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  1. #1

    Default Engine too cold, changed T-stat, now too HOT

    Not my first rodeo in changing thermostats or cooling systems but Im a little baffled. Car was never reaching operating temps, heater was never hot, always ran cool. All stock engine. I decided the t-stat was likely changed to a 160 so I pulled it. Sure enough, its a 160...Bought the stock 195 for it, now it gets way too hot, but the radiator doesnt get hot. I tried to get the best one the auto parts store had and it was fail-safe 195 degree.

    Burped the air out a few times and no help. Engine temps are pegged right on the line but no steam, overheating or boiling over. In fact engine doest seem all that hot but gauge says otherwise. I can touch the radiator hoses, it seems the radiator is just not hot, its all just "warm". Bottom of the radiator hose is not hot at all, top is like I said warm, hot but can easily hold in hand. Fan clutch seems fine and moves a lot of ai but like I said radiator never gets hot.

    Here is what ive noticed / tried. New radiator cap. I have a thermal gun and the tstat housing was barely over 190, even though my gauge is pegged. Intake manifold directly behind the t-stat housing is 200 +/-. With engine hot, radiator cap off, I watched and cooland dropped about an inch. Cap back on, let system pressurize. No change. Had wife rev enginewith cap off to see collant flow. It was very minumal, didnt seem to "suck" through the engine like my 69 302 does.

    This is what I thinkl it is:
    Air still in system, water pump, or bad "new" t-stat.

    So my thoughts are its the water pump, But heres the deal, I introduced this issue with the new T-stat, and it sure seems its not opening, or not opening early enough? Would a 180 tstat resolve this?

    Anything else I can test to rule it out being the pump or air in the system?

    All help appreciated!

  2. #2

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    Are we looking at the factory temperature gauge?
    Mike
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  3. #3
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    82GTforME's Avatar
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    Quote Originally Posted by Walking-Tall View Post
    Are we looking at the factory temperature gauge?
    Good point Mike. Do you have an infrared temp gun to verify the temps? The gauge may be reading incorrectly and you may actually be "normal". The gauge or the sending unit may be the issue.

    If it is the factory gauge, where was the needle sitting with the previous T-stat compared to teh new? One extreme to the other?
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  4. #4
    FEP Power Member Jerry peachuer's Avatar
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    He's using temp gun point and shoot

    Top and bottom hose should be comparable as far as temp (circulation) issue if not
    Try turning heater on full hot high and leave cap on and loosen the seal on a heater hose to let it weep out coolant but make sure you do watch temp with point and shoot see if it's just a burp that you need

    To me sounds like your coolant "moved a inch or so (as you mentioned) tells a story about propeller on pump is moving coolant

    Try to nose car into garage so it can build engine heat and see if your just not expecting something too soon

    It would also be ideal to double check your tester to see if it's within reason maybe boil water and use meat thermometer ?? And then test your point and shoot
    Just a thought

  5. #5

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    Thanks all.

    Yes, stock gauge. Gauge was reading fine, unless the engine was just running SUPER cold before. Gauge stayed just below middle point until I changed the thermostat out. Seems to work fine but I guess it could be the gauge.

    When I burped it I just just that, jacked front way up with cap off, heater on and let it run. I watched and didnt see much bubbles.

    I noted the collant lower an inch or two just once, when I think the thermostat opened...When I revved the car the coolant barely moves at all. Like I mentioned Im used to my 69 302, when you rev it, coolant lowers from the sucking power of the pump. The mustang, the coolant barely moves at all when revved..This is why I questioned the water pump.

    But I keep going back to, car never overheated until I changed the T-stat out.

    Im using a infrared pointer gun. Temp at thermostat housing was 180 and at times 195, manifold behind it was just above 200 degrees.
    Last edited by mdula; 12-02-2016 at 12:06 AM.

  6. #6

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    Quote Originally Posted by Jerry peachuer View Post
    He's using temp gun point and shoot

    Top and bottom hose should be comparable as far as temp (circulation) issue if not
    Try turning heater on full hot high and leave cap on and loosen the seal on a heater hose to let it weep out coolant but make sure you do watch temp with point and shoot see if it's just a burp that you need

    To me sounds like your coolant "moved a inch or so (as you mentioned) tells a story about propeller on pump is moving coolant

    Try to nose car into garage so it can build engine heat and see if your just not expecting something too soon

    It would also be ideal to double check your tester to see if it's within reason maybe boil water and use meat thermometer ?? And then test your point and shoot
    Just a thought
    Bottom hose was not hot at all, barely warm, top hose was hot but not nearly too hot to touch.

