Thermostat housing O-ring

[SoloTSi97]

Well, it seems that my thermostat housing wasn't the problem after all! I decided to double check everything I could think of while I had it apart again. Turns out, the coolant temp sensor under the intake manifold (next to the oil filter housing) wasn't reading properly. At room temperature (~70F), it was reading 4500 ohms. From what I'd read online, it should have been around 2100. I grabbed a new sensor from my local parts store and indeed it read 2100 ohms at the same temperature.

It's all back together now and the temperature gauge came right up to dead center for the first time in years! I had replaced this sensor before so had checked it off the list of possible causes. I guess I got a defective one. I'll probably get it replaced at FCP (where I bought it) so I have a spare.

I'm still on the lookout for a spare tstat housing, though, just in case!

[SoloTSi97]

Well, it seems that my thermostat housing wasn't the problem after all! I decided to double check everything I could think of while I had it apart again. Turns out, the coolant temp sensor under the intake manifold (next to the oil filter housing) wasn't reading properly. At room temperature (~70F), it was reading 4500 ohms. From what I'd read online, it should have been around 2100. I grabbed a new sensor from my local parts store and indeed it read 2100 ohms at the same temperature.

It's all back together now and the temperature gauge came right up to dead center for the first time in years! I had replaced this sensor before so had checked it off the list of possible causes. I guess I got a defective one. I'll probably get it replaced at FCP (where I bought it) so I have a spare.

I'm still on the lookout for a spare tstat housing, though, just in case!

Aaaand I spoke too soon. 🙃

The temperature gauge is working now, which is a nice change. But, after a few days the temperature plausibility code came back. So, I think I'm back where I started ... hunting for a thermostat housing.

[332]

I'm trying to understand the problem, is your car overheating? Is it not getting up to temp? You have a fault code, but the car drives wonderfully?

[SoloTSi97]

I'm trying to understand the problem, is your car overheating? Is it not getting up to temp? You have a fault code, but the car drives wonderfully?

tl;dr: It's now driving fine but I'm getting a fault code due to engine temp plausibility.

For a long time, the temp gauge never came up past the bottom dot (1/4 mark) and I frequently had a SES light due to engine temp plausibility. I had already replaced the tstat and both temp sensors (lower rad hose and behind the tstat housing) as an attempted fix but still had the same symptom. After reading about this tstat housing seal that can apparently stop sealing, I figured that was the cause and got busy with other things. A few years went by. Lol

Since some supposedly new tstat housings popped up recently on eBay, I ordered one along with a new tstat, water pump, sensors, hoses, etc, and figured I'd just do a cooling system refresh since I'd never done it. The tstat housing ended up falling through but I replaced everything else.

Now, the temp gauge is working! It comes up to the middle and moves around between 1/4 & 3/4 like it should. But, I'm still getting the SES light for the temp plausibility code. So, it's better... but not fixed.