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Old 08-05-2011, 01:36 PM
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Is she overheating? Engine Temp light stuck... '84 6.9

Ok, I'm probably just over-reacting, but I have a 300 mile trip planned, err... this afternoon, and I'm worried my coolant system isn't working correctly (assuming the worst here).

As you may have seen earlier, I cleaned my engine yesterday (link to post). Everything went fine, and the truck appears to be running ok.

However, this morning I noticed (as soon as I turned it on) the ENGINE TEMP light (below glow plug light on dash) was on, and wasn't turning off. I'm pretty sure this light would come on for only a second in the past (then turn off as soon as the truck was running).

I searched the forums and read that my possible issue is that I fried my "Over Temp Sensor" on the block when cleaning the engine? I may have the terminology wrong, here is what I'm referring to:
Click the image to open in full size.

When I unplug the wire to this sensor, the light goes out. The plug appears to be dry inside.

After driving the truck around the block, it's still on. I felt the upper radiator hose, and its VERY hot to the touch. The lower radiator hose is actually cold, more close to ambient temperature.

Is this normal? Do I have a clogged coolant system? Or is it completely normal to have 1 hot and 1 cool hose? Is the sensor just bad?

If the sensor is now bad, do I just unscrew it and replace it to fix this issue? Do I need to torque the new sensor to any specific degree?

Thanks in advance!
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Old 08-05-2011, 01:43 PM
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Some more info...

The other day I submitted a post about 2 broken head bolts (link to post). The truck ran fine before and after, and wasn't losing any fluids.

After putting in new head bolts, I noticed a couple drops of oil floating below the radiator cap, on the radiator cap, and around the rim of the cap hole. I cleaned that all off, and the coolant looks bright green.

I'm hoping that was just residual oil from having the 2 broken head bolts, and that no more oil is entering the coolant system after putting the new bolts in.

However, is it possible there is a huge clog of oil somewhere in the cooling system and that's why the bottom radiator hose is cold? (ie, no flow through system?)

Also, my overflow tank is empty, and my radiator is not completely topped off. Should I top of the radiator and fill the overflow tank half way with fresh coolant?

Thanks again. Mechanic in training.

Last edited by fj2u; 08-05-2011 at 01:55 PM. Reason: spellcheck
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Old 08-05-2011, 02:08 PM
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I have a feeling everyone is going to say I just fried my sensor, and that the bottom hose is suppose to be cold, and I need to stop expecting the worse.

If that is the case, I'm trying to figure out what sensor I need to order. Here are a few that I found on RockAuto.com, are any of these (or all) the same thing as the picture above? Why the huge price range?

Thanks again!

Last edited by fj2u; 08-05-2011 at 02:13 PM. Reason: perfectionist
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Old 08-05-2011, 02:47 PM
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Ok, the top hose shouldnt be VERY hot... it should be approxamately 185-195* when the engine is fully warmed up. The bottom hose should always be cooler than the upper as the coolant has passed through the radiator and been cooled. Try replacing your overtemp sensor, or you could simply leave this unhooked, i suggest making sure 100% that the gauge temp sensor is working correctly. Yes fill the raidiator while cold, and the overflow res. to 1/2 full with fresh 50/50 antifreeze. If youre still worried beyond there, let us knwo.
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Old 08-05-2011, 05:59 PM
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Pretty sure all those sensors you listed are the ones for the gauge, not the overtemp. When I swapped my head and was fighting to get that switch out, thought if it was only $8 I'd get a new one. The actual overtemp they had was around $70. Napa has two of them, one for $30 and one for $40. I just finally fought my old one out and put it in the replacement head.
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Old 08-05-2011, 10:02 PM
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I remember my 7.3 had an aftermarket mechanical temp sender, and i just used the one out of my 400. Threaded right into the reducer. Not sure if the specs are different but since mine came out of a 77 and the engine is in a 77 i figured it would all work out for the best. Besides, the 400 temp sender is alot cheaper.