  7. #7
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    Lower hose should be cooler than the upper .
    Cross flow radiators don't show the flow like the old waterfall style did.
    When I do anything to open the cooling system, and need to burp it this is what I do .

    Fill to top of radiator with coolant mix, fill overflow bottle to max hot level and a bit more .
    Let car idle until I have heat coming g out of the heater or defroster.
    Shut car off and let cool .
    Forgot to mention that I usually run a 16 pound cap as well .
    After car has cooled cold to the touch, recheck the overflow bottle.

    When the car cools , it will suck coolant from the bottle , back In to the radiator.

    Never have to raise the front and all that extra work.
    That is beer drinking time being wasted .
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  8. #8

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    Quote Originally Posted by ashley roachclip View Post
    Lower hose should be cooler than the upper .
    Cross flow radiators don't show the flow like the old waterfall style did.
    When I do anything to open the cooling system, and need to burp it this is what I do .

    Fill to top of radiator with coolant mix, fill overflow bottle to max hot level and a bit more .
    Let car idle until I have heat coming g out of the heater or defroster.
    Shut car off and let cool .
    Forgot to mention that I usually run a 16 pound cap as well .
    After car has cooled cold to the touch, recheck the overflow bottle.

    When the car cools , it will suck coolant from the bottle , back In to the radiator.

    Never have to raise the front and all that extra work.
    That is beer drinking time being wasted .
    AH Thank you for reminding me!!...I forgot to mention. Im missing an overflow tank. Car is basically without one. Ive never once had an issue with air in the system, I usually unhook a rear heater hose after a t-stat or water pump replacement and fill until coolant flows out of it. Put hose back on and do what you described. I went the extra mile with this one by raising the front, burping etc...I dont think the tstat is working. Or opening all the way.

    This wouldNOT be the first time a brand new tstat was defective.

    Since I dont have an extra aftermarket temp gauge...but I do have temp gun, where is the best place to point on the engine for an accurate temp reading? I figure, themanifild just behind the t-stat housing.

    Also I need to mention, after the cars gauge was pegged, I could pop the cap off, stick my finger in the coolant and not burn myself feels like a warm bath water.

  9. #9
    FEP Power Member 81coupe's Avatar
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    Wondering if you tested the new Thermostat before installing it? Factory Gauge is know to crap out though, but I have also had my share of bad replacements in the past. Top hose should be Hot like you stated. But however the bottom hose should be cooler, but not extremely cooler than the top.
    1981 Mustang Coupe: Rebuilt 91/306, Ported E7's, TF Spring kit, E-303 Cam, RPM Intake, Eddy 1406 Carb, FMS Dual Roller Timing set, March UD pulleys, Summit LT Headers, Summit 2-1/2" Chambered Mufflers w/ 2-1/2" FlowTech H-Pipe/ Flowtubes & 2-1/2" LMR SS Tailpipes. C4 trans with 8.8/ 2.73 Rear.

  10. #10
    FEP Power Member Jerry peachuer's Avatar
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    Heat soaked Coolant coming out of engine will be cooler than colder cooled coolant top hose ??

    Not the case for me on a stuck t stat and ford dual core rad

    It's possibly blocked at t stat

    Fail safe t stat sounds like you have a added hole for flow if it did get stuck closed ?? But some is getting by just by the design of your style possibly and keeping it from literally overheating with steam and such

    200 degree engine coolant coolant will be 200 degrees not 160 at lower hose and (cooled) at the top hose

    They should be both somewhat uncomfortable to touch

    My casethe top was vey hot and bottom Luke warm t stat stuck this was a 185 Stant and 16 lb rad cap on a aluminum 2 core rad with high flow eddy pump

    if you have restricted flow one hose will be cooler by a lot no measuring tool neeeed sort a thing not even a gauge to look at just your basic senses
    Last edited by Jerry peachuer; 12-02-2016 at 06:23 AM.

