This is really starting to get boring. 1996 f150 Inline 6. Two years ago bought it with Stop leak put in by previous owner (he shouldn't have even qualified as an owner) anyway. In the past two years to the month I've solved the overheat problem several times. Flush, 3 new thermostats, flush, new radiator, flush, new water pump when I got it etc. So every now and then it will want to go passed its typical between O and R and rise. Today when it started to do that. I pulled over turned it off for about one minute. Started up, drove and in a minute or two it started down. I haven't changed a Temp sensor. Just learned about that one on the wifes Saturn which has one for the gauge and another one for I guess the fan to know when to come on. Do you think its a Temp sensor on this truck, is there two of them, location. Off to google in the meantime, thanks for any input. I know this has been an issue with some.....chasing it around. Its the only thing wrong with the truck but it gets frustrating. O'yeah replaced radiator cap too.

 

Just a thought, as I posted about something similar a day or so ago. Be sure that you aren't just chasing an electrical gremlin. On my '92, 300, I have a similar problem, but it goes past the "L" of "normal". All I have to do is drive it for 20 mins, then when I'm park, turn the headlights and AC blower on. It will go from "M" to "L" rather quickly. A quick test is with electric windows. Press the up or down button and go to either direction. If completely up, press the button for a moment and watch the temp gauge. If it moves any, you have a high resistance somewhere in the wiring. I have a mechanical gauge installed in the heater hose line that never reads above 205, so I disregard the in dash gauge.

 

I would not put 100% faith in a Ford gauge. I'd put an aftermarket gauge in and compare the two. It's possible it's entirely in the gauge.

There are two temp sensors. One for the PCM, the other for the dash gauge. The one for the PCM is near the front of the engine, and the other is on the passenger side under the #6 exhaust port. It's a pain to get to. You will probably have to pull the starter to get to it.

 

I'm pretty sure its not the gauge as I can smell the vehicle when it gets up past the M. I hear you about an aftermarket gauge. It had a SUNPRO. Someone tried to steal the truck but could not, must of got frustrated so he/she ripped out the temp gauge. So, the PCM if faulty would create an engine to overheat? I understand the other sensor (hard to get one) is for temp gauge, if I've established its not the gauge then go for the PCM...in the meantime I'll install another aftermarket gauge.

 

Um, no. No one is saying that.

Engines overheat for a few different reasons. Not enough coolant, faulty water pump, clogged radiator (internally or externally), clogged coolant passages, thermostat problems including wrong temperature and stuck open/closed/missing altogether, and sometimes things like the fan clutch not working can do it under the right circumstances. And if there are electrical problems affecting the gauge, it might not even be overheating at all. Smell is a pretty good indicator though, I will give you that.

Products like stop-leak can plug coolant passages. Something to think about but really hard to diagnose without tearing the engine apart. I'd think it would be more of a consistent problem if that were the case though.

Anything else unusual happen while you were driving it? Anything unusual about the trip at all? Were you stuck in traffic? Were you on the highway? Were you towing or hauling anything? Running around town?

 

just like andym said, first thing to do is another gauge to confirm the overheating.

and, just like he said, stop leak (especially when idiots pour more than 1 bottle in), does what its designed to do. . . .blocks up passages. i pulled some heads off a boat that someone used stop leak to seal a rotten freeze plug (given the location of the plug, it was just as easy to replace it as it was to pour stuff in). . . .it overheated, i pulled the heads, and all of the passages that were cheerio sized or smaller were clogged and the stuff was baked to concrete-like hardness. had to really get violent to get it out.

this is absolutely the last thing to be checked, since its the most work. get the gauge hooked up, if its overheating pull the thermo and see if it'll overheat still. if it does, chances are its blocked up somewhere.

 

Much obliged. Haven't done the run without thermo yet. Going to get the Sunpro Gauge replaced first. Thanks again.

 

With the engine off, turn your fan clutch by hand, you should feel abit of resistance... if it spins very freely, a new fan clutch is in order!

 

I'll try that. I even had a mechanic look at it, he replaced the radiator cap...obviously that didn't work. Day two. Its like a yo-yo. It will go up then down up then down just driving around town 10 minutes between stops...can't do the work on it until Thursday

 

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the only thing I was doing is short trips around town...10 to 15 minutes and stop or turn off the Engine.

 

got home, took another look in the radiator, fluid down about 1/2 gallon. I haven't seen any white steam from the exhaust, engine runs fine. I'll have to monitor this closer to see if there are any specific leaks, sure hope its not a blown head gasket...don't see any indicators on the dip stick. Just finished reading a whole bunch in the forum on blown head gaskets.

 

4 miles to school, half way there this morning it really started to over heat. Steam from the hood, parked it, open the hood to see heavy steam out the back of the engine and appeared to be low.....holy crap...AAA picked it up, later in the day the mechanic replaced a 50 cent freeze plug that had a pin hole or pin holes that became bigger. I think the fluid that had been escaping yesterday going unnoticed was evaporating before it could hit the ground as I had watching it. So the reason why the gauge was going back and forth was due to the escaping antifreeze. All those other issues that I was fixing didn't have anything to do with the freeze plug. All is well now and I consider myself lucky. Inline 6...one tuff engine. Thanks for everyones input. See you next episode of........hope to do some preventive stuff instead.

 

Give it a good oil change, when you overheat any engine, it's a good idea.


Oil gets to hot and breaks down!

 

for the Oill change advise. I'll do that. With 189,000 miles I'm thinking with all the other stuff I've done to the truck, I might start planning a 250,000 to 260,000 mile rebuild....why those numbers...just got to start somewhere or do you have any advise as to when if you plan on keeping your truck. Some say just change the oil....whatelse