T-stat - does it come apart?

[JeffW]

This t-stat on my car has a slot on both of the covers to the guts. How does that thing come off? It looks Like I'm going to damage the caps when I take them off because the only way I can see to do it is with a large pair of wise-grips attached to it and a screw driver turning while you wrench on it. Is there an easier way or a special tool?

thanks,
Jeff

[Wayne 962]

Yup, the whole thing comes apart. There are some diagrams here:

http://www.pelicanparts.com/catalog/shopcart/911M/por_911M_oilsys_main.htm

-Wayne

[Jim Sims]

Mount the thermostat housing in bench vise with soft jaws. Make a tool out of flat steel bar stock that fully fills the "screwdriver" slot in the covers; make the bar longer so it extends out the side to form a lever or handle. Due to the aluminum alloy and location on the car some of these housings/covers corrode together and are not rebuildable but usually the problem are the threads that the oil lines attach to. If you get it apart be sure and coat the threads (but not the sealing surfaces) with some type of never seize compound when you reassemble. Jim

[JeffW]

I was going to try and do it with it still in the car. I guess I need to pull it out.

[Jim Sims]

If the oil line to thermostat threads lack never seize compound then there is a chance the aluminum threads of the thermostat housing will strip when you remove the oil lines. There is a fitting that can be used to some times replace/repair the thermostat housing threads if this happens. I read about one shop that always included a new thermostat housing in the repair estimate whenever external thermostat repairs were required as they were often seized at the threads and many times couldn't be saved. Do a search of the archives as there are hints about freeing oil line fittings. Good luck, Jim

[pkfrdh]

I just got done removing my t-stat from the car to verify if it was working or not. It seemed it was never opening up since the forward oil lines were never hot. I was worried so I decided to investigate it. Removing the lines are a potential hazzard. Let pentrating oil soak the threads over a couple of days to minimize the chance of stripping the threads. Each of the four lines to the t-stat can be a problem. Soak them several times a day over two days. Drain the oil in the motor and oil tank...tilt the car w/ the front higher than the rear. The proper wrench will also help minimize stripping as the special wrench has more contacts similar to a brake line wrench. I was lucky...all four of mine came loose with only using a high quality crescent wrench. It had been there since 1976 when my '77 911 was put together. After I took it out of the wheel well, I plugged the oil lines to stop the incessant dripping that goes on. The oil in the forward lines was identical to the oil in the motor indicating that at some point the oil had been circulating since the last oil change.

I tried to take the caps off of the t-stat, but they would not budge! Non hardened steel in the alum. grooves would bend and hardened steel was starting to destroy the caps. So I gave up on opening up the housing to check the spec.s of the two springs that control the t-stat. I was able to verify it opens up at temperature though. I connected hoses to each of the four outlets and submerged it in boiling water. The valves opened up and I was able to verify this when I could could get compressed air to pass from one compartment to the other out the forward outlets. Make sure no water gets into the thermostat, though this is not espcially critical since there is plenty of oil coating the inside of the t-stat.

I then did the only other thing available to do maintenance to it...I repeatedly filled it w/ ATF and shook it like crazy for two days to get all the sediment out of it! After the fourth time putting in fresh ATF, it finally came out clear (red) clean ATF. ATF is good to use since it is an inexpensive high detergent oil that is light weight enough to do the job and not harm the spring. Don't use a solvent as it will remove oil that has penetrated the springs. Never use a solvent that strips the oil that has penetrated any steel part you are cleaning. Only clean with solvent that maintains the penetrated oil. Gasoline is the worst! It strips penetrated oil deep within steel. Stipped steel starts out very dry and abrasive. orrosion occurs immediately w/ stripped steel. Spring steel is very prone to damage when stripped!

After it was clean, I reinstalled it and found out it comes out easier than it goes in. You have to tighten the lines in a sequence since they block each other out as you install them. And the way you torque them down affects how it twists around and how the oil lines to it twist around. If you use antisieze on the alum. threads, make sure you torque the nuts down good. I noticed the nuts tend to resist torqueing w/ antisieze. You really have to have a good hold on the t-stat to torque the oil line nuts. They may loosen up easier w/antisieze.

This system could have been designed better if they would have designed it it to have only one chamber w/ only one spring loaded valve that would move pass two different sets of ports to allow oil to either circulate forward or be shunted just to the rear if the temp drops. This would be better in that only one valve is dependent on function instead of two. As it is, if one functions and the other malfunctions, you have a problem. Both have to function at the same time.

Good luck in your R&R.

JGL