Normal operating temperature

In a previous thread about an A/C causing the temp to spike, someone said normal operating temp should be somewhere around the R and M on the gauge. Mine struggles to get to the N, and when it does make it there it doesn't stay long before it drops again. Because of this (I assume) my heater is less than optimal. The heater core is about a year old, as are the hoses. New radiator cap and T-stat. Where do I start figuring this one out?

Well, what thermostat did you put in? Some open at different temps. Maybe you got a cold one.

I installed a low temperature (160*) thermostat, and I never see my gauge move. The OEM thermostat is 197*. It sounds like you installed a similar thermostat like mine.

mine was supposed to be an OEM replacement, I think it was 190*.

You could check the temperature sending unit with an Ohmmeter to verify the output.

Any idea what output would be on that? I assume just pop the wire off the top of the housing for a reading? I'm not good with meters and generally require very specific instructions. Sorry.

It's the sensor with 1 wire going to it. In-between the intake tube and alternator, NOT the 2-pin one below the throttle body.

I couldn't tell you what the proper readings would be though. If you watch it and it moves and you can see the point where your thermostat opens, I'd call it good.

Check the attached PDFs for a temperature sending unit resistance chart.

Your aftermarket thermostat probably doesn't have a weep hole. I had to go to a dealership to grab a Motorcraft stat. Your aftermarket without the weep hole traps more steam inside the the engine building higher pressures while closed which scientifically means your engine will operate at a lower temperature. When it opens it will react that much more. The weep hole bleeds small amounts of steam out of the engine lowering the pressure which in turn raises the operating temp slightly.

My temp gauge with aftermarket idled around the "N" range. Motorcraft idles slightly higher about the "O" range. Slightly closer to OE spec back in the day probably.

The fact that your gauge goes up to N then drops again tells me your temp sending unit for the gauge is bad. New ones are about $5 and take 10 minutes to replace. I'm guessing the N is around 170 degrees. The stock thermostat is something like 195 or 198, I've never got a straight answer. That means the engine will probably run about 200 on the highway, maybe closer to 210. Mine runs 1/3-1/2 of the gauge with a 198 degree thermostat.

2stroke said:

The fact that your gauge goes up to N then drops again tells me your temp sending unit for the gauge is bad. New ones are about $5 and take 10 minutes to replace. I'm guessing the N is around 170 degrees. The stock thermostat is something like 195 or 198, I've never got a straight answer. That means the engine will probably run about 200 on the highway, maybe closer to 210. Mine runs 1/3-1/2 of the gauge with a 198 degree thermostat.

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You know, that's good enough for me. For $5 I'll take a chance that it's not and swap it out. I'll order one up and let you know what I find out.

Thanks guys!

Yeah if it goes up & drops back down the T-stat is opening& doing it's job. I'd leave it alone actually. Does your heat work? If so again I'd leave it alone.
I have a 180 in mine. I also live in hot humid 80+ all year FL. I have my heater core bypassed(no need for heat) & my gauge gets to just over N when warmed up.

My heat works ok blowing out of the panel, my defrost is less than stellar. Altogether I would say it's probably the worst Ford heater I've had.
Now back when I had my Gran Torino, that heater was incredible. That would burn your hand if you held it less than about 4-6" from the vent. I miss that car.

Just because a thermostat is new doesn't mean it works correctly.

I know nobody does it, but the "correct" way of installing a thermostat involves putting it in a pot of boiling water and using a thermometer to make sure it opens when the water temp gets up to whatever temp the thermostat is rated for. It's actually pretty risky not to check, since if you just install a thermostat that won't open and go driving - the engine will overheat rather quick.

If the thermostat is working correctly, then I'd agree it's the temp sending unit. They don't go bad often, but for the price, sure, it's worth throwing a new one at it to be sure. If that's not it, well, keep it as a spare just in case or for troubleshooting later on.

If it's not the thermostat and not the sending unit, it could be the gauge. You might have to take apart the dash and pull out the gauge assembly or at least pull it forward and look behind it to see if anything looks obvious, though gauges can go "bad" and just need to be replaced, but that's less common than even a temp sender.


As for thermostats, the stock Motorcraft 'stat opens at 190*F, most of the aftermarket ones like Stant open at 195 but some are around 192 or even as high as 197-198. It's just a "range" anyway, they don't actually open at that exact, precise temperature.

For the price, the 195 degree Stant Superstat seems like a good buy for the best performance in cold to warm/hot climates. A 180 degree thermostat might be an option if you live in the Southwest or where summers are 110+ degrees. A 160 degree 'stat is way too cold and will just keep the engine from ever gettting to operating temp and so mileage and performance will suffer.

With the 190-198 'stat, the heater should be able to get the interior really hot in winter, even in freezing temps.

A 180 degree thermostat might be an option if you live in the Southwest or where summers are 110+ degrees.

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That is what I used on our X. The temp stays around 175f in winter (gets to upper 20F's here) and in the summer months it'll be around 190f, even when I'm in stop/go traffic in 105f+. I am running a Hayden Severe Duty fan clutch which I'm sure is helping at idle.

I am measuring the temp of the coolant coming out of the intake as it head to the heater core on an analog gauge.

~Mark

There's nothing wrong with a 180 degree thermostat. I would have no problem running any from 180 degrees to 198. That said, none of them are an advantage over another. From what I can tell, a 180 blows just as hot as a 198 in the winter, at least I cant tell the difference. The 180 won't prevent overheating at all, but if its all you can get, run it.

I would still replace the temp sender, but I wonder if you do have another problem. The heaters in these explorers are great. The engines are a little slow to warm up, but after about 10 miles you should be sweating inside the cab, even down to -20 degree weather.

i had this problem. you might have even read my thread (i think it was on this site, too lazy to search for it). after chasing it for a while, it turned out the ac was just kicking on and off and causing drag causing the temp to rise and drop suddenly. so i unhooked it. after replacing all hoses and heater core, the problem persisted. couldnt get it right. finally one of my pulleys decided to go out several months afterward. while fixing that, i found that the hose behind the alternator (tight squeeze with alternator in the way) wasnt tightened down all the way.

problems been gone ever since, and i even drove it around in eastern washington in 115 degree heat this last summer and no changes, only when hammering it going through the hills.

Hmmm... I'll I have to look around. I did a lot of looking and found a small leak in my radiator hose. I thought after fixing that it would take care of the problem, but didn't. I think there's a possibility I may still have an ever so small leak somewhere, as I'll go through about half of my overflow tank in about 2 months. Maybe I'll have to do some exploratory surgery. I'll look around when I change the temp sending unit.

by the way, i have the 195 i think. its usually just above the C, but lately since its been around 70 degrees, its been ranging from the C line to a little under the N

just go rent a pressure tester from oreillys, hook it up to the radiator and pump it. if it loses pressure, theres a leak somewhere.