  11. #11
    FEP Senior Member Matt J's Avatar
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    Replacing your stock gauge with an aftermarket mechanical one that you can buy for 20 bucks at any local parts store is a ten minute job and will tell you once and for all what the actual internal engine temp is. I clipped one to the underside of the passenger side of the dashboard where I could see it but wouldn't be in anyone's way. Ran the sending unit wire through existing holes in the firewall, no need to drill anything. I left the old gauge in the dashboard, just tied up the sending unit wire in the engine bay to reconnect later if I wanted. Seriously, this is an easy job, and will cost the same as a few gallons of antifreeze.

    I see guys struggle with this a lot, just put a new gauge in there, even if for temporary use for a while, it will tell you exactly what you need to know while you're driving the car. Those laser thermometers work fine, but you can't be sure what it's picking the temp off of, a cheapo Sunpro gauge will give you what you need to know.

    It would be pretty normal for the car while running to temp to push some coolant out of the overflow hose as it expands, it draws it back in when the engine cools. You really need to have an overflow tank in there, not sure what year your car is, the 84 is the only year I know of that the tank is kind of hard to get, but anything will work. Go old school and use the beer bottle! If you don't have one, the coolant will pee out a little at a time and when the engine cools it will suck air back into the system. Could be a reason for the water pump failing, if it's going bad on you.

    Oh, air getting sucked in will also cause problems with the thermostat...
    Last edited by Matt J; 12-02-2016 at 02:02 PM.

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    From what you've written so far about your problem, you are saying it's running hot looking at the gauge, but everything else your saying is it's running normal at the engine and radiator. You changed from a 160 degree thermostat to a 195. That's a difference of 35 degrees. You never mentioned what year the vehicle was, carb or FI. If the stock gauge is calibrated for a 180 degree stat, then a 190 will put it over the high mark.

    What your saying is, the gauge shows hot but the engine is not. Temp readings at the intake are normal, hose temps sound normal, no boiling over, hoses not hot. So that all tells me it's fine. It's the gauge being used outside of it's normal limits.

    Again what year vehicle. A 180 degree would have been fine if it's a carb car. Then the gauge will be in the middle of the range.

  13. #13
    FEP Super Member cb84capri's Avatar
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    If it is a Motorad brand thermostat or some parts store private label it is likely garbage and needs to come out, from what I have heard the fail safe ones are even worse. In my daily drivers all I install are Stant branded thermostats and even those I boil in water in the kitchen before installing them and make sure they are opening when they should. Just because something's new, it doesn't mean it's good.

    If your upper rad hose is not getting hot and your gauge is pegged and temp gun saying the area in front of the housing is over 200 degrees the thermostat isn't opening. When the engine gets up to temp and the thermostat fully opens up it should start getting the upper rad hose so hot you can't stand to hold your hand on it. I always jack the nose of my car way up in the air when I refill the cooling system, and let it run with the rad cap off until the thermostat opens and it sucks all that coolant in and burps all the air out because the rad cap hole is now the highest point in the system. Then fill the rad all the way up put the cap on fill the overflow to the low line and drive the car. Then I'm off and driving it sober, lol!

    The thermostat was the change, it is most likely the culprit.

    Cale
    Last edited by cb84capri; 12-02-2016 at 12:17 PM.

  14. #14

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    Remove the fail safe stat. All they do is fail. Install descent 180* if carb and 195* if fuel injected

  15. #15

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    Man, thanks all for all the responses! Lots of help. I should have mentioned. Its a 86, FI. I went with the most expensive darn 195 t-stat the auto parts store sells to try to avoid this issue. Judging by my own experience, the tstat is not openeing. Like I said I had this happen once before on me with a new tstat.

    Lesson learned, test thermostats. Since the engine was fine prior, I'm betting the tstat is not opening all the way. Its supposed to fail open, according to the box. Im going to pull this one out, get a new one and TEST it in hot water first! I also want to test the one Im pulling just to hopefully prove it was not opening.

    Will let you all know how it turns out.

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    FEP Senior Member Matt J's Avatar
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    Hey, knowing that does bring up a few other things to think about...that engine is computer controlled, and needs to run at the proper temp to function correctly. I'm going to guess some here, but I think that engine is supposed to run with a 195 degree thermostat, it runs hotter than some of the older carbed cars (my 84 CFI car was the same way). When it runs hotter, coolant will come out of the radiator (it's supposed to), then suck air back in later because there's no reservoir. My guess (lots of guessing here I know) is that the PO put a cooler thermostat in it because there wasn't a reservoir for the coolant, instead of just replacing the reservoir. You now have it running at the right temp, but it's losing coolant, just a little and probably not enough to notice, and sucking air back into the system. Air can be getting behind the thermostat, as it's the highest point on the engine, and thus the thermostat isn't working.

