It has started to over heat again. Last year my 97 with 4.o was having overheating problems, radiator was pretty clogged so I replaced with factory new.
Last weekend on the highway it ran great until I stopped at a rest area. I pulled away and it went to the pin. I found the radiator low. At home I found the cap weeping and replaced it and the thermostat. Now she will go over 210 to 240 (on the gauge) at 65+ and higher on grades. I notice a slight drop in oil pressure at higher tempatures too confirming a high tempature.
A meat thermometer in the radiator say 190 when the gauge reads 210, could it be a bad sender? seperate problem though
The radiator is one year old, new cap & thermostat. Could I have a bad pump and a bad temp sensor?

Ok so it gets to 240 and doesn' puke? I'd change the sender and see if a new one tells the same truth as the old one.
Also I'd be wiggeling the fan to assure myself the clutch was in working condition. When cold the fan clutch should be fairly tight and the fan shouldn't spin when turned by hand.
As for the pump...very few indeed fail in any other way besides leaking coolant.. If it ain't leaking it should be good. In about one case of overheating out of many thousand the pump vanes rust away and fail to pump any more.. But this occurs when fluid other than coolant is used, and usually is not a consideration.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

After you replaced the cap and thermostat, did the radiator ever get low again?

I drove it last night after changing the cap and thermostat, and then did the post here, yes the temp started to rise after about 15 miles when I drove above 65 or so, at idle/city street speeds the temp goes to the normal on the gauge.

When I did the thermostat, I checked to see if there was any play in the pump, the bearing seem tight, and the pump dosent leak. The fan clutch seems normal.

How much good is a fan at 65+? Wouldn't you get a lot of air through the radiator with or without one at that speed?

"After you replaced the cap and thermostat, did the radiator ever get low again? "


I have the overflow tank connected. I will disconnect it before I drive it home tonight and check the level when it cools down and get back to you.

You say "started to rise" As one goes faster there is more heat in the engine.. The temp system in an engine is not rocket science. The temp changes from minute to minute slightly. Unless the coolant is puking out of the overflow the engine isn't hot.
But that said temp climbing as spped increases could easily be low coolant or poorly preforming viscus fan clutch.

Funny thing bout my Ranger.. The oil gauge is always either at zero (when off) or at halfway when running. I found there isn't a sending unit in the thing. Instead it has a switch that keeps the gauge at zero until reaching 7-1/2 lbs of pressure. At 7-1/2 lbs the switch closes and the gauge goes to halfway! Just a variation of the old idiot light. Makes the dash look good though.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

I wouldn't disconnect the overflow tank - that won't tell you anything. Practically every vehicle will expand coolant and port the excess to the overflow bottle. When the radiator cools, it will suck back coolant from the overflow tank. So what I'm saying is -- just about any car will lose coolant if the overflow tank is disconnected. When the coolant getsw hot, it will exit the radiator through the pressure cap, but won't be able to draw the coolant back into the radiator when the engine cools.

Yes Ford has done that with their gauges for a long time, probably kept a lot new cars out of the shop for warranty repairs.

The engine has never increased tempature when driving even with the AC on to over a sustained 80 mph. In my case something in the cooling system has failed.


I am guessing my radiator didn't clog up in a year, the coolant is still green and no signs of rust in it and this problem started suddenly too.

...my next step is the fan clutch. (probably pretty tired after 145,000 miles anyway) I will get one and bolt and try it out on the way home.

I'll let ya'll know,

Maybe you need to post the temps reached by the gauge.. If you can run it 80mph and it don't puke I wouldn't be too worried.
Also the fan clutch COOLS the coolant after it has been heated and read by the sender. If the temp don't KEEP rising forgetaboutit.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

I picked up a new fan clutch on the way home last night, Driving back in 80 degree heat, the temp gauge was about 220ish, I found that it had no power above 65, and would not go past 75, FYI the oil pressure was holding at 40psi at 65mph and was maybe 15psi at a stop light

I changed the fan clutch, and it was like someone played a country song......except I didn't get my money back.(LOL)

The temp went back to original, 210, the performance came back, it'll go over 80 and the oil pressure holds at 50+psi on the highway and 35psi at a stop light

It's what I had said, something broke, just had to sort it out