internal oil thermostat repair

[burgermeister]

The internal oil thermostat can be repaired for a lot less than the cost of a new one.

They supposedly don't go bad all that often, but mine certainly did go bad. My external one was not opening all the way either a few years ago, so I've got a 100% failure rate myself...

The plunger of the internal thermostat is the same as the plunger on the external thermostat, which can be bought for $50 rather than the $160 a new internal tstat costs.

First, use a screwdriver to pry the sheetmetal cap off the end of the thermostat. Out will come a spring (appears identical to the external tstat one) and a piston / plunger assembly. The pistons are different for the 2 thermostats - the oil "windows" are a few mm off - so label them somehow so they don't get confused.

The plunger assembly is a very light press fit in the piston - a couple of sockets and a bench vise remove it with zero effort. Do the same with the external thermostat part. Now you can press the good plunger assembly into the internal tstat piston using a couple of appropriate sockets. Bend the sheetmetal cap straight again, reassemble the piston / plunger & spring, and pop the cap back on. Takes about 15 minutes if you take your time.

Drop it in a pot of boiling water to make sure it opens.

Unfortunately I've already bought a new internal one, so I don't get to benefit from my messing around while waiting for rocker arms & heads ...

[Sboxin]

Thanks for the DIY instructions and photo.

If you don't mind...where did you get the repair kit, part number and cost ?

TIA,

Regards,

[burgermeister]

Here on Pelican 930-107-155-00-M322

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=930-107-155-00-M322&catalog_description=Regulator%20Piston%20for%20Sid e%20of%20External%20Thermostat%2C%20911%2F911%20Tu rbo%20%281974-89%29

(This is the repair kit for the external thermostat.)

[KTL]

Nice find Frank! That's another bit of data i'll add to the Porsche brain bank.

Certain Behr products always seem to be a bit unreliable. Between the BMW and Porsche stuff i've seen, radiators (coolant) and thermostats seem to be their pesky parts. Their oil coolers are pretty darn good.

As an aside to this internal oil t-stat discussion, I can add some comparision/diagnosis data to the t-stat operation for people trying to determine how their t-stat is working. I chose to remove the internal t-stat and replace with a blank piece like the 964, 993 and old RSR race cars had. What this does is send oil straight to the oil cooler location. My oil cooler was replaced with a 993 filter console and Canton racing filter.

What I can tell you is that when the t-stat is open/bypassed, the engine warms up very quickly. However when the oil cooler remains in place, that cooler is going to slow down the warmup. That engine oil cooler is VERY good at what it does!! W/out the cooler, I can fire up my car, drive a couple hundred yards down the paddock to pre-grid and the temp is already coming up. I shut the engine off until we get the 1 min. call to release the grid. By the time I get moving again, the temp gauge is almost up to 180.

[burgermeister]

Interesting. I can look forward (hopefully!) to a nice cool engine now! Of course it's really cool right now with its heads in Ann Arbor and its rocker arms in Oregon ....

The external (radiator style) cooler must also be pretty good. My internal thermostat was at best 1/4 open at 212 degF. 3/4 of the "windows" were still on the bypass side. But the engine stayed at a nice 220 deg even on the hottest days, only venturing up to 240 after 15 - 20 minutes of really beating on it at Grattan on a 90 deg day. I do have a manually switched 8" fan and some guiding sheetmetal from the (open) fog light location to the fender cooler.

[Hebster52]

Bringing up an old thread. Is it possible to repair an early style internal thermostat too? (pre-71)

How can I tell if mine works or not. Should one or both window open or close while heated in a boiling water?
Anyhow, nothing appears to visibly move on mine.....

Edit. Nevermind.. I appearantly didn't cook it long enough...

[burgermeister]

Hebster,

I do not know. All I can suggest is to take it out & see. If it is working properly, the "cold" window should be gone & the "hot" window should be fully open in boiling water.

As a follow up, the failure mode appears to be higher full-open temperatures. The new thermostat kept running temps around 220 longer, but really beating on it on track still resulted in the same peak temperatures (about 240 as measured by the gage, and 230 as measured by infrared thermometer at the oil return pipe). So the old thermostat must have gone full open also, just at a higher temperature than the new one.

[Walt Fricke]

Hebster

Burgomeister has solved the question of how to disassemble the newer thermostats.

The older ones - which have an adjusting scrrew sticking out the top - may unscrew from the top, because they have flats machined on the topmost part which should serve to hold that part while you use something else to turn the cylindrical lower part.

[Bear911]

Just a small addition to this helpful thread in case anyone has the same question as me....

I followed Burgermeister's recommendation and bought the $40 external thermostat repair kit. The new piston looked so new and shiny (and better quality!) I couldn't help wonder if it is really necessary to push out the new plunger and insert it into the old piston. Afterall, the openings are the same size, only about 1.5mm lower on the old piston. If the plunger pushes down far enough it would make no difference. Wrong assumption! The new external thermostat piston in the old internal thermostat housing left a 1mm gap in the top window during the boil test. I pushed out the plunger and placed it in the old piston. The top window closed fully.

[mikedsilva]

reviving an old thread... I went to pull apart my tstat on my 74 911.. 2.7. I had a large spring clip holding the cap on top of the spring.
Getting it out was easy enough.

Getting it back in so far has proved very difficult... I might just have to buy the new tstat from our host.

[burgermeister]

I am assuming you've got an external snap-ring like clip (like what holds the CV joints on the axles) holding the cap on, as opposed to the cap being snap-fit on the thermostat like the one in my car? Hard to tell w/out a picture. But, snap ring pliers are almost a must for any snap ring. Or do you have something different?