    I know I said it before, but a real temp gauge will tell you if the block is hot, even if the elbow isn't because the thermostat isn't open (which is where you're reading the temp with the laser thermometer). You need some sort of coolant reservoir for that setup to run correctly. Good luck!
    Last edited by Matt J; 12-02-2016 at 05:23 PM.

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    There is always the chance you put the thermostat in backwards also , just saying .
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    Mr. Preacher, let me clarify , the coolant in the top hose is the exit from the engine , bottom us the return.
    Coolant is cooler by the radiator and fan, so it should be cooler than coolant from the top hose.

    No you probably can not feel a difference with your hands, but he will be able to tell with the infrared temp gun .
    Remember ,the temperature bulb that opens the thermostat is below the top hose , so as to control the opening .
    Just to clear up my reply.
    clowns to the left of me , Jokers to the right

  19. #19
    FEP Power Member Jerry peachuer's Avatar
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    I would put a t stat that's exact temp replacement for that engine

    I had a ?? Brand from part store stick and my top hose was untouchable as far as how hot it was and the bottom was far cooler and you could hold onto sort a thing

    That alone should should lead you down a blockage concern hunt

    The gauges and point and shoot are all well and good but if there off 10 degrees you may have some panic possibly especially if your base check was cold and now your gauge is near the red

    Maybe precious owner did this to mask another area of concern ? ( 160 t stat install)

  20. #20
    FEP Power Member Jerry peachuer's Avatar
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    Precious =previous lol

  21. #21
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    I like the precious owner lol.
    clowns to the left of me , Jokers to the right

  22. #22

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    Quote Originally Posted by ashley roachclip View Post
    I like the precious owner lol.
    Whenever possible I always go with a Motorcraft T-Stat.

  23. #23

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    Okay guys, just went on a 25 min drive. I think I got it. First I found a guy locally parting out a mustang and I picked up an overflow tank. Cleaned it up got it in today Decided to replace the T-stat. Im getting good at installing it lol had it replaced in about 30 minutes. I got 2 t-stats, moto ones (crappy I know but all they had locally) a 195 degree and a 180 degree. Decided to test both on the stove with a thermometer in the water, and the 195 opened a little after 200 and the 180 opened at 190 and at 195 the tstat was wide open. After I pulled the 195 tstat I bought the first time, I decided to test it as well...Sure enough it opened fine too.

    But based on my test I decided to go with the 180. ran it last night after installing with rad cap on, let it cool, water level lowered a lot, filled it up. Ran it again till hot. Opened cap and let it pump over night. Then this morning topped it off, it lowered again. installed the overflow tank and filled it. Went for a drive.

    It stayed dead center the entire time. Heat is nice a warm, its 50 outside and I was comfortable, but core is still not "hot". Likely it needs a new core. But car never overheated. Texas 100 degree weather with AC on will be a true test and I still question the pump, and system, non the less it seems much much better.

    Here is my thought after all this. I still think I had air somewhere keeping my water pump from functioning correctly, the overflow tank helped with this to keep the system full. That along a new rad cap.

  24. #24
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    If the core is not hot, that doesn't mean it's bad. It shouldn't get hot to the touch. Sounds fine to me. You also said that it was an 86 FI car. Do you know if it has a chip plugged into the back end of the computer?, You can only run a 160 stat with a chip. The stock program will not run right with a stat that cool.

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    FEP Power Member 81coupe's Avatar
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    Good deal. When you pulled the old one out did you notice if it was backwards or not.
    1981 Mustang Coupe: Rebuilt 91/306, Ported E7's, TF Spring kit, E-303 Cam, RPM Intake, Eddy 1406 Carb, FMS Dual Roller Timing set, March UD pulleys, Summit LT Headers, Summit 2-1/2" Chambered Mufflers w/ 2-1/2" FlowTech H-Pipe/ Flowtubes & 2-1/2" LMR SS Tailpipes. C4 trans with 8.8/ 2.73 Rear.

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