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Thermostat problem?


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I have been having issues recently where my temp gauge will go from the O in normal to the M (N being cold L being hot). Its a 93 f-150. The thing is it does it all the time just goes back and forth. I drove for 10 miles on a flat road at a constant speed of 55 and it just kept going up and down gettin hot then going back down so its not like it was gettin hot on hills or under a load . It used to run pretty cool. Would a thermostat cause this or is this a water pump? I don't want to just start throwing parts at it is my only thing. (radiator is not the problem since it was flushed months before the problem occurred and the level always stays the same)

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Usually the waterpump will loose water/coolant thru the weephole. I'd feel around under the waterpump and see if its wet. Thermostat could very well be the problem. Should be a pretty simple & cheap job to replace the thermostat.

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Could be the sending unit for the gauge.

Does the motor ack like it's getting "hot"?

It doesn't really show any signs, but then again it does stay in the normal just on the high side, past the halfway, but I do figure it has to be something non gauge related as in its a motor issue. Because if I do go uphill for a while it will get hot then go back down. Hopefully its the thermostat. Trying to find a robertshaw for it, looks like I have to get it offline.

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I'm not one of them thar x-spurts, but it sounds like a failing/sticking thermostat. Let us know how changing it works out....

(God Forbid the heads/etc got warped etc by sum-body a-pourin cold water/coolant in whahl the motor was still hot after emptyin the coolin system hot when you was a-havin it flushed back then....)

Also, how about the radiator cap?

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I'm not one of them thar x-spurts, but it sounds like a failing/sticking thermostat. Let us know how changing it works out....

(God Forbid the heads/etc got warped etc by sum-body a-pourin cold water/coolant in whahl the motor was still hot after emptyin the coolin system hot when you was a-havin it flushed back then....)

Also, how about the radiator cap?

No, I flushed it when it was cold, let it sit, and refilled it when it was completely cold again. Is there any way to test the radiator cap myself or anything to look for?

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Good on ya, mxredneck for that part of flush technique - that method, with likewise proper rinse, takes forever, no? Did you flush whole cooling system including engine? Any chance that any flush debris is blocking any coolant channels in motor or thermostat? Is the overflow tubing/tank system clean/unrestricted? I (carefully!) clean that tank and tubing with special brushes that fit into those spaces. Last time I flushed, I used distilled water for rinse, had heater on hottest setting (I figure that the "radiator" for the heater - depending on heater design(?) - can use a flush, too), removed engine block plugs for both flush and rinse, kept all waste for toxic waste collection event, and refilled with so-called "lifetime" coolant - hope it works.

I'd look at cap for dirty/damaged gasket, corrosion/sludge on spring/sliding mechanism. Also examine radiator neck where cap seats for corrosion/sharpness/roughness which could damage cap gasket/compromise proper operation.

Your motor oil and coolant look normal? (No "whiteness" in the oil, no funny-looking coolant - from blown head gasket, etc?) Seems like I remember auto parts stores having a pressure-tester for caps - you need to know what yours was rated for. Repair shop should have such a tester? New cap shouldn't cost that much and is easy to replace - perhaps about time if it's original for your rig, no?

Edited by BSAVictor
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Good on ya, mxredneck for that part of flush technique - that method, with likewise proper rinse, takes forever, no? Did you flush whole cooling system including engine? Any chance that any flush debris is blocking any coolant channels in motor or thermostat? Is the overflow tubing/tank system clean/unrestricted? I (carefully!) clean that tank and tubing with special brushes that fit into those spaces. Last time I flushed, I used distilled water for rinse, had heater on hottest setting (I figure that the "radiator" for the heater - depending on heater design(?) - can use a flush, too), removed engine block plugs for both flush and rinse, kept all waste for toxic waste collection event, and refilled with so-called "lifetime" coolant - hope it works.

I'd look at cap for dirty/damaged gasket, corrosion/sludge on spring/sliding mechanism. Also examine radiator neck where cap seats for corrosion/sharpness/roughness which could damage cap gasket/compromise proper operation.

Your motor oil and coolant look normal? (No "whiteness" in the oil, no funny-looking coolant - from blown head gasket, etc?) Seems like I remember auto parts stores having a pressure-tester for caps - you need to know what yours was rated for. Repair shop should have such a tester? New cap shouldn't cost that much and is easy to replace - perhaps about time if it's original for your rig, no?

Radiator cap seems good, no sludge there or in the filler neck either. Coolant is as clean as the day I poured it in. The overflow tank works good and is clean too.

I'd say either a stat going haywire, or an air bubble in the cooling system somewhere.

I'm pretty sure its not a bubble because the level always stays the same. Plus I ran it with the cap off and squeezed the upper and lower hoses to try and get any bubbles out.

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Had a 92 f150 5.0 do the same thing, replaced the stat and changed the coolant. fixed

Use a good quality stat, not the cheapo's.

You can ground the wire to the sensor and the gauge will read full deflection just to rule out a bad gauge.

Some motor will do it when they get air entrapment and can drive you nuts, My buds 94 dodge cummins does it and after trying a couple different stats the dealer advised just live with it.

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Some motor will do it when they get air entrapment and can drive you nuts, My buds 94 dodge cummins does it and after trying a couple different stats the dealer advised just live with it.

