As I'm sure you've seen in my other threads, I rebuilt my cooling system a couple of weeks ago. Replaced LIM gaskets, plenum, radiator, water pump, repaired heater hoses, elbow o-ring, you get the picture. Afterwards, I had al the symptoms of a stuck open thermostat. I should mention I did break the clip on the coolant temperature sensor, but it'* a very snug fit and seems to be working properly. I plan on replacing it, but I don't think it'* the cause of these problems. So if the car were moving, temperatures would not increase. If I hit some traffic, the temperature would go up as expected if the thermostat is stuck open. So I went and bought a new one, drained just a bit of coolant and installed the new one. I did not use the gasket because the intake part of the thermostat housing has some minor damage so the gaskets have always seemed to leak on me. So I just used some thermostat/water pump gasket maker and let it sit overnight. Start it up the next day with the rad cap off, temperatures slowly increase as it should. Hits 195, the coolant level in the radiator drops since the thermostat opens and it fills the upper rad hose from where I had drained it to install the stat. So I'm happy, let it run a few more minutes to make sure temperatures don't continue to rise, all is well. So I put a NEW radiator cap on since the other was the original from what I could tell, and take it out for drive the next day. All the symptoms of a stuck open thermostat again!

Did I get a defect or is there something else that could be causing this? Is not using the gasket somehow making this thing get stuck open? Like maybe a small lip of silicon formed inside the opening when it was compressed and the thermostat is stuck on it? I really don't think it is the temp sensor connection since it cycled right when it read 195 when I was testing it.

A stuck open thermostat will not increase temp when you hit traffic as a symptom.

The symptom would be taking forever to get up to temp from a cool/cold start up.

Sounds to me like you have a air bubble in the engine. Pull off the t stat housing and fill the LIM through there if it'* low. Air gives a much cooler temp reading to the sensor than water.

Plus..you have two senders on your 94. One under the TB and one behind it IIRC.

Also make sure your radiator is clean and not plugged up. Do your fans turn on?

BillBoost,

I was under the impression the thermostat was stuck open because if I'm moving the coolant would not heat up because it is constantly flowing through the radiator, and the breeze from the car moving at high speed keeps it cool. When I'm in traffic or at a light, it would heat up because that air is no longer flowing over the radiator. Is that accurate? Can you further explain what you were saying?

The coolant was all the way up to the thermostat housing from the LIM when I pulled off the housing. I used a turkey baster to suck some out it was so high I had let the car heat up without the rad cap on the first time after install. Shouldn't this have allowed any air pockets to come out once the the thermostat opened?

Dan, not sure about the fans I'll have to check, but the radiator is brand spanking new, so I sure hope it'* not clogged.

A stuck open thermostat will not over heat. Coolant is always flowing. Over heating comes from lack of flow. either coolant, or air.

Right, that is what I was saying. It heats up slightly when the airflow over the radiator is reduced, not overheat.

When driving at highway speeds temps got up to around 120-130. With the old thermostat the needle would be all the way to the left when moving. Temperatures do increase slightly when moving slow / stopped

Ok..your description at first sounded backwards or sideways.

Yeah, you'll warm up a little more with a stuck open t stat. If fans aren't running then you could overheat sitting still even with an open t stat.

Which gasket didn't you put in. I'm more of a Series 2 guy. The S2 has a rubber gasket around it and then there'* a paper one designated to go on the housing to LIM. If you don't have the rubber one (if applicable) then that would cause hte issue you are seeing.

I've seen both, the one I have sitting at home now is the rubber one. It'* so thin though I didn't think it would make a difference. What'* the reason behind it?

Sealing water from passing by the closed thermostat and causing it to act like it'* open when it shouldn't be.

Ah crap, at least it'* an easy solution. Can I use some of the gasket maker with that or not recommended? Last time I tried that gasket I had some small leaks.