I've been checking the coolant temp trying to find out why my heater isn't producing even warm air. After driving 25 minutes(10 min at 45-50mph, 15 mins up a canyon road), the coolant temperature (at the radiator filler mouth) is around 120-130 degrees F. The thermostat is a new 180 deg one, the temperature gauge in the dash reads at about 2/5th and rarely gets up to 1/2 gauge.

I'd like some opinions about this, it doesn't seem right that the engine would be running this cool. That may or may not be the heater problem, but it's a good place to start. A year ago when the temp gauge ran at 1/2 gauge normally, the heater would put out a little warm air , but not very impressive.

John
1984 22R long bed, 5 speed.

Did you actually test the new thermostat prior to installing it? I always do that in a pot of hot water on the stove. Use a candy thermometer to see at what temp it starts to open and when it fully opens. See if that matches the stamped number. I have on more than one occasion tossed a "new" t-stat that just did not work as it should.

Do you think that if the thermostat was defective, opening at 120 deg, instead of 180 deg, would that keep my engine from warming up...even after driving 25 minutes?

I didn't test the thermostat, but I have thought a couple of times that the coolant was flowing when the thermometer was showing 130 deg. It's hard to tell, it might just have been the vibration from the engine running.

I could take the thermostat out and test it, but I need to know first if a bad one(opening too soon) would make that much of a difference.

Does anyone know how hot the coolant has to be to make the heater work properly.

Yes it can, my 3.0 was always running cool and crappy because the T-stat was bad and not closeing all the way.

Try this,

With a cold engine, take the rad cap off and adjust the coolant level to just cover the radiator core holes by appx. 1/2". ( you dont want it full because when your engine heats the level can come up and spill)

With a thermometer in the filler neck and in contact with the coolant, start engine and pay attention to temp. When thermostat is closed , you will have very little/no movement in the coolant as viewed through the neck. As the engine reaches a temp where the thermostat opens,(note this temp on your thermometer), you will see rapid coolant movement from one side of the rad to the other until it cools enough to close the thermostat.

If the thermostat is stuck open you will have a lot of fluid movement all the time.

Don't burn you self , use proper saftey measures to make sure you don't get splashed in the face with hot coolant.

Well, since the engine coolant runs at the approx. the temperature of the thermostat, yes, the t-stat does affect the coolant temperature. Why?
- http://auto.howstuffworks.com/cooling-system8.htm

And for heater output, check that the cable to the heater valve on the firewall is attached and can open the valve fully. How to tell? Look at it and pull off the hose and look inside to see if it opens fully and is not clogged internally. Then try back flushing the heater core. Back flush? That means flow (or FLUSH) water BACKwards through the heater core. How to do that? A garden hose nozzle shoved into the return line with the inlet line disconnected works wonders. Which line is which? Inlet is the one that has the heater valve on it.

>>>*One reason an engine won't heat up properly can be related to tuning. Very late ignition timing, or an overly rich fuel mixture can also be the cause.

An engine should reach normal operating temperature in time, even without a thermostat, it is just much slower.

Outside air temperature has quite an effect, too. ...*EB

When it was very cold (10-15 degrees F), I would have to put cardboard in front of my radiator to get the engine to warm enough so the heater would blow warm air.

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Really? Considering the over-capacity of a cooling system that can keep an engine from overheating in 100+ degrees ambient temps, it seems likely that without a t-stat limiting the cooling, the engine could not produce enough heat at sub-freezing ambient temps to ever warm up. Am I wrong?

Dave

>>>*Engines will reach normal operating temperature typically in most systems without the use of a thermostat. The real purpose of the thermostat is to assure quick warmup, this is for fuel efficiency and also emissions, plus the engine performs better at proper operating temperatures. That is all it does. Higher outside air temps are usually within a fairly narrow range, 100? is only 30? above room temperature, the system can handle that normally.

In very cold outside air temps the thermostat can close periodically as very cold air can draw a lot of heat out of the radiator. But normally once an engine reaches full temp the thermostat will never close.

All the thermostat does is keep the engine above a preset minimum, but typically the temp will seldom drop that low. If the thermostat is rated too high it could, but that isn't a good situation as there are areas in the block that are way over the boiling point.....*EB