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  1. #1
    FEP Member Hans's Avatar
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    Default Car is puzzling me

    Why does the temperature needle point constantly at the max "normal" limit and overheat at the traffic light, in the cold mornings. And runs at the normal lower temperature and doesn't overheat when the outside temperature in sunny afternoon is much higher . Commuting 30 miles both ways.
    I remedy the overheating by revving the engine to 4000 RPM and the temperature drops again.
    Thermostat is probably causing this I think. Or it's jinxed .

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  2. #2
    FEP Senior Member gt4494's Avatar
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    Default

    I vote thermostat!
    "If you can't explain it simply, you don't understand it well enough."
    Albert Einstein

    1984 20th Anniversary GT350
    Almost "Stock"

  3. #3

    Default

    Also check the thermal clutch. They can fail in various ways.

    When the engine is running warm/hot, park the car, with the hood up, window down, door closed, shut off the engine, and quickly look at the fan blades. The fan should be stopped, or stopped in another ~second. The fan should also have noticeable drag.

    Also, make sure that the radiator, and AC condenser are not blocked. If they are, the fan may be drawing air in from under the car. That prevents the radiator from cooling, and would also make the fan clutch colder, and therefore slip more (lot of slip when cold, little slip when hot).

    Good Luck!

  4. #4
    FEP Member Hans's Avatar
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    Default

    Thanks for the tips.
    This weekend I dig in to it.

    If the heater hoses are hot, there can't be a big air bubble around the thermostat, right? (Since the heater hose connects there.)

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  5. #5
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    Default

    You might also want to rule out an alternator or IVR issue. My car seemed to run hot until I turned on the seat heaters. The increased alternator output corrected the gauge readings.

    On another note, my 67 Tbird was running hot at speeds over 65 mph. Turns out it was never shifting into 3 rd gear. Lol.
    Fox Body/3rd Gen MCA Gold Card Judge
    84 SVO 24K miles, 85 Mclaren Capri Vert. 84 GT Turbo Vert.
    88 Mclaren Mustang Vert 20K miles, 89 Mustang LX Sport Vert,
    03 Mach 1 7900 miles, 74 Mustang II, 69 Mustang, 67 Mustang, 07 GT500,
    14 Mustang CS/GT, 15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

  6. #6
    FEP Senior Member gt4494's Avatar
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    Default

    My '84 started running hot but the gauge was right where it should be. didn't notice it till I had water coming out the tailpipes driving on the interstate Turned out the sensor went bad and it cost me a set of warped heads.

    I just recommend figuring it out sooner then later!.
    "If you can't explain it simply, you don't understand it well enough."
    Albert Einstein

    1984 20th Anniversary GT350
    Almost "Stock"

  7. #7

    Default

    I have found the thermostats produced today are incredibly badly made. I think I have gone through 4 or 5 in the last 7 years. Sometimes only lasting a few months. Fan is easy to check, so is the air flow. You could even pull the coolant temp sensor and check that too. Even a disconnected egr can cause heat issues. But I bet on a craptastic thermostat.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  8. #8
    FEP Member Hans's Avatar
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    Default

    Thanks for the tips.
    How can I test the coolant temperature sensor?
    Should it have a certain resistance value perhaps?
    Maybe I can purchase a new one from Rockauto to compare the two.

    I will check the alternator voltage output too just to be sure it doesn't spike on occasion.

    How do you guys burp the upper radiator hose? Any trick for that. (Don't think there's much air in it though.)

    I do have a new thermostat, housing and the little elbow hose in house fortunately.
    I keep spares because I have to have everything flown in.

    And what do you know: it's snowing since yesterday. Not comfy for a front yard wrencher.

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  9. #9

    Default

    What I was going to suggest is if you have a hotplate, pull the temp sensor and stick it heated water, check to see at what temp your gauge is reading where on the dash. If it bounces around you know something is up but each of these damn things appear to read differently, would be good to know what the actual temp is at points on your gauge. When I was troubleshooting I installed an aftermarket coolant temp gauge that used an ether line to monitor real coolant temps. Not worth that much trouble. Eventually I pinched the line during a race and now it's garbage.

    Burping most people do by filling with the front end jacked up as high as possible. That said, it has never been an issue with my 84. That cool little expansion tank thing works really well for allowing the air out and sucking fluid back in.
    Last edited by emerygt350; 04-01-2022 at 02:47 PM.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  10. #10
    FEP Senior Member gt4494's Avatar
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    Default

    I've never done it this way but it should work. Only difference is the FORD only has one wire so the second "wire" is the body of the unit or ground.

    https://itstillruns.com/test-sensor-...l-7927898.html
    "If you can't explain it simply, you don't understand it well enough."
    Albert Einstein

    1984 20th Anniversary GT350
    Almost "Stock"

  11. #11
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    Default

    If you don't have a hot plate, you could wrap the sensor and a thermometer in a heating pad. Or is it only us old guys who have heating pads?

