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  1. #1

    Default cooling issues (again)

    Greetings, all:

    Upon finally finishing the biannual replacement of the fuel pump- and that included a new tank that was a challenge to install (longer bolts), I managed to start the 86GT after not running for at least six weeks. Car started and idled good but the coolant overflow tank for some reason was already nearly full. Of course it spilled over and made a nice mess, about a pint or so of coolant on the ground. Thermostat took at least TEN minutes to open. When it did, all was well as the temp gauge stayed at halfway the entire time the car was on. I replaced the thermostat this summer and refilled the coolant. New thermostat seal and good hoses. The thing just takes forever to open.

    I've had a mountain of trouble with this car these past two years to the point of only putting about a hundred miles on it. Seems every time I turn the key something breaks. Not interested in getting stranded in the winter.

    Are Motorcraft thermostats junk? I use the factory replacement 190 degree Ford part. I've used them a number of times but lately cooling issues just won't go away.

    Any idea?

    Thanks much. At least it is back together and starts.

  2. #2
    FEP Member SECESH's Avatar
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    Just a thought about the cap. If it's not holding enough pressure too much coolant could exit into the reservoir. You've probably changed it already.
    Married to the same Mustang since 03/29/82

  3. #3
    FEP Power Member Ourobos's Avatar
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    My Bronco ran mid ways, a little higher. I pulled the 192 degree and went with a 180, which has always been my go to temperature. Now it' runs about 1/4 way where it should. I'd go with a 180, Motorcraft or Stant.
    1986 CHP SSP Coupe

  4. #4
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    I had some similar issues with over heating. The last two cars turned out to be the fan clutch. Replaced that and the problems went away. I’m not sure what years used them. I know 85 and up use them. It fixed the problem on the 67 Tbird and the 92 GT.
    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

  5. #5
    FEP Super Member erratic50's Avatar
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    Pressure cap, air pocket, thermostat in backwards, fan, fan clutch or a gummed up radiator

    Ideas to try:
    #9 wire the fan to a bolt and let it idle for a while. This will either eliminate the clutch or confirm it by forcing the fan to 100%

    Make sure the thermostat was installed spring in towards the intake

    use a pressure pump verify cap

    verify condition of fan shroud and fan

    replacement radiator or have the OE reconditioned

    Also of course make sure there are no leaks and no air pockets. Bleed from the highest point if you need to. I’ve had to loosen the temp sending unit and let air out until only water comes out before. These days I run a newer thermostat housing so there is a spot for a temp sensor for an electric fan there — good place to let air out if all else fails.

    make sure your overflow tank is good and has coolant. Make sure the hose and the barb on the radiator is good and the line is adequately clamped. Put you heater on high

    generally the manufacturers process to get air forced out of the system is by jacking the front of the car as high as you can safely with a floor jack on the K member. Verify the overflow tank is good and has coolant and line is on and clamped. Run the motor with the radiator cap off until the thermostat opens and you see coolant flow. Bring the engine up to 2500-3000 and hold it. Add coolant until it is as full as you can get, put the cap on, let the idle down

    let the car down and drive it. Take a few corners each way pretty aggressively. Heat on full blast while doing this. Let it heat cycle a few times

    you can always try bleeding air out if there is any doubt.
    Last edited by erratic50; 12-13-2018 at 08:55 AM.

  6. #6
    FEP Power Member plumkrazy's Avatar
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    What about wrong water pump?? thought I have read somewhere about 302's have 2 different water pumps depending on v-belt or serpentine belt. 50/50 mix of anti-freeze. Hope you can short it out.
    1 of 3 1985 Silver Grand Prix Capr's
    My first New car and still own 1986 Capri

  7. #7

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    Great ideas and thanks. Water pump isn't new but only has maybe 2000 miles on it. I flushed the system earlier this year. Upon refilling I bled it as much as possible. New fan clutch also- that really helped. Temp doesn't go above halfway on the dash gauge. The overflow had a nearly full hot amount when I started so I should have suspected something was up. Didn't try today but may do so tomorrow and see how it warms up. Maybe it pulled in air some other way due to a new leak? Have to give the engine a good look over to make sure no new leaks. I'll keep at it. Although it has been tedious. 20 months and only one hundred miles.

  8. #8

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    I tried again yesterday and ran it in the driveway- its been raining ever since. Thermostat took twelve minutes to open up but no overheating or leaking. Temp gauge never went beyond halfway left to right, say not quite touching the "M" in NORMAL. Which is good. The overflow tank had maybe an inch and a half of coolant in it when I started and that's what it had when I shut the car off. Just looked this morning and the same exact amount is present. No change. I did hear some gurgling during the first two minutes yesterday so likely some air still in the system would be my guess.
    May try again today but rain all day in these parts will keep me home, or at least the GT.
    Perhaps a leak somewhere allowing air to enter the cooling system? Maybe throttle body area? I'd suspect a leak but no coolant anywhere.

  9. #9
    FEP Power Member 85stanggt's Avatar
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    I have had the SAME issues. Everything is fine, but it will sometimes fill the overflow right up and then spill out. No explanations. I recently replaced the thermostat about 6 months ago with a new Motorcraft 192*F one I got off Amazon (new in Motorcraft packaging). It will sometimes get a little warm. And sometimes when I'm taking temp readings at the thermostat outlet it'll get above 200*F. I'm suspecting my new thermostat is bad myself. Where did you get yours from?

