Stuck thermostat

Hi Folks, Been having some temperature challenges lately with my 996, so I swapped in new radiators and an LN Engineering thermostat. Got it all back together tonight and it appears the thermostat is stuck closed. Ran it until the fans came on (101 indicated on the display) but the radiators aren't hot and the hose that comes off the thermostat is cool. Added about as much coolant back in as I drained out ( Airlift is a cool toy!), holds vacuum, had heat coming out in the cabin, and no leaks, so it seems everything is back in the right place. Before I pull it all apart again, any suggestions? I'm assuming the gasket is a single-use item, so I need another one before diving back in. Should I trust this thermostat insert? or assume it is bad in some way and get another one? Anyone run into issues with an LN insert in a Wahler housing? Thanks for your help.

Let it fully cool and run it again. U still may have a little air in the system?

So many questions I don't know where to start. What cooling challenges precipitated your work? Did you open the bale on top of the expansion tank? How many heating/cooling cycles have you gone through to lead you to the conclusion the thermostat is faulty? Did you install the LN thermostat the right way? Have you ever replaced the water/coolant pump? That is 101 degrees centigrade (C)? Are the fans both working on low and high speed?

@DBJoe996 -- The trigger was a reported oil pressure < 1bar from normal driving in hot weather, which I had only seen on the track before. As the weather got warmer I noticed the water temperature would climb even at moderate speed - ~50mph 4th gear no traffic- to the point where the fans would come on. My recollection was that didn't happen at lower speeds last year. Cleared out what little stuff was caught in front of the radiators and cleaned them with CRC coil cleaner. No difference. Since I could get the temperature to drop on the highway, I figured the aging radiators were operating at less than peak efficiency. Can't say what they look like inside, but even after cleaning with chemicals and low-pressure water there's still sand and crud stuck between the fins (winter, New England, it happens). So I ordered up a new pair of radiators. Cue the 'while you're in there' syndrome. While swimming in coolant I figured I'd swap in an LN thermostat. Just in case. Water pump and thermostat were replaced 2 years/12k miles back. 71C Wahler. And I put in one of those nice metal coolant hose connectors. Got it all back together last night. 4 gallons of coolant with the airlift, which is right about what came out when I allow for spillage. Bale open on the tank. Started it up and watched for leaks as the temperature display went past 70, 80, 90... (using the climate control readout -- not necessarily accurate, but consistent). Hit 101 and the fans came on, but the radiators were cold. Hoses to the radiators, cold Coolant in the tank was hot. Cabin heat was hot. The large hose that connects to the thermostat was cool relative to the others around it. That was a good place to stop for the night. Checked this morning, if I squeeze the lower radiator hose I hear bubbling in back, so it would appear the system is full of coolant. Apart from one top-off while it was heating up the level hasn't dropped. Only done the one cycle so far. Still up on the quickjack with the bumper off so I can check for leaks. Maybe I missed something on the install, but it looked like as long as the pin is in the hole, the 180 degree rotation of the 'ears' that latch it in would be the only chance of getting it wrong. The pin isn't quite the same between the Wahler part and the LN, thus the wondering about it playing well with an aftermarket housing vs. the official part. I will be back at it tonight now that things have cooled off. I'm assuming I need a new gasket if I pull it off again, so have to get a couple of those too. Thanks for the questions, sometimes walking back through it all brings up places where I may have gone awry.

Since you are basing all this on oil pressure, what type and weight of oil are you running? Is it fresh..less than 5,000 miles? The oil pressure sender is notorious for failing or not reading accurate, so have you replaced the oil pressure sender?

1500 miles/2 months on DT40 with a 2 year old sender. It isn't so much the absolute value as the difference from how it has behaved in the past that has me looking at it. edit -- Fans coming on in less than stop-and-go too.

I have heard of Wahler thermostats not opening correctly (there is a thread on here contrasting Wahler vs LN thermostats), but I have never heard of an LN thermostat failing. I thought the LN thermostat is certified by LN. I'm running out of ideas, but maybe 4 or 5 heating/cooling cycles would help. Do you have access to Durametric?

That's why I was upgrading to the LN . Wondering if it's just a tolerance thing making it stick, not like there's any parts to misbehave in there. I will hook up my durametric tonight to watch things heat up. Thank you for the ideas.

I believe the LN thermostat needs to be installed into the flange with a special tool. I'm not sure how easy or hard that is but perhaps something might be off there? I purchased my low-temp thermostat from FCP Euro and it came with a new flange all installed and ready to go. I've just installed it last week and no problems. Hope you figure it out!

Thermostats usually don't fail closed, they fail open as a fail-safe to not overheat. I've had new OEM porsche ones bad out of the box. I now boil them before install to confirm operation.

Reach out to LN, sure Charles or someone else there will respond promptly.

Well if you do ultimately remove the housing and thermostat, might be a good idea to put it in a pan of water on the stove and heat it up to observe how it opens.

@plpete84 From FCP it came with the housing? So not like the picture on their site? They are my preferred source but couldn't get it from them in time. I used a wrench to press the old one down to release and same for the new one. Maybe I twisted it. Putting it together I figured WCGW and didn't test it. Lesson learned.

Quotes source post: 18244678

Yes! It was a better price too - https://www.fcpeuro.com/products/por...er-99610601359 Plus you can't argue with the lifetime replacement part.

Ahhh, not the LN. Thus my confusion. I love lifetime replacement. It's a great way to recycle old fluids too. Like coolant. edit -- that's where I got the radiators and the coolant. But not the thermostat.

To close this out, I followed the advice of @Optionman1 and got in touch with LN. They were beyond great, sent me out a replacement plus the official tool in case the installation method was the issue. Assembled the new one (the tool does make it easier), tested it (learned THAT lesson!) and got it all back together without issue. Worked great. Cool morning highway temps when the thermostat is 'in control' are visibly lower on the analog display than with the 70C Wahler I had before. 200 miles in the heat it all behaved, though hot oil pressures are still lower than I would like to see that may be the gauge. (90F air, Climatronic reporting water at 95C, and Mr. Durametric reporting oil at 105-110C) Big thanks to the LN folks for the support and getting me back on the road!

Charles @ LN is the best. If only all businessmen were like him.