99 Ford Ranger 3.0

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DESCRIBE ISSUE....heat issue
I was driving in -30 degree weather when the vehicle's check gauge light came on. The temperature gauge needle was rising near the red line. I pulled over to let it cool down. Smelled anti-freeze in the cabin, could taste the sweetness on my lips. Once it cooled down, I drove it the rest of the way home and parked it. Steam was coming from the front of the vehicle, looked like it was on fire in that cold air. Let it cool down. Once I popped the hood, noticed that the coolant reservoir cap had popped open and it sprayed anti freeze all over the engine. I figured that it was a bad thermostat. I removed it and tested it in a pan of boiling water, it opened in the boiling water, and closed as it cooled down. Put the thermostat back in, filled it with coolant, burped the system, and drove it around until the engine reached normal operating temperature. I noticed that the temperature gauge would climb up to the middle, as it normally does when the engine heats up, and then drop down towards the cold on the temp gauge? Also, the heat would fluctuate from warm to cold when it did this? So I replaced the thermostat and gasket. Same result? Brought it to a local garage. They tested for head gasket leaks, none found. They said nothing wrong with the water pump. They replaced the thermostat and gasket again. Same result. They used a vacuum tool on the coolant system, said that it was good. I personally spoke to the auto tech and he told me that he thought that the heater core needed to be replaced. Talking about spending more than ole' trusty rusty is worth, lol! So I've been driving it around for a few days, the heat has gotten hotter, but it still fluctuates with the temperature gauge from hot to warm? Any ideas what to look at next?
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During those extreme conditions, super-cooled fluid from radiator might cause those conditions. Or, the thermostats that have been installed don't work like the old one. Like cheap and easy? Put some cardboard in front of radiator to keep the temperature fluctuations more moderate.
Thanx for the reply! I will try the cardboard trick when it gets that cold again.

I went to Napa to get the 1st thermostat, all they had was a 180, so I tried that. The repair shop put in a Motorcraft 195 thermostat.

I find it strange that the truck didn't have any problems last winter, and it got that cold on some days? The coolant system was flushed and replaced with 50/50 green coolant this past spring? There wasn't any signs of any problems, until THAT day?!

A buddy of mine, not an auto tech, told me that there are 2 sensors on my truck that are for the coolant. He said that 1 is a coolant temperature sensor, and the other is a sender that sends a signal to the temp gauge? He says that they rarely go bad, only if an engine overheats. Could one of those be causing the temp gauge & the heat to fluctuate?
A sensor connected to the computer would most likely cause problems with starting, stalling, bad gas mileage. A sensor connected to a gauge might cause the gauge to give inaccurate information. But, sensors will not cause fluctuation in heater output. If heater output goes up and down at the same time that the gauge goes up and down, the gauge is probably working OK.
The most common cause for heater output fluctuation is low coolant. Lots of variables to consider for a more general complaint of "my heater doesn't work as good as it should". The definition you have given of your problem is more specific (and unusual).


Hero Member
I've been wondering if the 50-50 antifreeze mixture was just a pinch off. Chart for 50-50 shows something like -35*F freeze point. If you were at -30*F and there was water left in the system before it was added... Where I'm going with this: Could the Radiator have frozen partially, limiting circulation and forcing the system to boiling? As Dan said, Cardboard would be enough to prevent that. Keep


Wrench. I help when I can
Well, -30f is close to what we get up here often. In our parts, that is -34c. So 50/50 solution is ideal. When I was working up north in the tundra, we had to go 70/30 for -55c temps.

So as JD wrote. Try to get some cooling strips from your local shop and test the coolant. Cheap. They can probably sell you one for a buck or two. That way, you can check acidity too at same time for freezing point.

After three or four stats, I would stop fussing with that as you are just intruding more and more air pockets in there and having to continually burp the system. Heads have been tested ok. T-stat is definitely ok after 4 or so.

I realize the coolant was replaced last spring, but check it anyway. As for the cardboard trick, sure why not. But I do know they sell front grill covers with a flap for these trucks just for conditions like this. We use these on ALOT/ A TON of trucks up here. Very common to see them. They should look like this.
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Wrench. I help when I can
That way, if you feel you are getting too warm, just open a flap or two to get some airflow. Or, just make your own out of an old vinyl sheet of some sorts. But you would need to be a seamstress and buy some velcro or buttons and blabla. Cardboard doesn't last too long up here. It just ends up disintegrating and getting in the condenser and rad fins and a heck of a mess to clean up when shyte hits the fans due to that. Yes, the pun was intended.

So if you do go the card board way, change that out very often. ;)

If you like old rusty or whatever you nicknamed it, the local Walmart probably has something that looks like the above picture. Just type in winter front grill cover on google, bing, or yahoo or fart a joke research engine type thingy that is kinda like I am feeling lucky today sort of thing. Tons of them on line.

This is what we call a big rig in a tuxedo.


Wrench. I help when I can
If your heater core was clogged, you wouldn't be getting any heat period.

If you are getting fluctuating heat, cap for some reason was open, engine overheated, that is just air in the system. Cap was probably put on wrong at some point. A regular car/truck OEM cap does not just pop open for any reason. Unless you have one of those stant pop lock caps that some ppl enjoy putting on their pride and joys. Usually see that in southern trucks and such. I am NOT a fan. Any idiot can pop that safety release valve with his/her shirt sleeve and not know it. They are merely a safety feature that is appropriate to have in hot environment's where engines are more likely to overheat. Up north, no use for that.

There is a procedure to properly "burp" and engine. For a ranger, quite straight forward.

So that was my $.02, but hey, opinions are like arseholes, everyone has one.
A great big thank you to all of you that have replied! As I've been driving the old ranger around the past days, the heat has gotten hotter in the cab. Outside temps have ranged between single digit fahrenheit temps into the 30's. Sometimes, on longer trips, I have to turn the fan down to the lowest level and also turn the temp down on the temp control knob? The needle on the temp guage still tries to drop down, but now, instead of cold air being blown through, it's just not as hot air? I still haven't tried the cardboard trick yet? I've been checking the fluids to see if anything is dropping low, but the coolant, oil, power steering, brake fluid levels remain steady? I don't see anything leaking under the truck either? Did it fix itself?