    I'm going to replace the water pump and the thermostat this week with new ones. And I have a Stant t-stat to go in there.

    Does anyone know why Stant didn't put the little bleed hole in theirs like the Motorcraft has?
    Last edited by 85stanggt; 12-18-2018 at 02:46 PM.
    1985 Mustang GT Convertible
    Stock and original @ 213k, except for dynomax ultraflos.

  10. #10

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    I've used Motorcraft thermostats for years and usually get them either at Rockauto or another online outlet but they must be new and in Ford packaging for me. I doubt the stats are bad. This summer I replaced the fan clutch and that made the biggest difference. No more overheating. I think I just have air in thesystem still and it needs purged. No way should a car take twelve minutes for the new stat to to pen unless maybe air is behind it. And still no overheating. I did mange to drive it very near home Monday for a few local trips- very short and it ran good. Same exact amount of coolant in the overflow. And no overheating or leaking.
    You could drill a hole or two in the stat if you wanted. Make sure the air is out and we should be good.

  11. #11
    FEP Super Member erratic50's Avatar
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    Depending on weather it can take a while for it to open. What are the temps outside there when it’s taking 12 min?

    is the bypass hose particularly swollen/enlarged? Is the thermostat drilled for additional bypass?

    Replace the temp sender. DO NOT use any type of sealer or Teflon tape on the new one. The compound they ship with is more than sufficient. Usually unneeded too, NPT are tapered and self sealing generally.
    Last edited by erratic50; 12-19-2018 at 09:32 PM.

  12. #12

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    Messed with the car today. Temps outside are around 40 degrees. But that's not the problem. What is it...?

    Leaking head gasket pumping coolant out the passenger valve cover. The visible part of the timing cover gasket is soaked green. SO the hole in the block I "repaired" last year apparently is now leaking.

    POS. Car turned to junk just sitting there. Only one hundred miles in two years due to ongoing maintenance issues, like overheating, ignition, timing, and I could go on. Pull the engine, rebuild, reseal, and on and on. It just doesn't stop.

    No hurry to waste more money on the clunker.

    JUNK.

  13. #13

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    Take a step back and relax a minute and ask yourself how much do I really like or want the car? I know from experience on this because a few years back I did the same thing after getting advice from someone to do the same thing. I got a friend involved and together we solved the problems on my car and now I believe it was worth the time effort and money. Don't give up on it yet. Hey if you want a new one just get $40k together and buy a new one. I personally hate car payments and rather enjoy working on the older cars. Keep chipping away at it and get some help. I did.

  14. #14

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    I removed the upper intake and the passenger side valve cover today. Didn't find much of anything. A little rust on one spring and noting else. The first photo shows this and the lighting makes it look like there is more rust but there isn't. Actually looks very good under there. No coolant in that area nor was there any on the dipstick.Name:  2018GTProbs 2.jpg
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    The next picture is where the coolant was seeping out. And it may not have been coolant. That is the spot where it leaked when installed last summer. Almost the very middle of the picture. I re-positioned the gasket and cover and tightened it down and no leak. That time it was oil. There is no real residue anywhere. No cracked head or freeze plugs. Looks very clean to me.Name:  2018GTProbs 1.jpg
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    What I did find was a small puddle of coolant on the lower intake manifold under the throttle body. The TB gasket has leaked before on me and unfortunately the gasket surface isn't quite smooth. There is a lot of crystalized coolant around that area of the TB. Definitely will replace it although I didn't take a photo of it. So the problem may very well be the TB area. But the timing cover gasket is soaked and likely my previous water pump bolt hole repair failed recently.
    If there is air getting into the cooling system, I suppose that would make it take twelve minutes for the thermostat to open. I can imagine the temp inside this engine. May explain the hole repair failure. So I now have two gaskets to to replace. TB and timing cover but unsure how to repair the hole correctly. With 80,000 miles on the engine and running good until recently, I hesitate to pull the engine and tear it down. If necessary then fine but that might wait until either Spring or a garage is found.
    The car probably is worth keeping but not worth many dollars right now. I found the casting date in the head when I took the cover off and that was cool. Plus the Ford oval and the Cleveland engine plant symbol. The date stamp was 5L16. November 16, 1985?
    Had a few beers and gave it some thought. Need to fix that hole properly and take it from there.
    Thoughts and comments?
    Thanks all.

  15. #15
    FEP Power Member 85stanggt's Avatar
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    I hope this helps put your mind at ease some more. I have the factory Ford repair manuals, and in them it describes how to bleed the car. In that description, it states to wait 10 minutes for the thermostat to open at which point it says to feel the underside of the upper hose for hot coolant flow. Mine takes that long. I think your car is acting normal in that respect.
    1985 Mustang GT Convertible
    Stock and original @ 213k, except for dynomax ultraflos.

  16. #16
    FEP Super Member erratic50's Avatar
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    I’d put a nice key to the surface with problems then apply JB weld and bring it back smith with 320 grit. Should hold up fine for this purpose


    i mentioned using nut style fasteners inside the water passage to secure a stud earlier. Doable and your best option imo.

    A nice nut with an oversized flange or a washer like is used on a grain bin (gasketed washer) then a nut inside would stabilize things for a stud nicely.

    Sure hope uou get this thing going!

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