  12. #12
    FEP Member Hans's Avatar
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    Default

    Top - cheap Summit, middle - replaced last year, bottom-currently used Stant thermostat.
    The first two open the same, before water boils. Stant is slower. Also the opening remains far smaller because of the valve that has an edge inside the seat where the others are almost flat.
    Then the Stant thermostat closes first again.
    Another observation: the Summit thermostat valve opens and moves sideways. Not straight. But when it closes it centers itself on the seat.


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  13. #13
    FEP Super Member erratic50's Avatar
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    Default

    make sure your pressure cap is good and no leaks

    fan clutch could be faulty

    Water pump impellers do go bad sometimes

    Radiators get clogged and need to be cleaned/reconditioned at times

    thermostats are hit and miss usually

    would get the 190 degree Motorcraft high flow thermostat

    It was originally designed for the EFI 386 series (big block 460) F series trucks

    Motorcraft RT-1067-A



  14. #14

    Default

    Is this carbed or injected?
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  15. #15
    FEP Member Hans's Avatar
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    Default

    Is this carbed or injected?

    The original 79 5.0 engine. Carbed there fore.


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  16. #16

    Default

    Ok, you could try a different thermostat temp without problems. On the fuel injected versions you need to be careful with cooler thermostats.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  17. #17
    FEP Member Hans's Avatar
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    Default

    Always something going to cause an issue:
    I purchased a replacement thermostat housing. Unfortunately the flange does not seal against my Airgap intake manifold.
    The Felpro gaskets do fit on the original housing (second picture), but not on the Dorman housing. The heater passage is shifted. I didn't notice because the Dorman housing came with its own gasket.
    I found out after reinstall of all parts on the engine when refilling the coolant... Poured out almost as fast as I could fill the radiator .

    The bottom piece of the sealing edge on the heater passage is severely pitted. (On the original housing.)
    I want to fix that with JB Weld or a similar brand paste.
    Is there a better way to do that?

    Regards, Hans.



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  18. #18
    FEP Power Member richpet's Avatar
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    If you're talking about a sealing surface I would use rtv gray over JB weld myself.
    I had a similar issue - bought a higher quality T-Stat which happened to have a slightly thicker flange so it would not seal. I ended up rtv -ing two gaskets together to create a thicker gasket. Now it's perfectly sealed.

    Sent from my Pixel 6 Pro using Tapatalk
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  19. #19
    FEP Member Hans's Avatar
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    See the pics please.
    The edge of the port is almost gone.
    I think filling up the rust pit in the edge of the port will reduce the likelihood of leaks later on.
    I do agree on using RTV in addition to the Felpro gasket.
    It remained leek free like that for nine years.

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  20. #20
    FEP Power Member richpet's Avatar
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    Default

    I used a housing from LMR and one sealing edge is super narrow, maybe 1/16"? It didn't line up exactly, but I had the part for too long to try and return it. No leaks. In fact the bypass tube is also offset some. But enough gets through to run properly.
    I do agree it is good to try and reduce the corrosion. But a new housing is only what, around $25 from them.
    Just a thought.

    Sent from my Pixel 6 Pro using Tapatalk
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  21. #21
    FEP Member Hans's Avatar
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    I found more people having the issue that on the Edelbrock 7521 manifold many of the thermostat housings don't fit.
    The bypass hole position is different.
    The old housings fit . The current ones not.
    Probably easier to fix my 79 housing. That has worked on said manifold 9 years without leaking. Despite the pitted edge.

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  22. #22
    FEP Member Hans's Avatar
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    Quote Originally Posted by richpet View Post
    I used a housing from LMR and one sealing edge is super narrow, maybe 1/16"? It didn't line up exactly, but I had the part for too long to try and return it. No leaks. In fact the bypass tube is also offset some. But enough gets through to run properly.
    I do agree it is good to try and reduce the corrosion. But a new housing is only what, around $25 from them.
    Just a thought.

    Sent from my Pixel 6 Pro using Tapatalk
    The LMR housing seems the same as the one that I got here. That doesn't fit.


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  23. #23
    FEP Member Hans's Avatar
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    First picture: See the kit that didn't touch the Edelbrock 7521 manifold flange at the bottom of the heater passage.

    Picture Two:
    The original 79 housing is dimensionally different. Distance between bypass port and mounting hole is 7mm less than of the replacement housing.

    So the old part goes back in. Including the Sems capscrews. I'm a sucker for original parts. The hoses are from 1978 too. Still okay.

    I think I discovered the cause of overheating. The thermostat was mounted backwards. The copper cylinder/ wax body pointed to the radiator hose. Should be at the engine side.

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  24. #24
    FEP Senior Member gt4494's Avatar
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    Good catch!! That will definitely cause issues. The pointed end is where the bimetal spring is that opens the thermostat up. In the hose it doesn't get hot water circulation so it can't open. Only heat it would see is from the intake metal to housing metal.
    "If you can't explain it simply, you don't understand it well enough."
    Albert Einstein

    1984 20th Anniversary GT350
    Almost "Stock"

  25. #25

    Default

    Nice catch.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

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