Not sure if this helps at all but i figured id throw it out there, i only use the sender in the block behind the water pump. But im starting to wonder now, as it seems pretty delayed sometimes. The engine will seem alot hotter than the gauge registers, then after sitting for 5 minutes the gauge jumps alot higher. This is somewhat normal, but mine seems a little excessive.
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Old 08-05-2011, 10:13 PM
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He needs the one for the light not the gauge, i have 2 new motorcraft sensors, if you need one pm me
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Old 08-05-2011, 10:56 PM
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To be honest too though, when you don't know the history of the maintenance, I would be awfully tempted to toss a new thermostat in too. It certainly won't hurt, and they don't last forever.
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Old 08-07-2011, 02:24 AM
joshofalltrades joshofalltrades is offline
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but your new stat must be OEM, as i hear the aftermarket ones are different and don't work right. there was a thread on that not too long ago, search for it.
as for your light issues, the fact that your light is on as soon as you start the engine proves that your sensor is bad or the wire is shorting to ground, and the fact that unplugging it turns the light off proves that the sensor itself is your problem
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Old 08-08-2011, 12:19 PM
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Thank you everyone for the great feedback. This is a fantastic community, resource and great group of people. I've learned a lot from all of you and appreciate those who take the time to reply to posts on this forum.

I chanced it and left Friday afternoon. It was also my first time on the freeway with the new truck, so I was a little nervous (Was she going to explode? Blow out those 2 broken head bolts I replaced? Blow a head gasket? Overheat and melt down?).

It did just fine! At some point the Engine Temp light went out and didn't return. Maybe the water burned off that was causing the short? Who knows. I did 60-65mph the whole trip and although a little loud and bouncy, she handled fine.

Last night (Sunday) I returned home and this time did 70-80mph the whole way. Amazingly, she was incredibly smooth at 70+mph. She purred like a kitten and all the shimmies and shakes seamed to dissapear over 70mph(!).

While not everyone would push their truck that hard, I really wanted to see if she could handle it and what she was capable of. Well she impressed me to say the very least. She had plenty of pedal to go to!

This truck is turning out to be one of the best purchases I've ever made.

Love my Ford!



PS- At one point I blew past a decked out 2010 lifted crew F350 turbo diesel (I was doing about 75+ at this point and I'm guessing he was doing about 60mph). After 27+ years these are still very capable trucks! Remember, this is a $2,000 truck vs a $50,000+ truck! enough said! (no offense to the new ford, just can't say enough about the old gal)...

Last edited by fj2u; 08-08-2011 at 12:26 PM. Reason: ps
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Old 08-08-2011, 01:24 PM
joe f350 joe f350 is offline
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what gear ratio and trans do u have
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Old 08-08-2011, 01:44 PM
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Quote:
Originally Posted by joe f350 View Post
what gear ratio and trans do u have
'84 with 4 speed manual. Gear ratio? You know, I have no idea, but I was going to post a thread on this topic.

Here is what I do know:
  • 1st gear: Rarely needed. Takes off from stop in 2nd with no lug and plenty of power (with little throttle) 95% of the time. Whats it for?
  • 2nd gear: See above.
  • 3rd gear: A pretty short gear. I have to RPM way up before I can shift to 4th...
  • 4th gear: Huge leap from 3rd, lugs if I shift too early from 3rd.

So what I noticed is I have to run the RPM's uncomfortably high before I shift from 3rd to 4th, or 4th will lug, as if I shifted way too early. Is this normal? In my modern manual transmission cars, it would be like shifting from 3rd to 5th gear. Does this make sense? Is this normal?

Example: I'm pulling a load up a steep grade. Speed limit is 35mph. In 3rd gear motor is screaming, engine temp rising... if I shift to 4th I lose all power and momentum. Have to push 3rd even harder before I can make it up the grade in 4th. Is this hard on the engine? I imagine these conditions would cause a lesser vehicle to blow a head gasket! Anyone else have a 4 speed with this experience?

PS - Doing 70+mph, the RPMs ran low, smooth, effortless; seemed to have plenty of room for more. The engine feels under much higher load just trying to get to 4th from 3rd on a slight grade.

Last edited by fj2u; 08-08-2011 at 01:46 PM. Reason: ps
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Old 08-08-2011, 02:04 PM
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Mine lugged a little when I shifted from 3-4 also but I'm kinda thinking it's just the gearing I have no clue what rpm I'm at my tack completely quit working after I pulled my instrument cluster and cleaned everything fuel gauge started working better my turn signal (in the dash) started working better but tach completely quit... I don't know though I run and drive my truck like I stole it
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Old 08-08-2011, 09:02 PM
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You have the T19 trans. and yes those have a rather very wide gap between 3rd and 4th.


If it still exists, post up your axle code that's on your door jam sticker, I will be able to tell you your gearing.


Since your truck is a 1984, it should have a Dana axle, and since you can even reach 80mph without hitting the governor, i'm guessing you have 3.54 gears.
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Old 08-08-2011, 09:59 PM
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or the super rare 3.08 dana 61
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Old 08-08-2011, 09:59 PM
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