Thermostat headaches

[supertremendous]

So 1992 Explorer XLT, never had an issue until yesterday. I live in saskatchewan so it gets damn cold here and driving down the highway yesterday (about 70mph) and suddenly my heater got very cold and my temp spiked into about the middle of the guage and the rpm went from about 2k to 2500 for about 5-10 seconds then the temp dropped and the heater warmed up again and this happens about every 2 minutes. So i guess im wondering if this could be a simple thermostat replacement or some sort of secret temp sensor somewhere giving a false reading.

 

[FR-425]

You need to put a winter front on it.

It's a truck, with an overkill cooling system.

Your thermostat will open and close and open and close.... if the engine is running to cold.

It's not broke.

A sheet of cardboard will do in a pinch.

 

[Anime]

Probably the thermostat.

When some thermostats fail, especially the OE Motorcrafts, they can completely or partially close off the flow, and so the temp gauge needle usually goes to the right, the engine chugs, and sometimes you even get boiling coolant and the pressure pushes the boiling coolant out the plastic overflow reservoir. Worst case scenario, the engine completely overheats, the head gaskets blow, the heads warp, it leaks oil, you have a lot of engine damage that is going to cost quite a bit to fix.

Easiest fix is a standard replacement 195 degree Stat Superstat, or just a regular 195 degree Stant, before the thermostat completely fails.

That's not to say it couldn't be something else - a partially blocked cooling system from sludge due to mixing coolants, or other rust/corrosion/crud in there blocking the thermostat, but in general, the thermostat replacement is least expensive the way to go (along with new coolant/water) when you have temp issues.

You may also want to do a 70% coolant / 30% water mix instead of 50/50 for more protection in freezing temps, although just pouring in a gallon of coolant and filling the rest with distilled water for a 50/50 mix is the easy way of doing it and still gives pretty good protection down to really cold temps.

 

[natenkiki2004]

Good info Anime. I've been thinking in the back of my head about researching thermostats as I'll end up replacing mine as preventative maintenance when the LIM comes off. Always wondered about the 180 vs 195 degree unit. Figured OE was 195 and being in a cooler climate, having it heat up more before opening would be good.

 

[Anime]

The stock Motorcraft is a 190 degree, and the aftermarket Stants are 195 degree, but those aren't very precise, a Motorcraft may open at 192 degrees and a Stant may open at 193 degrees. A thermostat that was precise to the degree would cost quite a bit of money.

The 180 degree thermostats are generally a bad idea. Using them was a performance "trick" years ago to keep the coolant sensor in open loop and basicaly get more "power" by causing the fuel system to dump more fuel into a "cold" engine that never got up to operating temperature. However, when the engine never gets up to operating temperature, neither does the catalytic converter or the exhaust or a lot of other systems that are designed to operate at that ~190-195 temp. You basically wind up ruining the emissions systems and a lot of other sensors running the system so rich and cool.

Of course, using a 180 degree thermostat in really, really hot climates is completely different, since the engine still gets up to that 190-195 degree temp from the heat radiating off the pavement/rocks/ground and the hot, hot air going through the radiator. Along with a severe duty fan clutch and 10/11 blade fan, such tweaks will help keep an engine from overheating in 100+ degree temps.

 

[OneofMany]

Your heater got cold when coolant was absent from the heater core due to air in the system. Even if the thermostat stuck closed the heater core would still be supplied with hot coolant because the thermostat only opens the system to the radiator.
Better check your cooling system closely. A Winter front will help you only if you have problems getting to operating temperature while driving. But you know this since you are from the land of Santa and I live in Georgia.

 

[OneofMany]

Here's a write up on LIM:
http://www.explorerforum.com/forums/showthread.php?t=384221&highlight=LIM