External Thermostat questions

[sean m]

All,
It appears that my external thermostat in the right rear wheel well is not opening. I took the car out for an hour drive on Saturday. Got the temp up......in fact.....way up. Temp got to about 230. Took it home and felt the pipes from the thermostat to and from the trombone and both were cool.

From using the search it appears I need a new plunger for the thermostat. My questions are....
1. Is there anything else I should do when in there?
2. Is the plunger the only thing I need to replace?
3. Anything else while I've got the pipes off?

This is my first adventure in the external thermostat and I want to make sure I've got it all done right the first time.

Thanks

[fintstone]

Good luck.

Oil thermostat rebuild / set

[schumicat]

you don't need to take the pipes off, just the big round slotted cover on the side (I used a pipe wrench to grip the edges). PP sells the plunger you need, get a new sealing ring too.

[boyt911sc]

Sean,

You could replace the paraffin valve of your auxiliary thermostat but that does not guarantee you have a working thermostat until you tested and confirmed its operation. Many would tell you about horror stories about the removal of the auxiliary thermostat. My very first one was a disaster. So I decided to explore more about this and come to conclusion that the lack of experience, knowledge, and correct tools contribute to this myth.



To do this project efficiently, I prefer removing the complete unit (oil lines and thermostat) off the car. It is faster and convenient by all means using a large vise mounted on a work bench than having it mounted on the car. I have obtained several sets of oil lines and thermostats from people who have given up dismantling the unit.

It will give you a peace of mind and confidence if you know that your auxiliary thermostat is opening and closing at the correct temperature/s than just hoping it is a good one. What happens if it does not work at all even after a new 'plunger'? I could provide a clean and good looking thermostat if anyone willing to test it on his engine for demonstration. No this will not happen.

Tony

[motogman]

SO this is new to me...

Can someone give a brief description of where this thermostate is located, it's purpose and how it works?

Most appreciated...

[fintstone]

Takes me about 10 minutes to change the plunger and spring without removing the thermostadt or lines from the car...pretty efficient if you ask me and did not mangle my lines or thermosadt...no myth; but if you are not very mechanically inclined, or have ham-sized forearms..by all means, pull the entire system out...maybe do an engine drop or rebuild the tranny while you are in there.

[boyt911sc]

Originally Posted by motogman

SO this is new to me...

Can someone give a brief description of where this thermostate is located, it's purpose and how it works?

Most appreciated...

motogman,

The auxiliary thermostat is located in the passenger side rear wheel well. See picture below:



I'll try to describe how this auxiliary thermostat works and others could chime for additional info. At oil temp. well below 186°F (+/-) approx., the warm oil is directly circulated back to the main oil tank. The auxiliary thermostat does not come into play until the oil temp. reaches the 180°F plus range. The line @ thermostat to the auxiliary cooler (trombone, Carrera cooler, etc). is permanently OPEN so there is oil in the auxiliary cooler after the engine has started. It is the return line from the cooler that is opening/closing. The upper oil line (shown in the picture) is the oil line from the engine. The lower line is the return line from thermostat to the oil tank. The inner oil line going to the cooler is the supply line. The outside line going to the cooler is the return line.

As the oil temp. approaches the 180°F plus range, the slide valve inside the thermostat starts to move. The amount of oil going to the oil tank is reduced and diverted to the auxiliary cooler. The cross-sectional area of the valve (closing) going to the oil tank is kept equal to that of the front cooler to maintain constant flow at any given temperature. Example: If valve opening to oil tank is 100%, return valve opening from cooler would be ZERO. At 90%, the cooler return valve would be 10% and so on.

Tony

[fintstone]

Originally Posted by motogman

SO this is new to me...

Can someone give a brief description of where this thermostate is located, it's purpose and how it works?

Most appreciated...

Note that not all 911s have an external oil cooler...and, as such, would have no external thermostat. It was optional in the early-mid 70s...but became standard equip later.

[sean m]

Thanks Fintstone......the link shows what I need.

I was only going to remove the pipes to insure there was nothing clogging them. It sounds like more trouble to get the pipes off than its worth.

I'll get a new plunger from Wayne.

[fintstone]

Originally Posted by sean m

Thanks Fintstone......the link shows what I need.

I was only going to remove the pipes to insure there was nothing clogging them. It sounds like more trouble to get the pipes off than its worth.

I'll get a new plunger from Wayne.

Good luck. You may have to remove a couple of clamps/fasteners and drop the lines and thermostadt down a bit on the car...but don't disconnect the hard lines unless you absolutely have to. You wouldn't have a blockage unless the car has sat for years or you engine has grenaded.