Tell your friend to find someone qualified to work on his truck. Air bubbles in the cooling system are nothing to 'just live with', especially in a diesel engine (cavitation and cylinder liner damage).

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Quit fooling around and replace the thermostat...it's real cheap and then you'll know what it's not...

Here's a trick I use on all my vehicles...I drill a small hole in the thermostat flange (.035"-.050") to allow air to bleed during the coolant re-fill and warm-up...the hole isn't big enough to interfere with the thermostats job of restricting coolant flow for warm-up, but makes most coolant systems bleed faster and better...

Some of the new vehicles thermostats have a similar by-pass already done...

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Si I finally replaced the thermostat today and I got as many air bubbles out as possible (I used a 195 degree thermostat). Well now it will idle up to temp and stay at a nice temp, but as soon as I start driving it goes hot. Doesn't overheat, but gets hot and stays up there from there on out. I am beyond frustrated with this truck. Its one problem after another.

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How bout ye radiator fan/clutch? Sometimes that mechanism wears out, no? It's not a solid/fixed fan, is it? (The fan's not electric on that model, is it?) Maybe the fan's not turning enough under driving conditions to properly cool radiator?

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How bout ye radiator fan/clutch? Sometimes that mechanism wears out, no? It's not a solid/fixed fan, is it? (The fan's not electric on that model, is it?) Maybe the fan's not turning enough under driving conditions to properly cool radiator?

Fan seems to be fine. Its a fan clutch type fan and it has the proper amount of resistance telling me its working ok.

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Si I finally replaced the thermostat today and I got as many air bubbles out as possible (I used a 195 degree thermostat). Well now it will idle up to temp and stay at a nice temp, but as soon as I start driving it goes hot. Doesn't overheat, but gets hot and stays up there from there on out. I am beyond frustrated with this truck. Its one problem after another.

Uh oh......this is starting to sound like either a clogged radiator or a bad head gasket really fast.

Start by getting an actual temp reading (in degrees) of what's going on. One thing I really hate about that era Ford trucks is the gauge is a guesstimate at best. Get a cheapy real gauge and hook it up and then you have some real numbers to evaluate rather than just "L-NORMAL-H"

Now, if you have access to one, these things are great for diagnosing a plugged radiator http://www.google.com/products/catalog?hl=en&client=firefox-a&q=laser+thermometer&cid=12955984420802696606&ei=A9BQTMarCZ_uyAXRyMTMBA&sa=title&ved=0CGQQ8wIwBzgA#p

Not a huge expense for a tool that can be damn handy. Take shots of different portions of the radiator and record different temps....if one spot is much cooler than the rest, you have a plugged rad....temps should be consistently diminishing from the inlet towards the outlet side.

If that isn't the issue.....ugh......

http://www.rxauto.com/block-test-kits.htm.

But first, I have to ask, did you test the thermostat on the stove with a thermometer before installing? Just cuz it's new doesn't mean it's any good (learned this the hard way).

EDIT: Another thing to check is a collapsing hose. Seen this happen before.....the spring that is installed inside the rad hose rots away. It's in there to prevent the hose from collapsing under the suction pressure of the water pump drawing coolant from the radiator. Put it in park, block the wheels, have a sober friend you trust get in and rev it up to get the water pump spinning (and sucking) really fast, and watch what the lower radiator hose does. I've seen a few collapse like a deflated balloon under this test.

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Sober, friend, trust, rev it up. Please do tell this story. It has to be good.

Had a co-worker once who wasn't the straightest-laced individual on the planet.

I came into work after having two days off, and the overhead door for the alignment rack bay was all boarded up, the alignment machine heads were all smashed up, and all the cables for them were stretched and torn. Also notice that a co-worker's toolbox is no longer where it used to be.

This gets me curious, so I ask.

Story I got goes like this:

"Yeah, John doesn't work here anymore"

"Why Not?"

"Get yourself a pop, pull a stool and get comfortable......

John pulls a truck in. Truck sounds like a battle tank. Work order lists 4 new tires, alignment, new exhaust (rotted off) and adjust the clutch.

John decides he's going to lunch, and the boss puts two of the flunkies on the job to do the exhaust, tires and clutch adjustment, saving the alignment for John.

John goes to lunch (at home-he lived two blocks away) where he consumed at minimum a 6 pack for lunch (according to the post accident blood alcohol tests), and quite possibly washed it down with a few heavy grade bong hits (noted by the doctor from the stink of his breath).

John returns to work and is told all that needs to be done is the alignment. He proceeds to install and calibrate the alignment heads, does the job (or at least goes through the motions), fires up the now quiet truck, and pops the now properly adjusted clutch, panics, floors it, and drives through the garage door (which he forgot to open) with the alignment heads still attached to the wheels, which are attached by cables to the alignment machine computer.

Big glass door, big crash, followed by and even bigger crash of the alignment machine toppling face down, shattering the screen and FUBARING the PC hardware in it. At this point, the cables break that were attaching the heads to the machine.

But it's not over yet......he's still got this truck floored, and now the heads proceed to fly off the wheels, smashing them all to hell, and before he realizes his mistake and takes his foot off the throttle, he smashed into another customers car in the parking lot, and the impact sends his hops and bong resin plugged head through the back window of the truck.

Just one more case of "Heavy Drinking Prevents Sound Thinking"

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