Does this trans thermostat need to be replaced?

I'm tracking down a leak in my daughter's cooling system. I replaced the radiator drain plug, which helped a lot, but there's still a small leak. I couldn't find any evidence of leaks around hose connectors, so I suspected the radiator itself, and just got done removing it. But as I was yanking on the expansion tank, I cracked the upper lip of the transmission thermostat:



I know conventional wisdom says to always replace any part when in doubt, and I believe this is the original thermostat (120K miles on the car), so I'm sure the overwhelmingly deafening response to my question will be that I should replace it, and I get that. But as far as the actual functionality of the thermostat, do the cracks in the areas shown in the picture really impact its performance, and/or are they likely to be the source of a leak, or is the damage largely cosmetic? The reason I ask is that the radiator doesn't appear to be leaking, and if a pressure test tomorrow could confirm that, she could be back on the road tomorrow. If I have to order a new thermostat, that keeps the car off the road several days. Thanks.

Edit: Whoa - not sure how I got the Andy Warhol effect to my photo! But hopefully the damage is clear (hard to miss!).

Trans fluid therm always breaks when you attempt to remove. Fragile part.
Replace always.

Looks like cracks do not affect operation. But I would not draw encouragement from that.

I removed it once before (two years ago) without breaking it, so I was pretty bummed I cracked part of it this time. Is it hard to get out of the piece it sits in? Seems to be stuck pretty tight.

I've got a manual, so never did the job. Only reporting that others always break it.


And new rads are under $150 complete! If doing ET and thermostat. How are your main hoses?


www.furiousmethod.com

Originally Posted by Variocam

I'm tracking down a leak in my daughter's cooling system. I replaced the radiator drain plug, which helped a lot, but there's still a small leak. I couldn't find any evidence of leaks around hose connectors, so I suspected the radiator itself, and just got done removing it. But as I was yanking on the expansion tank, I cracked the upper lip of the transmission thermostat:

Attachment 365708

I know conventional wisdom says to always replace any part when in doubt, and I believe this is the original thermostat (120K miles on the car), so I'm sure the overwhelmingly deafening response to my question will be that I should replace it, and I get that. But as far as the actual functionality of the thermostat, do the cracks in the areas shown in the picture really impact its performance, and/or are they likely to be the source of a leak, or is the damage largely cosmetic? The reason I ask is that the radiator doesn't appear to be leaking, and if a pressure test tomorrow could confirm that, she could be back on the road tomorrow. If I have to order a new thermostat, that keeps the car off the road several days. Thanks.

Edit: Whoa - not sure how I got the Andy Warhol effect to my photo! But hopefully the damage is clear (hard to miss!).

My money says there is a hairline crack in the ET. Look closely around the 1.00" cooling port about 6 inches up from the bottom of the ET- notorious for a hairline leak- especially on the old part number- still on sale at many sites, but now obsolete. Do not buy part number 17137787039 as it was notorious for cracking prematurely. Some sites still take you to this bad part number when you insert the new, redesigned part number...17117573781...trying to dump their old stock. Pay attention to make sure it is the new part number.

I think when you install a new Tranny T-Stat with your new ET the leak will stop.

So, if your rad checks good, and even if it has a leak, I hope you are planning to change the ET with the latest part number and a new T-stat so you do not overheat your transmission.

When I replaced the ET in July of 2010 (right after we bought the car), I ordered and received part number 17117573781E46 from OEMBimmerparts. I took a good look at it with a flashlight around the 1" cooling pot (along with the rest of the tank), and can't find a trace of a hairline crack. I'll have the radiator pressure tested tomorrow, and if it checks out OK, I think I'll button everything up as is and keep an eye on the coolant level. Replacing the radiator drain plug had a big impact on the coolant leak, so I'm wondering if what appeared to be fresh coolant leaking on the ground was in fact leftover coolant still sitting in the bottom of the drip pan sloshing around and continuing to dribble on the ground.

I had the radiator leak checked this morning, and sure enough, it's leaking, right in the area where I'm seeing coolant accumulate. The guy in the shop said it isn't repairable (I'll go with his recommendation, since I don't know enough about radiators to question him, but it does strike me that radiators are a little like race horses - the slightest little problem, and it's off the the glue factory), so I've got a new one on order.