for nearly a century, and its function is simple. The spring keeps the poppet valve closed, and a wax-filled actuator opens it when things get hot. As the oil in the housing reaches operating temperature, the wax inside the actuator expands, pushing the poppet valve open against the spring pressure, which determines the opening temperature. The stiffer the spring, the higher the opening temperature.

Grant

[boyt911sc]

Grant,

Thanks for the information. And I've sent a PM to Walt asking for some clarification about the 'wax' like device too. I was curious how these auxiliary thermostat work and have dis-assembled a few of them to investigate and study their function.

Walt,

Please accept my apology for contradicting your statement. I have not seen the wax-like material in the auxiliary thermostat during my quests and would dissect the valve next time I get the chance.

Tony

[uwanna]

Originally Posted by boyt911sc

Grant,

Thanks for the information. And I've sent a PM to Walt asking for some clarification about the 'wax' like device too. I was curious how these auxiliary thermostat work and have dis-assembled a few of them to investigate and study their function.

Walt,

Please accept my apology for contradicting your statement. I have not seen the wax-like material in the auxiliary thermostat during my quests and would dissect the valve next time I get the chance.

Tony

Tony,
If you ever have an old cooling system thermostat from a water cooled car, cut it open and you will see how this "wax thermostat" idea works. You could place the thermostat valve in your picture into a pan of water on a stove and slowly heat it up with a thermometer in the water and watch it open when it gets to the preset temp.
Grant

[dad911]

When you replaced the sender, did you use the one to match your gauge? (not the engine)

You could try placing the sender in boiling water to see if it is accurate.

[Joeaksa]

Originally Posted by Walt Fricke

Failure mode, for both the thermostat in the engine, and the external one, is closed. Which means oil doesn't go to the cooler - either of them, depending on which thermostat.

Yes and no.

You do NOT want the valve to fail open and allow cold thick oil to go to the oil coolers when the engine is first started or until it warms up.

I work with airplanes and its not unusual to have the same sort of valve on old piston airplanes fail and when the engine speed is increased it blows the oil coolers almost everytime.

The valve keeps the oil in the "engine side" of the system until it warms up, then the valve opens up to let the thinner, warmer oil into the "cooler side" of the system. This protects in several ways.

Joe A